Thrushes — Family Turdidae
Northern Wheatear Oenanthe oenanthe
The Northern Wheatear breeds widely in Alaska and northwestern Canada, but instead of migrating south it migrates far to the west, halfway around the world, to winter in sub-Saharan Africa. Along the Pacific coast of the lower 48 states it is only a casual vagrant, with 11 records for California and one for San Diego County.
Migration: The single Northern Wheatear known for San Diego County was in a patch of open sage scrub in the La Jolla Coast Preserve (O7) 18 October 2001 (D. W. Au, S. E. Smith; Garrett and Wilson 2003). This occurrence is the southernmost known for the Pacific coast of North America and one of only two for southern California.
Western Bluebird Sialia mexicana
The Western Bluebird is a common resident of San Diego County’s foothills and mountains, especially where meadows lie among groves of oak or pine. In winter the birds gather into flocks and move in search of berries, especially mistletoe. Despite being a cavity nester that must compete with many other species for scarce holes in trees, the Western Bluebird shows signs of spreading out of its primitive range, colonizing urban areas with mature trees and wide lawns.
Breeding distribution: Montane coniferous and oak woodlands constitute the core of the Western Bluebird’s range in San Diego County. In these habitats, daily counts late in the breeding season, when recently fledged young are common, range up to 60 in the Cuyamaca Mountains (N20) 16 July 2000 (B. Siegel), 90 on Hot Springs Mountain (E21) 14 July 2000 (K. L. Weaver, C. R. Mahrdt), and 100 in the Laguna Mountains (O23) 24 July 1998 (E. C. Hall, J. O. Zimmer). Toward the coast, the species becomes less abundant and more localized, but it is still common in many places, especially in northern San Diego County, with up to 20 in Valley Center (G11) 4 June 1997 (L. Seneca) and 20 in Horno Canyon, Camp Pendleton (D3) 25 June 1999 (D. C. Seals). The outline of the Western Bluebird’s distribution is basically similar to that of other oak woodland birds like the Oak Titmouse and Acorn Woodpecker, but the atlas effort revealed a surprising number of Western Bluebird nestings in south-coastal San Diego County outside this historic range. These records ranged as near the coast as an apartment complex on the west side of the University of California campus (O7; nest in a Nuttall’s Woodpecker hole in a wooden lamp post 31 May 1999, young in a nest box 6 June 2001, D. G. Seay), the San Diego River next to the Fashion Valley shopping center (R9; fledging young in both 1997 and 1998 from woodpecker holes in cottonwoods, J. K. Wilson), and Glen Abbey Cemetery, Bonita (T11; feeding young 18 June 2001, T. W. Dorman).
The eastern edge of the Western Bluebird’s range in San Diego County follows the eastern edge of oak woodland closely, with just a little extension into other trees infested with mistletoe, as in mesquites near Arsenic Spring (T28; two on 11 May 2001, F. L. Unmack). The species may summer irregularly in riparian woodland at Scissors Crossing (J22), where E. C. Hall noted two on 20 May 1998 and one on 21 June 1999 but J. R. Barth found none in 2002. Two nestings on the floor of the Anza–Borrego Desert were completely unexpected: one nest with two nestlings was in a dead planted tree at Canebrake (N27) 17 May 1998 (R. Thériault), and an adult female was tending three fledglings on the grounds of Borrego Springs High School (F24) 20 July 2000 (P. D. Jorgensen). Two in upper Indian Valley (P26) 9 May 1998 (P. R. Pryde) thus could have been nesting too. I know of no other instances of the Western Bluebird nesting in low desert anywhere in its range.
Nesting: The Western Bluebird is a secondary cavity nester, traditionally using holes in trees, usually excavated by woodpeckers. From 1997 to 2001 we noted nests in a wide variety of native trees as well as in eucalyptus trees and fan palms. The Western Bluebird is a leading patron of nest boxes. We also noted two nests in houses: under an eave or under roof tiles. One nest along Highway 80 between Boulevard and Bankhead Springs (T27) 3 May 1998 was in a splice sleeve on a large suspended telephone cable (F. L. Unmack). In its choice of nest site the Western Bluebird exemplifies the opportunism common to most secondary cavity nesters.
Our many observations of Western Bluebird nesting indicate that the species lays mainly from early April through the end of June, closely matching the range 4 April–29 June that Bent (1949) reported from California on the basis of 104 collected egg sets. Several observations, though, suggested that some birds started in late March; for example, a nest at Wilderness Gardens (D11) already had seven eggs on 5 April 1997 (V. Dineen), and fledglings at Bell Gardens, Valley Center (F12), 18 April 2001 (E. C. Hall, C. R. Mahrdt) must have hatched from eggs laid around 23 March.
Migration: The Western Bluebird occurs outside its breeding range in San Diego County mainly from October, exceptionally 23 September (1956, “flocks” at Blair Dry Lake, L24, ABDSP file), to early April. After 15 April migrants are normally rare, yet by far the largest concentration observed was on the latest recorded date, 24 April 1999. On that day, in San Felipe Valley (I21), a huge multispecies fallout of migrants included 370 Western Bluebirds (W. E. Haas).
