Blue-winged Warbler Vermivora pinus

Of the various eastern warblers reaching California, the Blue-winged is represented disproportionately more in the desert and less on the coast.  As a result, it is exceptionally rare in San Diego County.  The California Bird Records Committee has accepted only two from this area—and rejected three others as inadequately or not supported.

Migration: San Diego County’s well-described Blue-winged Warblers were in the Tijuana River valley 26 September 1964 (McCaskie and Banks 1966, Bevier 1990) and at Point Loma 30 September 1999 (J. C. Worley, T. Plunkett, Rogers and Jaramillo 2002).  Roberson (1993) listed the rejected records.  A specimen or photograph to support the Blue-winged Warbler in San Diego County is still lacking, though the species has been photographed once in adjacent Orange County (Heindel and Garrett 1995).

Golden-winged Warbler Vermivora chrysoptera

San Diego County seems to have got less than its fair share of both the Golden-winged and Blue-winged Warblers.  Though the California Bird Records Committee has accepted 67 records of the Golden-winged through 2002, only three of these are from San Diego County.  Yet one of the four hybrids between these species known in California was in San Diego County.

Migration: The county’s first Golden-winged Warbler was photographed in a residential area on the southeast side of Mount Soledad, La Jolla (P8) 6–12 October 1984 (J. Moore, Dunn 1988).  One in the Tijuana River valley (W10) 15 December 1990 (R. E. Webster, Heindel and Garrett 1995) was probably a late fall migrant rather than a winter visitor, though three Golden-winged Warblers have wintered elsewhere in coastal southern California.  In spring, one was along Keys Creek near Lilac (F11) 21 May 1991 (E. R. Lichtwardt, Heindel and Garrett 1995).

            A female photographed at Point Loma (S7) 15–19 May 2001 had some yellow on the underparts and so appeared to be a hybrid with a Blue-winged Warbler (P. A. Ginsburg, Garrett and Wilson 2003).

Tennessee Warbler Vermivora peregrina

 

From the 1960s and through the mid 1980s, the Tennessee Warbler was one of the more frequent eastern warblers reaching San Diego County as a fall vagrant, averaging about 10 per year.  By the end of the century, however, that rate had dropped considerably, to about three per fall.  The Tennessee Warbler also occurs in the county, though less frequently, as a winter visitor and spring vagrant.

 

Migration: The Tennessee, like most vagrant warblers, has been found primarily along the coast, especially at Point Loma.  The only fall record more than 13 miles inland is of one at Butterfield Ranch (M23) 5 November 1978 (G. McCaskie).  The species occurs mainly from mid September to late October, exceptionally as early as 27 August (1972, one in the Tijuana River valley, G. McCaskie).  It is also of nearly annual occurrence in spring migration, mainly in late May and early June.  Spring records range from 24 April (2000, singing male at Fallbrook Naval Weapons Station, E7, W. E. Haas) and 1 May (1985, Point Loma, E. Copper) to 21 June (1980, Coronado, AB 34:931, 1980; 1982, Point Loma, AB 36:1017, 1982) and 2 July (1970, two at Point Loma, AFN 24:718, 1970).  Reports from Culp Valley in late April and early May only (Massey 1998) are unseasonal enough to suggest misidentification.

 

Winter: Tennessee Warblers have remained on several occasions as late as the third week of December, resulting in one record for an Oceanside Christmas bird count (1979) and six for the San Diego count (1968–83), with up to three individuals in 1980 and 1983.  Records later in the winter are fewer, but include at least eight extending to mid January or beyond. 

 

Conservation: Of the warblers nesting in Canada’s boreal forest, some have decreased sharply as vagrants to southern California, and the Tennessee is among them.  Numbers at Point Loma as high as four in a day (4 June 1977, P. Unitt) have not been approached recently, though spring 2002 yielded three (R. E. Webster).  The most recent winter record for the county is of one in San Diego 18 January–25 February 1995 (R. E. Webster, NASFN 48:249, 1994).

Orange-crowned Warbler Vermivora celata

An inconspicuous little green bird, the Orange-crowned is second only to the Yellow-rumped as San Diego County’s commonest warbler.  Because of multiple subspecies and multiple seasonal roles, its status is complex.  It is common throughout the county in migration.  In winter it is common in the coastal lowland, less so farther inland.  As a breeding species the Orange-crowned Warbler is common in coniferous, oak, and riparian woodland, less so in ornamental shrubbery and coastal chaparral.  Its status as a widespread breeding bird and winter visitor appears to have evolved just in the 20^th century.  Like the Western Flycatcher the Orange-crowned Warbler was a stealth invader: the change in breeding and winter status went unappreciated because the process took decades and the species was always common as a migrant.

Breeding distribution: The Orange-crowned Warbler is widespread as a breeding bird in riparian, oak, and coniferous woodlands over most of the coastal slope of San Diego County, lacking only from the plateau east of Campo.  The population is more concentrated along the axis of the higher mountains and in northwestern San Diego County from Camp Pendleton east to Valley Center and Bear Valley (H13).  High counts are of 28 (23 singing males) along the Santa Margarita River north of Fallbrook (C8) 24 May 2001 (K. L. Weaver) and 21 in Woods Valley (H12) 19 June 1998 (W. E. Haas).  There are also concentrations farther south, in canyons and on north-facing slopes, as in San Clemente Canyon (P8; 12 on 29 May 1998, C. G. Edwards) and in stands of Tecate cypress on the north slope of Otay Mountain (U15; 26 on 25 May 1999, G. L. Rogers).  The breeding range only barely spills onto the east slope of the mountains where oak woodland is still thick, as at 4500 feet elevation in the middle fork of Borrego Palm Canyon (F22; two on 16 June 1999, D. C. Seals).  Single birds at Lower Willows (D23) 12 June 1994 (C. Sankpill, L. Clark), 4 July 1998 (B. Getty), and 24 June 2002 (J. R. Barth) suggest the Orange-crowned Warbler is an occasional nonbreeding summer visitor at this riparian desert oasis.

Nesting: Orange-crowned Warblers usually nest on the ground, screened behind dense undergrowth, often on steep slopes or banks (Sogge et al. 1994).  As a result, the nests are difficult to find.  The only one described by atlas observers, though along a popular trail along Doane Creek (E14) 13 June 1999 (P. Unitt et al.), was typical in being nestled in a hollow on a cut bank.

            Along the coast, Orange-crowned Warblers begin nesting in mid March, with observations of nest building as early as 14 March (near the mouth of Las Pulgas Creek, E3, R. and S. L. Breisch) and fledglings as early as 11 April (Bonita, T11, P. Unitt).  Four egg sets collected along the coast 1916–28 range from 26 March to 24 April.  Nesting at higher elevations is later in the season, with egg laying continuing at least through mid June.  Orange-crowned Warblers may nest late at low elevations, too, as attested by fledglings being fed at Point Loma (S7) 18 July 1998 (C. G. Edwards) and along the Santa Margarita River north of Fallbrook (C8) 29 July 1999 (K. L. Weaver).

Migration: The Orange-crowned Warbler is an early migrant.  In spring, the birds begin moving through parts of the Anza–Borrego Desert, where they do not winter, in mid February.  Early dates for these migrants are 15 February (1999, six in Smuggler Canyon, L25, R. Thériault) and 18 February (2000, seven in Sunset Wash, I26, L. J. Hargrove), possibly 13 February (2001, one near Little Clark Dry Lake, E27, R. Thériault).  By late February the species can be numerous (up to 40 in Indian Canyon, O27, 25 February 1998, P. K. Nelson), and similar concentrations can be encountered at any time from then through early May when the weather compels migrants to pause.  Peak migration is in April, with up to 80 at Agua Caliente Springs (M26) 7 April 1994 (Massey 1998).  A fallout as large as the “thousands” grounded during a severe windstorm near Banner (K21) 22 April 1967 (G. McCaskie) has not been reported since, though regular monitoring of nearby San Felipe Valley, now known as a corridor for migrants, could detect such events.  During May the last of the migrants continue north; late dates are 26 May (1998, four at Yaqui Flat, I23, P. K. Nelson) and 28 May (1999, one at Southwest Grove, Mountain Palm Springs, P27, D. G. Seay).  Fall migrants become common in mid August but may be on the move as early as mid July, as in the Salton Sink (Patten et al. 2003).

Winter: Wintering Orange-crowned Warblers are concentrated in the coastal lowland, mainly in riparian woodland and ornamental trees and shrubbery.  Maximum winter counts during the atlas’ term were of 42 in Coronado (S9) 15 December 2001 (R. E. Webster), 24 in Imperial Beach (V10) the same day (C. G. Edwards), and 29 at San Elijo Lagoon 22 December 2000 (G. C. Hazard).  At higher elevations the species is uncommon (maximum six at Descanso, P20, 11 December 1998, P. Unitt) but occurs widely in riparian and oak woodland.  Winter records extend as high as 4600–4700 feet elevation as near Shingle Spring (D21; one on 21 December 1999, L. J. Hargrove), on the middle fork of Borrego Palm Canyon (E22; one on 19 December 1999, P. D. Jorgensen), and at Lake Cuyamaca (M20; one on 2 December 2001, C. G. Edwards).  In the Anza–Borrego Desert wintering Orange-crowned Warblers are uncommon and restricted to irrigated areas and oases.  In this area the maximum daily count before 15 February is of four at Bow Willow Palms (P26) 9 January 2000 (M. B. Mulrooney).

Conservation: As a breeding species, the Orange-crowned Warbler has increased greatly in San Diego County, extending its range in the process.  This change is due to the subspecies V. c. lutescens expanding south.  Of this subspecies, Willett (1912) wrote that only “a few remain through the summer and breed in the cañons and on the brushy mountain sides” of southern California.  He cited no specific breeding records as far south as San Diego County.  Stephens (1919a) called lutescens an “abundant migrant,” not mentioning any breeding, though he collected a specimen in the Cuyamaca Mountains 6 June 1889 (SDNHM 1349).  The only eggs taken by the early collectors were from the breeding range of subspecies sordida on the coastal strip.  In the 1970s breeding Orange-crowned Warblers were fairly common only at Point Loma, uncommon in montane coniferous woodland, and rare elsewhere (Unitt 1984).  The species was not confirmed breeding on the mainland of Baja California until 1987 (Unitt et al. 1995).  Thus the evidence suggests that lutescens has spread and increased vigorously over the past century.

            While the breeding range of lutescens was expanding south, the winter range was expanding north.  Stephens (1919a) did not mention any wintering by this subspecies, and Dawson (1923) wrote that it “apparently passes entirely beyond the state in winter.”  Brewster (1902), however, wrote that lutescens “winters as far north as San Diego,” and the subspecies was collected in winter as early as 1904 (30 December; Witch Creek, J18, FMNH 148559).  Now the species is locally common in winter, more widespread, and most of the birds appear to be lutescens.

            The reasons for the Orange-crowned Warbler’s expansion are still a mystery.  The spread parallels that of the Western Flycatcher, a species of similar habitats but completely different nesting habits.  The warbler is only rarely a host to the Brown-headed Cowbird (Sogge et al. 1994), giving it an advantage for much of the 20^th century over other small insectivorous birds.

Taxonomy: Three of the Orange-crowned Warbler’s four subspecies occur in San Diego County, and the fourth is a likely vagrant.  V. c. lutescens (Ridgway, 1872), bright yellow and lightly streaked, is the most common in migration, both spring and fall.  It breeds in the Pacific coast district of North America, south to San Diego County or northwestern Baja California.  It appears to be the widespread breeding subspecies and the most common in winter as well, though better specimen support for this statement is needed—most existing specimens are of migrants. 

Vermivora c. orestera Oberholser, 1905, breeds in the Great Basin/Rocky Mountain region.  Each sex considered separately, it is less yellow than lutescens, and the females have grayish heads.  It reaches San Diego County as a migrant and winter visitor, uncommon or fairly common, at least from 21 August (1908, Cuyamaca Mts., Grinnell and Miller 1944, MVZ 3942) to 24 April (1909, Witch Creek, FMNH 148483). 

Vermivora c. sordida (Townsend, 1890) breeds on the islands off southern California and Baja California, locally on the nearby mainland.  It is darker than lutescens, with heavier streaking below, especially on the undertail coverts.  It has bred at least at Torrey Pines (N7), Point Loma (eggs collected, WFVZ), Coronado (A. M. Ingersoll in Willett 1912), and canyons in San Diego (WFVZ; nest in a “decorative hanging fern basket inside a small lath house” in Golden Hill, S9, Abbott 1926).  In one of California’s more unusual bird migrations, sordida disperses to the mainland during its nonbreeding season.  Grinnell and Miller reported such migrants from mid July through March, and all 18 San Diego County specimens fit within this window, except for one from Poway Grade 29 April 1918, at that time possibly a local breeder.  Vermivora c. sordida ranges as far inland as the San Luis Rey River 0.5 mile west of Henshaw Dam (G16; 10 September 1996, SDNHM 49614), Julian (K20; 5 August 1908, MVZ 3819), the Cuyamaca Mountains (1 September 1908, MVZ 3944), and 1.3 miles northwest of Morena Conservation Camp (S21; 14 November 1983, SDNHM 42815).  With the spread of lutescens, however, the gap between the breeding ranges of lutescens and sordida mapped by Grinnell and Miller (1944) has closed, and it is possible that lutescens is swamping out sordida on the mainland.  Specimens in known breeding condition are needed to test this hypothesis.

Vermivora c. celata (Say, 1823), breeding in the transcontinental taiga zone, is even less yellow than orestera; the head is always gray, and in some females the yellowish on the underparts is reduced to irregular blotches.  It reaches southern California as a rare migrant and winter visitor (Grinnell and Miller 1944).  One specimen from San Diego County has been reported, collected at Witch Creek (J18) 24 April 1909 (Willett 1912), but on examining this specimen I found is actually orestera (FMNH 148483).  Nevertheless, nominate celata is reconfirmed elsewhere in southern California by recent specimens from the Channel Islands and Imperial Valley (SDNHM, Patten et al. 2003).

Nashville Warbler Vermivora ruficapilla

In spring, if the rains have been good, the desert blooms, insects proliferate, and warblers like the Nashville can stop to refuel on their way from western Mexico to the Pacific Northwest.  The Nashville Warbler is primarily a spring migrant through San Diego County, most numerous on the desert slope.  It is uncommon as a fall migrant and rare as a winter visitor.  Our atlas effort revealed the species for the first time in summer in San Diego County, with three records of apparently unmated males on Palomar Mountain—the first summer sightings of the Nashville south of the San Bernardino Mountains.

Breeding distribution: The Sierra Nevada represents the southern end of the Nashville Warbler’s traditional breeding range.  It has been only since 1970 that small numbers have been found summering in the Transverse Ranges, with breeding confirmed at least in the San Gabriel Mountains (AB 37:1028, 1983) and on Big Pine Mountain, Santa Barbara County (Lentz 1993).  Field work for this atlas yielded three observations on Palomar Mountain, the first summer records of the Nashville Warbler for San Diego County.  Two were from the confluence of Doane and Pauma creeks, elevation 4475 feet (D14), where males sang at length 24 June 1997 and 18 June 1998 (P. D. Jorgensen).  The third record was of a male at Sourdough Spring, at 5725 feet 0.25 mile northeast of High Point, Palomar Mountain (D15), 12 July 2000 (K. L. Weaver).  In no case did the birds appear paired, and nesting of the Nashville Warbler as far south as San Diego County is still unconfirmed.  These are the only summer records south of the San Bernardino Mountains, as no definite records for the San Jacinto Mountains have been published; “Mill Creek, San Jacinto Mountains” (AB 41:1488, 1987) is an error for the San Bernardino Mountains.

Migration: Nashville Warblers arrive in spring at the end of March or beginning of April.  During the atlas period first reports ranged from 27 March (1997, two at Agua Caliente Springs, M26, E. C. Hall) to 1 April.  The earliest spring date ever is 21 March (1970, Valley Center, G11, AFN 24:673, 1970).  Spring migration peaks in late April. Numbers are higher in the Anza–Borrego Desert and on the east slope of the mountains than on the coastal slope, though the species is seen throughout the county.  The highest count in a day during the atlas period, 20 near San Felipe (H20) 24 April 1999 (A. P. and T. E. Keenan), was from the San Felipe Valley corridor traveled by many birds following the lowest routes from the desert to the coast.  By mid May most Nashville Warblers have finished passing through, and the latest spring date is 25 May (1998, one at Tamarisk Grove Campground, P. D. Jorgensen).

