New World Blackbirds and Orioles  — Family Icteridae

Bobolink Dolichonyx oryzivorus

 

When the Tijuana River valley was covered with alfalfa fields, the Bobolink was a regular fall visitor there.  When these fields were abandoned, sightings of the Bobolink in San Diego County almost ceased.  Bobolinks reaching the coast of California, however, may all be misoriented immatures; even the birds breeding in eastern Washington and eastern Oregon apparently head far to the east before turning south toward the winter range in South America.

 

Migration: In San Diego County, the great majority of Bobolinks have been seen in the Tijuana River valley.  There are only a few records from other sites in the coastal lowland and only one from the Anza–Borrego Desert, of up to two at the Borrego sewage ponds (H25) 13–25 September 1997 (P. D. Jorgensen, FN 52:129, 1998).  The Bobolink is, or was, most frequent in late September and early October; fall dates range from 3 September (1973, Tijuana River valley) to 13 November (1976, same location, G. McCaskie).

            There are also four records in late spring and summer, one from Point Loma (6 June 1974, AB 28:854, 1974), three from the Tijuana River valley (3 June 1977, AB 31:1049, 1977; 25–26 July 1976, AB 30:1005, 1976; 24 June 1995, NASFN 49:983, 1995).

 

Conservation: In the 1960s and 1970s the Bobolink was irregularly common in the Tijuana River valley, with up to 60 between 26 September and 18 October 1969 (AFN 24:100c, 1970).  In the 1980s the numbers dropped abruptly.  From 1997 through 2003 the only record, besides that at the Borrego sewage ponds, was of three in a small tomato field in the Tijuana River valley (V11) 15 October 2001, with one remaining to 22 October (G. McCaskie).

Red-winged Blackbird Agelaius phoeniceus

Probably no bird is more common in freshwater marshes across North America than the Red-winged Blackbird.  Even San Diego County, in spite of the aridity of its climate, has enough wetlands to support the Red-winged as a common if localized permanent resident.  Creation of reservoirs has created new blackbird habitat, and the birds’ gathering in large flocks in winter gives the impression that they are doing well.  But breeding Redwings need open uplands for foraging as well as marshes for nesting.  Urbanization eliminates this habitat, and the blackbirds’ retreat from development is already evident in San Diego.

Breeding distribution: Though most characteristic of freshwater marshes, the Red-winged Blackbird takes advantage of small isolated creeks, scattered ranch ponds, and thick stands of mustard.  As a result, it is widely distributed over San Diego County’s coastal slope, recorded as at least a possibly breeding species in 78% of atlas squares outside the Anza–Borrego Desert and confirmed nesting in 58% of them.  Gaps correspond mainly to rugged terrain covered largely by chaparral like Aguanga Ridge (D15/D16/E16) and Otay Mountain (U15/V15).  The intensively developed area of metropolitan San Diego is a conspicuous gap. Larger concentrations correspond to marshes near grassland or pastures where large numbers of blackbirds can forage.  Such sites lie in Warner Valley (up to 350 in the east arm of the valley, G19, 25 June 2000, P. Unitt), the Mesa Grande area (up to 275 southeast of Mesa Grande, I17, 5 May 1999, D. C. Seals), Santa Maria Valley (up to 300 northeast of Ramona, K15, 25 May 1998, M. and B. McIntosh), Los Peñasquitos Lagoon and lower canyon (up to 260 at the lagoon, N7, 2 May 1999, D. K. Adams), and from Sweetwater Reservoir south to Otay Mesa (up to 375 at Upper Otay Lake and north end of Lower Otay Lake, T13, 14 April 2000, T. W. Dorman).

            As long as habitat is available, the Red-winged Blackbird does not appear limited in San Diego County by elevation; it nests up to 5400 feet in Laguna Meadow (O23; 60, including fledglings being fed by adults, 24 July 1998, E. C. Hall, J. O. Zimmer).  In the Anza–Borrego Desert the Red-winged Blackbird breeds along San Felipe Creek east to Sentenac Ciénaga (J23; up to 83 on 14 June 1998, R. Thériault), in some years probably down to the mouth of Sentenac Canyon (I23; three on 23 May 1997, P. K. Nelson).  Other desert sites of confirmed or probable Red-winged Blackbird nesting are in the agricultural area of the northern Borrego Valley (E24; 16, with adults feeding young, 15 April 2001, P. D. Ache), at the Borrego sewage ponds (H25; 12, with adults building nests and feeding young, 25 May 1998, P. D. Jorgensen), Vallecito (M25; up to eight, including pairs, 27 April 1998, M. C. Jorgensen), Carrizo Marsh (O29; four, including pairs, 25 April 2001, M. C. Jorgensen), and springs in Carrizo Gorge (R27; six, with up to three singing males, 29 April and 14 May 2000, G. Rebstock, L. J. Hargrove; S28; 12, with four singing males, 6 May 2001, R. Breisch).  Nesting at most desert locations is probably irregular; Massey (1998) reported a fledgling at Lower Willows (D23) in 1994, but from 1997 to 2001 we had only a single record there (two on 25 April 1998, B. L. Peterson).  The birds in Carrizo Gorge may need to commute out of the gorge to McCain and Jacumba valleys to feed.

Nesting: In San Diego County Red-winged Blackbirds nest usually in marshes of cattail or bulrush, anchoring the nest to several vertical leaves.  Other substrates are common too, including black mustard over dry ground.  Atlas records indicate that most Red-winged Blackbirds begin laying in the first week of April.  A few lay earlier, as early as mid March, as implied by observations of nest building as early as 3 March 1997 at Scissors Crossing (J22; L. Allen), an occupied nest 13 March 2001 at Rancho Santa Fe (L8; A. Mauro), and adults feeding young 27 March 1998 in Dameron Valley (C15; K. L. Weaver).  Egg laying probably continues to the end of June, as implied by observations of nest building as late as 26 June 1999 at Potrero (U20; R. and S. L. Breisch), a nest with eggs 5 July 1997 near San Luis Rey (G6; M. R. Smith), and an occupied nest 14 July 1997 at Sweetwater Reservoir (S13; P. Famolaro).  Thus the season is slightly longer than implied by the 20 March–18 June spread of 38 egg sets collected 1911–36.

Migration: There is evidence for only slight long-distance movement of Red-winged Blackbirds in and out of San Diego County (see Taxonomy).  Rather, most of the birds appearing away from breeding locations are making short-distance movements.  Our only spring records of Red-winged Blackbirds more than one atlas square away from where the species likely breeds were from the Anza–Borrego Desert, of one at Canebrake (N27) 18 April 1999 (R. and S. L. Breisch) and one at Ocotillo Wells (I29) 1 May 2000 (P. Unitt).

Winter: The Red-winged Blackbird appears more abundant in winter than during the breeding season because many birds then gather into large flocks (up to 1200 in San Marcos, J8, 26 December 1998, D. and C. Batzler; 840 in Escondido, J10, 22 December 2000, W. E. Haas; 620 in the Tijuana River valley, V10, 18 December 1999, W. E. Haas).  But the winter distribution of the Red-winged Blackbird in San Diego County differs little from the breeding distribution.  Only sporadically do small flocks invade the urban area of San Diego at any distance from where the birds breed (up to 13 at Seaport Village in downtown San Diego, S9, 13 December 1998, Y. Ikegaya).  Large numbers may remain as high as 5400 feet elevation at Big Laguna Lake (O23; up to 62 on 21 January 2002; E. C. Hall, J. O. Zimmer).  In the Anza–Borrego Desert the species leaves the more isolated oases, becoming localized in winter to San Felipe, Earthquake, and Borrego valleys (up to 68 at Ram’s Hill, H25, 20 December 1998, R. Halford; 75 at Sentenac Ciénaga, J23, 11 January 1998, P. Unitt).

Conservation: The Red-winged Blackbird has proven more adaptable than many marsh birds.  Its ability to nest as scattered pairs has saved it from the fate of the colonial Tricolored Blackbird.  The installation of reservoirs and ponds has been a positive factor that has compensated in part for loss of habitat to stream channelization and urbanization.  It can take quick advantage of changes in its favor: in 1984, when the mouth of the Tijuana River estuary was blocked, hundreds colonized and nested, departing again once the estuary mouth was open and the tides returned (P. D. Jorgensen).  But the Red-winged Blackbird’s adaptability has its limits, as can be seen in the species’ absence over most of central San Diego.  Over this area the blackbirds nest only along the San Diego River in Mission Valley (R8, R9, Q10) and at the mouth of Rose Canyon at the northeast corner of Mission Bay (up to 20, nests probable, 15–30 May 1999, E. Wallace).  Even if marshes suitable for nesting remain within the city, surrounding developed uplands do not offer the abundance of insects needed for the blackbirds to raise their young.

Taxonomy: The resident subspecies of the Red-winged Blackbird in southwestern California is A. g. neutralis Ridgway 1901 (type locality Jacumba, U28).  It has the bill thick, the female's underparts wholly and heavily streaked with dark, her upperpart feathers edged with pale chestnut and yellow-buff, and the male's epaulet broadly edged with buff.  Only four of the 76 San Diego County Red-winged Blackbird specimens in the San Diego Natural History Museum demonstrate migration from outside the range of neutralis.  These four females are A. g. nevadensis Grinnell, 1914, from the Great Basin/intermountain region, as indicated by their more rusty, fewer buff fringes on the upperpart feathers: National City (T10) 4 January 1914 (SDNHM 33498) and 28 January 1921 (SDNHM 33545), Jamacha (R14) 4 January 1924 (SDNHM 2783), and Bonita (T11) 6 January 1929 (SDNHM 12328) Agelaius g. nevadensis is partially migratory and has been reported previously as close to San Diego County as San Timoteo Canyon, Riverside County (Grinnell and Miller 1944) and Bard, Imperial County (Patten et al. 2003). 

Van Rossem (1926) reported a male collected at Witch Creek (J18) 13 April 1904 as A. g. californicus Nelson, 1897, breeding in the Central Valley, in which the female has the belly blacker than in neutralis and the male has less or no buff edge on the epaulet. Two females collected 15 October 1923 at Jamacha (SDNHM 2801, 2806; van Rossem 1926) have the more narrowly streaked underparts of A. g. sonoriensis Ridgway, 1887, from the desert Southwest, but they have the thicker bill of neutralis.  No specimens from the Anza–Borrego Desert are available to test whether the Red-winged Blackbirds in this area could be sonoriensis, which breeds commonly in the Salton Sink. 

Tricolored Blackbird Agelaius tricolor

The Tricolored Blackbird is one of California’s amazing natural treasures: a songbird whose biology follows the model of a colonial seabird.  Tricolored Blackbirds nest in large, dense colonies, usually in freshwater marshes, and forage in nearby grassland, pastures, or agricultural fields.  Colonies once ranged up to 200,000 nests, but elimination of marshes and development of surrounding uplands has reduced the population greatly, especially in southern California.  The Tricolored Blackbird is recognized as a highest-priority species of special concern by the California Department of Fish and Game.  The San Diego County population is probably 5000–8000 birds, concentrated in 20–30 colonies.  In spite of the Tricolored Blackbird’s demanding requirements for breeding, in the nonbreeding season it forages readily in artificial habitats like dairies, lawns, garbage dumps, and parking lots.