Winter: Western Bluebirds remain throughout their breeding range in San Diego County year round, even at high elevations (up to 18 near the summit of Hot Springs Mountain, E20, 13 February 1999, K. L. Weaver, C. R. Mahrdt). But they also spread in fall and winter into the Anza–Borrego Desert. In this region, they seek developed and agricultural areas or fruiting fan palms and mistletoe, avoiding other habitats. The birds are usually in small flocks, occasionally in flocks of dozens. By far the highest daily count for a single atlas square in the Anza–Borrego Desert was of 604 in Borrego Springs (F24) 20 December 1998 (R. Thériault et al.).
The Western Bluebird spreads in winter in the coastal lowland as well, more numerously in the north county, less so to the south. It does not normally reach Point Loma or the Tijuana River valley; Greenwood and Mount Hope cemeteries in San Diego (S10; up to 22 on 18 December 1999 and 16 December 2000, C. Sankpill), Lower Otay Lake (U13; up to 8 on 21 January 2001, T. Stands, S. Yamagata), and Marron Valley (V16; 5 on 1 December 2001, J. K. Wilson) marked the southwestern limits of its winter dispersal during the atlas period. The margin of the winter range in the coastal lowland parallels the margin of the breeding range, suggesting that these winter visitors are only short-distance dispersers.
Conservation: Over much of its range the Western Bluebird is in decline, apparently as a result of loss of nest cavities to logging and fire suppression, and from competition for cavities with European Starlings and House Sparrows (Guinan et al. 2000). In San Diego County, however, despite many competitors for nest sites, the Western Bluebird appears to be holding its own and actually extending its breeding range. In spite of a few nesting records from Rose Canyon and Balboa Park from 1915 to 1926 (Abbott 1927d), the species’ breeding range stayed static for decades. So the nestings we observed in the city of San Diego from 1997 to 2001 were unexpected and appeared to represent new colonizations. The spread continued after the atlas period into 2002, with nesting that year in Presidio Park (R8) and Balboa Park near the Hall of Champions (S9; P.Unitt), adding two more squares beyond those in which the Western Bluebird had nested previously.
Why should the Western Bluebird in San Diego County be bucking the general trend? The planting of trees in what was once treeless scrub created new prospective habitat, and the spread of Nuttall’s Woodpecker into urban areas as a breeding species has brought a primary cavity excavator into an area that once had none. The bluebird may be adapting to novel nest sites such as the crevices behind the leaf bases of certain species of palms, the most likely site for the birds that fledged young in Balboa Park. Installation of hundreds of nest boxes in Orange County in the late 1990s increased the population just to the north of San Diego County greatly (R. Purvis unpubl. data). As people notice bluebirds appearing, they may set up nest boxes appropriate for them, accelerating the increase. The small numbers of Western Bluebirds nesting in the heavily developed areas of San Diego County so far only hint at this species’ becoming an urban adaptor. Yet another possibility is a general southward range expansion, paralleling that of the Orange-crowned Warbler and Western Flycatcher. Stephens (1919a) called the Western Bluebird a “common winter resident” but said that only “a few breed in the mountains.”
Taxonomy: Western Bluebirds so far collected in San Diego County are the Pacific coast subspecies S. m. occidentalis Townsend, 1837. Even winter specimens from the Anza–Borrego Desert have the reduced chestnut on the back suggesting occidentalis rather than S. m. bairdi Ridgway, 1894, which breeds in the intermountain region and reaches southeastern California as a winter visitor.
Mountain Bluebird Sialia currucoides
In winter, the season when it reaches San Diego County, the Mountain Bluebird contradicts its name, seeking flat valley floors. Extensive grasslands, plowed fields, and dry lake beds are the species’ principal habitats in San Diego County. The Mountain Bluebird is highly irregular in southern California, usually localized and uncommon. But in rare invasion years it is seen in flocks of hundreds, an amazing sight of glittering blue against the plain brown earth. Unfortunately, the Mountain Bluebird cannot withstand urbanization—winter visitors as well as breeding birds can lose habitat to development.
Winter: The Mountain Bluebird is quite localized in San Diego County, as tracts of grassland or bare dirt large enough to attract it are few and scattered. On the coastal slope, the bluebird’s principal sites are Warner Valley, Santa Ysabel Valley, Santa Maria Valley (Ramona grasslands), Lake Cuyamaca, and an arc surrounding Otay Mountain, from Otay Mesa north to Sweetwater Reservoir, east to Jamul and Dulzura, and south to Marron Valley. On the desert side of the mountains, the main sites are the Borrego Valley, San Felipe Valley, Earthquake Valley, and Blair Valley.
The species’ numbers are so irregular, however, that the birds may be rare or absent even at favored sites in some years. The Mountain Bluebird’s irregularity was on full display during the five years of field work for this atlas. In 1998–99 and 2001–02, scarcely 30 individuals were reported each winter. In 2000–01, however, San Diego County received perhaps the greatest invasion of Mountain Bluebirds ever recorded. Daily counts in a single atlas square that winter ranged as high as 160 near Peg Leg Road in the Borrego Valley (F25) 17 December (L. J. Hargrove, P. Unitt), 200 along Rangeland Road, Ramona (K13) 16 January (L. and M. Polinsky), 150 at Sweetwater Reservoir 22 February (P. Famolaro), 240 between Dulzura and Sycamore Canyon (T16) 13 January (L. J. Hargrove), and 270 in Marron Valley (V17) the same day (E. C. Hall). That winter, Mountain Bluebirds ranged practically to the coast, where they are rare, with three at the Tijuana River estuary (V10) 29 January (T. Stands, S. Yamagata), seven at the mouth of Las Pulgas Canyon (E4) 11 and 17 February (P. A. Ginsburg), and 70 about 3.5 miles inland near San Mateo Creek (C2) 19 February (J. R. Barth).