            In fall, the Nashville Warbler is uncommon in San Diego County, as it is one of those species whose primary migration route swings east, the birds avoiding Baja California and a crossing of the Gulf of California on their way to a winter range in western mainland Mexico.  Fall migrants may appear as early as 29 July (2000, one along Agua Dulce Creek, Laguna Mountains, O23, J. R. Barth).

Winter: The Nashville Warbler is a rare but annual visitor along the coast.  One to five individuals were reported during each winter of the atlas’ five-year term, for a total of 12.  The species was found on 22 of 34 San Diego Christmas bird counts 1968–2002, with up to three noted on three counts in the 1970s.  In the north county wintering Nashville Warblers are much rarer than around metropolitan San Diego, with no reports on Rancho Santa Fe Christmas bird counts and only one on an Oceanside Count (two on 23 December 1980).  Other reports along the north coast are of one at San Onofre (C1) 20 January 2001 (J. M. and B. Hargrove) and one in Vista (G7) 4 January 2002 (C. Andregg).  There are two winter reports from farther inland, of one in Carney Canyon (H15) 2 January 1999 (M. Dudley) and two in Ballena Valley (K17) 25 February 2002 (D. C. Seals).

Conservation: Breeding in the undergrowth of coniferous forests, the Nashville Warbler may be taking advantage of the second growth that follows logging.  Results of both the Breeding Bird Survey (Sauer et al. 2003) and counts of migrants on Southeast Farallon Island (Pyle et al. 1994) imply that the western subspecies ridgwayi is increasing on a broad scale.  Numbers of Nashville Warblers observed in San Diego County 1997–2001, however, were less than could be found in the 1970s, though our protocol for this atlas did not emphasize migrants.

Taxonomy: The western subspecies, the Calaveras Warbler, has been known as V. r. ridgwayi since van Rossem (1929) proposed this as a substitute name.  The Calaveras Warbler’s original name, V. r. gutturalis (Ridgway, 1874), was preoccupied by Vermivora gutturalis (Cabanis, 1860), when the Flame-throated Warbler of Costa Rica and Panama was placed in the same genus with the Nashville.  If the Flame-throated Warbler is transferred to the genus Parula, as in the 7^th edition of the A. O. U. checklist, van Rossem’s substitution is unnecessary but retained because of the provision in the latest version of the code of scientific nomenclature that conserves such changes if they happened before 1961. The eastern subspecies of the Nashville, V. r. ruficapilla (Wilson, 1811), is still unconfirmed in California, though all other warblers with similar ranges reach the state regularly.

Virginia’s Warbler Vermivora virginiae

Though Virginia’s Warbler breeds in the Great Basin and Rocky Mountains, it is a rare vagrant to coastal southern California, in fall almost exclusively.  Since 1962, when Guy McCaskie discovered it in fair numbers in the Tijuana River valley, its frequency has decreased precipitously.  By the beginning of the 21^st century only two or three were being reported in San Diego County per year.

Migration: Though San Diego County is not on Virginia’s Warbler’s normal migration route, the species is most frequent here in September, like other western warblers, not shifted later in the season like vagrants from the east.  There are many records for August, one as early as the 13^th (1972, Tijuana River valley, G. McCaskie), and few later than mid October.  All fall records for Virginia’s Warbler in San Diego County are from the coastal lowland, except for one at Jacumba (U28) 3 September 1963 (AFN 18:75, 1964).

            There are three spring records, one from Encinitas (K6/K7; 29 April 1979, AB 33:806, 1979), two from Point Loma (S7; 15 May 1988, G. McCaskie, AB 42:482, 1988; 3 May 2001, J. C. Worley).

 

Winter: San Diego County has seven winter records of Virginia’s Warbler, all for the coastal lowland.  Unitt (1984) listed three; more recent were three in January and February 1990 (AB 44:331, 1990, Rancho Santa Fe Christmas bird count) and one at La Jolla (P7) 16 March 2001 (P. K. Nelson).

 

Conservation: The highest number of Virginia’s Warblers reported in San Diego County per fall was 35 in 1962, when McCaskie was the county’s only birder searching out vagrants (McCaskie and Banks 1964).  In spite of the increase in observers, by the mid to late 1970s, the rate had dropped to five to ten per year (Unitt 1984).  Thus the current rate of two per year continues a 40-year trend of decline.  No significant decrease has been reported in the species’ breeding range, so the reason for this decrease in San Diego County is not clear.

Lucy’s Warbler Vermivora luciae

Colonizing only in 1990, Lucy’s Warbler is a recent addition to San Diego County’s breeding birds.  It is still rare and confirmed nesting at only one site, the thicket or bosque of mesquite in the center of the Borrego Valley.  Its stay in the area is only three months, from mid March to early June.  Though a few sightings elsewhere in the desert suggest that Lucy’s Warbler could colonize additional stands of mesquite, the future of the bosque in Borrego Valley is clouded by continued pumping of groundwater that could lower the water table until the trees can no longer reach it. 

Breeding distribution: Lucy’s Warbler has one of the most limited distributions of any breeding bird in San Diego County, confined to the mesquite bosque on the floor of the Borrego Valley.  Its numbers are low, the maximum count of singing males per day being seven on 8 April 1997 and 23 March and 27 April 1998 (R. Thériault).  All were seen within atlas square G25, with only one singing male on the southeast side of Borrego Sink in G26 (1 May 2000, P. Unitt).  Vegetation maps of the area show the habitat covering about 2500 acres, but the warblers occupy it only sparsely.  The total population is no more than a few dozen pairs, and probably less.

            The possibility of Lucy’s Warbler colonizing additional sites in the Anza–Borrego Desert is raised by one at Tamarisk Grove Campground (I24) 1 May 1997 (P. K. Nelson) and one in Vallecito Valley (M24) 5 May 2002 (J. R. Barth).  Though extensive mesquite thickets suitable for the species are at both sites, in both cases the birds were evidently unmated and could not be found on subsequent dates.

Nesting: Atypically for a warbler, Lucy’s usually nests in tree cavities, old Verdin nests, or behind slabs of loose bark (Johnson et al. 1997).  The one certain nest found in San Diego County was being built in a cavity of a mesquite 6.5 feet off the ground 22 April 1997 (R. Thériault).  On this day, four independent juveniles were foraging together near the adult female gathering nest material, suggesting the adult was starting a second nest.  Another probable nest, from which a bird was flushed, was about 15 feet off the ground under a section of bark loosened by a mesquite branch that had partially broken (G26, 1 May 2000).  Earlier observations of breeding activity include a bird carrying an insect larva 10 May 1993 and a family group the following day (P. Unitt).

Migration: Dates for Lucy’s Warbler in the Borrego Valley extend from 11 March (1997, two singing males) to 4 June (1998, three singing males and one independent juvenile, R. Thériault).  The arrival date agrees with that in southern Arizona (Phillips et al. 1964) and along the lower Colorado River (Rosenberg et al. 1991).  The late date may not be completely representative, the birds becoming less detectable when singing ceases. But Thériault’s visits to the same site on 11 and 15 June 1998 did not reveal any, and Lucy’s Warbler is a famously early migrant.  Johnson et al. (1997) found its numbers near Phoenix greatly diminished even by late June.

            Lucy’s Warbler also occurs as a rare fall vagrant near the coast, with over 50 individuals now reported.  Most are found in August and September, though dates range from 19 July (1982, Tijuana River valley, R. E. Webster, AB 36:1017, 1982) to 12 November (1979, same locality, G. McCaskie).  Inland, fall migrants have been found also at Borrego Springs (12 October 1969, AFN 24:100b, 1970) and Jacumba (two on 26 August 1967, AFN 22:91, 1968).  An especially unusual record, outside the species’ migration periods, was of one at Point Loma 2 June 1982 (R. E. Webster, AB 36: 895, 1982).

           

Winter: Lucy’s Warbler is a casual winter visitor around San Diego with four records, of one at Coronado 15–20 December 1979, one in the Tijuana River valley 15–25 December 1979, one on the San Diego Christmas bird count 17 December 1983, and one in San Diego 7 January 1986 (R. E. Webster, AB 40:335, 1986).

Conservation: As a breeding species, Lucy’s Warbler is a recent arrival in San Diego County, first noted in the Borrego Valley in April 1990 (J. O'Brien, AB 44:498, 1990).  It is certain that the species colonized about this time, for birders had visited the site regularly in spring since the Crissal Thrasher was discovered there in the 1950s.  Since the original colonization, however, the warbler’s numbers have remained low.  With further development of the Borrego Valley and overdraw of the water table, the mesquite bosque, a habitat unique in San Diego County, could be killed and Lucy’s Warbler extirpated—just as dramatized near Tucson by Johnson et al. (1997).  Throughout its range, Lucy’s Warbler has had a checkered history, extirpated from the Salton Sink (Patten et al. 2003), crashing then recovering partially along the lower Colorado River (Rosenberg et al. 1991), spreading in the Grand Canyon (Johnson et al. 1997) and elsewhere in Arizona as mesquite supplanted grassland (Phillips et al. 1964).

Northern Parula Parula americana

Unlike many eastern warblers, the Parula occurs in San Diego County at all seasons.  It is now more frequent in spring (about two per year) than in fall (about one per year).   There are seven winter records, including one of a bird that returned for four successive years.  Most interesting, there are over a dozen summer records, of up to three individuals, part of the species’ trend toward increase and colonization of California.

Migration: In fall the Northern Parula is rather typical of eastern warblers, occurring largely along the coast, with most records for Point Loma and the Tijuana River valley.  Fall dates range from 17 August (1985, Coronado, S9, E. Copper) to 16 November (1975, Tijuana River valley, AB 30:129, 1976).  In spring, however, the story is different.  Most spring vagrants are late, occurring in late May and early June, but records of the Parula are scattered throughout the season, with several in April, and range from 24 March (Borrego Springs, G24, 24 March 1978, AB 32:1056, 1978) to 4 June (1989, Point Loma, D. Parker, AB 43:538, 1989).  Most spring records are from Point Loma, but there are also three for the Anza–Borrego Desert, with one 2.5 miles south of Ocotillo Wells (J28) 5 May 2000 (J. R. Barth) and another in Borrego Palm Canyon (F23) 14 May 2001 (R. Waayers).

Breeding distribution: Even though the Parula has not been confirmed breeding in San Diego County, it has nested repeatedly along the coast of northern California and as near San Diego County as the San Bernardino Mountains (Patten and Marantz 1996, AB 46:1179, 1992).  Since 1988, when one was near the Forest Service’s San Luis Rey Picnic Ground (G16) 22 May (M. and B. McIntosh, P. Unitt), San Diego County has had at least 16 Parulas from June to mid July, all in native riparian or coniferous woodland.  The species recurred along the San Luis Rey River near the Forest Service picnic ground in 2000 and 2001, with three singing males maintaining adjacent territories 10 June–4 July 2001 (W. E. Haas).  A pair was along Agua Dulce Creek, Laguna Mountains (O23) 11 June–4 July 1992 (T. Clawson, AB 46:1179, 1992).  Nine additional locations for single individuals are scattered around the county from the San Luis Rey River near Pala (D10; 12 July 1991, E. R. Lichtwardt, AB 45:1162, 1991; 4–7 July 2000, D. Bylin, W. E. Haas) south to Jamul Creek (T15; 8 June 1999, P. Unitt) and east to San Felipe Creek at Scissors Crossing (J23; 5 July 2002, J. R. Barth, NAB 56:487, 2002) and La Posta Creek near La Posta Service (S23; 15 June 2000, L. J. Hargrove).

 

Winter: San Diego County’s seven winter Parulas have all been in the coastal lowland.  None was during the five-year atlas period, but one appeared the following winter at Santee (P12) 26 December 2002–2 January 2003 (M. B. Mulrooney, NAB 57:258, 2003).  One returned to the San Diego Zoo (R9) for four consecutive winters 1988–91 (AB 45:322, 1991).

 

Conservation: Since 1972, the Northern Parula’s frequency in California in spring and summer, like that of several warblers of the southeastern United States, has increased significantly.  The Parula was a major participant in the irruption of southeastern warblers to California in 1992.  Evidence for various factors explaining these events is still equivocal (Patten and Marantz 1996).

Yellow Warbler Dendroica petechia

 

The Yellow Warbler symbolizes mature riparian woodland, that is, streamside cottonwood, willow, alder, and ash trees that have reached their full height.  It is a fairly common breeding summer resident in this habitat, though the habitat itself is scarce and patchy.  Though the Yellow Warbler is recognized by the California Department of Fish and Game as a species of special concern, since the late 1980s San Diego County’s population has increased, evidently in response to the widespread trapping of the Brown-headed Cowbird, which parasitizes the warbler heavily.  The Yellow Warbler is also common as a migrant passing through the county.  It is rare as a winter visitor, in riparian woodland near the coast almost exclusively.

Breeding distribution: The Yellow Warbler’s distribution is one of the more difficult to interpret, because migrants headed north may be seen through much of the season when the local population is nesting, and in the same habitat.  Males sing freely in migration, negating that clue to territoriality.  The interpretation of just what sightings to designate as in “suitable habitat” thus required judgment and review in the context of the entire data set.  With the population expanding, some birds were pioneering into marginal habitat.  Three late June records for the Anza–Borrego Desert mock any attempt to define a “safe date” after which no spring migrants are seen.  The designations of breeding as “probable” and “possible” must be taken more literally for this species than for many others.

Despite these caveats, the Yellow Warbler’s breeding distribution is clear: riparian corridors on the coastal slope.  There is one area of known breeding on the desert slope, San Felipe Valley (J22; 50—probably including some migrants—on 21 May 1999, E. C. Hall; feeding young 13 July 2001, P. Unitt).  A singing male in a cottonwood grove at San Ignacio at the headwaters of Borrego Palm Canyon 16 June 1999 (E22; P. Unitt) suggests breeding at that site.

In the coastal lowland, breeding Yellow Warblers are most widespread from Carlsbad north, more localized farther south.  At low elevations the species is more confined to larger streams; in the foothills and mountains it takes advantage of narrow strips and patches of riparian trees.  Surface water favors Yellow Warblers strongly but is probably not essential, as long as groundwater suffices to support tall trees.  The Yellow Warbler’s attachment to mature riparian woodland in southern California contrasts with its habitat in the more humid parts of its transcontinental range, where it inhabits lower thickets and disturbed and early successional habitats (Lowther et al. 1999).

Some sites where breeding Yellow Warblers are exceptionally numerous are the Santa Margarita River north of Fallbrook (C8; 64, including 60 singing males, 24 May 2001, K. L. Weaver), the east end of Lake Hodges (K11; 50, including 40 singing males, 18 April 1997, E. C. Hall), and the Tijuana River valley (W11; 40, including 30 singing males, 27 June 1998, P. Unitt).  Away from the main rivers numbers are much smaller.  Still, San Diego County appears to be one of the main population centers for the Yellow Warbler in California, along with the Santa Ynez River in Santa Barbara County and the east base of the Sierra Nevada in Mono County (S. Heath pers. comm.).

 

Nesting: Yellow Warblers build a cup nest, placing it typically in upright forks of twigs.  One nest in Peutz Canyon (P16) was along the trunk of an alder tree, supported by a slab of loose bark (M. B. Stowe, P. Unitt).  The two nests whose height our observers estimated were about 23 and 35 feet above ground—well above the average height reported by studies elsewhere (Lowther et al. 1999).

Though many Yellow Warblers arrive in March, apparently they do not begin nesting until well into April.  Our dates of breeding activity are consistent with dates of 20 egg sets collected 1903–1931: 3 May–10 June; Sharp (1907) reported 20 June.  The nesting schedule implied by our observations allows ample time for the birds to raise two broods.  Previous studies (Goossen and Sealy 1982, Lowther et al. 1999) found the Yellow Warbler only rarely attempting two broods, but these studies were made at latitudes far to the north of San Diego.  Indeed, virtually all of what has been published on the Yellow Warbler’s biology comes from regions remote from southern California.