Breeding distribution: Tricolored Blackbird colonies in San Diego County are now so few that they can be listed individually (Table 9).  They are concentrated in two areas: north-central San Diego County from Dameron Valley and Oak Grove south to Ramona and Santa Ysabel, and the Campo Plateau from Potrero to Jacumba.  The roster is not exhaustive; a few colonies undoubtedly passed undetected on private ranches or water-district lands we were unable to reach; such properties are the sites of most of the known colonies.  Unconfirmed colonies are likely especially in La Jolla Valley (L10; 20 on 7 May 2000, K. J. Winter), at Miramar Lake (N10; 50 on 23 June 1999, K. J. Winter), Merigan Ranch, Descanso (P20; 15 on 18 April 1997, P. Unitt), Lake Murray (Q11; up to 30 on 9 June 2000, N. Osborn), La Posta Valley (S23; up to 20, males displaying, 11 April 1999, L. J. Hargrove), and McCain Valley (R26; 12 on 11 May 1999, L. J. Hargrove).  Some colonies may remain active for years; that at Jacumba has been used continuously since at least the 1970s.  But others shift from year to year (a predator-avoidance strategy in many colonial birds), and others become unusable if the nesting marsh is trimmed or cut completely (as at the pond at Magnolia Ave. and Highway 78 in Ramona) or the surrounding uplands are developed.  The paucity of colonies in the coastal lowland where marshes are more numerous suggests that foraging habitat sufficient to support a large colony, not availability of nesting sites, has become the most important factor limiting the population.

Table 9  Known Tricolored Blackbird Colonies in San Diego County, 1997–2001
Colony	Square	Years known Active	Maximum count	Observers
Dameron Valley	C15	1997, 1998	200	K. L. Weaver
Oak Grove	C16	1998, 1999	840	K. L. Weaver
Sunshine Summit	D17	1999, 2000	25	P. Unitt
Puerta La Cruz	E18/F18	2000, 2001	250	P. K. Nelson, P. Unitt, M. G.  Mathos
Swan Lake	F18	2000, 2001	1000	P. Unitt, M. G. Mathos, P. K. Nelson
Warner Ranch	G18	1999, 2000	18	P. K. Nelson, J. K. Wilson
Bonsall	F8	2000	20	J. Evans
Mesa Grande NW	H16	1999	12	E. C. Hall, J. O. Zimmer
Pamo Valley	I15	2000	1280	W. E. Haas
Mesa Grande SE	I17	2000	160	W. E. Haas
Santa Ysabel Ranch	I18	2000	260	S. E. Smith
Boden Canyon	J14	1999, 2000, 2001	40	C. R. Mahrdt, R. L. Barber, O. Carter, L. Comrack
Ramona W.D. Pond	K13	1998, 2000	1000	P. von Hendy, W. E. Haas, P. Unitt
East Ramona Pond	K15	1998, 1999	400	M. and B. McIntosh
Lindo Lake	P14/O14	1997, 1998, 2000	220	M. B. Stowe
Viejas Casino	P18	1999, 2000	600	K. J. Winter
Tule Lake	T27	2000	30	J. K. Wilson, F. L. Unmack
Twin Lakes	U20	1999, 2000, 2001	150	R. and S. L. Breisch
Campo	U23	1997, 1998, 1999, 2000, 2001	1000	D. S. and A. W. Hester, P. Unitt
Jacumba	U28	1997, 1998, 1999, 2000	300	F. L. Unmack
La Media Rd.	V13	1998, 1999, 2000, 2001	100	P. Unitt

Nesting: Most colonies are in cattail marshes, but Tricolored Blackbirds also nest in blackberry thickets (as in Santa Ysabel Valley, I18) or stands of black mustard (as on Otay Mesa, V13).  Like the Red-winged Blackbird, the Tricolored attaches its nest to several usually vertical stems or leaves.  But the male Tricolored defends a territory of as little as 1.8 square meters, and as many as six females build nests within one square meter (Beedy and Hamilton 1999).  Nesting within a colony is often synchronized, so that all young may hatch and fledge within a few days of each other. Large colonies may include one or more successive waves of peripheral settlement. But different colonies are often unsynchronized, some establishing themselves up to nine weeks after others.  The birds may shift to a second site and renest in the same season (Hamilton 1998).  The schedule of Tricolored Blackbird nesting we observed in San Diego County 1997–2001 fits within that reported from the Central Valley by Beedy and Hamilton (1999), though with nest building at Twin Lakes, Potrero (U20) 19 June 1999 (R. and S. L. Breisch) it runs later than known from egg sets collected in the county 1890–1962 (latest 26 May).

Migration: Tricolored Blackbirds wander nomadically when not breeding, and some are seen sporadically away from nesting habitat through the breeding season.  Some of these, such as 85 at a dairy 1.9 miles south of Ramona (L15) 22 April 2000 (P. Unitt), were within a few miles of known colonies.  But others, such as eight at the east end of the basin of Lake Cuyamaca 13 April 1999 (J. K. Wilson), six along the Kelly Ditch Trail in the Cuyamaca Mountains (L20) 14 July 2000 (E. C. Hall), and two in Marron Valley (V17) 16 May 2000 (P. Beck), were far from any suspected colony.  Particularly unusual were seven flying over a chaparral-covered ridge 1 mile east of Mount Laguna (O24) 16 June 2001 (P. Unitt) and the only recent records for the Anza–Borrego Desert, of 13 caught and released from a cowbird trap at Whitaker Horse Camp (D24) 24 April 2002 (N. Collin) and one in feeding in horse corrals at Borrego Springs (G24) 11 May 2002 (K. and P. D. Jorgensen).  Old records from the desert slope are of specimens collected by Frank Stephens at “Palmetto Spring” (i.e., Palm Spring, N27) 1 April 1895 (SDNHM 792) and in San Felipe Valley near Scissors Crossing (J22) 4 April 1895 (SDNHM 793).

Winter: Though Tricolored Blackbirds may leave their breeding colonies in the winter, they still prefer to roost in marshes.  In San Diego County it appears that most of the population does not shift a great distance.  Sometimes large flocks are seen in winter at nesting colonies: up to 700 at Swan Lake 10 December 2000 (M. G. Mathos, J. R. Barth) and 500 at Oak Grove (C16) 26 February 2000 (K. L. Weaver).  Some large winter flocks elsewhere could represent undiscovered nesting colonies: 300 in Lawson Valley 1 December 2001 (M. B. Stowe), 250 near Dulzura (T16) 31 January 2001 (D. W. Povey), 400 in Japatul Valley (Q18) 17 January 2001 and 525 in Hill Valley (T25) 4 February 2001 (P. Unitt).  In north-coastal San Diego County wintering Tricolored Blackbirds are generally inconsistent (most regular around Bonsall and in the San Dieguito Valley), but the numbers may be much larger than are known to breed in this area (up to 200 in Rancho Santa Fe, L8, 28 December 1997; 190 at the Hollandia Dairy, San Marcos, I9, 27 February 1999, W. E. Haas). In south-coastal San Diego County a few still winter around Mission Bay and the San Diego River mouth, where they forage on lawns (maximum 20 at Robb Field, R7, 1 March 1999, V. P. Johnson).  Considerable numbers wintered at the Otay dump (U12) until 1998 (135 on 19 December 1998, W. E. Haas), and Santee Lakes (P12) remains a regular wintering site, possibly for birds originating from the Lindo Lake colony (up to 70 on 19 December 1997, E. Post—fewer since).  But over most of metropolitan San Diego the Tricolored Blackbird is now rare even as a winter visitor.

Conservation: The history of the Tricolored Blackbird in San Diego County has been one of continuous decline.  In the early 1860s, J. G. Cooper (in Baird 1870) considered the Tricolored Blackbird “the most abundant species near San Diego.”  Neff (1937) listed five colonies in San Diego County’s coastal lowland in 1935 and 1936, of up to 1000 nests.  None of these persists today.  The Dairy Mart pond in the Tijuana River valley (V11; Unitt 1984) is no longer a colony.  San Diego Christmas bird count results show a sharp decline from the mid 1980s through 2001, with only a single Tricolored Blackbird reported in the latter year.  The pattern on the Oceanside count is similar: the Tricolored Blackbird was formerly abundant in the lower San Luis Rey River valley, but a 95% drop from 1990 to 1991 was never reversed; the species was missed on the count for the first time in 2001. 

Elimination of marshes undoubtedly contributed to the Tricolored Blackbird’s population collapse, but loss of foraging habitat to development probably played an even greater role.  For the species to nest successfully, it may need large colonies for proper social stimulation (Orians 1980).  And a large colony requires a considerable habitat with abundant prey like grasshoppers.  The critical mass for the population to be self sustaining is doubtless larger for the Tricolored Blackbird than for species that live as dispersed pairs.

Can the decline be arrested or reversed?  Critical questions that still need to be answered include the extent of foraging habitat needed to support a viable colony and the number of alternative colony sites needed to support a viable population.  Only one of the colonies, in Boden Canyon, lies on land devoted primarily to conservation, but the water in the pond was taken to fight a fire in August 2001; the pond did not refill in the following year of drought, and the blackbirds abandoned the colony in 2002 (L. Comrack).  The only colony on public parkland, that at Lindo Lake, is already surrounded by development.  Sustaining the Tricolored Blackbird will require the cooperation of water districts and private landowners.  Can new colonies be attracted to restored or artificial marshes put near foraging habitat?  Even though it lasted only two years, a colony formed in 1990 in a revegetation project in Mission Valley (R9) the first year after artificial islands were installed in the San Diego River.  But the Tricolored Blackbird likely poses one of the most difficult conservation problems among North American birds.

Western Meadowlark Sturnella neglecta

Grassland is the Western Meadowlark’s most typical habitat, but coastal marshes, open sage scrub, disturbed weedy areas, and even desert sinks host the species too.   The Western Meadowlark is fairly widespread and common as a breeding species but is even more widespread and common as a winter visitor, when it gathers into flocks.  The meadowlark survives cattle grazing and replacement of native grasses with exotics, but it does not adapt to urbanization and is susceptible to the ill effects of habitat fragmentation.  Though heard all over the coastal mesas a century ago, in most of the city of San Diego the meadowlark’s song has now fallen silent.

Breeding distribution: Western Meadowlarks concentrate in San Diego County’s remaining large tracts of grassland.  The largest numbers of breeding birds were reported from Warner Valley (up to 75 near Puerta La Cruz, E18, 12 May 2001, P. K. Nelson), Ballena Valley (K17; 60 on 12 June 2000, D. C. Seals), and Santa Maria Valley (up to 106 northeast of Ramona, K15, 26 April 1999, M. and B. McIntosh).  Other areas important to the species are Camp Pendleton, Santa Ysabel Valley, Air Station Miramar, Proctor Valley, Rancho Jamul, Otay Mesa, and Campo Valley.  Western Meadowlarks are widely but patchily distributed elsewhere: many atlas squares that are largely developed or covered largely by chaparral lack them.  Along the coast they inhabit coastal wetlands (up to 20 at San Elijo Lagoon, L7, 14 May 1997, A. Mauro; 20 in the Tijuana River estuary, V10, 16 May 1998, B. C. Moore).  A few persist around Mission Bay on weedy bayfill (e.g., two on the south shore, R8, 31 May 1998, C. B. Hewitt).  In the Anza–Borrego Desert the Western Meadowlark is fairly common at Sentenac Ciénaga (J23; up to 16 on 14 June 1998, feeding young in an extensive area of yerba mansa, R. Thériault) but uncommon to rare on valley floors elsewhere.  Some birds advertise territories but apparently find the habitat insufficient and move on in the middle of the breeding season.  Nevertheless, a few remain and nest at least irregularly, both in the agricultural area of the Borrego Valley (E24; three, including fledgling, 31 May 2001, J. Fitch) and in sinks (Clark Dry Lake, D26; three, including feeding young, in a weed patch amid mesquite and tamarisk 30 April 2001, J. R. Barth).  These records are the first of Western Meadowlarks breeding in the Anza–Borrego Desert (cf. Massey 1998), though the species breeds fairly commonly in the agricultural lands of the Coachella and Imperial valleys (Patten et al. 2003).