Migration: The Mountain Bluebird occurs in San Diego mainly from November to mid March. Early dates are 18 October 1998 (one in Blair Valley, L24, R. Thériault) and 25 October 1984 (one at Point Loma, S7, R. E. Webster, AB 39:104, 1985). Late dates are 2 April 2001 (six in Borrego Springs, F24, M. L. Gabel), 3 April 1998 (one in Blair Valley, R. Thériault), and 4 April (1884, one at San Diego, Belding 1890).
Conservation: One would hardly think that a bird that seeks areas with as little vegetation as possible could suffer habitat loss, but this is what has happened in San Diego County. In the 1960s and 1970s the Mountain Bluebird was found annually for the San Diego Christmas bird count in Rancho Otay (U12). Since then urban sprawl has spread past the eastern edge of the count circle and is eating away at much of the bluebird’s traditional habitat from Otay Mesa north to San Miguel Mountain. Since 1980 the Mountain Bluebird has been found on only two San Diego counts. Elsewhere in San Diego County, the Ramona grasslands are also prime Mountain Bluebird habitat threatened by urban encroachment. Keeping to grassland, sparse sage scrub, and agriculture, the bluebirds retreat from the urban growth front. The response of wintering birds to habitat fragmentation is poorly studied, but the Mountain Bluebird is a prime subject with which this topic could be addressed.
Townsend’s Solitaire Myadestes townsendi
Townsend’s Solitaire is a bird of coniferous forest at high elevations. Its breeding range extends south to the Santa Rosa Mountains—falling just a few miles short of San Diego County. The species thus reaches San Diego County principally as a rare migrant and winter visitor to the mountains, though there are also three summer records. Feeding on flying insects in summer, Townsend’s Solitaire shifts to a diet largely of berries in winter.
Winter: In San Diego County, Townsend’s Solitaire is most numerous in the higher mountains. Our highest counts were of six on Hot Springs Mountain (E20) 26 January 2002 (K. L. Weaver), seven on Volcan Mountain (I20) 17 December 2001 (R. T. Patton), and six on Cuyamaca Peak (M20) 17 January 2000 (E. Wallace). The solitaire’s frequency decreases with decreasing elevation. In the coastal lowland, the only report from 1997 to 2002 was of one in Balboa Park (R9) 2 January 2001 (J. Roberts). Only one Townsend’s Solitaire has been seen on any San Diego Christmas bird count, 1953–2002, and only one has been seen on any Oceanside count, 1976–2002. The species is more frequent in the Anza–Borrego Desert, though still rare, with nine records during the atlas period.
Like other frugivorous winter visitors, Townsend’s Solitaire varies considerably in numbers from year to year. During the five-year atlas period, solitaires were scarce in 1997–98 (only six reported) and 1999–2000, more numerous in 1998–99, 2000–01 (53 reported), and 2001–02.
Migration: Townsend’s Solitaire occurs primarily from mid October, exceptionally 29 September (1973, one at Point Loma, AB 28:109, 1974) to mid March, with a few remaining into April (latest 21 April 1999, one along Boulder Creek near Eagle Peak, M18, R. C. Sanger). Stragglers have been noted three times in May: one at Point Loma 8–9 May 1990 (B. and I. Mazin, AB 44:497, 1990), one in the Tijuana River valley 24 May 1963 (AFN 24:375, 1963), and two at Palomar Mountain lingering to 25 May 1983 (R. Higson, AB 37:913, 1983). Though still quite rare, Townsend’s Solitaire is considerably more frequent along the coast (especially at Point Loma) as a migrant than as a winter visitor.
Breeding distribution: Townsend’s Solitaire is another of those mountain birds whose elevational range in summer lies above the tops of San Diego County’s highest mountains. It breeds south to the Santa Rosa Mountains of Riverside County, where it is rare (Weathers 1983). Nevertheless, there are three summer records from San Diego County, one from the Palomar Observatory (D15), of one bird 19 July 1980 (AB 34:931, 1980), and two from Middle Peak, Cuyamaca Mountains (M20), of one bird 19 July 1987 (R. E. Webster, AB 41:1488, 1987) and an apparent pair 19 June 1988 (P. Unitt).
Taxonomy: Townsend’s Solitaires in San Diego County, like those elsewhere in the United States, are of the paler subspecies M. t. townsendi (Audubon, 1838).
Gray-cheeked Thrush Catharus minimus
Though it breeds far to the west of the longitude of California, even into northeastern Siberia, the Gray-cheeked Thrush passes far to the east of the state on its way to and from a winter range in South America. It is only a casual vagrant to California, largely in fall from mid September to late October. Thrushes of the genus Catharus are less susceptible to errors of navigation than most other long-distance migrants.
Migration: The three records of the Gray-cheeked Thrush in San Diego County are all from Point Loma (S7): 1 October 1986 (R. E. Webster, Langham 1991), 2–10 October 1987 (G. McCaskie, Roberson 1993), 10–11 September 1990 (V. P. Johnson, Heindel and Garrett 1995). Though none is supported by a specimen, the second and third birds were photographed, and the third was trapped and examined in hand.