 

Migration: Spring arrival of the local population of the Yellow Warbler is in March, typically in the last week, sometimes in the third week.  One along the Sweetwater River near Jamacha (R14) 8 March 1998 (M. and D. Hastings) was exceptionally early.  Migrants headed farther north become frequent in mid April, peak in May, and occur regularly through the first week of June.  Numbers of spring migrants seen in a day at nonbreeding localities may run as high as 40, as in Vallecito Valley (M24) 24 May 1999 (P. D. Jorgensen).  Two at Tamarisk Grove (I24) 16 June 1998 (P. D. Jorgensen), one in Borrego Springs (F24) 20 June 1998 (M. L. Gabel), and another nearby in Borrego Springs (G24) 21 June 1998 (P. D. Jorgensen) were very late stragglers, later than any spring Yellow Warbler recorded in the Salton Sink (Patten et al. 2003).

            Fall migration takes place mainly from mid August to mid October, but at least some of the local population remains on its breeding territories, the males still singing, through early September.

 

Winter: In winter the Yellow Warbler is a rare but annual visitor, mainly in riparian willows, also in ornamental plantings.  Usually only a single individual is seen at a time, but multiple birds are regular in the Tijuana River valley, up to 8 around the Dairy Mart pond (V11) 19 December 1998 (G. McCaskie).  The birds can survive the winter successfully and even return to the same spot in successive years, as one has done to Myoporum trees at Famosa Slough (R8).  Almost all records are from low elevations near the coast, inland to Valley Center (G11) and Lindo Lake (P14), with one notable exception: one near the navy’s La Posta Microwave Station (T23), elevation about 3000 feet, 21 February 1998 (C. R. Mahrdt).

 

Conservation: The Yellow Warbler is well known throughout its range as a frequent host of the Brown-headed Cowbird—and famous for its response of flooring over parasitized nests to build a new nest atop the old.  Nevertheless, many parasitized Yellow Warblers end by raising cowbirds anyway.  Like that of many other riparian songbirds, the population of the Yellow Warbler in southern California collapsed during the mid 20^th century under the double onslaught of the cowbird invasion and the elimination of riparian woodland.  Then, once the Least Bell’s Vireo was formally listed as endangered in 1986, cowbird trapping began at many sites throughout the county, and the Yellow Warbler was among the species whose numbers resurged.  Unfortunately, rigorous numerical data with which these changes in Yellow Warbler abundance could be assessed are lacking, and habitat changes, like the regrowth of riparian woodland in the Tijuana River valley, have played a role too.  In 1984, I called the species only “uncommon” as a summer resident, and counts of dozens in a day along a two- or three-mile strip of river, as found at the most favorable localities now, were unknown.  The species has refilled apparently all of the San Diego County range from which it retracted before 1980.  From 1997 through 2002, we recorded only a single instance of cowbird parasitism on the Yellow Warbler—a female feeding a fledgling cowbird in Kit Carson Park (J11) 24 June 1998 (W. Pray).

Regulations restricting the removal of riparian woodland and channelizing of streams have been critical in slowing the loss of the Yellow Warbler’s habitat.  Also, the damming of rivers has largely eliminated the flooding that once knocked over large trees, allowing more woodland to mature to the point where it attracts Yellow Warblers.  Continuing negative factors, though, are the proliferation of the exotic giant reed, which replaces native riparian trees, and the pumping of groundwater, which lowers the water table to the point where these trees can no longer survive.

 

Taxonomy: The Yellow Warblers nesting in San Diego County, and most migrants as well, are D. p. morcomi Coale, 1887.  The few Rocky Mountain specimens I have seen do not differ consistently from California specimens, dissuading me from following Browning (1994) in resurrecting brewsteri Grinnell, 1903, for the California population (Patten et al. 2003).  Spring males have a yellow forehead contrasting with the greenish remainder of the upperparts.   Each age and sex class considered separately, morcomi is brighter yellow than rubiginosa Pallas, 1811, the darker subspecies breeding along the Pacific coasts of Alaska and British Columbia.  Spring males of rubiginosa have the entire crown green down to the base of the bill.  D. p. rubiginosa migrates through San Diego County in both spring and fall.  Its spring migration is concentrated in the second half of May (7 of 9 SDNHM specimens for this interval), though records extend from 7 April to 1 June (Unitt 1984).  Four fall specimens are from 8 to 15 October, a late one from 21 November, part of the pattern suggesting that rubiginosa is a late migrant in fall (Patten et al. 2003).  Though no winter specimens have been collected, most or all of the Yellow Warblers occurring in winter are bright yellow, implying morcomi.

 

Chestnut-sided Warbler Dendroica pensylvanica

The Chestnut-sided Warbler is a regular fall vagrant to San Diego County, its recent numbers varying from one per year as in 2000 to five in 2002.  There are only five records of spring vagrants.  Twelve Chestnut-sided Warblers are known to have wintered in San Diego County, all since 1983, suggesting the species could be adding southern California to its winter range—there are also 12 winter records from the Salton Sink (Patten et al. 2003).

Migration: In fall the status of the Chestnut-sided typifies that of many eastern warblers.  All records are for the coastal lowland, most from Point Loma (S7), from mid September to late October.  One at Coronado (S9) 17 August 1985 (E. Copper) was exceptionally early.  The spring records are from the Tijuana River valley 5–6 June 1965 (AFN 19:511, 1965), the Sweetwater River at Jamacha (R14) 29 May 1974 (AB 28:854, 1974), Point Loma 5 June 1977 (AB 31:1049, 1977) and 22–23 May 2001 (M. Farley, NAB 55:357, 2001), and Lower Willows (D23) 19 May 2001 (M. L. Gabel, NAB 55:357, 2001).  The last is the county’s only record outside the coastal lowland.

 

Winter: Since two Chestnut-sided Warblers were noted on the Oceanside Christmas bird count 24 December 1983, the species has been found in San Diego about every other winter.  Some of the birds have been in native riparian woodland, as at Kit Carson Park, Escondido (K11; two from 30 December 1993 to 2 January 1994, Escondido, K. L. Weaver, NASFN 48:249, 1994; one on 30 December 2000, P. Unitt).  Others have been in gardens or ornamental trees in heavily urbanized areas, such as one on the grounds of the Self-Realization Fellowship, Encinitas (K6), 20 March 2001 (G. C. Hazard, NAB 55:357, 2001), one in a parking lot between the Marriott and Hyatt hotels along downtown San Diego’s waterfront (S9) 18 November 2001–9 March 2002 (M. M. Rogers, NAB 56:225, 2002), and one in the Little Italy neighborhood of downtown San Diego (S9) 19 November–24 December 2003 (M. Sadowski).

Magnolia Warbler Dendroica magnolia

 

The Magnolia is one of the more frequent vagrant warblers reaching San Diego County in fall.  Recent annual totals have varied from two in 2002 to about 10 in 2001.  There are also six records in spring and one in winter.

 

Migration: San Diego County records of the Magnolia Warbler are largely from the usual coastal vagrant traps, in recent years from Point Loma (S7) almost exclusively.  One at Palomar Mountain 2 October 1979 (AB 34:203, 1980) was exceptional.  Occurrences are concentrated from late September to mid October but range from 5 September (1986, Point Loma, R. E. Webster, AB 41:146, 1987) to 22 November  (1964, Rancho Santa Fe, L8, AFN 19:81, 1985).

            Of the six spring records, four are from Point Loma: 18 June 1970 (AFN 24:645, 1970), 25 May 1983 (R. E. Webster, AB 37:913, 1983), 26 May 1993 (M. B. Stowe, AB 47:454, 1993), and 6 June 2001 (R. E. Webster, NAB 55:483, 2001).  One was at sea 75 miles off San Diego 5 June 1979 (AB 33:806, 1979), and one was in Cuyamaca Rancho State Park 8 June 1991 (J. F. Walters, AB 45:497, 1991).

 

Winter: The single winter record is of one at Point Loma November 1999–7 January 2000 (R. E. Webster, NAB 54:106, 222, 2000).

 

Conservation: Occurrences of the Magnolia Warbler in California increased significantly from 1972 to 1994, in an inverse correlation with the abundance in eastern Canada of the Cape May and Bay-breasted Warblers and their primary prey, the spruce budworm (Patten and Burger 1998).

Cape May Warbler Dendroica tigrina

 

The Cape May Warbler commutes between a breeding range mainly in central and eastern Canada and a winter range mainly in the West Indies, so California is far from its normal migration route.  Vagrants here were strongly concentrated from the mid 1970s to the mid 1980s, a period when the Cape May Warbler’s principal summer prey, the spruce budworm, proliferated in eastern Canada, probably leading to a spike in the warbler’s population (Patten and Burger 1998).  There are about 28 records for San Diego County.

 

Migration: Fall records of the Cape May Warbler in San Diego County are all from Point Loma, the Tijuana River valley, or Otay Mesa, except for one at Carlsbad 23 November 1962 (AFN 17:71, 1963).  Fall dates range from 14 September (1991, Point Loma, R. E. Webster, AB 46:151, 1992) to 23 November.  San Diego County went without a single Cape May Warbler from 1993 to 2003, when one was at Point Loma 1–14 November (D. V. Blue).  There are three spring records, all from Point Loma, of a female 1–3 June 1977, a male 9 June 1977 (AB 31:1048, 1977), and a male 30–31 May 1987 (B. Florand, AB 41:489, 1987).

 

Winter: The Cape May Warbler is known to have wintered in San Diego County twice, with one at Point Loma 10 November 1979–6 January 1980 (AB 34:308, 1980) and another in the nearby neighborhood of Loma Portal (R8) 25 December 1986–16 February 1987 (G. McCaskie, AB 41:331, 1987).  The latter foraged primarily in eucalyptus trees, toward the end of its stay becoming stained almost completely black with eucalyptus pitch.

Black‑throated Blue Warbler Dendroica caerulescens

 

In spite of breeding only in eastern North America and wintering in the West Indies, the Black-throated Blue Warbler is a regular visitor to California.  San Diego County gets the species nearly every year, with up to 12 in 1988.  The species is disproportionately scarce in spring, when there are only three records for the county.  It has been found three times in winter also.

 

Migration: As for most vagrant warblers, San Diego County records of the Black-throated Blue are concentrated along the coast.  A few, though, are scattered farther inland, as at Valley Center (G11; 11 November 1971, AB 26:123, 1972), Grable Ranch (M16; 29 September 1992, R. T. Patton), and 1.3 miles southwest of Iron Mountain (M13; struck the window of a house about 4 October 1998, SDNHM 50143).  The species occurs rather late in the fall; dates range from 29 September to 6 December (1987, San Diego, P. D. Jorgensen, AB 42:323, 1988), with the winter records excluded.

            The spring records are of one at Point Loma (S7) 18 May 1992 (M. B. Grossman, AB 46:482, 1992), one at Clark Dry Lake (E26) 4 June 1995 (M. L. Gabel, Massey 1998), and one in Cuyamaca Rancho State Park 9 June 1995 (J. Herried, NASFN 49:982, 1995).

 

Winter: San Diego County’s three wintering Black-throated Blue Warblers were at Old Mission Dam (P11) 25 December 1974–5 January 1975 (AB 29:744, 1975), Oakzanita Springs (O20) 20 December 1995–1 January 1996 (at the unexpectedly high elevation of 3860 feet, D. W. Povey, NASFN 50:225, 1996), and Coronado (S9) December 1998–28 March 1999 (H. Weeks, NAB 53:210, 1999).

 

Taxonomy: The Black-throated Blue Warbler is often divided into two subspecies; only the more northern nominate D. c. caerulescens (Gmelin, 1789) is likely to reach California, and all of California’s identifiable specimens are of it.

Yellow-rumped Warbler Dendroica coronata

The Yellow-rumped Warbler is probably San Diego County’s most abundant winter visitor.  If the White-crowned Sparrow exceeds it, it is not by much.  Eucalyptus groves and other exotic trees planted in developed areas suit the Yellow-rumped Warbler at least as much as natural sage scrub, chaparral, and woodland.  The birds are strongly concentrated in the coastal lowland but are found almost throughout the county, lacking only from the most rugged parts of the Anza–Borrego Desert.  As a breeding species, however, the Yellow-rumped Warbler is a recent colonist, rare and confined to coniferous forest on San Diego County’s highest mountains.  Because almost all Yellow-rumped Warblers are readily distinguished in the field as belonging to either the eastern or the western group of subspecies, and the status of each is so different, this account refers to them by their traditional names, Audubon’s Warbler for the yellow-throated western birds, Myrtle Warbler for the white-throated eastern ones.  See under Taxonomy for the status of the Myrtle.

Winter: San Diego County must be near the core of the Audubon’s Warbler’s winter range.  The species is common to abundant from the coast up to about 2500 feet elevation.  In this region, daily counts commonly reach into the hundreds, occasionally over 1000 (1300 around Lake Hodges, K10, 22 December 2000, R. L. Barber).  At higher elevations the birds become uncommon and more localized to developed areas.  Above 3500 feet elevation they can be missed, and at the county’s highest elevations they are rare.  Above 5000 feet elevation in the Laguna Mountains, for example, we never encountered more than one individual per day.  In the Anza–Borrego Desert Audubon’s Warbler is abundant in the developed areas of Borrego Springs (up to 328 north of Palm Canyon Drive, F24, 19 December 1999, P. K. Nelson) but much less common in native desert habitats.  It is rare to absent in the least-vegetated tracts of desert and lacking entirely from the pinyon–juniper zone of the Santa Rosa and Vallecito mountains.

Migration: In fall, Audubon’s Warblers may begin arriving in the first week of September or may not show up until mid September.  By the end of September they are common.  The end of fall migration is governed by the weather and food supply (Terrill and Ohmart 1984).  In spring, the birds are apparently on the move by late February, certainly by March (Massey 1998).  Numbers as high as 36 in Blair Valley (L24) 21 February 1998 (R. Thériault) and 40 at Butterfield Ranch (M23) 26 February 2000 (E. C. Hall) had not been approached at these desert locations earlier in the winter.  Audubon’s Warblers depart in late April and early May; by mid May they are scarce.  Stragglers are occasional even in the first week of June.  From 1997 to 2001 the latest were two in Ballena Valley (K17) 5 June 2000 (O. Carter); in 1995 there was one as late as 9 June (San Diego, R. E. Webster, NASFN 49:308, 1995).  There is also one unseasonal summer record far from plausible breeding habitat, of one at Blue Sky Ecological Reserve, Poway (L12), 23 June 1998 (M. and B. McIntosh, FN 52:504, 1998).

Breeding distribution: Audubon’s Warbler is another of those birds, like the Fox Sparrow, Green-tailed Towhee, and Dusky Flycatcher, whose breeding habitat lies in an elevation zone barely pierced by San Diego County’s highest peaks.  The warblers are now of annual occurrence in the Cuyamaca Mountains, with up to eight, including five singing males, on Middle Peak (M20) 11 June 2000 (R. E. Webster) and six on Cuyamaca Peak (M20) 5 June 2001 (M. B. Mulrooney).  On Cuyamaca Peak almost all Audubon’s Warblers are found on the northeast slopes, with only one report from the south slope (N20; adult with fledgling 18 June 2000, G. Hazard).  On Cuyamaca Peak the birds occur above 5200 feet elevation, but on Middle Peak they go down to 4920 feet (R. E. Webster).  Since 1986 Audubon’s Warblers have summered at least irregularly above 6000 feet elevation near the summit of Hot Springs Mountain (E20).  The maximum count there is of four, all singing males, 9 June 2001 (K. L. Weaver, C. R. Mahrdt).  One on the steep north-facing slope south of Doane Pond in Palomar Mountain State Park (E14) 21 May 2000 (G. Hazard) could have been a late migrant but was more likely a summering bird, as previous summer sightings from Palomar are known (Unitt 1984).

Nesting: In the higher mountains of southern California, Audubon’s Warblers usually nest in the outer branches of the middle levels of conifers.  A nest on Middle Peak in 2004 was in a burned canyon live oak retaining toasted leaves.  Dates of fledglings range from 18 June to 14 July; sightings of adults carrying insects, possibly to young still in the nest, are as early as 27 May.

Conservation: Yellow-rumped Warblers may have benefited from urbanization, urban trees offering more habitat than sage scrub.  In any case, no trends in the number of winter visitors are obvious.  As a breeding bird, however, the species is a recent arrival.  Though the first summer report, from Palomar Mountain, was as long ago as 1949, the species’ breeding was not confirmed until 1986, with a pair feeding fledglings on Hot Springs Mountain 12 July (G. McCaskie, AB 40:1256, 1986).  Unitt (1981) had not found the warblers on this mountain in 1980, so it is almost certain the birds first colonized about the time they were confirmed breeding.  They became regular on Cuyamaca Peak only in the late 1980s as well.  Thus Audubon’s Warbler is part of the pattern exemplified by several breeding birds of southern California’s high mountains, extending their range to the comparatively low summits of San Diego County’s peaks.  Sometimes, as in the case of Audubon’s Warbler, this means filling in a gap between the San Jacinto Mountains to the north and the Sierra San Pedro Mártir to the south.