Nesting: Western Meadowlarks nest on the ground in dense grass or other low vegetation.  The birds often build a dome or roof over the nest, screening it from above and making it difficult to locate.  Atlas observers reported only three.  Though egg collections demonstrate that Western Meadowlarks lay in San Diego County as early as 11 March, atlas observations reveal that early April to late June is the principal season for meadowlark nesting in San Diego County.  Reports of nest building near Warner’s Ranch (G19) 17 June 2000 (J. D. Barr) and a nest with eggs near Dyar Spring, Cuyamaca Rancho State Park (N21) 13 July 2000 (S. Martin) are later than previous egg dates (to 15 June, Sharp 1907) but from elevations higher than most collected sets.  We noted no winter nesting, as reported by Sechrist (1915b) and Abbott (1927c) during relatively wet winters.

Migration: During migration and winter Western Meadowlarks spread into habitats like open desert and sparsely vegetated disturbed areas unsuitable for their breeding.  In spring, migrants or winter visitors occur in such areas to mid April (11 April 1998, one near Five Palms Spring, G29, G. Rebstock, K. Forney; 20 April 1997, four near Greenwood Cemetery, S10, P. Unitt).  Later scattered records from marginal desert habitat may be of birds scouting for possible breeding territories but unable to attract a mate (e.g., one near Middle Willows, C22, 14 May 1997, P. D. Jorgensen).

Winter: At this season the Western Meadowlark is considerably more abundant than during the breeding season.  Maximum daily counts range up to 250 at Lake Henshaw (G17) 27 December 1999 (D. Aklufi), 368 between Poggi Canyon and Otay Valley (U12) 20 December 1997 (W. E. Haas), and 450 in Rancho Jamul (S15) 14 January 2001 (P. Unitt).  The winter distribution is similar to the breeding distribution, though, with rather little spread into areas where breeding birds are absent.  Among these latter areas are open spaces within the city of San Diego (up to 50 around the radio towers at Emerald Hills Park, S11, 12 December 1999, P. Unitt).  The Western Meadowlark occurs irregularly even at high elevations through the winter (up to 40 at 4600 feet in the upper basin of Lake Cuyamaca, L21, 5 January 1999, J. K. Wilson; 32 at 4700 feet near Dyar Spring, N21, 20 January 2002, R. C. Sanger; 10 at 5400 feet in Laguna Meadow, O23, 6 December 1999, D. S. Cooper).  In the Anza–Borrego Desert wintering Western Meadowlarks occur mainly on golf courses and on sandy valley floors (up to 30 near Little Clark Dry Lake, E27, 7 December 2000, R. Thériault; 30 at Vallecito, M25, 25 February 1999, M. C. Jorgensen).

Conservation: The Western Meadowlark has survived heavy grazing of its grassland and replacement of native plants by foreign weeds, though these factors likely depressed the population.  The meadowlark forages as readily in disturbed areas as in pristine habitat.  But as a ground-nesting and ground-foraging species it has no ability to adapt to urbanization.  As a result, there are now large gaps in what was once undoubtedly a nearly continuous distribution though the coastal lowland.  Bolger et al. (1997) reported the Western Meadowlark to be susceptible to the effects of fragmentation, and this is implicit in the atlas results as well.  Nesting birds are highly sensitive to human disturbance (Lanyon 1994).  Disturbed grassland constitutes much of the meadowlark’s remaining habitat in San Diego County but has been given low priority in habitat-conservation plans.  Large areas of former meadowlark habitat, as around the eastern fringe of Chula Vista (T13/U12/U13) were developed and eliminated during the five-year atlas period.  On the positive side are acquisition as wildlife habitat of San Felipe Valley and Rancho Jamul by the California Department of Fish and Game and part of the Ramona grasslands by the Nature Conservancy.

Taxonomy: The two described subspecies of the Western Meadowlark, S. n. confluenta Rathbun, 1917, and S. n. neglecta Audubon, 1844, are said to intergrade in San Diego County (AOU 1957).  S. n. confluenta is darker, with heavier black barring on the upperparts and larger spots on the sides and flanks; it breeds in the Pacific Northwest and possibly south through coastal California.  Nominate neglecta occurs farther south and east.  The difference between the subspecies is obscured in worn plumage, and Lanyon (1994) considered them poorly differentiated.

Yellow-headed Blackbird Xanthocephalus xanthocephalus

San Diego County lies at the southwestern margin of the Yellow-headed Blackbird’s breeding range, so the species occurs here mainly as a rare migrant and winter visitor.  Colonial, the Yellow-headed Blackbird has probably nested in the county irregularly, but the first colony described in any detail was discovered in 2000 at Tule Lake near Boulevard.  Like that other colonial blackbird, the Tricolored, the Yellow-headed has suffered population decline in California, and it is recognized as a species of special concern by the California Department of Fish and Game.

Breeding distribution: Only one nesting colony was confirmed during the atlas’ five-year term, within a private ranch near Boulevard at Tule Lake (T27).  On 20 April 2000, F. L. Unmack and J. K. Wilson discovered 15 adults at a marsh within the lake, the males displaying and the females building nests.  On 6 June at least three nests had nestlings, and at least one young had fledged.  The colony was still active with more fledglings (20 individuals total) on 21 June.  In 2001 the numbers were larger, with 50 adults and nests with nestlings on 6 June and 20 individuals, including fledglings, on 27 June (J. K. Wilson).

            Other possible nestings were in nearby McCain Valley (R26), with four on 11 May 1999 (L. J. Hargrove), and near Rangeland Road northwest of Ramona (K13), with two and a suspected nest 26 May 2000 (P. M. von Hendy).  The marsh in McCain Valley was dry in 2001, hosting a few Red-winged but no Yellow-headed or Tricolored Blackbirds.  Sightings of the Yellow-headed elsewhere during the atlas period most likely represent migrants, though 20 southwest of Ramona (L14) 24 April 1999 (F. Sproul) suggest the possibility of another colony in the Santa Maria Valley.

Nesting: The Yellow-headed has the narrowest requirements of any of North America’s blackbirds: it nests in deeply flooded freshwater marshes only (Twedt and Crawford 1995).  Like those of the Red-winged and Tricolored, the nests of the Yellow-headed are usually wrapped around several vertical leaves of cattail or tule.  Though colonial, and often polygynous, the Yellow-headed Blackbird seems to be more successful in small colonies than the Tricolored, and small colonies can get by with less foraging habitat surrounding the colony.  The site at Tule Lake is typical.

Migration: As a spring migrant, the Yellow-headed Blackbird occurs most consistently in the Borrego Valley, sometimes in small flocks.  Reported numbers range up to 35 at the Borrego sewage ponds (H25) 3 May 1997 (H. L. Young) and 20 at Borrego Springs (G24) 30 April 1997 and 19 April 1999 (P. D. Ache).  Also of note in the desert were 13 at Agua Caliente County Park (M26) 4 May 2000 (D. C. Seals).  Along the coastal slope numbers are much smaller, with a maximum of seven at Sweetwater Reservoir (S12) 4 May 1998 (P. Famolaro).

Spring migration of the Yellow-headed Blackbird takes place largely in April and early May.  During the atlas period, spring records ranged from 1 April (2001, one at Borrego Springs, G24, P. D. Ache) to 13 May (1998, one in the San Dieguito Valley, M8, J. Lesley) and 14 May (1998, one at Borrego Springs, G24, M. C. Jorgensen).  There are a few later records of nonbreeding summering individuals: one at Lake Cuyamaca (M20) 28 May 1998 (A. P. and T. E. Keenan); one at San Elijo Lagoon (L7) 12 July 1998 (B. C. Moore); one at Discovery Lake (J9) 17 July 1998 (J. O. Zimmer).  Yellow-headed Blackbirds seen by early August (one at O’Neill Lake, E6, 6 August 1997, P. A. Ginsburg) are probably fall migrants; Phillips et al. (1964) reported such migrants arriving in southern Arizona in July.  Migrants are occasionally seen in flocks in the Borrego Valley in fall as well as spring, with up to 25 at Ram’s Hill (H25) 12 October 1998 (P. D. Jorgensen).

Winter: The Yellow-headed Blackbird has become rare as a winter visitor to San Diego County.  Atlas observers recorded the species only six times at this season 1997–2002.  Three of these records were from the Santa Maria Valley: 16 along Rangeland Road (K13) 20 February 1999 and five there 2 January 1999 (P. M. von Hendy); 15 southwest of Ramona (L14) 11 December 1998 (F. Sproul).  Three were from scattered other locations: one along Woods Valley Road (H12) 2 January 1999 (C. Bingham), one in San Pasqual Valley (J12) 14 December 1998 (P. A. Ginsburg), and one in the Tijuana River valley (V10) 15 December 2001 (L. and M. Polinsky).  Yellow-headed Blackbirds have deserted their former area of winter concentration in the lower San Luis Rey River valley.

Conservation: The discovery of the colony at Tule Lake in 2000 notwithstanding, the trend of the Yellow-headed Blackbird’s numbers in recent years has been sharply downward.  It is likely that the species bred at least irregularly in the past.  Refuse excavated from the nineteenth-century stage station at Carrizo Marsh (O29) contained numerous bones of both male and female Yellow-headed Blackbirds (S. Arter, P. Unitt).  Albert M. Ingersoll (in Willett 1912) believed the Yellow-headed Blackbird “probably breeds at Warner’s Ranch” (G19).  Stephens (1919a), while providing no details and never collecting a specimen, said that it bred “in small colonies in tule marshes.”  Sams and Stott (1959) wrote “a few records of breeding locally (Murray Res.).”  The Yellow-headed Blackbird summered at the Dairy Mart pond in the Tijuana River valley (V11) in 1979 and 1981 (Unitt 1984).

            The species has become much scarcer since the late 1970s.  In the lower San Luis Rey River valley (at Guajome and Whelan lakes and nearby dairies, G6/G7), the flocks of the 1960s and 1970s (Unitt 1984) dwindled to single digits in the early 1980s.  Since 1984, the Oceanside Christmas bird count has recorded only a single individual.  On the San Diego count the Yellow-headed Blackbird was found on 7 of 11 counts in the 1960s, with a maximum of 21 in 1963, but its frequency declined thereafter, with only a single individual noted since 1990.

            Local factors, especially the urbanization of farm and pasture land, are undoubtedly contributing to the Yellow-headed Blackbird’s decline in San Diego County.  But factors operating on a broader scale, closer to the species’ population centers, are probably more important.  Threats identified by A. Jaramillo (unpubl. data) are loss of nesting habitat to drainage of marshes and pesticide contamination; the species feeds predominantly in agricultural areas.

Rusty Blackbird Euphagus carolinus

 

The Rusty Blackbird nests in the taiga zone of Alaska and Canada and winters mostly in the southeastern quadrant of the United States.  It is a rare visitor to California in fall and winter.  The six records for San Diego County are almost the southernmost along the Pacific coast, as there are just two records for northern Baja California and one from northwestern Sonora.

 

Winter: Sefton (1926) collected one at the former Monte Vista Ranch, Jamacha (R13), 14 November 1925 (SDNHM 10163).  Sight records are of one at Borrego Springs 27 November 1964 (AFN 19:81–82, 1965), one at Point Loma 9–10 November 1974 (AB 29:124, 1975),  two in the Tijuana River valley (W11) 11–28 February 1981 (P. Unitt, AB 35:337, 1981), one there 28 October 1983 (G. McCaskie, AB 38:248, 1984), and one near Oceanside (G6) 22 February–20 March 1987 (G. McCaskie, AB 41:332, 1987).

 

Conservation: The lack of reports since 1987 reflects a downturn in the Rusty Blackbird’s rate of occurrence throughout California.