Swainson’s Thrush Catharus ustulatus
San Diego County straddles Swainson’s Thrush’s main migration route along the Pacific coast of North America, so the species passes through in large numbers, however inconspicuously. The average San Diegan is more likely to find the low-flying Swainson’s Thrush dead—killed by a cat or having flown into a window—than to see the bird alive. The county lies at the southern tip of the species’ breeding range, so Swainson’s Thrush is rare here as a breeding bird, confined to a few stands of riparian woodland.
Breeding distribution: San Diego County’s small breeding population of Swainson’s Thrush centers on the lower Santa Margarita River in Camp Pendleton. From O’Neill Lake (E6) downstream to Stuart Mesa Road (G5), there may be as few as seven pairs. After spring migrants have departed, the highest counts in single atlas squares were of four birds near O’Neill Lake (E6) 2 July 1998, two, including a fledgling, near the base airfield (E5) 28 June and 22 July 2000 (P. A. Ginsburg), three, including a pair, between Rifle Range Road and the north end of Ysidora Basin (F5) on 28 June 1998, and two in Ysidora Gorge (G5) 19 June 1998 (R. E. Fischer). Breeding was confirmed along the Santa Margarita by a nest with nestlings near Rifle Range Road (F5) 28 June 2000 (J. M. Wells) and a fledgling being fed a short distance farther upstream, just north of the base airfield, 28 June–22 July 2000 (P. A. Ginsburg). Swainson’s Thrush also breeds along the lower San Luis Rey River in Oceanside, with one near Lawrence Canyon (H5) 11 July 1999 (J. Determan) and up to four, including a nest, about 0.5 mile downstream of the Oceanside airport (G5) 2–14 June 2000 (J. M. Wells). It is likely that a few other Swainson’s Thrushes breed elsewhere in northwestern San Diego County, along the Santa Margarita and San Luis Rey rivers, San Mateo Creek, Las Pulgas Creek, and De Luz Creek, though the only other records during the atlas period after migration were of up to four singing males along San Mateo Creek, San Onofre State Beach (C1), 14 June–7 July 1997 (L. Ellis), three birds (two singing males) along Las Pulgas Creek (E4) 27 June 2001 (P. A. Ginsburg), and up to three birds (two singing males) along the San Luis Rey River near Gird Road, Bonsall (E8), as on 23 July 1999 and 27 June 2001 (P. A. Ginsburg). Records before 1997 attest to Swainson’s Thrushes summering along the Santa Margarita River north of Fallbrook (C8).
Elsewhere in San Diego County there are only a few scattered records of Swainson’s Thrushes summering. A single singing male was along Temecula Creek near Oak Grove (C16) 20 June 1998 (K. L. Weaver). A single singing male along the San Luis Rey River near Rincon (F13) 12 June 1999 (E. Wallace) could have been an exceptionally late migrant. A single bird was along Santa Maria Creek in Bandy Canyon 25 June 1999 (P. von Hendy, B. Hendricks). Two singing males about 3800 feet elevation in Juch Canyon along Wynola Road (J19) 12 July 1999 (S. E. Smith) furnished the only summer record for Swainson’s Thrush in San Diego County’s mountains. One singing male summered along the San Diego River near Santee Lakes in 1999 and 2001; on 4 July 2001 it was carrying berries from an ornamental tree into a dense riparian thicket, apparently feeding young (M. B. Mulrooney). Up to two singing males along the Tijuana River near Saturn Blvd. (W10) 30 June–2 July 2001 (M. B. Mulrooney) were the southernmost summering Swainson’s Thrushes ever found; the previous southernmost record was based on an egg set collected at Bonita (T11) 10 June 1914 (WFVZ 65276).
Nesting: In California, Swainson’s Thrush typically nests at heights under 2 meters in riparian woodland with a rather closed canopy (T. Gardali unpubl. data). Little is known of the species’ nesting in San Diego County, however. The nest found by J. M. Wells along the San Luis Rey River was about 2.25 meters up in a giant reed—an invasive pest plant that hardly constitutes a traditional nest site. This nest had four eggs on 2 June 2000 and nestlings about four days old on 14 June, suggesting the clutch had been completed around 30 May. The nest along the Santa Margarita River had nestlings about eight or nine days old on 28 June 2000, suggesting that clutch was completed around 8 June. The three egg sets collected in San Diego County are dated 31 May, 10 June, and 26 June.
Migration: In spring, Swainson’s Thrush is a rather late migrant through San Diego County, with peak numbers in May. From 1997 through 2001, our dates for spring migrants ranged from 11 April (1998, one in Arroyo Seco del Diablo, N28, R. and S. L. Breisch) to 11 June (1999, one in Black Canyon, I16, K. J. Winter) and 12 June (1999, one in Oceanside, H5, J. Determan). Over the five years, the early dates ranged from 11 to 28 April, but the earliest date ever reported for the species is 1 April (1996, San Mateo Creek mouth, C1, L. J. Edson, NASFN 50:333, 1996), from a site where it is known to summer. Thus, as for many other species with a wide range on the Pacific coast, it appears that the local population arrives earlier than migrants headed farther north. Migrant Swainson’s Thrushes are usually seen in small numbers, seldom more than six per day. The species’ secretive habits mean that many birds are overlooked. But occasional larger concentrations are noted, up to 30 on 14 May 1998 at Scissors Crossing (J22; E. C. Hall), a riparian oasis along the primary corridor for migrants crossing from the desert to the coast. One found near Tecolote Canyon (Q9) 15 May 2002 (S. K. Niemann, SDNHM 50638) had been banded as a juvenile at the Wright Wildlife Refuge just north of Eureka, California, 17 August 2001 (T. L. George pers. comm.).