Taxonomy: The dominant subspecies of the Yellow-rumped Warbler in San Diego County is D. c. auduboni (Townsend, 1837).  In the western United States, north of southeastern Arizona, Audubon’s Warbler is often divided into two subspecies, smaller auduboni in the Pacific states, larger D. c. memorabilis Oberholser, 1921, in the Rocky Mountain region.  The size difference, however, needs better quantification before its ability to define a subspecies can be assessed.  Breeding males of memorabilis tend to be blacker than those of auduboni, but the difference is of no help in identifying the birds in their winter plumage.

            The Myrtle Warbler reaches San Diego County as an uncommon winter visitor, flocking indiscriminately with Audubon’s Warblers in riparian woodland but avoiding dry scrub.  Most records are from the coastal lowland, but there are some from Borrego Springs and as high as 3200 feet elevation near Warner Springs (F19; one on 18 December 2000, C. G. Edwards).  The highest count during the atlas period was of 11 at Lake Hodges (K10) 22 December 2000 (R. L. Barber), but past daily tallies run as high as 30 in Tijuana River valley 17 December 1977 (P. E. Lehman).  Dates for the Myrtle range from 5 October to 23 May (Unitt 1984).  The Myrtle Warbler too is usually divided into two subspecies; only the larger, more western D. c. hooveri McGregor, 1899, has been reported from California.

Black-throated Gray Warbler Dendroica nigrescens

William E. Haas

The handsome Black-throated Gray Warbler occurs in San Diego County primarily during migration, but even then it is only uncommon to fairly common.  It is rare but regular in winter, when several are found annually, mainly in riparian woodland or ornamental trees.  Historically, the species was rare in summer, though the atlas study revealed small numbers in mixed conifer–oak woodland in all of the county’s higher mountain ranges.  Remarkably, in the late 1990s a population burgeoned in the canyon of the San Luis Rey River just below Lake Henshaw, swelling to more than 70 pairs by 2003.

Breeding distribution: The Black-throated Gray Warbler is most widespread on Hot Springs Mountain, where it occurs uncommonly around the base as well as near the summit (up to five, including four singing males, in Lost Valley, D21, 25 June 1998, P. Unitt).  It breeds more sparsely on Palomar Mountain (two family groups one quarter mile apart near the Palomar Observatory, D15, 12 July 2000, K. L. Weaver), on Volcan Mountain (H20; one on 23 or 30 May 1999, A. P. and T. E. Keenan; I20; three 30–31 May 1993, P. Unitt), in the Cuyamaca Mountains (up to six, including four singing males, at William Heise County Park, K20, 19 May 1998, E. C. Hall), and in the Laguna Mountains (up to five singing males near Oasis Spring, N23, 24 May 2001, K. J. Winter).

            Completely unexpected was the Black-throated Gray Warbler’s colonization of the San Luis Rey River between Lake Henshaw and La Jolla Indian Reservation.  Other nesting locations for the species in San Diego County are at elevations of 4200 feet and above, but the section of canyon the warblers inhabit along the San Luis Rey ranges in elevation from 2300 to 2700 feet.  The Black-throated Gray first appeared as a summer visitor in this area, which Haas has studied intensively since 1993, only in 1995, when it nested.  The numbers soon ballooned astonishingly, reaching at least 25 pairs in 2000 and at least 70 in 2003.  Elsewhere in San Diego County the species’ breeding habitat is patchy woodland of pine and oak, especially the canyon live oak, at least on Palomar and Hot Springs mountains (K. L. Weaver).  But along the San Luis Rey the coast live oak dominates, with velvet ash and willow trees at the water’s edge.

Nesting: Haas has found 26 Black-throated Gray Warbler nests along the San Luis Rey River; all were as described by Bent (1953), built of grasses and leafy forbs, bits of cocoons, dry leaves, plant down, and hair, always with feathers woven into the interior lining.  Harrison (1978) reported that nests are woven together and suspended from the branch with spider webs; E. C. Hall observed a female making repeated trips for nest material to spider webs at William Heise County Park.  Nests found recently in San Diego County were built well out on lower to intermediate limbs of coast live oaks along the San Luis Rey River, in canyon live oaks on Palomar and Hot Springs mountains, in incense cedar in the Cuyamaca Mountains, and in ponderosa pine on Palomar (W. E. Haas, K. L. Weaver).  All nests were 15 or more feet above the ground; two along the San Luis Rey River were over 40 feet above the ground.

            Bent (1953) reported clutch sizes of three to five, with four the usual number. Along the San Luis Rey River fledglings are usually three or four per brood, with some variation from year to year, possibly related to weather and availability of prey.  The Black-throated Gray Warbler is generally thought to have only one brood per year, but observations of adults with nest material into June and nests with eggs as late as July suggest double broods (Guzy and Lowther 1997).  During the atlas period at least two pairs along the San Luis Rey River raised two broods per year, in 1999 and 2001 (W. E. Haas).

            In San Diego County Black-throated Gray Warblers lay eggs at least from early May to mid June.  Most young have fledged by mid July.

Migration: In spring, the Black-throated Gray Warbler arrives annually in late March.  During the atlas period, first dates ranged from 24 to 30 March.  One in Balboa Park (R9) 10 March 1998 (J. K. Wilson) had presumably wintered in the area; the earliest spring arrival date recorded is 20 March (1976, AB 30:886, 1976; 1983, AB 37:911, 1983).  Migrants continuing northward pass through the county primarily in April; our largest counts were of 22 at Wilderness Gardens (D11) 5 April 1997 (V. Dineen), 28 in Carrizo Valley (O28) 19 April 2000 (D. C. Seals), and 25 at Vallecito (M25) 29 April 1997 (M. C. Jorgensen).  Few are seen after the middle of May; our latest records of spring migrants are of two along Vallecito Creek near Campbell Grade (M23) 20 May 1999 (R. Thériault) and one near Barrel Spring (G20) 24 May 1998 (C. G. Edwards).  The birds arrive in local breeding habitat beginning in late April and remain through July.   Fall migration extends mainly from 15 August (1998, one along Roblar Creek, C5, J. M. Wells) through November.  Single birds along the Elephant Tree Trail (K29) 3 December 1991 (A. G. Morley) and at Tamarisk Grove (I24) 4 December 1988 were probably late migrants.  Fall migrants are fewer than spring migrants, with no more than five per day and usually only one or two.

Winter: San Diego County lies at the northern edge of the Black-throated Gray Warbler’s usual winter range.  Countywide, about 10 were reported per year through the atlas period. Eight on the San Diego Christmas bird count 18 December 1999 was a record high for the county, though the maximum per atlas square per day was only two.  Almost all wintering Black-throated Gray Warblers are in the coastal lowland, but birds near Margarita Peak (B5) 31 January 1988 (W. E. Haas) and near Oakzanita (O20) 13 and 28 January 1999 (D. W. Povey, M. B. Stowe) were at elevations up to 3900 feet in oak woodland more suited to breeding.  There are also three late December records from the Borrego Valley from Anza–Borrego Christmas bird counts.

Conservation: Although the Black-throated Gray Warbler is not a common species, its numbers in San Diego County appear to be on the rise.  Reasons for the sudden expansion into the oak woodlands below the Lake Henshaw dam could include displacement from forest at higher elevations following a nearby fire in 1999 and the low level of cowbird parasitism currently enjoyed by all songbirds nesting at this site.  This species may be a good colonizer once it invades suitable new habitats; for example, it has colonized Vancouver Island only since 1950 (Guzy and Lowther 1997).  It also responds positively to the early successional stages of forest regeneration within certain forest types (Paige et al. 1999).

 

Taxonomy: The Black-throated Gray Warbler is sometimes divided into two subspecies, a shorter-winged nominate D. n. nigrescens (Townsend, 1837) breeding west of the Cascade Range in the Pacific Northwest, south to northern California, and a longer-winged D. n. halseii (Giraud, 1841) with more white in the tail breeding in the remainder of the species’ range.  Morrison (1990) identified a difference in song between these two populations in Oregon, but adequate testing of the size and plumage differences over the entire range of the species, which would allow a decision on the subspecies’ validity, has yet to be done.  Migrants and winter visitors to San Diego County are presumably nominate nigrescens, but the identity of the local breeding population is unclear.  When he proposed the division of the Black-throated Gray into two subspecies, Oberholser (1930) included southern California in the breeding range of halseii.

Black‑throated Green Warbler Dendroica virens

 

The Black-throated Green Warbler replaces the Hermit and Townsend’s east of the Rocky Mountains.  Like other warblers breeding in Canada’s boreal forest, however, it strays to California regularly in fall migration.  One or two are reported in San Diego County in most years, with six in 1975 and 1986.  There are only two records in spring.  The pace of winter records has accelerated since the first in 1978: at least seven Black-throated Green Warblers have wintered in the county, some of them returning repeatedly.

 

Migration: Most of San Diego County’s Black-throated Green Warblers have been along or near the coast, but two have been in the Anza–Borrego Desert, at Yaqui Well (I24) 24 October 1963 (AFN 18:75, 1964) and Clark Dry Lake (D25) 15 November 1989 (D. and M. Hastings, AB 44:164, 1990).  Most occurrences are from mid September through early November; earliest was one in San Clemente Canyon (P8) 7 September 1974 (AB 29:123, 1975).  The two spring records are of a male photographed near San Diego 7 June 1987 (L. Walton, AB 41:489, 1987) and one at Point Loma (S7) 27–29 May 1996 (R. E. Webster, NASFN 50:334, 1996).

 

Winter: Sites of San Diego County’s wintering Black-throated Green Warblers are Guajome Lake (G7; returned four consecutive winters 24 December 1995–6 February 2000, P. A. Ginsburg, NAB 54:106, 222, 2000), Buena Vista Lagoon (H5; 22 December 2001, P. Unitt, NAB 56:224, 2002), Spring Valley (R12) 20 January–21 February 2002 (M. Hastings, NAB 56:224, 2002), Coronado (S9; 30 November–2 March 2002, E. Copper, NAB 56:107, 2002), National City (T11; returned seven consecutive winters 27 November 1996–19 February 2003, D. W. Aguillard, NAB 57:118, 258, 2003), and Otay Valley (V11; returned three consecutive winters 16 December 1978–15 February 1981, AB 35:336, 1981; also 18 December 1999, P. Unitt, NAB 54:222, 2000).  In 1998 the bird in National City remained as late as 10 April.

 

Conservation: The upsurge of wintering Black-throated Green Warblers beginning in 1995 suggests an expansion of the species’ winter range, as the rate of fall records has not accelerated.

Townsend’s Warbler Dendroica townsendi

A bird of coniferous forests in its breeding range in the Pacific Northwest, Townsend’s Warbler is partial to conifers as it passes through San Diego County on its way to and from its winter range in the mountains of Middle America.  The species winters commonly on the coast of central California and increasingly in southern California.  It is still uncommon as a winter visitor in San Diego County but uses planted conifer, alder, and eucalyptus trees more than native oaks and willows.  Its spread as a winter visitor may reflect urbanization, climate change, or both.

Migration: Townsend’s Warbler occurs in San Diego County most commonly as a spring migrant.  It is less abundant than some other migrant warblers, like the Orange-crowned, Wilson’s, or Yellow, but occasionally concentrations are seen, such as 50 at Vallecito (M25) 29 April 1997 (M. C. Jorgensen), 20 near Little Stonewall Creek (M21) 6 May 1999 (P. D. Jorgensen), and 25 on the ridge of the Santa Rosa Mountains just south of the Riverside County line (C27) 3 May 2000 (P. Unitt).  On the last date, the birds were migrating northwest with other warblers from dawn to 9:00 AM, flying up the canyons out of the desert, stopping for only a few seconds in the pinyons on the ridge, then continuing their flight.  Reflecting the origin of most of the migrants in western mainland Mexico, Townsend’s Warblers are more numerous in spring in the eastern half of the county than along the coast.  They arrive typically in mid April; 8 April (2000, one at Ocotillo Wells, I29, R. Miller) is the earliest spring date from a location where the bird probably did not winter.  Migration peaks in early May, then trails off to the end of that month.  From 1997 to 2001 the latest spring date reported was 31 May (1999, one at Sentenac Ciénaga, J23, R. Thériault), though stragglers have been noted in past years through the first week of June.

            An unprecedented summer record was of two singing Townsend’s Warblers in sycamores along the San Luis Rey River at 2600 feet elevation 0.85 mile southeast of the San Luis Rey Day Use Area (G16) 16–23 June 2000 (W. E. Haas).

            Fall migrants begin arriving in August, exceptionally as early as 28 July (2001, one at Buena Vista Lagoon, H6, J. Smith et. al.).  Wintering birds, however, do not seem to occupy their habitat before October.

Winter: Wintering Townsend’s Warblers concentrate in a narrow strip along the coast, using both native riparian woodland and ornamental trees in parks, cemeteries, and residential areas.  High counts are of 14 in Balboa Park (R9) 15 December 2001 (V. P. Johnson) and 14 in Imperial Beach (V10) 18 December 1999 (C. G. Edwards).  In the inland valleys wintering Townsend’s Warblers are sparser but can be found in small numbers especially where the white alder is a major component of riparian woodland or used in landscaping.  Numbers in this area range up to five along the Santa Margarita River north of Fallbrook (C8) 10 January 1999 (L. Ale), five in Kit Carson Park, Escondido (J11), 29 December 2001 (P. Hernandez), exceptionally 11 in Valley Center (G11) 28 February 2002 (S. L. and S. J. Farrow).

            One unexpected revelation of the winter phase of the study was the regularity of Townsend’s Warblers in the pine–oak woodland of San Diego County’s mountains.  The Palomar, Hot Springs, Volcan, and Cuyamaca mountains all stand out as isolated regions of Townsend’s Warbler wintering.  We recorded the species on 27 occasions above 3000 feet elevation, usually single birds, but up to three at Palomar Mountain (E15) 30 December 1999 (E. C. Hall) and three on West Mesa, Cuyamaca Mountains (N20), 3 January 1999 (B. Siegel). In the Anza–Borrego Desert and on the Campo Plateau wintering Townsend’s Warblers are rare; during the atlas period there were only two records in each area.

Conservation: In spite of being a species of mature coniferous forest breeding in an area subject to massive logging, Townsend’s Warbler appears to be expanding its breeding range in the Pacific Northwest southward, possibly at the expense of the Hermit Warbler (Rohwer and Wood 1998, Rohwer et al. 2001).  Numbers on San Diego Christmas bird counts are greater now than in the 1960s, possibly because of increased area landscaped with the conifers and white alder trees preferred by wintering Townsend’s Warblers.  The change may be part of a trend going back decades, as Willett (1933) said that Townsend’s Warbler wintered in southern California only “occasionally,” and Stephens (1919a) did not mention its wintering in San Diego County at all.  The species’ wintering in San Diego County’s mountains appears to be a recent development, possibly the result of climatic warming.  Such warming is most evident in this area by an increase in winter low temperatures at higher elevations.

Hermit Warbler Dendroica occidentalis

One of our most attractive western warblers, in San Diego County the Hermit Warbler is also one of the least commonly seen.  It is now uncommon in spring migration, rare in fall migration, and very rare in winter.  There are no midsummer records; the San Bernardino Mountains are the southern tip of the Hermit Warbler’s breeding range.  Reflecting their habitat preference at other seasons, migrants are often seen high in conifers, be they planted as landscaping in urban parks.  Unfortunately, the species’ numbers may be declining.  Both the main breeding habitat, forests of Douglas fir in the Pacific Northwest, and the main winter habitat, pine–oak forests in the mountains of Middle America, are subject to large-scale logging.  Better quantitative data are needed, but the number of migrants moving through San Diego County appears less than it did 30 years ago.