Brewer’s Blackbird Euphagus cyanocephalus

 

Another colonial icterid, Brewer’s Blackbird was one of southern California’s early urban adapters.  It became a common resident in city parks and shopping centers and capitalized on the clearing of chaparral for ranchettes in the countryside.  But it remains common in the less developed regions of the county where ponds, low grass, and open ground offer foraging.  For nesting, exotic dense-foliaged vegetation suits it even better than native trees.  Around rural houses, Italian cypresses attract Brewer’s Blackbirds the way fan palms attract Hooded Orioles.  Brewer’s Blackbird is a recent colonist at Borrego Springs.  Yet in spite of these adaptations to civilization, something in the urban environment is not right, for Brewer’s Blackbird is disappearing from many of its former haunts in San Diego.

Breeding distribution: Brewer’s Blackbird is fairly widespread over the coastal slope.  The larger gaps in its distribution correspond mainly to areas thickly covered with chaparral and little open country or water.  Some smaller gaps, though, include considerable suitable habitat.  Colonial habits lead to a patchy distribution.  The greatest numbers of breeding birds are along the Highway 79 corridor from Oak Grove (C16) south through Warner Valley to Santa Ysabel (J18), in the Santa Maria Valley, and on the Campo Plateau.  Daily counts of Brewer’s Blackbirds during the breeding season range up to 200 around Warner’s Ranch (G19) 17 June 2000 (J. D. Barr) and 302 in Ramona (K15) 25 May 1998 (M. and B. McIntosh).  Numbers along the coast can also be large: up to 150 at La Costa (J7) 8 July 1998 (C. C. Gorman) and 70 at Los Peñasquitos Lagoon (N7) 1 August 1998 (S. Grain).

            On the desert slope, breeding Brewer’s Blackbirds extend down San Felipe Valley and Banner Canyon to Earthquake Valley (J23/K23; up to 30 on 13 June 2001, R. Thériault).  The species also breeds at Butterfield Ranch in Mason Valley (M23; 25, plus active nests, 22 May 2001, P. K. Nelson).  Elsewhere in the Anza–Borrego Desert, Brewer’s Blackbirds breed only in the developed and agricultural areas of the Borrego Valley, where they are recent colonists.  Though first reported breeding at the Roadrunner Club (F24) only in 1995 (M. L. Gabel in Massey 1998), Brewer’s Blackbirds are now common around irrigated developments, with up to 40, plus nests with nestlings, at Club Circle (G24) 15 April 2001 (L. and M. Polinsky).

Nesting: Brewer’s Blackbirds build their bowl-shaped nest in a wide variety of situations: in trees, shrubs, or on the ground.  The common theme is that the nest is screened from view behind thick vegetation.  The Italian cypress, an exotic ornamental growing as a narrow column, offers just this kind of screening.  It appears that in San Diego County Brewer’s Blackbirds often select the Italian cypress preferentially, and eight of 16 Brewer’s Blackbird nests whose sites atlas observers described were in this single species of tree.  Eight of 24 sites described by egg collectors were also cypresses, so this preference was established decades ago.  Other elevated sites reported by atlas observers included, of native plants, California rose, and, of ornamental plants, pine, podocarpus, bottlebrush, Natal plum, oleander, and ivy growing over the wall of a shopping center.  Ground sites were on a creek bank in the Cuyamaca Mountains and under a bed of baby sun rose iceplant separating a gas station from a street.

            Atlas records indicate that Brewer’s Blackbirds usually begin nest building in late March, begin laying about 1 April, and continue to lay until about 26 June.  Exceptional early nesting is attested by a bird gathering nest material at the Camp Pendleton golf course (F6) 26 February 1999 (B. E. Bell) and an occupied nest in Encinitas (K6) 19 March 2000 (J. Ciarletta).  This pattern is practically identical to that of 26 egg sets collected in San Diego County 1897–1934: range 31 March–28 June, except for one dated 5 March 1932.

Migration: Brewer’s Blackbird migration is noticeable only in parts of the Anza–Borrego desert where the species does not nest.  There were six spring records during the atlas period, from 20 March (2001, nine at Whitaker Horse Camp, D24, K. L. Weaver) to 1 May (1999, six near Font’s Point, F27, G. Rebstock, K. Forney).  Massey (1998) also reported Brewer’s Blackbird as a rare spring migrant in the Anza–Borrego Desert’s natural habitats.  Previous desert records extend as late in the spring as 20 May (Unitt 1984).  Fall migration is less well known, but a few Brewer’s Blackbirds have been noted at nonbreeding locations beginning 26 September (1998, one at Tamarisk Grove, I24, P. D. Jorgensen).

Winter: Where foraging is good, Brewer’s Blackbirds gather into large flocks in winter, up to 1400 southwest of Ramona (L14) 3 January 1998 (W. E. Haas) and 1000 in the San Pasqual Valley (J12) the same day (M. and S. Cassidy).  But the species’ distribution in winter differs little from that during the breeding season.  Even in urban areas its dispersal away from breeding colonies seems slight; for example, from 1997 to 2002 we never recorded Brewer’s Blackbird at Greenwood, Mount Hope, and Holy Cross cemeteries (S10) and only once even at Point Loma (S7), so often visited by birders. Brewer’s Blackbird may be irregular in winter at the higher elevations, where snow covers the ground for days.  We had no winter records for San Ignacio at 4900 feet elevation on the east flank of Hot Springs Mountain (E21), where counts during the breeding season ranged as high as 18 per day.  But at Laguna Meadow (O23), 5400 feet elevation, wintering Brewer’s Blackbirds were found repeatedly, in numbers as high as 28 on 24 December 2001 (P. Unitt).

Conservation: Brewer’s Blackbird seems ideally adapted to an urban lifestyle.  Shade trees and ornamental shrubbery offer it better nest sites than native vegetation.  It forages readily on lawns, disturbed open areas, and even parking lots.  Furthermore, the importation and management of water have created lakes and ponds that offer breeding habitat in many areas where once there was none.  It seems likely that Brewer’s Blackbird’s population in San Diego County increased with settlement and irrigation, though all the early writers already described it as common.  Now, however, the trend appears to be heading into reverse.  Some colonies persist in heavily urbanized areas, as on the campus of City College (S9) and at Colina del Sol Park (R11).  But Brewer’s Blackbird now appears absent from Point Loma, where it occurred during the breeding season as recently as 1995.  In western and central Balboa Park our only record during the breeding season was of three birds nesting 14 May 1997 (J. K. Wilson); none have been noted subsequently.  The species was formerly common there.  Brewer’s Blackbird is now absent from the campus of San Diego State University, where it was once common too.  Totals of over 1000 on the San Diego Christmas bird count, routine from the 1960s to the early 1980s, are no longer reached.  The totals for Oceanside in 2000 and 2001 were the lowest for that count since 1976.  Why should Brewer’s Blackbird be going into decline?  One possible factor is a disease of the feet that leads to loss of toes and ultimately the entire foot.  This condition has been common among Brewer’s Blackbirds in San Diego for decades.

Taxonomy: No new information on geographic variation in Brewer’s Blackbird has come to light since Rea (1983) tentatively recognized three subspecies based largely on variation in the females.  Specimens from San Diego County, as elsewhere in coastal California, are E. c. minusculus Oberholser, 1920, with short wings, thin bill, and pale gray female.  An exception is one female from La Mesa Heights (R12) 2 October 1926, larger and browner and so apparently a migrant of E. c. cyanocephalus (Wagler, 1829) from the Great Basin and Rocky Mountains (Unitt 1984).

Common Grackle Quiscalus quiscula

 

The Common Grackle occurs mainly east of the Rocky Mountains but is gradually increasing as a vagrant to California.  Since the first in 1967, records in the state have accelerated to total 61 by 2002.  The California Bird Records Committee has accepted just four for San Diego County.

Migration: Of the county’s four committee-endorsed records of the Common Grackle one is for fall, one is for winter, and two are for spring.  The fall record is the first for California, of one collected along La Cresta Road between El Cajon and Crest (Q14/Q15) 20 November 1967 (SDSU 2092, Roberson 1993).  Unfortunately, the original label was apparently lost between the early 1980s and the early 1990s, before the specimen was catalogued, so the identification of SDSU 2092 as the specimen from La Cresta Road is only by inference.  The spring records are of one at Point Loma (S7) 23 April 1992 (V. P. Johnson, B. Jones, Heindel and Patten 1996) and one photographed at Butterfield Ranch (M23) 14 April 2000 (J. E. Solis, J. E. Hunter, G. C. Hazard, McKee and Erickson 2002).  Another spring report, of one “seen in flight” at Point Loma, was apparently not submitted to the records committee (FN 51:929, 1997).

Winter: One at Carlsbad (I6) 9 February–26 March 1977 was photographed (Luther 1980).

Taxonomy: All of California’s Common Grackles have been Bronzed Grackles, Q. q. versicolor Vieillot, 1819, expected because it is the migratory subspecies widespread across the northern part of the species’ range.

Great-tailed Grackle Quiscalus mexicanus

Otherworldly shrieks, brazen demeanor, and a tail that defies the laws of aerodynamics made the arrival of the Great-tailed Grackle in San Diego County impossible to miss.  Few other birds have spread in North America so aggressively.  Invading from the Imperial Valley, Arizona, and Sonora, the Great-tailed Grackle was first recorded in San Diego County in 1977 and first noted nesting in 1988.  After that it increased rapidly, by the new millennium becoming a locally common resident around lakes and marshes.  Though largely a wetland species, usually nesting over or near water, the Great-tailed Grackle is almost a commensal of man.  It forages on lawns, around livestock, and in the food courts of shopping centers as long as these are within commuting distance of marshes.

Breeding distribution: As a newly colonizing species, the Great-tailed Grackle has a distribution that is still patchy, though quickly filling in.  The patches or colonies are scattered throughout the county at low to moderate elevations.  Current regions of concentration in the coastal lowland are as follows: along the San Luis Rey River from Oceanside (H5) to Pala (D10), with up to 50 in the San Luis Rey valley near Interstate 15 (E9) 14 May 2000 (C. and D. Wysong); Lake Hodges/San Pasqual Valley, with up to 40 at the lake (K10) 14 June 1999 (R. L. Barber); from Santee to Lakeside, with up to 20 at Santee Lakes (P12) 10 May 1998 and 21 March 1999 (B. C. Moore); Lower Otay Lake (U13), with up to 50 on 11 April 2001 (T. W. Dorman); and the Dairy Mart pond in the Tijuana River valley (V11; 20 on 12 March 2000, P. Unitt).  Higher in the foothills the species is sparser, but substantial colonies are in San Vicente Valley (L16; up to 20 on 27 June 2000, J. D. Barr) and at Sunshine Summit (D17), where the grackles nest at ponds in a mobile-home park (up to 40 on 3 June 2001, P. K. Nelson).  At 3310 feet elevation the latter is highest colony in the county.  Great-tailed Grackles nest also at lakes, ponds, and marshes on the Campo Plateau, from Potrero (U20) to Jacumba (U28).  In this region they are still in small numbers except at Jacumba (up to 25 on 21 April 1999, F. L. Unmack).  In the Anza–Borrego Desert the grackle is confined as a breeding species to developed areas, in the Borrego Valley (up to 24 at Club Circle, Borrego Springs, G24, 15 April 2001, L. and M. Polinsky), at Ocotillo Wells (I28/I29; up to 13 on 26 April 2001, J. R. Barth), and at Butterfield Ranch (M23; up to 25 on 22 May 2001, P. K. Nelson).  Only single grackles were seen at other desert locations (Earthquake Valley, Vallecito, Agua Caliente County Park), though the species could colonize them too.