Fall migrants occur mainly from September to mid October; dates range from 26 August (1972, San Marcos, I9, AMR 4094) to 8 November (1981, Point Loma, S7, J. L. Dunn, AB 36:218, 1982), exceptionally 1 December (1964, San Diego, SDNHM 35141).
Winter: A Swainson’s Thrush in Coronado (S9) 15–16 December 1979 (G. McCaskie) had an injured wing, probably accounting for its remaining so late. All other winter reports from California presumably are of misidentified Hermit Thrushes; Swainson’s has been collected in winter no nearer than Nayarit in western Mexico.
Conservation: As a species restricted for breeding to riparian woodland, Swainson’s Thrush has suffered from the removal and degradation from most of this habitat in southern California. Stephens (1919a) called it a “rather common summer resident,” but by the 1970s it was rare in this role. From 1997 to 2001 we did not find the species at several locations from which Unitt (1984) reported it in the 1970s. Perhaps the most serious current threat to Swainson’s Thrush habitat in San Diego County is the proliferation of the giant reed, which was accelerated along the lower Santa Margarita River by the floods of 1993. Along the coast of northern California, Swainson’s Thrush’s reproductive success appears insufficient to sustain the population, for unknown reasons (T. Gardali unpubl. data). Loss of wintering habitat in southern Mexico and Central America may account for the species’ disappearance from seemingly unaltered breeding habitat in the Sierra Nevada (Marshall 1988).
Taxonomy: Swainson’s Thrushes occurring in San Diego County are Russet-backed Thrushes, the ustulatus subspecies group breeding along the Pacific coast from southeastern Alaska to San Diego County. Within this group, three subspecies have been described, the paler, grayer C. u. oedicus (Oberholser, 1899), breeding from southern California north to the inner Coast Ranges and Sierra Nevada of northern California, the darker, more rufous C. u. ustulatus (Nuttall, 1840), breeding from northwestern California north through the Pacific Northwest, and the very rufous C. u. phillipsi Ramos, 1991, breeding on the Queen Charlotte Islands of British Columbia. No specimens of San Diego County’s breeding population have yet been collected. Among migrants, ustulatus is by far the most abundant. Of 44 spring specimens, collected from 29 April to 10 June, apparently only two are drab enough to qualify as oedicus: one from Borrego Springs (G24) 10 May 2000 (P. D. Jorgensen, SDNHM 50462) and one from Chula Vista (U11) 19 May 1990 (S. Kingswood, SDNHM 46849). Of 19 fall specimens, collected from 7 September to 1 December, only one, from San Diego 25 October 1981 (J. Shrawder, SDNHM 41615), even approaches oedicus. I have not seen specimens that would allow me to distinguish phillipsi from ustulatus, but the former may pass through San Diego County as well.
Hermit Thrush Catharus guttatus
In winter, the Hermit Thrush is common in chaparral and riparian or oak woodland, foraging quietly on the ground for insects or plucking berries from shrubs. Smaller numbers occur in sage scrub, desert-edge scrub, parks, and residential areas. The species is also taking on a new role, a few birds beginning to colonize shady forest in the county’s mountains. Field work for this atlas yielded the first confirmations of Hermit Thrushes breeding in San Diego County.
Winter: Wintering Hermit Thrushes are widespread over San Diego County’s coastal slope, most concentrated in and near the Santa Margarita Mountains in the county’s northwest corner. But large numbers can be seen anywhere in dense chaparral, with up to 146 around Lake Hodges (K10) 27 December 1998 (R. L. Barber et al.) and 60 at Cabrillo National Monument and Fort Rosecrans Cemetery, Point Loma (S7), 15 December 2001 (J. C. Worley). The Hermit Thrush can be fairly common even at high elevations (up to 12 near High Point, Palomar Mountain, D15, 21 December 1999, K. L. Weaver). In the Anza–Borrego Desert it is rare, occurring mainly at oases at the base of the mountains.
Numbers of Hermit Thrushes in San Diego County vary somewhat from year to year, though less so than those of other frugivorous winter visitors. At lower elevations, this variation was rather modest from 1997 to 2002, but in some previous years it was striking. Totals on Christmas bird counts (results of all six counts in the county combined) illustrate this: 651 in 1989–90 and 737 in 1990–91, versus 40 in 1991–92 and 38 in 1995–96. This variation could be due to annual variation in both the numbers reaching San Diego County and to variation in the birds’ distribution within the county, according to food availability and whether mountain chaparral is covered with snow. In the mountains, the Hermit Thrush was much more numerous in the winter of 1998–99, with little snow, than in the winter of 1997–98, with far more.
Migration: The Hermit Thrush occurs in San Diego primarily from late September through April. By mid May it is rare. During the atlas period 19 May (1999, one at Lake Domingo, U26, J. K. Wilson) was our latest date except for stragglers at Point Loma 22 May 1999 and 4 June 1998 (P. A. Ginsburg). An even later straggler was at the same location 6 June 1984 (R. E. Webster, AB 38:961, 1984).