Migration: The Hermit Warbler passes quickly through San Diego County on its spring migration; the birds are strongly concentrated in late April and early May.  The range of spring dates recorded during the atlas period essentially equaled that recorded previously, extending from 12 April (one on the east slope of Whale Peak, L26, J. R. Barth) to 6 June (2000, one along upper La Posta Creek, P24, D. C. Seals).  First spring dates from 1997 to 2001 varied from 12 to 21 April.  During atlas’ five-year term, highest daily count was of 15 near Little Stonewall Creek, Cuyamaca Mountains (M21), 6 May 1999 (P. D. Jorgensen); subsequently, 30 were around the head of Chariot Canyon (L21) 26 April 2003 (R. C. Sanger).  The Hermit is widespread through San Diego County in spring migration but, like other migrant warblers, may be concentrated by headwinds as it ascends the east slope of the county’s mountains.  Preferring conifers, it often pauses in montane woodland.

            Fall migrants are known from 19 July (1987, one on Middle Peak, M20, R. E. Webster, AB 41:1489, 1987) to early November.  Some adults may pause in San Diego County’s mountains in August, but the scattered individuals seen later in the fall are probably all straggling immatures.  San Diego County lies astride the Hermit Warbler’s spring migration route but off its fall migration route.

Winter: Far from the species’ main winter range in central Mexico, small numbers of Hermit Warblers winter regularly on the coast of central California.  South of Point Conception, their numbers decrease markedly. At the latitude of San Diego County the Hermit Warbler is very rare.  Six individuals were reported during the five-year atlas period, at O’Neill Lake (E6, 19 December 1997, P. A. Ginsburg), near Bonsall (F8, 6 December 2000, P. A. Ginsburg; 23 December 2000–12 February 2001, J. Evans), in Kit Carson Park (K11, 2 January 2001, J. D. Barr), in Mt. Hope Cemetery (S10, 19 December 1997–22 January 1998, P. Unitt, FN 52:259, 1998), and at the Dairy Mart pond, Tijuana River valley (V11, 19 December 1998–23 January 1999, G. McCaskie, NAB 53:210, 1999).  Only about 20 Hermit Warblers have been noted wintering in the county ever.  Interestingly, nearly half of them have been in north-coastal San Diego County, in spite of birders’ more intensive coverage of the south coast, implying the species’ north–south trend of winter abundance is perceptible even within San Diego County.

Conservation: The Hermit Warbler appears to be on the decline as a migrant through San Diego County.  It can no longer be called “fairly common to common,” as I did in 1984.  Concentrations of 30 to 40 in a day, as seen occasionally in the 1960s and 1970s, are no longer encountered along the coast.  Likely negative factors for this bird of mature coniferous forest are logging of both the summer and winter ranges and displacement at the northern edge of the breeding range by Townsend’s Warbler (Rohwer and Wood 1998).

Blackburnian Warbler Dendroica fusca

 

In spring the Blackburnian Warbler, the male with its flaming orange throat framed in black, is one of the most spectacular warblers.  In California, however, the Blackburnian is seen in fall almost exclusively, when it can be confused with the immature female Townsend’s Warbler.  The Blackburnian occurs in San Diego County nearly annually, typically with only one or two reported.  Two winter records are surprising because the species winters mainly in South America.

 

Migration: The fall of 2001 was an exceptional year for the Blackburnian Warbler in San Diego County, yielding at least six individuals on Point Loma (S7).  Most of the county’s Blackburnians have been there or in the Tijuana River valley.  The most inland fall locality is Old Mission Dam (P11; 27 September 1977, B. Cord), except for the single record for the Anza–Borrego Desert, at Agua Caliente Springs (M26; 10 October 1977, AB 32:262, 1978).  The county’s only spring record is of a male at Point Loma 4 June 1985 (R. E. Webster, AB 39:351, 1985).

 

Winter: One Blackburnian was in Santee (P12) 26 December 1988 (D. S. Cooper, AB 43:368, 1989); another was in Imperial Beach (V10) 8 December 2003–14 February 2004 (M. Sadowski).

Yellow-throated Warbler Dendroica dominica

The Yellow-throated Warbler is one of the scarcer eastern warblers reaching California, though 17 have been recorded in San Diego County.  Most eastern warblers occur here predominantly in fall, so the Yellow-throated is unusual in that over half have been found in spring.  Furthermore, though most spring vagrants show up in late May and early June, five of San Diego County’s nine spring Yellow-throated Warblers were found in April.

Migration: The nine spring records range in date from 10 April (1997, Point Loma, S7, P. A. Ginsburg, Rottenborn and Morlan 2000) to 7 June (1979, Point Loma, Binford 1983).  All are for Point Loma except for one for Presidio Park (R8) 23 April 1974 (Luther et al. 1979) and one for Encinitas (K6/K7) 29 April 1979 (Luther et al. 1983).  The seven fall records range in date from 19 September (1973, Point Loma, AB 28:110, 1974) to 5 November (1979, Point Loma, Craig 1972).  All are for Point Loma except for one for the Tijuana River valley 3 October 1976 (Dunn 1988), one for Torrey Pines State Reserve (N7) 8–9 October 1986 (Langham 1991), and one for Solana Beach (L7) 24 October 2001 (P. A. Ginsburg; Garrett and Wilson 2003).

Winter: Just six Yellow-throated Warblers have been reported wintering in California.  One of these was in San Diego County, frequenting palms planted in a business park on Mira Mesa (N9) 24 January–21 March 2001 (T. R. Clawson, Garrett and Wilson 2003).

 

Taxonomy: Fifteen of San Diego County’s Yellow-throated Warblers were of the white-lored subspecies D. d. albilora Ridgway, 1873.  Two, however, were apparently the yellow-lored nominate D. d. dominica (Linnaeus, 1766), which breeds along the Atlantic coast, east of the Appalachian Mountains: at Point Loma 15 October–5 November 1969 (Craig 1972) and at Solana Beach 24 October 2001.  No Yellow-throated Warbler has yet been colleted in San Diego County, though the bird at Point Loma was examined in hand and photographed.

Grace’s Warbler Dendroica graciae

Grace’s Warbler nests just across the California border in the mountains of southern Nevada and northwestern Arizona, perhaps occasionally in the mountains of the eastern Mojave Desert.  But it is only a rare vagrant to southern California’s coast.  There are 14 well-supported records for San Diego County, 11 of fall migrants, three of winter visitors, two of which involve birds returning for successive years.  Even in migration and winter Grace’s Warbler has a strong preference for conifers or trees, like athel tamarisk, whose foliage mimics that of conifers.

Migration: San Diego County’s fall Grace’s Warblers accepted by the California Bird Records Committee are all from the Tijuana River valley (four) or Point Loma (seven).  Their dates range from 8 September (1968, Point Loma, Craig 1970) to 29 October (1966, Tijuana River valley, SDNHM 36047, the only specimen).  Two 1987 sightings published in American Birds but not submitted to the committee fall within these dates.

Winter: One was at La Jolla (P7) 13 February–3 April 1988 (R. E. Webster; Pyle and McCaskie 1992).  One was in Fort Rosecrans National Cemetery, Point Loma, 20 September 2001–20 April 2002 (G. McCaskie, Garrett and Wilson 2003), evidently returning 11 September 2002–2 February 2003 and 11 September 2003; it was joined by another Grace’s Warbler after 9 November 2003.  One at the San Dieguito River mouth, Del Mar (M7), 9 November 2001 (E. Copper; Garrett and Wilson 2003) returned the next year, being seen 8 January 2003 (NAB 57:258, 2003).

Pine Warbler Dendroica pinus

Characteristic of pine forests of eastern North America, the Pine Warbler is a rare but increasing vagrant to California.  The California Bird Records Committee has accepted 24 records for San Diego County, 17 for fall, six for winter, and one for spring.

Migration: San Diego County’s fall Pine Warblers have all been found in the Tijuana River valley (eight) or at Point Loma (eight), except for one in Presidio Park (R8) 6 November 1988 (Pyle and McCaskie 1992).  Their dates range from 4 October (2001, Point Loma, R. E. Webster; Garrett and Wilson 2003) to 10 November (1992, Point Loma, R. E. Webster, Heindel and Patten 1996).  The records committee rejected the report for 18 September 1971; well-supported California records of the Pine Warbler are notably late in the fall.  The single spring record is of a singing male in Torrey Pines State Reserve (N7) 5–6 June 1987 (J. O'Brien; Langham 1991).

 

Winter: The California Bird Records Committee has accepted one winter record for Coronado (S9), 15 December 1984–9 March 1985 (E. Copper, Bevier 1990), one for San Diego, 3–21 March 1991 (D. M. Parker, Heindel and Garrett 1995), and three for Point Loma, 12–23 December 1983 (R. E. Webster, Roberson 1986), 6 January–12 April 1992 (P. A. Ginsburg, Heindel and Patten 1996), and 3 April 2002 (V. P. Johnson, Cole and McCaskie 2004).  Two wintering Pine Warblers were found at Veterans’ Park, Imperial Beach (V10) 7 December 2003–27 January 2004 (M. Billings).

 

Conservation: California occurrences of the Pine Warbler spiked from 1983 to 1993, perhaps reflecting a spike in the species’ total population.  A possible long-term change is the Pine Warbler’s increasing frequency in winter; California’s first winter record was in 1978, yet by 2002 winter records statewide reached 25.

 

Taxonomy: Nominate D. p. pinus (Wilson, 1811) is the subspecies breeding throughout the eastern United States except Florida and is the subspecies reaching California.

Prairie Warbler Dendroica discolor

 

Even though it breeds mainly in the southeastern United States and winters mainly in the West Indies, the Prairie Warbler is seen nearly annually as a fall vagrant in San Diego County.  There are five records in winter but none in spring.

 

Migration: Fall records of the Prairie Warbler in San Diego County are mainly from Point Loma and the Tijuana River valley, with a few as far inland as Otay Mesa (V11) and O’Neill Lake (E6; 27 September 2000, P. A. Ginsburg).  They are concentrated from early September to mid October but range from 16 August (1977, Tijuana River valley, AB 32:263, 1978) to 14 December (2002, Cabrillo National Monument, Point Loma, J. C. Worley).  The latter bird was apparently attempting to winter, as it had been in the area continuously from 23 September.

 

Winter: San Diego County’s five definitely wintering Prairie Warblers were in Otay Valley (V11) 19 December 1969–24 January 1970 (AFN 24:540, 1970), Coronado (S9) 15 December 1979–6 January 1980 (when found dead, SDNHM 41418), Los Peñasquitos Canyon (N8) 3 November 1991–5 April 1992 (C. G. Edwards, AB 46:151, 315, 1991), Santee (P12) 31 March 1996 (D. Yee, NASFN 50:225, 1996), and in the Anza–Borrego Desert at Carrizo Palms (R28) 8 February 1998 (J. O. Zimmer, FN 52:259, 1998).

 

Taxonomy: San Diego County specimens of the Prairie Warbler are nominate D. d. discolor (Vieillot, 1807), the subspecies widespread in the eastern United States.

Palm Warbler Dendroica palmarum

The Palm Warbler’s name is a historical accident.  The species nests in the taiga zone east of the Rocky Mountains and winters mainly in the southeastern United States, the Yucatan Peninsula, and West Indies, where it prefers rather open, scrubby habitats whether these have palms or not.  It is a rare but regular fall migrant and winter visitor to the California coast, less frequent in San Diego County than farther north.

Migration: In San Diego County, as elsewhere in California, the Palm Warbler is seen mainly along the coast.  As for other eastern warblers, Point Loma and the Tijuana River valley account for most sightings, but the Palm Warbler has been seen at many other sites as well.  Exceptionally far inland were one at Lindo Lake (O14) 31 October 1999 (M. B. Mulrooney), two at Lake Henshaw (G17) 4 October 1982 (R. Higson AB 37:225, 1983), and the three fall records for the Anza–Borrego Desert, of single birds at Tamarisk Grove (I24) 12 November 1989 (M. Green, AB 44:164, 1990) and 12 October 1996 (P. D. Jorgensen) and in Quartz Vein Wash (I25) 22 October 1996 (P. D. Jorgensen).

            The Palm Warbler occurs rather late in fall migration, mainly from early October to mid November.  One at Point Loma 9 September 1981 (D. Rawlins, AB 36:219, 1982) was exceptionally early.  The number of Palm Warblers reported per fall in San Diego County recently has varied from about eight in 2001 and 2002 to only one in 2000.

            Sightings of Palm Warblers through the end of April most likely represent wintering birds.  Individuals known to have wintered have remained in the Tijuana River valley to 10 April 1983 (J. Oldenettel, AB 37:913, 1983) and at Greenwood Cemetery (S10) to 20 April 2002 (M. Lubin).  The only records more likely to represent spring migrants are from O’Neill Lake (E6) 6 May 2003 (P. A. Ginsburg), Point Loma 7 May 1982 (R. E. Webster, AB 36:895, 1982) and 7 June 2003 (D. Langhoff), and Agua Caliente Springs (M26) 4 May 1996 (G. L. Rogers, NASFN 50:334, 1996).

 

Winter: One or two wintering Palm Warblers are noted in San Diego County annually.  The five-year atlas period, 1997–2002, yielded nine.  All of the county’s wintering Palm Warblers have been within 10 miles of the coast, except for one at the Morena Conservation Camp, elevation 3060 feet (S21/S22), 23 January 1999 (S. E. Smith).

Conservation: Like some other eastern warblers, the Palm Warbler had a spike in the numbers found in San Diego County in the late 1970s.  The San Diego Christmas bird count recorded its maximum of nine in the Tijuana River valley 15 December 1979.  No decrease since then has been reported in the breeding range or elsewhere in California, so the apparent change may be due to local habitat changes (fewer low, damp weedy areas) or simply a change in birders’ habits in fall migration (narrower focus on Point Loma, which lacks riparian scrub more appealing to Palm Warblers).

Taxonomy: As expected, it is the Western Palm Warbler, D. p. palmarum (Gmelin, 1789) that occurs predominantly in San Diego County.  There are, however, nine records of D. p. hypochrysea Ridgway, 1876, even though it breeds east of Hudson Bay.  Unitt (1984) listed seven through 1981; subsequently, one was at Point Loma 15 October 1985 (C. G. Edwards, AB 40:160, 1986) and one was at San Diego 16 October 1993 (G. McCaskie, AB 48:153, 1994).

Bay‑breasted Warbler Dendroica castanea

 

Breeding in mainly in Canada’s boreal forest, the Bay-breasted Warbler fluctuates in numbers with its primary prey, the spruce budworm.  Numbers of vagrants reaching California vary in tandem, so that the warbler averaged one per fall in San Diego County from the 1970s to the mid 1980s but only 0.2 per fall by the turn of the century.

 

Migration: Most of San Diego County’s approximately 41 Bay-breasted Warblers have been at the usual sites for vagrants, Point Loma and the Tijuana River valley.  None has been found farther inland than Otay Mesa (V13; 29 September 1973, AB 28:110, 1974).  Fall dates range from 9 September (1991, Point Loma, R. E. Webster, AB 46:151, 1991) to 20 November (1985, same location, C. G. Edwards, AB 40:160, 1986), unless one at Coronado 17–21 December 1983 (R. E. Webster, AB 38:358, 1984) is considered a late fall straggler rather than a wintering bird.

            Four Bay-breasted Warblers have been noted in San Diego County in spring, at Point Loma 5–6 June 1979 (AB 33:806, 1979) and 25–28 May 1981 (E. Copper), at Coronado (S9) 15 June 1983 (E. Copper, AB 37:913, 1983), and at Pine Valley (P21) 23 June 1993 (C. G. Edwards, AB 47:1151, 1993).

 

Winter: The one Bay-breasted Warbler clearly wintering in the county was in San Diego 30 December 1983–10 April 1984 (T. and G. Quinn, AB 38:358, 1984).

 

Conservation: From 1973 to 1987 the Bay-breasted Warbler was found in San Diego County almost annually, with up to four in 1974 and three in 1987.  Subsequently its frequency declined sharply.  From 1994 through 2003 there were only two records, both from Point Loma, 26 September 1995 (G. L. Rogers, NASFN 50:117, 1996) and 20–21 September 2001 (J. C. Worley, NAB 56:108, 2002).  Patten and Burger (1998) found the high correlation between numbers of the Bay-breasted Warbler reported in California and of the spruce budworm in eastern Canada second only to that for the Cape May Warbler.