Nesting: The Great-tailed Grackle is flexible in its choice of nest site, often in stands of cattails, as at Sunshine Summit, Lower Otay Lake, and Jacumba, but also in willows, as in the Tijuana River valley, palms, as in the Heart of Africa exhibit at the Wild Animal Park, and ornamental shade trees, as in the schoolyard at Borrego Springs.  Like those of the smaller marsh blackbirds, the nest is supported from the side by several leaves or stems.  The birds are colonial and frequently polygynous (Johnson et al. 2001).

            Atlas results constitute the first significant body of information on the Great-tailed Grackle’s nesting schedule in San Diego County.  Nest building starts as early as 29 March (along the San Diego River near Lakeside, P13, 29 March 1997, D. C. Seals), but no observations of adult females carrying food items suggest egg laying earlier than 25 April.  The birds continue to lay until at least 1 July, as implied by a nest with eggs at the upper end of Sweetwater Reservoir (S13) 14 July 1997 and a nest with nestlings there 28 July 1997 (P. Famolaro).  Fledglings may still be following their mothers late in the summer, as at the Roadrunner Club, Borrego Springs (F24), 28 August 2000 (P. Unitt).

Migration: The Great-tailed Grackle’s schedule of movement in and out of the higher elevations where it does not winter is still poorly known.  Our earliest date for these areas is 12 March (2000, one in San Vicente Valley, L16, J. D. Barr).  Grackles are seen occasionally away from breeding colonies even in June (two in Chihuahua Valley, C18, 2 June 2001, J. M. and B. Hargrove; one in Corte Madera Valley, R20, 20 June 1998, J., E., and K. Berndes).

Winter: At this season, the Great-tailed Grackle’s distribution in the coastal lowland is similar to that in the breeding season.  The birds vacate elevations above 1000 feet almost completely, however, disappearing from Sunshine Summit, the Ramona area, and the Campo Plateau except Jacumba (up to eight on 1 February 2000 and 23 January and 16 February 2001, F. L. Unmack).  In the Anza–Borrego Desert, wintering grackles are known only from developed areas around Borrego Springs, where their numbers may be somewhat smaller than in the breeding season (maximum count 13 on 30 December 1998, P. D. Ache).  In the coastal lowland, occasional individuals or small flocks wander some distance from known colonies (e.g., six in San Dieguito Valley, M8, 23 December 2001, P. Unitt); presumably this is how new colonies are pioneered. 

Conservation: Over much of San Diego County, the Great-tailed Grackle population appeared to be entering its exponential growth phase in the late 1990s.  The species was first recorded in the county at Sweetwater Reservoir (S12) 5 February 1977 (AB 31:375, 1977) but not again until November 1981.  After that, however, sightings increased rapidly.  The first recorded breeding was in July 1988, at the Dairy Mart pond in the Tijuana River valley (V10), when two pairs fledged young (G. McCaskie, AB 42:1341, 1988).  This colony grew quickly, and new ones soon formed elsewhere.  In the Tijuana River valley, however, grackle numbers peaked in 1993, when the total on the San Diego Christmas bird count hit 200.  Smaller numbers since suggest the colony may be limited by lack of foraging habitat.  In spite of the Great-tailed Grackle’s ready use of man-made environments, urban development offers little habitat to a large bird that feeds its young principally on insects taken from the ground.

Taxonomy: The first Great-tailed Grackles reaching California arrived from Sonora or southern Arizona.  The earliest specimens were Q. m. nelsoni (Ridgway, 1901), the smallest of the subspecies, in which the females are pale—honey blonde on the breast when in fresh plumage.  By the late 1980s some specimens closer to the larger Q. q. monsoni (Phillips, 1950), with dark females, had invaded the Imperial Valley, after colonizing central Arizona from the Chihuahuan Desert and blending with nelsoni (Rea 1969, Patten et al. 2003).  The two specimens so far available from San Diego County, one picked up in a residential area two blocks from the Dairy Mart Road colony (V11) 12 July 1999 (SDNHM 50303), the other from Camp Del Mar in Camp Pendleton (G4) 30 June 2001 (S. M. Wolf, SDNHM 50569), are both juveniles; in juvenile plumage nelsoni and monsoni are not well differentiated.

Bronzed Cowbird Molothrus aeneus

Like its better-known relative the Brown-headed Cowbird, the Bronzed Cowbird invaded southern California from the southeast.  Unlike that of the Brown-headed, though, the pace of the Bronzed Cowbird’s invasion has been glacial.  Though the Bronzed was first recorded in San Diego County in 1973, 30 years later it is still rare, with only 17 records.  Most of these are from or near the Anza–Borrego Desert, and some resulted from efforts to trap Brown-headed Cowbirds.  Like the Brown-headed, the Bronzed Cowbird is a brood parasite, laying its eggs in the nests of other usually medium-sized songbirds.

Breeding distribution: The Bronzed Cowbird was not confirmed breeding in San Diego County 1997–2001, though likely it did breed.  A male was displaying to two females 2.9 miles west of Jacumba (U27) in spring 1997 (F. L. Unmack), then an apparent independent juvenile (no red evident in eyes) was in the agricultural area of the north Borrego Valley (E24) 11 June 2001 (P. D. Jorgensen).  The only previous confirmation of the species’ reproducing in the county was the juvenile seen with Brewer’s Blackbirds at Jacumba (U28) 13 July 1974 (J. L. Dunn).  But all three specimens from the Anza–Borrego Desert are males in breeding condition with enlarged testes.

Nesting: Though Brewer’s Blackbird is the only host of the Bronzed Cowbird known in San Diego County, other suitable species are readily available.  Lowther (1995) listed the Northern Mockingbird and Hooded Oriole, common in San Diego County, as the birds most frequently reported parasitized by the Bronzed Cowbird.  Lack of suitable hosts is no block to the Bronzed Cowbird’s further increase.

Migration: The Bronzed Cowbird is primarily spring and summer visitor to southern California.  With two exceptions, San Diego County records extend from 13 April (1991, one at Lower Willows, D23, P. D. Jorgensen) to 17 July (1974, pair at Jacumba, AB 28:951, 1974).  Of San Diego County’s 17 Bronzed Cowbird records, eight are from the Borrego Valley, one from Tamarisk Grove Campground (I24) 10 May 2003 (P. D. Jorgensen), and five from the Jacumba area (one in 1997, four in consecutive years 1973–76).  There are three records from the coastal slope, only one on an expected date (6 May 1999, one at Dehesa, Q15, W. E. Haas).  The other two coastal records are among the few winter records of the Bronzed Cowbird for California.

Winter: Two records, of immature males at Whelan Lake (G6) 28 February–21 April 1987 (J. O'Brien, AB 41:332, 490, 1987) and in a cowbird trap in the Tijuana River Valley (V10) 1 December 1998 (J. Wells, J. Turnbull, SDNHM 50154).

 

Conservation: The Bronzed Cowbird was first noted in San Diego County 3 June 1973, at Jacumba.  The rate of occurrence is increasing only slowly, with gaps between records 1977–86 and 1992–96.  The species’ history in southeastern California, where it arrived in 1951 but is still scarce, suggests it does not have the Brown-headed Cowbird’s capacity to increase explosively and threaten a broad spectrum of hosts.

 

Taxonomy: Bronzed Cowbirds from southern California are M. a. loyei Parkes and Blake, 1965, well differentiated from the other two subspecies in its comparatively large size and thick bill, gray not black female, and violet-rumped silky-plumaged male.  For San Diego County this identification is attested by three specimens trapped in the Anza–Borrego Desert, two from Whitaker Horse Camp (D24; 23 June 1990, SDNHM 46772; 28 April 1997, SDNHM 49914) and one from Circle K Ranch (G25; 3 June 1998, SDNHM 50058), as well as the December specimen from the Tijuana River Valley.

Brown-headed Cowbird Molothrus ater

As the only brood parasite common in southern California, the Brown-headed Cowbird plays a major role in the community of birds.  It is native to North America but a rather recent immigrant to San Diego County, arriving in numbers about 1915.  It is highly migratory but found in the county year round.  Conversion of scrub and woodland to agriculture and cities enhanced the habitat for a bird that feeds on the ground, often among livestock.  As the cowbird’s population increased, that of some hosts decreased, some nearly to extirpation.  With the formal listing of the Least Bell’s Vireo as endangered, trapping of cowbirds became a tool for recovering the vireo.  How this trapping should be carried out over the long term has become one of the major questions in San Diego County wildlife management.

Breeding distribution: The Brown-headed Cowbird is widespread as a breeding bird in San Diego County, lacking only in sparse desert scrub or mountains thickly covered in forest or chaparral.  But currently, over most of the county, the species is only fairly common.  Of over 1300 records in the atlas database from late April through July, only nine are of more than 15 individuals.  The highest numbers among these are 35 in northwest Escondido (I10) 16 May 1999 (E. C. Hall) and 33 near Mt. Gower (L17) 30 May 1999 (R. C. Sanger).  High numbers earlier in the season are likely of flocks of migrants or lingering winter visitors.  Some gaps in the observed distribution, as in parts of Camp Pendleton, Mission Gorge (P11), and along the Sweetwater River above Sweetwater Reservoir (S13) appear due to trapping, carried out at Camp Pendleton since 1983, at Mission Gorge intermittently since 1985, and along the Sweetwater intermittently since 1986.  Conversely, there appears to be a somewhat greater concentration in the inland valleys from Fallbrook and Rainbow south to Escondido and Valley Center, from Ramona to Mesa Grande and Warner Springs, and near Vallecito.  But over much of San Diego County the cowbird’s abundance seems fairly uniform, implying that trapping is reducing the cowbird’s population on the scale of the entire county, not just within some limited radius of the traps.  Yet the trap operators report that the numbers of cowbirds caught has remained constant over time.  The areas of trapping could be acting as a population sink.

Nesting: The Brown-headed Cowbird is a brood parasite, laying its eggs in the nests of a wide variety of small insectivorous songbirds.  Atlas observers recorded 16 species that the cowbird parasitized successfully, as judged by nestlings or fledglings being tended by foster parents: Common Yellowthroat (10 times), Song Sparrow (6), Hooded Oriole (6), Hutton’s Vireo (6), Bell’s Vireo (5), Blue-gray Gnatcatcher (3), Wrentit (3), Western Flycatcher (3), Black-tailed Gnatcatcher (2), and Yellow Warbler, Dark-eyed Junco, Red-winged and Brewer’s Blackbirds, California Towhee, Western Wood-Pewee, and Phainopepla (once each).  Further records of cowbird eggs in nests and observations of female cowbirds entering nests—attempts at parasitism whose success was uncertain—involve Bell’s Vireo (5 times) and the Common Yellowthroat, Lark Sparrow, Warbling Vireo, Black-chinned Sparrow, Black-tailed Gnatcatcher, California Gnatcatcher, Verdin, and Lesser Goldfinch (once each).  All of these are suitable hosts except the Lesser Goldfinch, which feeds its young on regurgitated seeds rather than insects.  Additional hosts represented among 38 egg sets collected 1915–52 are the Willow Flycatcher, now rare, and the American Goldfinch, an unsuitable host for the same reason as the Lesser.  Bell’s Vireo has long been a favored host, though the number of recent records of parasitism of it may be disproportionately high because of the intensive monitoring directed at this endangered species.

            Atlas records suggest that cowbirds generally begin laying in late April.  The schedule we observed thus accords with the schedule of 38 egg sets collected 1915–1952, which range from 27 April to 30 June.  Thus host species that nest early in the spring, mainly sedentary residents, may be able to raise a brood before cowbirds begin laying.  Most summer visitors, starting later in the spring, do not have this opportunity.  Two early May records of cowbird fledglings from the Anza–Borrego Desert, however, demonstrate that a few cowbirds begin laying in early to mid April (Vallecito Valley, M24, 4 May 2001, B. Siegel; Agua Caliente Springs, M26, 11 May 1998, E. C. Hall). 