Even without the specimens that would prove the birds are of different subspecies, the pattern of the Hermit Thrush’s migrations assures us that the county’s incipient breeding population is different from the wintering population. So far the breeding population has been recorded only from 15 May (1999, one on Cuyamaca Peak, M20, G. L. Rogers) to 19 July (1998, three or four singing along Chimney Creek, E15, Palomar Mountain, D. S. Cooper, FN 52:504, 1998), but further observations would likely extend this interval.
Breeding distribution: Summering Hermit Thrushes are now known in San Diego County from the Palomar, Hot Springs, Volcan, and Cuyamaca mountains, though still in very small numbers. In all areas, they occur in deep forest on north-facing slopes. During the atlas period, they were found most frequently on Palomar Mountain (eight records), between 4400 and 5200 feet elevation from upper Pauma Creek (D14; up to two—a pair—on 15 July 1999, P. D. Jorgensen) southeast to Chimney Creek. On Volcan Mountain (I20), an adult and a fledgling were at 5000 feet elevation in a steep northeast-draining canyon 28 June 2000 (A. P. and T. E. Keenan)—at the same site as one or two singing males 31 May 1993 (P. Unitt, AB 47:1151, 1993). In the Cuyamaca Mountains, above 5200 feet elevation, summering Hermit Thrushes are known from both Cuyamaca Peak (M20; one on 23 May 1998 and 15 May 1999, G. L. Rogers) and Middle Peak (M20; two singing males 11 June 2000; adult feeding barely fledged young 2 July 2000, R. E. Webster). The first summer record of the Hermit Thrush in San Diego County was from Hot Springs Mountain (E21) 24 June 1980 (Unitt 1981), but there have been no subsequent reports from this site.
A Hermit Thrush was in pinyons at 5600 feet elevation on the north slope of Villager Peak, Santa Rosa Mountains (C27), 2 June 1999 (P. D. Jorgensen). The habitat is atypical for breeding Hermit Thrushes, and visits to the site in 2000 and 2001 did not reveal the species again, so most likely this bird was a wanderer.
Nesting: No nest of the Hermit Thrush has yet been found in San Diego County; the fledglings seen on Volcan Mountain and Middle Peak in 2000 constitute the only evidence for the species’ breeding here. Elsewhere in the western United States, the species nests on the ground or up to moderate heights in small trees. The dates of the fledglings seen in San Diego County suggest egg laying in early June.
Conservation: San Diego County’s remaining large tracts of chaparral are central to the winter range of at least one subspecies of Hermit Thrush, C. g. guttatus. Hermit Thrushes use modified habitats as well, orchards, parks, and gardens with adequate shrubbery. Because they are active mainly on and near the ground, however, when the light is dim, in these habitats they suffer considerable predation from domestic cats and mortality from striking wires and windows.
The traditional southern limit of the breeding range of the Hermit Thrush was the San Bernardino Mountains (e.g., Grinnell and Miller 1944). Thus the species’ appearance in summer in San Diego County represents a southward range extension, more likely the result of natural range expansion than the birds being overlooked in the past.
Taxonomy: The Hermit Thrush shows great variation in its broad range, but in spite of the studies of Aldrich (1968) and Phillips (1991), the interpretation of this variation leaves much to be desired. At the San Diego Natural History Museum we have 122 skins of the species from San Diego County, in part because the birds so often fly into windows or otherwise come to grief in places where people find them. But without a broad sample of specimens from the breeding range, categorizing the variation in the San Diego sample can be only rudimentary. Nevertheless, it is clear that the bulk of Hermit Thrushes wintering in San Diego are the subspecies C. g. guttatus (Pallas, 1811), with a medium brownish-gray back and breeding at least in south-coastal Alaska. A significant minority of the specimens (about 15) have darker upperparts, deeper gray flanks, larger blackish breast spots, and a deeper buff wash on the breast. These are apparently C. g. vaccinius (Cumming, 1933), breeding on and near Vancouver Island. San Diego County represents the southern limit of this subspecies’ winter range (Phillips 1991). The Hermit Thrushes of southeastern Alaska, C. g. nanus (Audubon, 1839), also winter in San Diego County, in numbers smaller than those of guttatus. They are more rufous above than guttatus but not as dark as the species’ dark extreme.
Between Vancouver Island and the Olympic Peninsula is an abrupt break. Along the Pacific coast from Washington to central California breeding Hermit Thrushes are paler and longer billed, though even smaller in other dimensions, than those farther north. This subspecies is C. g. slevini (Grinnell, 1901), which occurs in San Diego County primarily as an uncommon migrant. Its identity may be suspected even in the field on the basis of its pale grayish upperparts, small sparse breast spots, and pale flanks. One specimen has been collected in fall (Volcan Mt., 9 October 1993, SDNHM 48587), two in early spring (4 April 1877, Campo, U23, SDNHM 1701; 11 April 1984, La Posta Truck Trail, R24, SDNHM 42997). C. g. slevini winters mainly in the tropical dry forest of western Mexico, but San Diego County may be at the northern fringe of its normal winter range. A. R. Phillips identified specimens from Balboa Park 15 December 1958 (SDNHM 30128) and Pacific Beach 18 February 1971 (SDNHM 37879) as C. g. jewetti Phillips, 1962, which he split from slevini on the basis of browner birds from the Olympic Peninsula. Subsequently he recognized jewetti only inconsistently (Monson and Phillips 1981, Phillips 1991).