Blackpoll Warbler Dendroica striata

 

In the 1960s and 1970s the Blackpoll Warbler was one of the most frequent eastern warblers seen as a fall vagrant to San Diego County, so much so that a birder searching for land birds along the coast from late September to mid October could expect to see one or two.  Since then the species’ abundance has decreased precipitously, so that by the beginning of the 21^st century the average for the county per year was just two to three.

 

Migration: Recent totals for the Blackpoll Warbler in San Diego County are one in 1999, one in 2000, five in 2001, three in 2002, and two in 2003.  Like other eastern warblers, the Blackpoll has been found in the coastal lowland almost exclusively.  The county’s only fall records elsewhere are of one at Agua Caliente Springs (M26) 4 October 1977 (AB 32:263, 1978) and one at Lake Henshaw (G17) 7 November 1980 (AB 35:228, 1982).  The species’ fall dates range from 3 September (1973, Otay Mesa, V13, G. McCaskie) to 26 November (1987, Tijuana River valley, E. Copper, AB 42:138, 1988) and 2 December (2003, Guajome Lake, G7, P. A. Ginsburg).

            In spring, the county has seven records, three for Point Loma, 21 June 1966 (McCaskie 1970b), 13 May 1982 (R. E. Webster, AB 36: 895, 1982), and 8 May 1985 (R. E. Webster, AB 39:351, 1985), one for the Tijuana River valley, 24 June 1978 (AB 32:1210, 1978), one for Solana Beach (L7), 18–21 May 1991 (P. A. Ginsburg, AB 45:497, 1991), one for Santa Ysabel (J18) 21 June 1998 (S. E. Smith), and one for Carrizo Marsh, Anza–Borrego Desert (O29), 18 May 1994 (P. D. Jorgensen, NASFN 48:342, 1994).  One at La Jolla (P7) 16–17 July 1998 (S. E. Smith, FN 52:504, 1998) probably never made it to its breeding range.

 

Conservation: The Blackpoll Warbler’s decline in San Diego County may reflect a change in the breeding range.  Data from the Breeding Bird Survey 1996–2001 suggest a decline in the breeding population in at least the western end of the species’ range, in Alaska and British Columbia (Sauer et al. 2003).

Cerulean Warbler Dendroica cerulea

 

The Cerulean Warbler is one of the rarest eastern warblers reaching the Pacific coast as a vagrant: the California Bird Records Committee has accepted just 15 for the state.  Two of these are for San Diego County.

Migration: Both of the accepted records are for Point Loma in spring: one photographed 26–27 May 1979 (Luther et al. 1983) and one seen 7 June 1992 (R. E. Webster; Heindel and Patten 1996).  Three reports in fall have been rejected or not submitted.

Conservation: The Cerulean Warbler is in serious decline.  The situation is reflected in the petering out of occurrences in California: 11 from 1974 to 1988 but only three from 1989 through 2003.

Black-and-white Warbler Mniotilta varia

The Black-and-white Warbler differs from other warblers in its habit of creeping on trunks and large branches, like a nuthatch.  Its range is largely east of the Rockies, but it is regular in small numbers in San Diego County.  Seasonally, it is spread rather evenly.  Annually, about four to five are reported each fall, three to four each winter, and two to three each spring.  There are even a few summer records.

Winter: The Black-and-white is less concentrated along the coast than many eastern warblers; there are many reports from riparian woodland inland.  In winter, however, the species is known from the coastal lowland only, inland as far as Kit Carson Park, Escondido (J11/K11), as from 3 December 1998 to 12 February 1999 (W. Pray).  The atlas period from 1997 to 2002 yielded 14 wintering Black-and-white Warblers, with up to two together at the Dairy Mart pond, Tijuana River valley (V11) 19–26 December 1998 and 15 December 2001 (G. McCaskie).

Migration: In recent years, the number of Black-and-white Warblers reported in San Diego County each fall has ranged from two in 2002 to seven or eight in 2003.  Thirteen Black-and-white Warblers were noted in spring 1997–2001, and the pace picked up subsequently, with six in 2002 and seven in 2003.  Again, most records are for the coastal lowland, but a few are at higher elevations, such as one at Wynola (J19) 2 June 2000 (S. E. Smith).  In the Anza–Borrego Desert, one was in Borrego Springs (G24) 5 June 1990 (A. G. Morley, AB 44:1188, 1990), one was at Yaqui Well (I24) 23 April 1997 (P. K. Nelson), one was at Vallecito (M25) 12 May 1999 (M. C. Jorgensen), and one was at Canebrake (N27) 16 May 2002 (C. Smith).

            Because the Black-and-white Warbler occurs in San Diego County at all seasons, its migration schedule can be determined only approximately.  Fall migration begins by 6 September (1966, Point Loma AFN 21:79, 1967) and peaks from late September to late October.  One Black-and-white Warbler near Mt. Woodson (L13) 15 April 1998 (P. M. von Hendy) was probably a spring migrant rather than wintering; the one at Yaqui Well 23 April 1997 certainly was.  Spring records are scattered through June, with a few birds apparently remaining to summer.  Sightings that might be considered summer records are of single birds at the east end of Lower Otay Lake (U14) 13 July–21 August 1975 (AB 29:1034, 1974), in the Tijuana River valley 17 June 1984 (G. McCaskie, AB 38:1063, 1984), in La Jolla (P8) 14 July 1986 (J. Moore, AB 40:1256, 1986), in San Diego 10–11 July 1991 (W. E. Haas, AB 45:1162, 1991), at Old Mission Dam (P11; singing male) 10 August 2000 (M. B. Stowe), on Villager Peak, Santa Rosa Mountains (C27) 17 June 2001 (R. Thériault, NAB 55:483, 2001), and one near Scissors Crossing (J22) 23 June 2002 (J. R. Barth, NAB 56:487, 2002).

American Redstart Setophaga ruticilla

The American Redstart is traditionally regarded as the most frequent of the eastern warblers in California.  With scattered pairs now breeding in the northern part of the state, and small numbers wintering annually in the Imperial Valley, the redstart’s label as “eastern” is wearing thin.  In San Diego County the species occurs most frequently in fall migration, with several found annually.  But it is also regular in winter, with an average of about four per year, and in spring migration, with an average of about one per year.

Winter: In San Diego County the American Redstart winters in the coastal lowland, in both ornamental trees and native riparian woodland.  The number seen each year through the atlas period varied from one in 1997–98 to nine in 1998–99.  The maximum per site is three, at Guajome Lake (G7) 13 December 1998 (S. Grain, P. A. Ginsburg) and at the Dairy Mart pond, Tijuana River valley (V11) 15 December 2001 (G. McCaskie).

Migration: In migration redstart records are mainly from the coastal lowland but there are also several from the Anza–Borrego Desert, for example, of one at Scissors Crossing (J22) 8 September 2000 and one at Lower Willows (D22) 27 May 1999 (P. D. Jorgensen).  Fall occurrences begin 11 August (1987, Buena Vista Lagoon, H5, M. and M. Johnson) and peak from mid September through October.  Wintering birds have remained as late as 20 April (2000, Whelan Lake, G6, P. A. Ginsburg).  Spring occurrences extend from 24 April (1964, Tijuana River valley, AFN 18:488, 1964) to 27 June (1987, Buena Vista Lagoon, D. B. King) and 30 June (1993, Encinitas, K7, B. E. Daniels, AB 47:1151, 1993), with a peak from mid to late May.  Records later in the summer are of one at Point Loma (S7) 9 July 1967 (AFN 21:605, 1967), one at Old Mission Dam (P11) 17 July 1975 (AB 29:1086, 1975), one at Lake Henshaw (G17) 26 July 1998 (R. A. Hamilton, FN 52:504, 1998), and one that apparently returned two consecutive years to the Tijuana River valley, seen 30 July 1989 and 27 May–30 June 1990 (G. McCaskie, J. Oldenettel, AB 43:1369, 1989; 44:1188, 1990).

Prothonotary Warbler Protonotaria citrea

The Prothonotary was once one of the rarest eastern warblers reaching California, but it has been one of the participants in the recent surge of species originating from the southeastern United States (Patten and Marantz 1996).  Reported from San Diego County first in 1967, the Prothonotary has kept up a pace of slightly over one county record per year since 1977, to a total 34 by the end of 2003.  Most occurrences are in fall, but eight are in spring, two in winter.

Migration: Most of San Diego County’s Prothonotary Warblers have been at the usual sites for vagrant warblers, Point Loma and the Tijuana River valley, but a few have been found elsewhere in the coastal lowland, one as far as inland as Pauma Valley (E12, 30 September–1 October 1995, D. Rawlins, NASFN 50:117, 1996).  Fall records range from 1 September (1989, La Jolla, SDNHM 46026) to 4 November (1967, Point Loma, AFN 22:91, 1968) with a peak in late September and early October.  Two additional specimens were picked up at Olivenhain (K8) 21 October 1991 (SDNHM 47838) and in the gorilla enclosure at the San Diego Zoo (R9) 22 September 2002 (SDNHM 50657).  Spring records range from 3 May (1996, San Diego, M. U. Evans, NASFN 50:334, 1996) to 7 June (1977, Tijuana River valley, Luther et al. 1983).

 

Winter: Though it typically winters in tropical swamps, the Prothonotary Warbler has wintered twice in San Diego County, once in San Diego’s neighborhood of University Heights (R9) 25 January–20 March 1987 (R. Abnet, Roberson 1993), once in Greenwood Cemetery (S9) 12–15 December 2003 (D. W. Aguillard, J. O. Zimmer).

Worm-eating Warbler Helmitheros vermivorus

In spite of having a limited breeding range in the eastern United States, the Worm-eating Warbler is known in California from over 90 well-supported records, 13 of them from San Diego County.

Migration: Most of San Diego County’s Worm-eating Warblers have been at Point Loma (S7).  Other sites represented are Chula Vista (U11, 18 September 1960, SDNHM 30219, Huey 1961a—California’s first Worm-eating Warbler), Otay Mesa (V13; 12 September 1971, Bevier 1990), Old Mission Dam (P11; 16–21 August 1973, Luther et al. 1979), the Tijuana River valley (10 September 1974, Roberson 1986), and Coronado (S9; 22 September 1988, E. Copper, Patten and Erickson 1994).  The records range in date from 16 August to 26 October (1977, Point Loma, Luther 1980).  One spring record, from Point Loma 27 May 1985 (E. Copper, AB 39:351, 1985), has not been evaluated by the California Bird Records Committee.

Ovenbird Seiurus aurocapilla

 

The Ovenbird is the most terrestrial of the warblers, walking inconspicuously on the ground.  In spite of concerns about a population decline due to fragmentation of the forests where it breeds, the Ovenbird remains a regular vagrant to California.  In San Diego County, it is recorded at a rate of about two per fall and about one every other spring.  The atlas study yielded one unprecedented summer sighting of the Ovenbird on Palomar Mountain.

 

Migration: Fall records of the Ovenbird in San Diego County are all coastal except for a sighting of two at Agua Caliente Springs (M26) 4 October 1977 (AB 32:263, 1978).  Their dates range from 17 August (1982, found dead at Ocean Beach, R7, preservable as skeleton only, SDNHM 47987) to 27 November (1982, AB 37:225, 1983), peaking from mid September through October.  There are at least 25 county records in spring, most from Point Loma, the others from elsewhere in the coastal lowland, except for sightings of one at Tamarisk Grove (I24) 23 May 1977 (C. Stuteville) and one along the Azalea Glen Trail, Cuyamaca Rancho State Park (M20), 8 May 1999 (G. L. Rogers).  Spring records range from 1 May (2003, Cabrillo National Monument, S7, S. E. Smith) to 18 June (1988, San Diego, B. and I. Mazin, AB 42:1341, 1988), with a strong concentration in late May and early June.

            The unique summer record is of one along Kolb Creek, Palomar Mountain (D15) 7 July 1998 (K. L. Weaver, FN 52:504, 1998).

 

Winter: San Diego County has two early winter records of the Ovenbird, at Point Loma 23 December 1983 (J. M. Langham, AB 38:359, 1984) and at Western Hills Park (Q8) 26 December 2001 (T. Brashear, NAB 56:224, 2002).

 

Taxonomy: The two specimens for San Diego County preserved as study skins, from Point Loma 22 May 1966 (SDNHM 36029) and Bonita (T11) 17 October 1999 (SDNHM 50339), are both nominate S. a. aurocapilla (Linnaeus, 1766), being as dark and green as specimens from New York.

Northern Waterthrush Seiurus noveboracensis

 

The Northern Waterthrush breeds west to Alaska and winters in the coastal mangroves of Baja California.  Yet it is rarely seen as a migrant and winter visitor in San Diego County.  Some of this rarity is due to the species’ habits: it walks on the ground in the dense understory of riparian woodland, staying close to water or hopping through branches hanging low over water.  Often it reveals itself only by call, a characteristic loud “chink.”

 

Winter: In San Diego County, the Northern Waterthrush is primarily a winter visitor to the coastal lowland.  Since 1985 winter records have been almost entirely from the Tijuana River valley, where the species occurs annually.  During the atlas period our only counts of more than a single individual were of two in the valley west of Hollister Street (V10) 18 December 1999 (W. E. Haas) and two at the Dairy Mart pond (V11) 1 January 2000 (G. McCaskie).  Five were in the valley in December 1990 (R. E. Webster, AB 45:322, 1991).  The Northern Waterthrush has also been seen repeatedly along the lower Otay and San Luis Rey rivers, the latter accounting for the Oceanside Christmas bird count picking up the species in 1981 and 1984.

 

Migration: Northern Waterthrushes wintering in the Tijuana River valley may arrive as early as 6 September (2003, G. McCaskie) and remain as late as 4 May (1980, AB 34:817, 1980).  The earliest fall date recorded for the county is 13 August (1966, San Diego, AFN 21:79, 1967).  Sightings of the Northern Waterthrush at the usual sites for vagrant fall warblers on Point Loma (S7) are exceptional (24 September 2002, J. K. Wilson; 6 September 2003, W. McCausland).  A Northern Waterthrush in Los Peñasquitos Canyon (N8) 11 April 1999 (P. A. Ginsburg) was our only spring migrant during the atlas period.  Outside the coastal lowland, the Northern Waterthrush has been recorded four times in the Anza–Borrego Desert, at Lower Willows (D23) 4 May 1980 and 18 May 1981 (the latest spring record for San Diego County, A. G. Morley), at Agua Caliente Springs (M26) 8 May 2002 (J. K. Wilson), and along Vallecito Creek at the east end of Mason Valley (M23) 2 September 1984 (SDNHM 43173).

Louisiana Waterthrush Seiurus motacilla

For decades, the Louisiana Waterthrush was known in California from a single specimen.  Then, in 1985, this bird of forest streams from the eastern United States began participating in the upsurge of vagrancy of southeastern warblers (Patten and Marantz 1996).  Through 2002, records statewide stand at 14, just one from San Diego County.

Winter: The single Louisiana Waterthrush known from San Diego County frequented a drainage ditch near the Salk Institute, La Jolla (O7), 9 February–21 March  1990 (J. O’Brien; Patten and Erickson 1994).  The identification is supported by photographs.

Kentucky Warbler Oporornis formosus

The Kentucky Warbler is rare but increasing as a vagrant to California.  In summer 1992 an unprecedented irruption brought at least 36 to the state’s riparian woodlands, two to San Diego County, with one more the following summer.  Eight of the county’s 16 records are for fall, four are for spring, and one is for winter.

Migration: San Diego County’s fall records of the Kentucky Warbler extend from 14 September (1990, Point Loma, S7, D. W. Aguillard; Heindel and Garrett 1995) to 16 November (1983, Del Mar, M7, D. Delaney; Roberson 1986).  All are along or near the coast.  At 2.5 miles from the coast, the single specimen, from Paso del Sol, Del Mar (M8), represents the fall record farthest inland (D. R. Grine, SDNHM 49223).  Four spring records are all from Point Loma: 4 June 1968 (Craig 1970), 5–7 May 1987 (R. E. Webster; Langham 1991), 28 May 1995 (G. L. Rogers, NASFN 49:311, 1995), and 22 May 2001 (M. B. Mulrooney, NAB 55:358, 2001).

   The incursion of summer 1992–93 was noted most in Santa Barbara and Kern counties, but it yielded three Kentucky Warblers in San Diego County: one along Noble Creek (O22) 8 June 1992 (B. Cord; Heindel and Patten 1996), one along Sandia Creek (C7) 19–22 June 1992 (K. L. Weaver; Heindel and Patten 1996), and one in Green Valley, Encinitas (K7) 30 June–2 July 1993 (B. E. Daniels, D. R. Willick; Erickson and Terrill 1996).