Migration: The Brown-headed Cowbird is highly migratory, and at least in spring San Diego County’s breeding and wintering populations overlap considerably.  A few cowbirds appear in riparian woodland surrounded by chaparral-covered mountains, far from wintering concentrations in open valleys, in early March.  But most of the breeding population does not arrive until early April.  Meanwhile, wintering flocks may remain until late April (100 southwest of Ramona, L14, 24 April 1999, F. Sproul).  The Great Basin subspecies M. a. artemisiae visits San Diego County, and its schedule helps illustrate the cowbird’s long-distance migrations (see Taxonomy).

Winter: At this season the Brown-headed Cowbird is much less widespread than in summer.  And it is much more concentrated—around cows.  Some wintering birds forage on lawns, at garbage dumps, and on disturbed open ground, but the large flocks occur most often at dairies and in pastureland.  Winter numbers run as high as 500 near El Monte Park (O15) 15 January 2000 (D. C. Seals), 420 at a dairy in San Marcos (I9) 27 February 1999 (W. E. Haas), and 350 at the Otay dump (U12) 19 December 1998 (W. E. Haas).  Most of the winter records are from the coastal lowland, but concentrations occur regularly as high as 3600 feet elevation, as in Hill Valley (T25; up to 210 on 22 January 2000, R. B. Riggan).  At higher elevations atlas results show the cowbird localized in winter to pastoral valleys like Warner, Descanso (P20), Japatul (Q18), and Round Potrero (T20).  We recorded the cowbird on only four occasions in winter between 3600 and 5400 feet elevation, but these included a flock of 20 at Pine Valley (P21) 8 January 1998 (J. K. Wilson) and a single bird at Laguna Meadow (O23; 5400 feet) 21 January 2002 (E. C. Hall).  In the Anza–Borrego Desert wintering cowbirds are localized to developed and agricultural areas in the Borrego Valley, where numbers range up to 35 in Borrego Springs on 24 January 1999 (P. D. Jorgensen).

Conservation: Before 1915, the Brown-headed Cowbird occurred in San Diego County only as an occasional migrant.  In that year, the front of the species’ expanding range, moving west and north, hit San Diego (Laymon 1987, Rothstein 1994).  A population explosion ensued.  In 1919 Frank Stephens was still calling the cowbird a “rare straggler” in the county, but 14 years later, Willett (1933) wrote, for all coastal southern California, that the cowbird “is well established throughout our district, frequenting the willow regions in large numbers in summer and found commonly around farms and in parks at other seasons of the year.”  By the 1970s the cowbird’s more susceptible host species, the Willow Flycatcher, Bell’s, Cassin’s, and Warbling Vireos, Blue-gray Gnatcatcher, and Yellow Warbler had declined, but the more resilient ones remained common, sustaining the cowbird’s numbers.

            The formal listing of the Least Bell’s Vireo as endangered in 1986 opened the way to management by cowbird trapping.  Since then, areas trapped most consistently have been Camp Pendleton, the lower San Luis Rey River valley, San Pasqual Valley, Mission Trails Regional Park, the Sweetwater River from Jamacha to Bonita, the Tijuana River valley, and Anza–Borrego Desert State Park.  According to data compiles by the Least Bell’s Vireo/Southwestern Willow Flycatcher Working Group, in 2003, 6391 trap-days in San Diego County yielded 1235 cowbirds (P. Famolaro unpubl. data).

Taxonomy: The breeding subspecies of the Brown-headed Cowbird in San Diego County, as elsewhere in southern California, is the Dwarf Cowbird, M. a. obscurus (Gmelin, 1789), small, with the bill tapered, the female pale, and the nestling with a yellow gape.  It is also the dominant subspecies in winter and migration.  Molothrus a. artemisiae Grinnell, 1909, breeding in the Rocky Mountain region, is larger and also has a tapered bill, but fresh-plumaged females are darker and nestlings have a white gape.  It is apparently uncommon in San Diego County, occurring at least as a spring migrant and represented by three specimens, one from Borrego Springs 30 April 1896 (SDNHM 768), one trapped at Whitaker Horse Camp, Anza–Borrego Desert (D24), 8 April 1988 (SDNHM 45604), and one given to wildlife rehabilitators from an unknown location in northern San Diego County in May 1979 (SDNHM 41375).  Molothrus a. artemisiae undoubtedly occurs in fall and winter as well; L. M. Huey collected a specimen on Los Coronados Islands within sight of San Diego 5 September 1914 (SDNHM 33654).  Fleischer and Rothstein (1988) found obscurus invading the range of artemisiae and intergrading with it in the Sierra Nevada of Mono County.  Thus with the secondary contact of artemisiae and obscurus the distinction of these formerly well-differentiated subspecies is being blurred, and southern California is likely in the path of these intergrades’ migration.  Finally, one specimen of the eastern subspecies M. a. ater (Boddaert, 1783) has been picked up in San Diego County, at Coronado (S9) 1 March 1978 (SDNHM 40587; Unitt 1984).  It is identified by its more bulbous, not smoothly tapered, maxilla.

Orchard Oriole Icterus spurius

 

Two species of oriole breed in eastern North America, the Baltimore and the Orchard.  The Orchard is the less frequent as a vagrant to California but still reaches San Diego County in fall at the rate of about one every other year.  There are about 20 records for winter and two for spring.  Because the Orchard and Hooded Orioles are so similar in the female and immature plumages, the Orchard must be identified in southern California with caution. 

 

Migration: San Diego County’s fall records of the Orchard Oriole are all from the coastal lowland, except for one from Santa Ysabel (J18), of an adult male 10 October 1987 (W. McCausland, AB 42:139, 1988).  Fall dates range from 28 August to 6 December (Unitt 1984) but are concentrated from mid September through late October.  The maximum reported per fall is five in 1964 and 1982.  During the atlas period 1997–2002, four Orchard Orioles were recorded from San Diego County in fall, all at Point Loma (S7). 

            Dates of birds known to have wintered range from 5 November (1983, San Diego, L. Zarins, AB 38:248, 966, 1984) to 21 April (1985, Point Loma, C. G. Edwards, AB 39:351, 1985).  The two spring records are from Point Loma 22 May 1980 (AB 34:817, 1980) and near Rincon (F13) 30 April 1989 (F. S. Armstrong, AB 43:538, 1989).

 

Winter: San Diego County’s winter records of the Orchard Oriole are largely from metropolitan San Diego, though two have been found on Oceanside Christmas bird counts, 26 December 1982 and 22 December 1990.  As with the Baltimore Oriole, the winter records are from ornamental trees in parks, cemeteries, and residential areas.  February 1984 had three wintering Orchard Orioles (AB 38:359, 1984), but the five-year atlas period had only one, in Greenwood Cemetery (S10) 11–19 January 2002 (M. B. Mulrooney, NAB 56:225, 2002).

 

Taxonomy: All Orchard Orioles north of the Mexican border, including the single specimen from San Diego County (Tijuana River valley, 19 October 1962, SDNHM 30472), are nominate I. s. spurius (Linnaeus, 1766).

Hooded Oriole Icterus cucullatus

The southern California lifestyle suits few birds more than it does the Hooded Oriole.    The iconic palm trees are the oriole’s primary nest site and source of nest material.  Where palms are absent, the orioles turn readily to eucalyptus.  They patronize hummingbird feeders eagerly.  They are far more numerous along palm-lined streets and in eucalyptus groves than in their primitive habitats of desert palm oases and riparian sycamores.  Though adapted to the urban landscape, the Hooded Oriole keeps tightly to its schedule of migration.  In San Diego County it is common in spring and summer but very rare in late fall and winter.

Breeding distribution: The Hooded Oriole occupies two main zones of San Diego County: the coastal lowland and lower foothills and the canyons draining into the Anza–Borrego Desert.  On the coastal slope, the oriole is most common below 2500 feet elevation in suburbs and agricultural valleys.  It spreads uncommonly as high as 3500 feet only where palms or eucalyptus trees are planted around buildings.  In this zone there are substantial areas where the birds are rare or absent, as on Otay and Tecate mountains and between Potrero and Campo.  Between 3500 and 4600 feet there are few records: near Julian (J20), six, including adults feeding young, 26 June 2001 (O. Carter et al.); at Lake Cuyamaca (M20), a pair 28 May 1999 and one bird 2 July 1999 (A. P. and T. E. Keenan); at Pine Valley (P21), one on 17 May 1997 (J. K. Wilson); near Yellow Rose Spring (R23), one on 13 May 1997 and two the following day (L. J. Hargrove).  Only the last were in natural habitat, and the birds at the last two locations were most likely migrants.

            One of the surprises of the atlas effort was persistence of Hooded Orioles in small numbers in sycamores away from palms and eucalyptus groves.  This was most noticeable in northern Camp Pendleton and the San Mateo Canyon Wilderness, the only region of the coastal lowland where entire atlas squares still lack any development other than a few dirt roads and trails.  Daily counts in this area ranged as high as seven in San Mateo Canyon (B3) 27 May 2001 (P. Unitt).

            In the Anza–Borrego Desert, the Hooded Oriole’s distribution traces the lower east slope of the mountains where oases of California fan palms dot the canyons.  There are usually only two or three pairs of orioles in each grove (Massey 1998), but counts ran as high as 10 at Carrizo Palms (R28) 6 May 1998 (J. O. Zimmer) and 20 at Agua Caliente County Park (M26) 4 June 1998 (E. C. Hall).  Smaller numbers use riparian woodland without palms, e.g., six near Banner (K21) 16 April 1999 (P. K. Nelson) and three at Sentenac Ciénaga (J23) 14 June 1998 (R. Thériault).  The Hooded Oriole is uncommon to fairly common in orchards, nurseries, and developed areas around Earthquake Valley, Borrego Springs, and Ocotillo Wells but rare and irregular at native palm oases away from the base of the mountains (birds themselves never seen but old nest in palm in Travertine Palms Wash, C29, 24 January 2000, R. Thériault).  Hooded Orioles at Seventeen Palms and Five Palms Spring (G29; two or three on 5 April 1997, one on 11 April 1998, G. Rebstock, K. Forney) were migrants only.

Nesting: The Hooded Oriole’s predilection for nesting in palms has been known for a century (e.g., Wheelock 1904).  It is so familiar to southern California birders that atlas participants seeking to confirm the species’ nesting targeted palms.  The birds strip the fibers from the leaves, weave a pouch, and sew it to the underside of a leaf. Twenty-eight of 39 nests whose site atlas observers described were in fan palms (the Mexican as well as the California); only one was in a Canary Island date palm.  Nests in eucalyptus trees are also common (atlas observers described three), placed within a cluster of leaves that forms a canopy over the nest.  Near the De Luz Fire Station (C6) 5 June 1999, K. L. Weaver found Hooded Orioles nesting almost colonially in eucalyptus trees with Bullock’s Orioles, about six pairs of each species in a small grove.  Four nests were in sycamores, presumably the species’ original nest site in coastal San Diego County (two of these were in mistletoe clumps within a sycamore, one under a Red-shouldered Hawk nest).  The Hooded Oriole’s preference for a canopy occasionally leads to its suspending the nest from man-made structures, as reported by Bent (1958) and Hardy (1970).  In San Diego County, one nest was attached under the eave of a house, one was under a building’s second-story deck, and one with nestlings was under the shade of a light fixture in a campground.

            Hooded Orioles begin building nests in early April, with one record for 29 March.  Nestlings are heard from about 1 May to 1 August, suggesting laying mainly from mid April to mid July.  The 42 egg sets collected 1895–1936 range from 21 April to 4 August.  Adults carrying insects at Banner 16 April 1999 (P. K. Nelson) imply occasional laying in the first few days of April.  The prevalence of Hooded Oriole nesting in June and July suggests the birds raise two broods in a season in coastal southern California, as elsewhere (contra Pleasants and Albano 2001).