Finally, the birds summering in San Diego County’s mountains must be C. g. sequoiensis (Belding 1889), though no specimen has yet been collected. C. g. sequoiensis breeds from the Sierra Nevada south to the mountains of southern California and migrates to and from a winter range in the mountains of western Mexico with only rare stops in the Mojave Desert. It is pale like slevini but larger with heavier breast spots.
Wood Thrush Hylocichla mustelina
This handsome bird breeding in the eastern United States is only a rare vagrant to California, with 16 well-supported records from 1967 through 2001. These are spread through fall, winter, and spring, though all from San Diego County are for late fall.
Migration: The California Bird Records Committee has accepted four records of the Wood Thrush from San Diego County: one collected in the Tijuana River valley (W10) 18 November 1967 (McCaskie 1971; SDNHM 36355), one seen at the same locality 25 October 1978, found killed by a cat the following day (not preserved; AB 33:216, 1979), one photographed at Point Loma (S7) 24 October–6 November 1981 (B. E. Daniels; Binford 1985), and one seen there 1–25 November 1982 (D. and N. Kelly; Morlan 1985). Details of another sighting at Point Loma 21 October 1990 (R. E. Webster, AB 45:152, 1991) were never submitted.
Rufous-backed Robin Turdus rufopalliatus
A species of western mainland Mexico, the Rufous-backed Robin has, since the 1960s, been dispersing annually in small numbers north to Arizona in fall and winter. Nine of these vagrants are known to have strayed west to southern California, one reaching San Diego County.
Winter: The single Rufous-backed Robin known for San Diego County was photographed on the lushly landscaped grounds of the Casa del Zorro, Borrego Springs (H25), 16 March–16 April 1996 (K. Ellsworth; McCaskie and San Miguel 1999). Though the bird occurred in early spring, its long stay suggested it was a winter visitor, presumably passing unnoticed until March. Other California records range from November to early April.
American Robin Turdus migratorius
A traditional harbinger of spring in northern North America, the American Robin is a traditional harbinger of winter in San Diego County. At that season it is an irregular visitor, common in some winters, scarce in others, as flocks roam in search of berry-bearing plants like toyon, wild grape, California coffeeberry, and many ornamentals. Since the 1940s, however, the American Robin has spread south as a breeding species, occupying mountain forests, orchards, urban parks, and college campuses year round.
Breeding distribution: The American Robin’s patchy distribution in San Diego County is explained by its three habitats: montane forest, orchards, and parks and residential areas with shade trees and lawns. In San Diego County’s mountains, the robin is fairly common among conifers (up to 12 at Palomar Mountain, E15, 18 June 1999, E. C. Hall, C. R. Mahrdt), locally so in higher-elevation oak woodland with few or no conifers (up to 13 around Hulburd Grove, O19, C. Anderson). It inhabits all the wooded ranges, south to Corte Madera Valley (R20/R21; up to five on 20 June 1998, J. K. Wilson).
The importance of orchards as American Robin habitat in San Diego County became clear only as a result of the atlas field work. The region from De Luz and Bonsall east to Pauma Valley and Valley Center, extensively planted with avocado and citrus groves, emerges as one of the robin’s major population centers. Some of our highest counts of breeding robins were around such orchards (up to 20, 1 mile northeast of Heriot Mountain, C12, 1 April 2000, J. Determan; 18 between Fallbrook and Monserate Mountain, D9, 19 May 1999, E. C. Hall).
In urban parks and residential areas breeding robins are still local. They are fairly common in a few places (up to 24 in southern Balboa Park, S9, 28 April 1997, Y. Ikegaya) but lacking from much seemingly suitable habitat. Berry Community Park, Nestor (V10; one on 18 July 1997, C. G. Edwards) and parks in Chula Vista (U11/U12) mark the southern limit of the robin’s range along the coast of San Diego County—and thus on the Pacific coast of North America.
Outside these three main habitats, there are scattered records from rural areas with oak groves or lawns, southeast to Boulevard (T26; two including a singing male 6 June 2001, J. K. Wilson).
Nesting: The American Robin may nest high or low, in a wide variety of trees or shrubs. The nest is often well screened by foliage, but we also noted nests in more open trees like eucalyptus and Coulter pine. Because the American Robin is a recent colonist of San Diego County, no eggs have been collected here, and atlas data are the best information yet on the species’ breeding schedule. They suggest the species lays mainly from April through June, in agreement with the 6 April–14 July range of 46 egg sets from elsewhere in California (Bent 1949). In the less constrained environment of orchards and lawns, however, a few birds start earlier, possibly in the second week of March, as shown by one carrying nest material at Point Loma (S7) 1 March 1997 (J. C. Worley), one carrying food to a nest at the Pala Mesa resort (D9) 23 March 1997 (M. San Miguel), and a fledgling along San Marcos Creek at Rancho Santa Fe Road 26 April 1997 (J. O. Zimmer). A robin carrying nest material in Presidio Park (R8) 1 July 1998 (C. Mann) and fledglings being fed in Coronado (S9) 4 August 1997 (M. Molloy), and at Granite Spring, Cuyamaca Mountains (N21) 25 August 1999 (P. D. Jorgensen) suggest egg laying as late as July.