 

Winter: The county’s single wintering Kentucky Warbler was along Agua Hedionda Creek, Vista (I7), 15–25 March 1999 (P. A. Ginsburg, NAB 53:210, 1999).

Connecticut Warbler Oporornis agilis

The Connecticut Warbler breeds not in Connecticut but in Canada’s boreal forest, east of the Rocky Mountains.  It is a rare vagrant to California, though undoubtedly many are missed; Connecticut Warblers walk quietly on the ground, concealed under dense vegetation.  There are six well-supported records for San Diego County, five in fall, one in spring.

Migration: The California Bird Records Committee has accepted two fall records of the Connecticut Warbler from the Tijuana River valley (27 September 1963, SDNHM 30776; 19 September 1974, Binford 1985), two from Point Loma (4–12 October 1980, Binford 1985; 14–15 September 1990, G. McCaskie; Heindel and Garrett 1995), and one from San Diego (14 September 1978, Luther et al. 1983).  The single spring record is of a bird trapped and photographed at Point Loma 4 June 1968 (McCaskie 1970).

Mourning Warbler Oporornis philadelphia

A close relative of MacGillivray’s Warbler, the Mourning Warbler replaces that western species in the boreal forest east of the Rocky Mountains.  The Mourning is a rare vagrant to California, probably often overlooked because of its preference for dense vegetation and its similarity to MacGillivray’s Warbler.  The California Bird Records Committee has accepted five records of the Mourning for San Diego County.

Migration: The five records are all for late September and early October.  Four are for Point Loma: 3 October 1968 (McCaskie 1970, SDNHM 36933), 8 October 1982 and 20 September 1983 (R. E. Webster; Roberson 1986), and 21–25 September 2002 (J. C. Worley; Cole and McCaskie 2004).  One is for the Tijuana River valley: 21 September 1985 (G. McCaskie, Bevier 1990).  No documentation was submitted for two other records published in American Birds.  The individual at Point Loma in 2002 was remarkable for being an adult male; the vast majority of vagrant warblers are immature.

Taxonomy: In spite of subsequent statements that hybrid Mourning × MacGillivray’s Warblers are unknown, the apparent hybrids collected in Alberta and studied by Cox (1973) are still preserved in the San Diego Natural History Museum.

MacGillivray’s Warbler Oporornis tolmiei

A bird of dense, low vegetation, MacGillivray’s Warbler is easily overlooked.  As a result, it appears to be the scarcest of the western warblers in San Diego County.  Nevertheless, it is a regular if uncommon migrant in both spring and fall, best found in spring at oases along the east base of the mountains.  Though San Diego County is apparently off the species’ main migration route, some birds do follow the pattern of many other migrant landbirds, using the canyons on the county’s desert slope as routes for breaching the barrier of the mountains on their journey northwest.  MacGillivray’s Warbler is expanding its breeding range south, but in San Diego County so far this expansion has generated but a single summer sighting from Palomar Mountain.

Migration: In spring, MacGillivray’s Warbler is seen in San Diego County most numerously on the desert flank of the mountains, the birds pausing as they seek the routes of least resistance to the coastal slope.  The high count during the atlas period exemplifies this pattern (nine in Oriflamme Canyon, L22, 23 April 2001, R. Thériault), as do other high counts (25 at Banner, K21, 15 April 1978, P. Unitt; 11 near the head of Rodriguez Canyon, K21, 26 April 2003, S. D. Cameron).   The species’ main spring migration period is mid April to mid May, but we recorded the species twice in late March.  The earliest date, 23 March (1997, one at Mescal Bajada, J25, M. and B. McIntosh), appears to be the earliest ever for San Diego County and equals the earliest for the Salton Sink (Patten et al. 2003).  The latest spring date is 28 May (2000, one near White Oak Spring, A3, L. J. Hargrove), except for a specimen (SDNHM 37194) from Mount Helix (R12) dated “June 1967” with no more exact information.

            Fall migrants occur primarily from mid August through mid October, rarely as late as mid November.

Winter: MacGillivray’s Warbler is very rare in winter in southern California, which is well north of the main winter range in western mainland Mexico.  Eleven have been recorded around metropolitan San Diego at this season, most recently in 1992.  Another was reported on the Anza–Borrego Christmas bird count 29 December 1985.

 

Breeding distribution: The Sierra Nevada was the southern end of MacGillivray’s Warbler’s traditional breeding range (Grinnell and Miller 1944).  In the final third of the 20^th century, small numbers colonized the higher elevations of the Transverse Ranges of southern California (Lentz 1993, Dunn and Garrett 1997).  In 1987 two or three summered on Black Mountain in the San Jacinto range of Riverside County (R. McKernan, AB 41:1489, 1987).  In San Diego County there is only one summer record, of a singing male in Doane Valley, Palomar Mountain State Park (E14), 9 June 1994 (M. B. Stowe, NASFN 48:989, 1994).  There was no suggestion of breeding.

Conservation: MacGillivray’s Warbler is a bird of coniferous forest, but one of the understory, not the canopy.  As a result, it capitalizes on the new low growth that follows logging.  Data on the trends of the species as a whole are conflicting (Pitochelli 1995), but the number of migrants passing through San Diego may be on the increase.  Though Stephens (1919a) called MacGillivray’s Warbler “rather common,” the same term he used for Townsend’s, the San Diego Natural History Museum had no specimens from the county before 1963.  Now these have swelled to 22.  As an understory species, MacGillivray’s Warbler is liable to collision with windows and capture by domestic cats, so the upsurge in specimens may be related more to the hazards of migrating through an increasingly urban environment rather than in increase in the number of birds themselves.

Taxonomy: Most specimens of MacGillivray’s Warbler from San Diego County are the more brightly colored subspecies of the Pacific coast region, O. t. tolmiei (Townsend, 1839).   The one exception known was collected in Tubb Canyon (H23) 14 April 1938 (LACM 73980).  Its dull grayish-olive upperparts and small size (tail 51 mm, wing chord 57 mm) match O. t. monticola Phillips, 1947, or O. t. austinsmithi Phillips, 1947, if the latter is separable (Patten et al. 2003).  It is a surprise that the one specimen of the Rocky Mountain subspecies should be so early in the spring, for the typical pattern is that spring migration of Rocky Mountain subspecies lags that of their Pacific coast counterparts (cf. Wilson’s Warbler, for example).

Common Yellowthroat Geothlypis trichas

The Common Yellowthroat is second only to the Song Sparrow as the commonest bird of San Diego County’s riparian woodland.  Freshwater marshes and even uplands overgrown with rank weeds like fennel or white sweet clover also offer good habitat.  The yellowthroat is common in both summer and winter but not sedentary.  Wintering birds move into ornamental shrubbery and thickets of dry weeds where the species does not breed, and migrants show up occasionally even in desert scrub or chaparral. Despite its preferring wetland habitats and being a principal host of the Brown-headed Cowbird, the Common Yellowthroat has sustained its numbers in San Diego County better than have many other small insectivorous birds.

Breeding distribution: As a bird primarily of riparian woodland and freshwater marshes, the Common Yellowthroat is most numerous in the valleys of the coastal lowland.  Counts in one atlas square on a single day ranged as high as 107 (70 singing males) in lower Los Peñasquitos Canyon (N8) 7 May 2000 (P. A. Ginsburg et al.).  With increasing elevation the yellowthroat’s habitat becomes scarcer and the birds less abundant, though they are still locally common, as near Mesa Grande (H17; 23 on 12 May 2001, C. and J. Manning) and along Buena Vista Creek in Warner Valley (G19; 25 on 24 June 2000, E. C. Hall).  Yellowthroats breed up to about 4500 feet elevation in the Palomar and Cuyamaca mountains.  On the desert slope they breed at riparian oases, especially Lower Willows (D23; up to 26 on 12 May 2001, B. L. Peterson) and Sentenac Ciénaga (J23; up to 33, including 26 singing males, 7 June 2000, R. Thériault), uncommonly elsewhere.

Nesting: Common Yellowthroats nest in dense, low undergrowth, sometimes on the ground.  Atlas results revealed their breeding season to be broader than the 14 April–14 June attested by 23 egg sets collected from San Diego County 1902–35 (WFVZ) and even the 4 April–10 July attested by 66 from throughout California (Bent 1953).  Observations of nest building along the Sweetwater River in Sunnyside (S12) 5 March 1999 (T. W. Dorman) and fledglings in Mission Valley (Q10) 12 April 1998 (P. Unitt) suggest that yellowthroats begin laying as early as mid March.  Observations of nest building at the upper end of Sweetwater Reservoir (S13) 13 July 1998 and fledglings at O’Neill Lake (E6) 12 August 1998 (P. A. Ginsburg) suggest they continue laying as late as mid July.

Migration: Away from sites where it breeds and winters, the Common Yellowthroat is an uncommon migrant.  Seldom are more than two such migrants seen in a day, though maximum counts of them range up to eight in Borrego Springs (G24) 25 April 1998 (P. D. Ache) and seven in Rodriguez Canyon (L22) 26 April 1999 (P. Unitt).  Peak spring migration is in April (30 of 46 records), but dates range from 15 March (1997, four at Borrego Springs, G24, P. D. Ache) to 25 May (2000, one in Rodriguez Canyon, J. R. Barth).  Postbreeding dispersal evidently begins as early as 10 July (1997, one at Chollas Lake, R11, C. G. Edwards).

Winter: Though Common Yellowthroats breeding farther north invade San Diego County in migration and winter, the species winters mostly in the same areas where it breeds.  Wintering Common Yellowthroats are strongly concentrated in the coastal lowland, where over 100 per day can be found in marshes and riparian undergrowth (e.g., 135 at Lake Hodges, K10, 26 December 1999, R. L. Barber).  Some birds use ornamental shrubbery and patches of low weeds away from water.  The maximum count of birds wintering in nonbreeding habitat is of six at North Island Naval Air Station (S8) 18 December 1999 (R. T. Patton).  Above 1500 feet elevation the species is generally uncommon, more numerous only in Warner Valley (up to 20 near Swan Lake, F18, 18 December 2000, G. L. Rogers).  Winter records at exceptionally high elevations are of single birds at 4600–4650 feet at Doane Pond, Palomar Mountain State Park (E14; 27 February 2000, J. K. Wilson, A. Mauro), and Lake Cuyamaca (M20; 1 February 1999, A. P. and T. E. Keenan).  In the Anza–Borrego Desert the Common Yellowthroat is a rare winter visitor to irrigated places in the Borrego Valley (up to four in the north end of the valley, E24, 19 December 1999, P. R. Pryde), with one record from a natural oasis where the species does not breed (three at Mountain Palm Springs, O27, 8 January 2000, P. K. Nelson)

Conservation: There is no strong evidence for significant changes in the numbers or status of the Common Yellowthroat through San Diego history.  Even though marshes and riparian woodland have been much reduced, the yellowthroat persists in small remnants and readily recolonizes regenerated habitat.  Though perhaps the most frequent foster parent to the Brown-headed Cowbird in San Diego County, the Common Yellowthroat did not decrease grossly when the cowbird invaded, if one may judge from general assessments in the literature; the yellowthroat has always been common. Like other common hosts, it likely benefited from the widespread trapping of cowbirds initiated in the late 1980s.

Taxonomy: Subspecies of the Common Yellowthroat remain poorly quantified; the validity of many is uncertain.  Grinnell (1901) distinguished the yellowthroats of southern California as G. t. scirpicola on the basis of their brighter color, more extensive yellow on the belly and more rounded wing than in G. t. occidentalis Brewster, 1883, of the Great Basin.  G. t. scirpicola has been maintained through successive editions of the American Ornithologists’ Union checklist though synonymized by Ridgway (1902) and Phillips et al. (1964).  Similarly, a darker subspecies G. t. arizela Oberholser, 1899, of the Pacific Northwest and northern California was recognized by the A. O. U. (1957) but not by Grinnell and Miller (1944) or Marshall and Dedrick (1994).  Yellowthroats from the ranges of both arizela and occidentalis may be expected to reach San Diego County in migration.  One subspecies universally recognized is G. t. sinuosa Grinnell, 1901, breeding in the salt marshes of the San Francisco Bay area and distinguished by its smaller size as well as darker color and browner flanks.  It is partially migratory and known in San Diego County still from only two specimens, from San Diego 30 October 1914 (SDNHM 33397, Willett 1933) and San Diego Bay 3 March 1939 (SDNHM 18054).  With the elimination of over 80% of the salt marshes around San Francisco Bay sinuosa has become rare (Marshall and Dedrick 1994).  Presumably the numbers of birds dispersing south has been reduced proportionately, and the even greater level of habitat loss in southern California could select against migrants.

Hooded Warbler Wilsonia citrina

 

Over the last two decades of the 20^th century, several warblers nesting in the Canadian taiga decreased as vagrants to California, while several others nesting in the southeastern United States increased.  Preeminent among the latter is the Hooded Warbler, which irrupted from 1992 to 1994, nesting in California for the first time in Los Angeles and Kern counties in 1992.  The species was first reported from San Diego County in 1967, but by 2003 at least 50 had been seen here.

 

Migration: Unlike most vagrant warblers, the Hooded is more frequent in San Diego County in spring than in fall.  Fall records number 13, extending from 11 September (1988, Point Loma, S7, J. L. Dunn, AB 43:170, 1989; 2002, Oceanside, H5, S. Gustafson, NAB 57:118, 2003) to 28 November (1967, Borrego Palm Canyon, F23, McCaskie 1970).  The last record is the only one for fall not along the coast.

            Hooded Warbler records in spring and early summer (there is no clear division between the two) extend from 16 April (1993, Green Valley, K7, D. R. Willick, AB 47:454, 1993) to 30 June (1998, banded in West Sycamore Canyon, O12, P. A. Campbell, FN 52:504, 1998).  Most at this season are along the coast, but some are well scattered inland in riparian woodland where the species might nest, as along the Santa Margarita River north of Fallbrook (C8) 5–19 June 1992 and 24 May 2001 (K. L. Weaver), along Fallbrook Creek in the Fallbrook Naval Weapons Station (D6) 1 June 2001 (P. A. Campbell), along Keys Creek near Turner Reservoir (G11) 22 May 1992 (C. G. Edwards), and along Kitchen Creek between Highway 80 and Interstate 8 (R22) 14 June 1993 (P. Unitt, AB 47:1151, 1993).  Six spring records from the Anza–Borrego Desert encompass one from Culp Valley (G23; 15–16 June 1997, R. Thériault, FN 51:1055, 1997), one from Tamarisk Grove (I24; 15 May 2003, M. B. Mulrooney), three from Agua Caliente Springs (M26), and one from Dos Cabezas Spring (S29; 11 May 1973, AB 27:822, 1973).  The Hooded Warbler’s irregularity continued through the atlas period with yearly totals varying from zero in 1999 and 2000 to six in spring 2001.

 

Winter: Four Hooded Warblers are known to have wintered in San Diego County, one at Sweetwater Dam (S12) 17 December 1977–27 January 1978 (AB 32:401, 1978), two in residential areas of Coronado (S9), 11 December 1988–18 March 1989 (G. McCaskie, AB 43:368, 1989) and 31 October 2002–7 March 2003 (E. Copper, NAB 57:118, 259, 2003), and one nearby at North Island Naval Air Station (S8) 15 December 2001 (R. T. Patton, NAB 56:224, 2002).

 

Conservation: The sudden upsurge in Hooded Warblers in California may represent the beginnings of a range expansion.  Patten and Marantz (1996) reviewed several hypotheses such as unusual weather conditions, displacement from degraded habitat, and population increase that might account for the change.  The convergence of multiple factors seems likely.

Wilson’s Warbler Wilsonia pusilla

The intense yellow of Wilson’s Warbler is a common sight in San Diego County during spring and fall migration.  As a winter visitor the species is rare but annual.  But as a breeding bird Wilson’s Warbler has the barest toehold in the county, which lies at the southern tip of its breeding range.  The known breeding population is only three or four pairs, though it could increase with continued suppression of cowbirds and preservation of riparian woodland.  But the larger-scale trend is not good—the Pacific coast subspecies of Wilson’s Warbler is in decline over much of its range.