Migration: Hooded Orioles return to San Diego during March; they are rare during the first half of the month, common by the end.  From 1997 to 2001 first arrival dates ranged from 26 February to 18 March.  Adult males precede females.  Arrival in the last few days of February is exceptional; no dates earlier than 26 February are known (2000, one at Borrego Springs, F24, M. L. Gabel; one at Agua Caliente County Park, M26, E. C. Hall).  Records of spring migrants far from nesting habitat in the Anza–Borrego Desert peak in late April and extend as late as 9 May (2000, one at Split Mountain, L29, J. R. Barth).  In fall, adult males depart in August, the young of the year largely in the second week of September.  Stragglers occur rarely through October.

           

Winter: The Hooded Oriole has been slower than many species to respond to the newly available winter habitat offered by urban trees.  At this season it remains rare; some winters, like 1999–2000, pass with no records at all.  Wintering birds are usually single (though sometimes with other wintering orioles).  The maximum winter numbers reported were three on the San Diego Christmas bird count 21 December 1968 and five at Point Loma during the winter of 1963–64 (AFN 18:289, 1964), but the possibility of the Orchard Oriole may not have been fully appreciated at the time.  From 1997 to 2002, 10 individual wintering Hooded Orioles were reported in San Diego County.  Most of these were within 5 miles of the coast, but two were somewhat farther inland, one in San Luis Rey Heights (E8) 3 December 2000 (P. A. Ginsburg) and a female in Kit Carson Park (J11) 23 February 1999 (W. Pray).  The only previous winter record so far inland was of one on the Escondido Christmas bird count 1 January 1993.  One in Borrego Springs (G24) 23 January 1999 (M. C. Jorgensen) was the first in winter in the Anza–Borrego Desert, though the species occurs nearly annually in winter in the Salton Sink (Patten et al. 2003).

Conservation: In California the Hooded Oriole has become practically a commensal of man, expanding its range considerably with settlement and urbanization, so one would hardly think it a conservation problem.  Along the middle Gila River and lower Rio Grande, however, the population has declined (Rea 1983, Pleasants and Albano 2001).  The Hooded Oriole is a frequent host of the Brown-headed Cowbird; in 1975, S. I. Rothstein found that 16 of 23 nests around Santa Barbara had been parasitized (Friedmann et al. 1977).  The Hooded Oriole is one of the more likely birds to be affected by the spread of the American Crow; atlas observers noted crows depredating Hooded Oriole nests.  Suspending their nests from the lowest leaves of urban palms renders the birds vulnerable to tree trimming during the nesting season.  Yet the local population is vigorous, colonizing new habitat as soon as it becomes available.  For example, in Mission Valley (R9) in 1991, the orioles nested in a condominium complex within the first year after it was built and landscaped with transplanted full-grown fan palms (P. Unitt).

Taxonomy: The only subspecies of the Hooded Oriole in California is I. c. nelsoni Ridgway, 1885.  Males are paler, with less black on the face, than the subspecies of southern Texas and eastern Mexico; females have the flanks yellowish rather than gray.

Streak-backed Oriole Icterus pustulatus

The Streak-backed Oriole is a primarily Mexican species that is spreading gradually north, first confirmed nesting in Arizona in 1993 (Corman and Monson 1995).  The California Bird Records Committee has accepted six records of vagrants to California, three for San Diego County.

Migration: Huey (1931a) collected the first Streak-backed Oriole known in the United States, at the Lake Murray dam (Q11) 1 May 1931 (SDNHM 14521).  McCaskie saw one in the Tijuana River valley 22 September 1962 (McCaskie and Banks 1964).  The records committee rejected two other sightings there in 1962 and 1963 (Roberson 1993).

Winter: The county’s one wintering Streak-backed Oriole was in a residential area of Pacific Beach (Q7; slightly south of La Jolla as originally reported) 10 December 1984–29 April 1985 (Dunn 1988).  The identification is supported by photographs.

Conservation: The specter of escapees hangs over sightings over the Streak-backed Oriole as for many other Mexican species. Hamilton (2001) did not report the Streak-backed Oriole among the many cage birds he saw in shops in northern Baja California, but I saw one for sale on the streets of Tijuana in the mid 1980s.

Taxonomy: The specimen is the expected subspecies of northwestern Mexico, I. p. microstictus Griscom, 1934.

Bullock’s Oriole Icterus bullockii

Open woodland, woodland edges, and scattered trees are home to one of San Diego County’s most colorful birds, Bullock’s Oriole.  Riparian edges, sycamore groves, and oak woodland were the species’ primitive habitat, and the birds are still common there.  Bullock’s Oriole also takes full advantage of eucalyptus and other exotic trees in rural areas, where its characteristic baglike nest can be found easily—even long after the birds themselves have headed south.  The species is primarily a summer visitor and migrant in San Diego County; only a few individuals are found each winter.

Breeding distribution: Bullock’s Oriole breeds over practically the entire coastal slope of San Diego County.  The largest numbers are in the inland valleys; there are fewer right along the coast, and the species is absent as a breeding bird from Point Loma and Coronado.  The zone of greatest concentration appears to extend from Wynola (J19) and Santa Ysabel (J18) north through Mesa Grande (H17) and Warner Valley to Lake Henshaw (G17) and Warner Springs (F19), where the orioles are common both on the valley floors and in the wooded hills (31 around Mesa Grande 12 May 2001, C. and J. Manning; 30 at Lake Henshaw the same day, R. and S. L. Breisch).  Even small oak groves or scattered ranches offer enough habitat for a few pairs, so the distribution appears almost uniform at the scale of the atlas grid.  There were few atlas squares (D18, V15, V18) so completely covered with treeless chaparral that the orioles were missed.  Bullock’s Oriole is sparse at the higher elevations, above 5000 feet, but is lacking only near the summit of Hot Springs Mountain (E20), the county’s highest peak.

            On the desert slope, Bullock’s Oriole breeds in the riparian woodland along Coyote and San Felipe creeks and where trees are irrigated around buildings, as at Tamarisk Grove (I24), in Earthquake Valley (K23), and at Butterfield Ranch (M23).  In the low desert Bullock’s Oriole breeds uncommonly in the Borrego Valley (maximum count of breeding birds four, including one building a nest, at Ellis Farms nursery, F25, 13 May 2001, P. D. Ache).  Near Ocotillo Wells (J28) the closest suggestion of breeding was an apparent pair 5 May 2000 (J. R. Barth).  In southern San Diego County breeding Bullock’s Orioles extend into the desert no farther than Vallecito (M24/M25; six on 11 June 2002, J. R. Barth et al.).  The gap in the range is the result of lack of habitat; Bullock’s Oriole is a common breeding bird in the cultivated areas of the Salton Sink (Patten et al. 2003).

Nesting: Bullock’s Oriole builds its nest in the middle to upper levels of trees and large shrubs, often at edges or hanging over an opening.  The nests are thus easy to see if not to reach, so atlas observers reported many.  Described sites were in coast live oak (10), sycamore (6), eucalyptus (6), willow (3), mistletoe (2), mulefat (1), catclaw (1), mesquite (1), and deodar cedar (1), at heights of 7 to 60 feet.  The pensile nests are woven of a variety of filaments: observers described nests built predominantly of grass, horsehair, dodder, and fishing line.

            Twenty-eight egg sets of Bullock’s Oriole collected 1889–1935 range in date from 22 April to 18 June, but atlas records imply a somewhat wider spread, from early April to early July.  The two records suggesting laying as early as the first week of April were both in the wet spring of 1998 (adults carrying insects near Upper Otay Lake, T13, 19 April, J. F. Walters; fledgling at La Costa, J7, 25 April, M. Baumgartel).

Migration: Bullock’s Oriole occurs throughout the county as a spring migrant, moving commonly through desert habitats where it does not breed.  It arrives typically in mid March.  From 1997 to 2001 dates of first arrivals ranged from 11 to 18 March.  The earliest date reported for San Diego County is 5 March (1982; AB 36:893, 1982), possibly 1 March (Cooper 1880).  The locally breeding population presumably arrives first, with migrants headed farther north coming through mainly in April, then in decreasing numbers through May.  Records for places in the Anza–Borrego Desert where the species does not breed extend as late as 17 May (2001, one in Carrizo Valley, O28, D. C. Seals).  In fall, the local population departs in July and August, and migrants after 1 September are rare.

Winter: Bullock’s Oriole is a rare winter visitor, regular in urban parks and well-wooded residential areas in San Diego, occasional in riparian woodland elsewhere in the coastal lowland.  The maximum daily count in a single atlas square during the atlas period was four in Balboa Park (R9) 1 December 1998 (J. K. Wilson), but the San Diego Christmas bird count 19 December 1998 totaled five, and earlier Christmas bird counts have gone as high as 14 in San Diego 17 December 1988 and 6 in Oceanside 27 December 1981.  The atlas effort generated the first winter records for the Bullock’s Oriole in San Diego County outside the coastal lowland, of single birds at Banner (K21) 16 January 1999 (M. B. Stowe), Earthquake Valley (K23) 23 December 1999 (G. P. Sanders), Simmons Canyon (R24) 22 January–7 February 2000 (A. P. and T. E. Keenan, J. Larson), and Campo (U22) 31 January 2000 (C. R. Mahrdt, E. C. Hall).  Still farther inland Bullock’s Oriole is a casual winter visitor in the Salton Sink (Patten et al. 2003).

Conservation: There has been no obvious change in the abundance of breeding Bullock’s Orioles through San Diego County history.  The species takes readily to low-density development and has probably spread with the planting of shade trees around rural ranches.  Trash like ribbon and string offers it nest material superior to natural substances.  But intensive urbanization disfavors it; in the inner city it is found mainly in parks and around school campuses planted with sycamores or eucalyptus, or in eucalyptus trees bordering open areas.  Conversely, wintering of Bullock’s Oriole is largely a result of human modification of the landscape—the planting of exotic trees, especially eucalyptus, on whose flowers the orioles feed.  Wintering of Bullock’s Oriole was first recorded in San Diego County in 1957, except for Cooper’s (1880) mention of one in San Diego 1 March (1862?).

Taxonomy: Bullock’s Oriole is usually divided into two subspecies, I. b. parvus van Rossem, 1945, breeding mainly in California and western Arizona, and the slightly larger I. b. bullockii (Swainson, 1827), over the rest of the species’ range.  The difference is most pronounced in wing length, but even on this basis the distinction is only marginally valid.  Comparison of 19 breeding males of parvus (type locality Jacumba, San Diego County) from San Diego and Imperial counties (mean wing chord 95.2, standard deviation 1.95; Patten et al. 2003) with samples from British Columbia (Okanagan), Colorado (Greeley), and southern Idaho (from Rising and Williams 1999) yields adequate separation by the 75% standard as quantified by Patten and Unitt (2002).  But the same comparison with samples from Kansas (Elkhart), Oklahoma (Boise City), and northern Nevada does not, so Bullock’s Oriole is best considered monotypic.

Baltimore Oriole Icterus galbula

Originating in eastern North America, the Baltimore Oriole is a rare migrant and winter visitor in California.  Around the turn of the millennium, reports from San Diego County were averaging one to two per fall and one every other winter.  Records of spring migrants may number as few as eight total.  Wintering of the Baltimore Oriole in southern California, like that of some other orioles and tanagers, is linked to ornamental flowering trees, especially eucalyptus.