Migration: American Robins do not follow a rigid schedule of migration, at least in southern California. Rather, they move nomadically through their nonbreeding season. From 1997 to 2002, dates of birds away from breeding habitat ranged from 10 October (1998, one at Borrego Springs, G24, P. D. Jorgensen) to 24 April (2000, one in San Felipe Valley at the east base of Volcan Mountain, J21, P. K. Nelson). A couple of reports later in April from sites where the species was missed later in the spring were from urban or agricultural areas that it could colonize. Even a single robin in Borrego Springs (G24) 14 May 1998 (P. D. Ache) could have been a prospective colonizer. The species has nested irregularly at Brawley in the Imperial Valley since 1992 (Patten et al. 2003), though Belding (1890) reported a late straggler at Campo 14 May 1884.
Winter: As a winter visitor the American Robin is widespread but very irregular, abundant in some years, scarce in others. Even within the county invasions take place at different times. During the five-year atlas period, robins were by far most numerous in eastern San Diego County in 2000–01, whereas in coastal north county they were most numerous in 2001–02. High counts in a single day in one atlas square were 186 south of De Luz (C6) 6 January 2001 (K. L. Weaver) and 175 near Wooded Hill, Laguna Mountains (P23) 19 February 1999 (E. C. Hall, J. O. Zimmer). In the Anza–Borrego Desert the American Robin is confined largely to developed areas and mesquite thickets festooned with mistletoe.
Conservation: As a breeding bird the American Robin is a recent colonist of San Diego County, first reported breeding in the Cuyamaca Mountains by Grinnell and Miller (1944) and in the coastal lowland at Rancho Santa Fe (L8) in July 1951 by Mead (1952). Over the next 50 years, breeding robins spread widely. The distribution by the end of the millennium was much broader than known just 20 years earlier (Unitt 1984). The spread has continued past San Diego County with the species colonizing the sierras Juárez and San Pedro Mártir in Baja California in the 1990s (Erickson et al. 2001).
Lawns with earthworms, of course, offer the robin a suitable habitat lacking before urbanization, but the reason why the range expansion included natural montane forest as well is less clear. Possibly the urbanization of southern California allowed the entire region’s population to increase to the point where the birds moved into all suitable habitats. But the southward spread of other montane birds suggests that other, more subtle factors could be playing a role with the robin as well.
Taxonomy: The only subspecies of the American Robin known from southern California is T. m. propinquus Ridgway, 1877, pale and usually lacking white corners to the tail.
Varied Thrush Ixoreus naevius
Finding a Varied Thrush in San Diego County is always a pleasant surprise, a reminder of the rainforests of the Pacific Northwest. This rare and irregular winter visitor occurs mainly in the oak and coniferous woodland in the foothills and mountains, though records are scattered almost throughout the county.
Winter: The Varied Thrush reaches San Diego County only irregularly, though its incursions often coincide with those of other irruptive winter visitors. In some years there are none, in others there are a few scattered individuals, and occasionally there are modest numbers. During the atlas period, the number of individuals noted per year was zero in 1997–98, six in 1998–99, 13 in 1999–2000, zero in 2000–01, and six in 2001–02. The best-documented incursions were in 1906–07, 1924–25, 1972–73, 1983–84 (highest totals on Christmas bird counts that year, with three on the San Diego count and 12 on the Lake Henshaw count), 1989–90, and 1996–97. The only records of more than a single bird in one atlas square per day from 1997 to 2002 were of four in Palomar Mountain State Park (D14) 26 February 1999 (P. D. Jorgensen), four in the Cuyapaipe Indian Reservation (P24) 28 January 2000 (D. C. Seals), and two in the Manzanita Indian Reservation (R25) 22 January 2000 (J. K. Wilson). Past reports ran as high as 16 along Agua Dulce Creek, Laguna Mountains (P23), 17 January 1978 (C. G. Edwards).
The Varied Thrush may be most frequent on Palomar Mountain; seven of the 18 records during the atlas period were from this area. It is least frequent in the Anza–Borrego Desert, but even here there are about a dozen records total, from oases and developed areas, south to Tamarisk Grove (I24).
Migration: Records of the Varied Thrush in San Diego County range mainly from mid October to March. After invasion years, stragglers have occurred at Point Loma (S7) as late as 13 May in 1984 (B. and M. McIntosh, AB 38:961, 1984) and 17 May and 6 June in 1997 (R. E. Webster, FN 51:928, 1054, 1997). As expected in an irruptive species, Varied Thrush migrations follow no well-defined schedule.
Taxonomy: The subspecies of the Varied Thrush differ in the color of the upperparts of the females, brown in the more coastal, more southern I. n. naevius (Gmelin, 1789), grayish with variable brown tips in the more inland, more northern I. n. meruloides (Swainson, 1832). Both subspecies occur in San Diego County, but meruloides is much the more frequent, at least among the more recent specimens. Of the 13 skins of female Varied Thrushes in SDNHM, two to five are naevius, the southernmost known of this subspecies (Unitt 1984). Complicating the identification is the foxing of specimens: with time, the gray feathers turn brownish, making meruloides look more like naevius.
Phillips (1991) split off the Varied Thrushes from the southern segment of the breeding range of meruloides as a new subspecies godfreii, intermediate between meruloides and naevius, but I have not seen specimens allowing me to evaluate this proposal.