Breeding distribution: Summering Wilson’s Warblers were recorded in only two areas of San Diego County during the five-year atlas period, along the Santa Margarita River in Camp Pendleton and on Palomar Mountain.  Along the Santa Margarita, all were in a 2-mile segment from just east of Rifle Range Road to the mouth of Pueblitos Canyon (F5; P. P. Beck, B. E. Kus, J. M. Wells), except for one a short distance farther downstream in Ysidora Gorge (G5) 19 June 1999 (R. E. Fischer).  Never was more than a single pair or family seen on one day.  At the confluence of Doane and French creeks (D14), a single male apparently summered each year 1997–2000, but the only observation of more than one bird was of a pair 28 July 1997 (P. D. Jorgensen).

Nesting: Along the California coast, Wilson’s Warblers typically nest in shrubbery, in contrast to the rest of their range, where they typically nest on the ground (Ammon and Gilbert 1999).  Egg records from southern California specify that in this area they select primarily nettle and blackberry as nest sites (Ammon and Gilbert 1999), and observations from San Diego County agree with this preference.  Of two nests seen being built along the lower Santa Margarita River, one was in nettle (F5; 4 May 1999, P. P. Beck), the other in blackberry (F5; 30 May 2000, J. M. Wells).  The only evidence of success was a fledgling accompanying the adult female 6 July 1999.  It was the result of a replacement clutch, as it was in the territory with the nest in nettle, after that nest failed (P. P. Beck).

Migration: Wilson’s Warbler is common throughout San Diego County as a spring migrant.  Arrival dates during the atlas period ranged from 11 to 20 March, though arrival as early as 6 March has been reported (Belding 1890).  Numbers are greatest at desert oases and along the corridor from San Felipe Valley to Warner Springs.  High counts during the atlas period were of 80 around Scissors Crossing (J22) 14 May 1998 (E. C. Hall), 75 at Vallecito (M25) 12 May 1999 (M. C. Jorgensen), and 65 at Agua Caliente Springs (M26) 12 May 1997 (E. C. Hall).  The last migrants depart during the first week of June; the latest spring date is 7 June (1999, two at Banner, K21, P. K. Nelson).  Wilson’s Warbler’s migration period is long in fall as well; arrival may be as early as 1 August (1998, one at Los Peñasquitos Lagoon, N7, S. Grain), and some birds seen in December may still be heading south.

Winter: Wilson’s Warbler is a rare winter visitor to ornamental shrubbery and riparian woodland in the coastal lowland.  Though some seen in early December could be late migrants, others have been tracked over the entire winter, such as one at Guajome Lake (G7) 13 December 1998–6 March 1999 (P. A. Ginsburg, C. C. Gorman).  During the atlas period, reports averaged nine individuals per year.  The maximum daily count, of four in Balboa Park (R9) 20 December 1997 (V. P. Johnson), was the only one of over two individuals.  Wintering Wilson’s Warblers extended inland to Bonsall (E8; up to two on 3 December 2000, P. A. Ginsburg), the Wild Animal Park at San Pasqual (J12; one on 23 January 2001, M. Farley), and Lakeside (P13; one on 8 January 1998, D. C. Seals), except for one in San Vicente Valley (L16), elevation about 1500 feet, 27 February 2000 (J. D. Barr).  The last might have been a very early spring migrant, though even farther inland there is a record from a Lake Henshaw Christmas bird count (one on 27 December 1982) and another from an Anza–Borrego Christmas bird count (two on 2 January 1993).

Conservation: San Diego County is at the southern tip of Wilson’s Warbler’s breeding range, and the species has never been common here as a breeding bird.  Previous specific records are of a nest with eggs at San Pasqual (J12/13; Sharp 1907), reports of the species as a “summer resident” at Poway (M11) and “breeding” at Julian (K20; Belding 1890), a pair summering along Reidy Creek in 1980 (H10; K. L. Weaver), one along the Santa Margarita River 21 June 1984 (L. Salata, AB 38:1063, 1984), and two singing males, an adult female, and a fledgling along the Santa Margarita River (F5) 11 July 1995 (P. Unitt).  In spite of the meagerness of these records, however, it is likely that the species once bred more commonly.  Stephens (1919a) said that Wilson’s Warbler “breeds in small numbers in oak forests and in willow groves” in San Diego County.   For coastal southern California as a whole, Willett (1933) called it a “common summer resident.”  Currently, this status applies only north of Point Conception (Lehman 1994).  Thus the species’ breeding range has retracted out of southern California almost entirely, presumably in response to the invasion of the Brown-headed Cowbird.  In southern and central California cowbirds parasitize Wilson’s Warblers heavily (Friedmann et al. 1977, Ammon and Gilbert 1999).   Cowbirds are likely contributing, along with degradation of riparian woodland, to the decrease in Wilson’s Warbler numbers now evident all along the Pacific coast (e.g., Pyle et al. 1994).  Currently, in the coastal lowland, daily counts as high as 30 are unusual even at the peak of spring migration; in the 1970s, counts of 75 in this area were not exceptional (Unitt 1984).  Along the lower Santa Margarita, years of cowbird trapping have reduced the parasitism rate on all hosts in this area to practically zero, allowing locally breeding Wilson’s Warblers the beginning of a recovery.  But another threat to the riparian woodland in this area has arisen in the proliferation of the giant reed, which displaces native plants.

Taxonomy: The Pacific coast subspecies W. p. chryseola Ridgway, 1902, is the dominant subspecies of Wilson’s Warbler in San Diego County.  Though there are no specimens of the breeding population, it is undoubtedly chryseola, as is the single winter specimen, from Balboa Park 21 December 1927 (SDNHM 11646; not pileolata as reported originally by Abbott 1928a).  In spring, the early arrivals are presumably all chryseola; specimens extend at least from 28 March (1904, Witch Creek, J16, FMNH 151436) to 14 May (1989, Point Loma, S7, SDNHM 47989).  Fall specimens range at least from 4 August (1908, Volcan Mountain, I20, MVZ 3861) to 7 October (1966, Point Loma, SDNHM 36040). 

Wilsonia. p. pileolata (Pallas, 1811) breeds from the Great Basin and Rocky Mountains north to Alaska; it is a duller yellow than chryseola on both the underparts and upperparts.  Small numbers come through in spring migration, generally after the peak of chryseola.  The six specimens in the San Diego Natural History Museum extend from 2 May (1924, 2 miles northwest of La Mesa, Q11, SDNHM 9325) to 22 May (1961, Spring Valley, S12, SDNHM 30269).  The single fall specimen of pileolata is also on the late side, from San Luis Rey (G6) 6 October 1962 (SDNHM 3179).  The pattern of migration of the two subspecies in San Diego County is similar to that in the Salton Sink to the east (Patten et al. 2003).

Canada Warbler Wilsonia canadensis

 

Breeding east of the Rocky Mountains and wintering in South America, the Canada Warbler is a vagrant to California.  It reaches San Diego County at a rate of about one per year, so far occurring only in fall migration.

 

Migration: About 42 Canada Warblers have been reported in San Diego County, from the first in 1967 through 2003.  All have been near the coast; Otay Mesa (V13) is the site of the record farthest inland.  Their dates range from 6 September (1976, San Luis Rey River, Oceanside, G6, R. Bacon) to 15 November (1969, Tijuana River valley, AFN 24:100c, 1970) with a peak from late September to mid October.  The number reported per year has varied from zero, as in 1998, to four, in 2000.  Since the late 1960s there has been no trend in the species’ frequency.

Red-faced Warbler Cardellina rubrifrons

The Red-faced Warbler breeds in high mountains north to Arizona but is one of the rarest warblers reaching California as a vagrant, with just 13 well-supported records through 2002.  The California Bird Records Committee has accepted three from San Diego County.

Migration: All three of the county’s accepted records of the Red-faced Warbler are from Point Loma.  Two are for spring, one photographed 21–24 May 1977 (G. McCaskie et al., Luther et al. 1983) and one seen 29 May 1996 (R. E. Webster, P. A. Ginsburg, McCaskie and San Miguel 1999).  One is for fall, 11–12 September 1982 (R. E. Webster et al., Morlan 1985).  The records committee did not have evidence sufficient to accept the report from Old Mission Dam 26 August 1974 (AB 29:124, 1975).

Painted Redstart Myioborus pictus

 

The Painted Redstart nests in mountain forests from Arizona south through Mexico and is a vagrant to California.  The nesting attempt in San Diego County’s Laguna Mountains in 1974 is one of only two known for California.  Most of the county’s 44 records are for fall, with nine for winter, three for spring, and two for summer.

 

Migration: In fall the Painted Redstart is reported in San Diego County at the rate of about one per year.  Except for one at Agua Caliente Springs (M26) in the Anza–Borrego Desert 1–2 October 1996 (M. Graham, NASFN 51:121, 1997), all fall reports are coastal, inland to Lakeside (O14/P14; 14 October 1991, C. M. Keller, AB 46:152, 1991).  The number reported per year has varied from zero to three, as in 1986 and 1996.  Fall dates range from 24 August (1993, Tijuana River valley, D. W. Aguillard, C. H. Reiser, McCaskie and San Miguel 1999) to 8 November (1987, Point Loma, S7, R. Fowler, AB 42:139, 1988). 

            The three spring records are from Borrego Springs 1 April 1979 (AB 33:898, 1979), Sorrento Valley (N8) 1 May 1994 (D. K. Adams, NASFN 48:342, 1994), and Encinitas (K7) 24 May 1995 (D. W. Aguillard, NASFN 49:311, 1995).

 

Winter: The nine winter records are all for the coastal lowland.  Unitt (1984) listed five; subsequent ones are from Point Loma 20 December 1986–22 March 1987 (R. Arn, AB 41:331, 1987), Coronado (S9) 25 November 1987–21 March 1988 (E. Copper, AB 42:139, 323, 1988), Mission Valley (R9) 30 January–27 February 1990 (M. E. Gowan, AB 44:331, 1990), and San Diego 2 February 1998 (T. Hartnett, FN 52:259, 1998).

 

Breeding distribution: The two summer records are of one along Jaybird Creek, Palomar Mountain (E13), 25 June–6 August 1969 (AFN 23:696, 1970) and a pair along Agua Dulce Creek, Laguna Mountains (O23), 23 May–29 July 1974.  The nest of this pair, with recently hatched chicks, was found 6 July, but by 13 July the nest was deserted and the chicks were dead (Unitt 1974).

Yellow-breasted Chat Icteria virens

The song of the Yellow-breasted Chat, a  mockingbirdlike series of repeated whistles, “chacks,” and “churrs,” is a characteristic sound of dense riparian woodland.  Though often maddeningly difficult to see, the chat is a locally common summer visitor.  Like many other riparian birds, it is a frequent host of the Brown-headed Cowbird.  After a decline during the middle of the 20^th century, the Yellow-breasted Chat has increased in numbers considerably since the mid 1980s, presumably in response to the widespread trapping of cowbirds.

Breeding distribution: Yellow-breasted Chats occur widely in San Diego County’s coastal lowland wherever there is substantial riparian woodland.  They are strongly concentrated, though, in the northwest, not only along the Santa Margarita and San Luis Rey rivers, but along smaller creeks too, like San Mateo, San Onofre, Las Pulgas, Aliso, and De Luz.  Daily counts in this area go as high as 40 (36 singing males) along the Santa Margarita River north of Fallbrook (C8) 24 May 2001 (K. L. Weaver).  Another large concentration is the San Benardo and San Pasqual valleys east of Lake Hodges.  When the water level in Lake Hodges drops, the exposed basin is quickly colonized by shrubby willows offering the Yellow-breasted Chat ideal habitat (K11; maximum count 50, including 45 singing males, 3 June 1997, E. C. Hall).  Farther south concentrations are along lower Los Peñasquitos Canyon (N8; up to 21, including 15 singing males, 2 May 1999, P. A. Ginsburg), the San Diego River from Mission Gorge to Santee (Q11/P11–13), the Sweetwater River from Sweetwater Reservoir to Jamacha (S13/R13–14; up to 30 in R13 on 15 May 1998, D. and M. Hastings), Jamul and Dulzura creeks from Lower Otay Lake to Pio Pico Campground (U14/T15), the Tijuana River valley (V10–11/W10–11; up to 20, including 18 singing males, along the river east of Hollister St., W11, 27 June 1998, P. Unitt), and in Marron Valley (V16/V17).  Away from these areas the chat is uncommon.

            Above 1500 feet elevation on the coastal slope, chats are possibly irregular.  Four sites in this area emerged during the atlas’ term: San Luis Rey River between Lake Henshaw and the La Jolla Indian Reservation (F16/G16; up to six near the San Luis Rey Day Use Area, G16, 24 June 2001, W. E. Haas), Buena Vista Creek near Warner’s Ranch (G18–19; up to three singing males east of the old ranch house, G19, 24 June 2000, E. C. Hall), Cottonwood Creek between Lake Morena and Boulder Oaks (S22; two singing males 9 May 1999, R. and S. L. Breisch), and Hauser Canyon (T20; one on 15 May and 5 June 1997, J. M. Wells). 

On the desert slope, the Yellow-breasted Chat is known or suspected to breed along Coyote, San Felipe, Vallecito, and Boundary/Carrizo creeks, as well as at Agua Caliente Springs (M26; three singing males 27 April 1998, D. C. Seals), in Canebrake Canyon (N27; two singing males 25 April 1998, M. U. Evans), and at Carrizo Marsh (up to six on 6 May 1998, P. D. Jorgensen).  Desert numbers are largest along the larger creeks, Coyote (up to 17 at Lower Willows, D23, 12 May 2001, B. L. Peterson) and San Felipe (up to 15, including 10 singing males, in San Felipe Valley, I21, 13 June 1999, J. O. Zimmer).

Nesting: Yellow-breasted Chats hide their nests in extensive thickets of dense vegetation, making them difficult to find.  Almost all evidence of breeding that atlas observers reported was sightings of fledglings or adults carrying insects.  These observations correspond closely with the range of dates of the 50 egg sets collected from 1889 to 1948, 4 May–6 July.  The one exception is a record of an adult carrying food to young at the east end of Sweetwater Reservoir (S13) 8 May 1998 (P. Famolaro); this date implies eggs laid by 27 April.

Migration: Yellow-breasted Chats usually return to San Diego County in the second week of April.  The schedule of their arrival varies somewhat from year to year; during the atlas’ five-year term dates of first reports ranged from 26 March to 17 April.  Arrival of chats in March, as observed in 1997, had not been reported previously (one at the east of Sweetwater Reservoir, S13, 26 March 1997, P. Famolaro; three along the Sweetwater River near Highway 94, R13, 31 March 1997, D. and M. Hastings).  Migrants are seen only rarely away from breeding habitat, most often at desert oases.  Our 12 records of such migrants during the atlas’ term ranged from 17 April (1999, one at Dos Cabezas Spring, S29, A. P. and T. E. Keenan) to 17 May (1999, one at Yaqui Well, I24, P. K. Nelson).  Fall migration begins by early August, as attested by one at Cabrillo National Monument (S7) 3 August 2001 (J. L. Coatsworth).  Most birds depart in mid September, with only rare stragglers seen later in the fall.

Winter: There are only two records for the Yellow-breasted Chat in San Diego County as late as December, of one at Otay 2 December 1973 (AB 28:694, 1974) and one in the Tijuana River valley (V10) 16 December 2000 (W. E. Haas).  Possibly these were late fall migrants rather than wintering birds.

Conservation: Stephens (1919a) called the Yellow-breasted Chat “rather common” in San Diego County; Willett (1933) called it “common” through the lowlands of coastal southern California in general.  By the 1970s, however, it was uncommon, with a count of six in a day being high (Unitt 1984).  The chat evidently fell into the same trap as the Willow Flycatcher and Bell’s Vireo, suffering simultaneously from the widespread destruction of riparian woodland and the invasion of the Brown-headed Cowbird.  The chat is known as a common cowbird host over much of its range (Friedmann 1963), including southern California (e.g., Hanna 1928).  The chat’s recent rebound has taken place since cowbird trapping was initiated and appears concentrated where that trapping has been focused.  Nevertheless, other factors play a role too.  The rate of destruction of riparian woodland slowed after the Least Bell’s Vireo was designated as endangered in 1986, and some habitat has regenerated, especially in the Tijuana River valley and at the heads of reservoirs.

Taxonomy: Only the western subspecies I. v. auricollis (Deppe, 1830) is yet known from California.