Migration: The Baltimore Oriole is most frequent in San Diego County in fall, mainly from late September through October.  The earliest date is 9 September (1991, Point Loma, S7, R. E. Webster, AB 45:323, 1991).  Nine in 1974 is still the record total for one fall.  Wintering birds have stayed as late as 24 April (1968, Point Loma, AFN 22:577, 1968), so seven Baltimore Orioles discovered from late March to April may have been wintering rather than spring migrants.  The eight records later in the spring range from 11 May (1986, Point Loma, J. Oldenettel, AB 40:256, 1978; 1994, Torrey Pines State Reserve, N7, M. B. Stowe, NASFN 48:342, 1994) to 27 May (1967, Point Loma, S7, AFN 21:542, 1967).  Only one of the latter was during the atlas period (18 May 2001, Point Loma, J. C. Worley, NAB 55:358, 2001).  All records are from the coastal lowland.

Winter: San Diego County’s winter records of the Baltimore Oriole are scattered from near Fallbrook (D7; 30 January 1995, I. S. Quon, NASFN 49:200, 1995) to Coronado (S9/T9; three records) but many are from Balboa Park (R9).  Flowering eucalyptus trees there were largely responsible for the winter maximum, seven on the San Diego Christmas bird count 18 December 1982.  The atlas period had three wintering Baltimore Orioles, at Coronado (T9) 19 December 1998, at Balboa Park 15 December 2001 (R. E. Webster), and at Greenwood Cemetery (S10) 16 December 2001 (G. McCaskie).

Taxonomy: The Baltimore and Bullock’s Orioles hybridize regularly in a narrow zone in the Great Plains.  One hybrid has been seen in San Diego County, at Point Loma 26–28 April 2000 (M. Lubin, P. A. Ginsburg).

Scott’s Oriole Icterus parisorum

No bird symbolizes high desert more than Scott’s Oriole, and few birds are as strongly linked to specific plants in San Diego County as Scott’s Oriole is to the desert agave and Mojave yucca.  The birds are distributed sparsely even in prime habitat, so they are uncommon over most of their range: the mountains and bajadas of the Anza–Borrego Desert and arid chaparral of the Campo Plateau.  A few birds are scattered farther west.  Scott’s Oriole is mainly a summer visitor, but the species winters in small numbers as well, mainly at lower elevations in the Anza–Borrego Desert and in a few large stands of prickly pear on the coastal slope.

Breeding distribution: In San Diego County Scott’s Oriole’s distribution centers on the rim of the Anza–Borrego Desert: the east slope of the Peninsular Ranges mainly between 1000 and 5000 feet elevation.  Even there the species is generally uncommon; maximum daily counts are 10 in lower Grapevine Canyon (I23) 7 April 1998 (P. K. Nelson) and 12 between Table Mountain and In-Ko-Pah County Park (T29) 16 April 1999 (D. C. Seals).

Field work for the atlas revealed nesting Scott’s Orioles extending in smaller numbers into low desert on alluvial slopes and washes, rarely into gardens on valley floors (single singing males in Borrego Springs, G24, 11 June 1999, R. Thériault, and at the Borrego Air Ranch, H26, 12 July 1998, M. L. Gabel).  The orioles may be able to spread to lower elevations only after wet winters; in the drought-plagued later years of the atlas’ term we found only old nests in low desert.

            Another surprise was that Scott’s Oriole breeds in small numbers on the Campo Plateau, especially in patches of semidesert habitat like Miller Valley (S24; pair, female collecting yucca fiber, 22 June 2000, L. J. Hargrove).  A few pairs are scattered in chaparral with chaparral yucca but no Mojave yucca, as along the Noble Canyon Trail 1.8 miles north-northeast of Pine Valley (P22) 24 April–16 May 1997 (R. A. Hamilton).  A few extend west of Pine Valley and Campo, south of Interstate 8, as far as Lee Valley (S16; one coming to hummingbird feeder 15 June 1999, J. R. Barth) and near Dulzura between Marron Valley Road and Dulzura Summit (U17; apparently two pairs 17 May–20 July 1998, D. Povey).

            Two other small populations on the coastal slope correspond to enclaves of semidesert habitat.  One is in the gorge of the San Diego River above El Capitan Reservoir (L17/M17; up to two singing males 22 May 1999, R. C. Sanger), extending southeast to near Tule Springs (N18; six, including fledglings, 2 July 2001, E. C. Hall) and upper Conejos Creek (N19; singing male 27 June 2001, J. R. Barth).  The other is presumably an extension from the Aguanga area of Riverside County, running from Dameron and Oak Grove valleys (C15/C16/C17) to Chihuahua Valley (C18) and Rocky Mountain (D18).  In this region the birds are rare except in Dameron Valley (C16; maximum seven on 27 June 1998, K. L. Weaver).

Nesting: Scott’s Oriole’s baglike nest resembles that of the Hooded and Bullock’s Orioles.  Most commonly, Scott’s Oriole attaches its nest under the leaves of a Mojave yucca, at the base of the clump of living leaves.  Eighteen of 30 nests atlas observers described were in yuccas.  Paul Jorgensen notes that the birds typically select the tallest Mojave yucca in their territory as a nest site.  Yucca fibers are the staple nest material.  Where agaves offer good foraging but there are no yuccas, the orioles nest in a variety of other plants, selecting sites that offer the greatest shelter and concealment.  Such sites were in mistletoe clumps in paloverde (3), catclaw (2), or mesquite (1), smoketree (2), indigo bush, jojoba, and California fan palm (1 each).  Where there is no yucca, vine tendrils provide nest material.

            Because only one set of Scott’s Oriole eggs was ever collected from San Diego County, atlas data provide the best information to date on the species’ nesting schedule in this area.  The nine dates of nests with eggs range from 16 April to 15 June.  A fledging at Hapaha Flat (L26) 2 May 2001 (D. C. Seals) indicates egg laying can take place as early as the first week of April, while the female nest building in Miller Valley 22 June 2000 suggests it can take place as late as the last week of June.  Very likely there is substantial variation in the timing of breeding with local conditions of vegetation, rainfall, and elevation.

Migration: The schedule of Scott’s Oriole migration is now clouded by birds wintering in breeding habitat.  From 1997 to 2001, arrival dates varied from 27 February to 16 March, though the earliest of these records, of a singing male near Yaqui Well (I24) 27 February 1997 (P. K. Nelson), was from a site where the species winters occasionally.  Scott’s Oriole may be a short-distance facultative migrant, moving to take advantage of seasonal food supplies, rather than a longer-distance calendar-driven migrant like the Hooded and Bullock’s Orioles.  September and October reports from Culp Valley (G24/H24; Massey 1998) mean that some birds occur in breeding habitat at an elevation of 3000 feet in every season of the year.  The schedule of wintering birds is still poorly known; they may arrive by 3 November (1999, one in Borrego Springs, G24, R. Thériault) and depart as late as 18 April (1998, one in north Borrego Valley, E24, P. K. Nelson), though there are few reports from the Borrego Valley after 1 March.  On the coastal slope, at sites where the species is not known to breed, there were no records during the atlas period after 27 February (2000, one at Rancho Cuca, F14, P. Unitt), yet in the 1970s in Pauma Valley (E12) Eleanor Beemer noted Scott’s Orioles repeatedly as late as mid May (Unitt 1984).  Again, substantial annual variation seems likely.

            Along the coast Scott’s Oriole is very rare, as both a migrant and winter visitor.  The only ones noted 1997–2001 were along the south side of the Tijuana River valley (W11, one on 12 March 2000, P. Unitt; W10, one 9 April–16 July 2000, G. Hazard; W10, one on 22 April 2001, P. R. Pryde).

Winter: Scott’s Oriole winters uncommonly in the Anza–Borrego Desert, mainly in date palms and ornamental shrubbery around houses (up to nine in Borrego Springs, G24, 14 December 1997, P. D. Ache; seven at Canebrake, N27, 8 January 2000, R. and S. L. Breisch; four at Ocotillo Wells, I28, 20 December 1999, P. Unitt) and at native palm oases (up to seven at Carrizo Palms, R28, 6 January 2000, J. O. Zimmer; four at Mortero Palms, S29, 25 February 1999, A. Young).  In typical breeding habitat with yucca and agave, wintering Scott’s Orioles are rare but recorded as high as 5350 feet elevation in the Santa Rosa Mountains 1.2 miles north-northwest of Villager Peak (C27; three on 19 January 2000, P. Unitt).  Totals on Anza–Borrego Christmas bird counts have ranged from 4 to 23 (2 January 1993).  On the Lake Henshaw count, which extends into desert scrub in San Felipe Valley, the species is irregular with only one or two per year, except on 20 December 1993 when there were 26.  Atlas data reveal substantial annual variability as well: more than three times as many Scott’s Orioles were reported in the winter of 1999–2000 than in any other winter of the project’s five-year term.

            On the coastal slope south of Interstate 8, Scott’s Oriole is rare in winter (11 records 1997–2002).  At least some of the birds were at the same sites as those in the breeding season and probably year-round residents (e.g., up to three near Dulzura Summit, U17, 5 February 2001, D. W. Povey).  Others were taking advantage of temporary food sources like prickly pears near Bancroft Point (R12; six on 12 January 2000, N. A. Inman) or flowering eucalyptus in North Jamul (R15; three on 1 January 2000, P. Unitt).  On the coastal slope north of Interstate 8, winter occurrences appear even more strongly tied to fruiting prickly pears.  The primary site there is the grounds of the Wild Animal Park and adjacent San Pasqual Battlefield State Historical Monument (J12/J13), where the thickets of prickly pears are large.  The maximum count in a single atlas square 1997–2002, nine on 2 January 2000 (J13; K. L. Weaver), was also the highest total for the area on an Escondido Christmas bird count.  Other cactus-dominated sites of more than a single wintering Scott’s Oriole include the Fallbrook Naval Weapons Station (D7; four on 11 February 2000, K. L. Weaver), Pauma Valley (E12; two on 15 February 2001, K. Fischer), Rancho Cuca (F14; up to four on 27 December 1999, S. Berg), Pamo Valley (I15/J15; two on 2 January 2000, W. E. Haas), and Sherilton Valley (N19; three on 17 and 18 December 1999, G. and R. Wynn).  Where the supply of fruit was small, as in Sherilton Valley, the birds moved on after exhausting it.  Wintering Scott’s Orioles often occur in small flocks. 

Conservation: Most of Scott’s Oriole’s breeding habitat in San Diego County lies in rugged wildernesses conserved in Anza–Borrego Desert State Park or under the jurisdiction of the Bureau of Land Management.  In Dameron Valley, however, the habitat is privately owned and undergoing piecemeal development, possibly eliminating not only the Scott’s Orioles but also one of the most biogeographically interesting sites in San Diego County, a patch of semidesert scrub with many desert plants and animals isolated on the coastal slope.  Scott’s Orioles once bred to some extent in the coastal sage scrub now replaced by metropolitan San Diego.  Only two locations were reported, Balboa Park (R9/S9; several spring/summer records 1901–15, K. Stephens 1906, Grey 1915, Stephens 1915) and Telegraph Canyon (U11/U12/T13; nest 16 May 1890, Browne 1891), but the Mojave yucca was once common on south-facing slopes.

            The regularity of Scott’s Oriole in winter became clear only in the 1980s, more likely as a result of the establishment of the Escondido and Anza–Borrego Christmas bird counts than from a change in status.  The historic winter range of Scott's Oriole lies not far south of San Diego—both Anthony (1894) and Huey (1926a) found it in January and February near San Quintín, just 150 miles south of the border. The date palms and gardens in the Borrego Valley are a new habitat that the birds only recently learned to exploit.  But the palm oases and prickly pear thickets are native habitats, and records for each dating back to 1968 and 1947, respectively (Unitt 1984), suggest that Scott’s Orioles occurred but were seldom noticed.  On the coastal slope, cacti have been much reduced, along with the coastal sage scrub of which they are usually a part.  Conservation of the remaining stands, so critical to the San Diego Cactus Wren, would favor wintering Scott’s Orioles too.