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YELLOW WARBLER (Dendroica Petechia) Sacha K

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YELLOW WARBLER (Dendroica Petechia) Sacha K II SPECIES ACCOUNTS Andy Birch PDF of Yellow Warbler account from: Shuford, W. D., and Gardali, T., editors. 2008. California Bird Species of Special Concern: A ranked assessment of species, subspecies, and distinct populations of birds of immediate conservation concern in California. Studies of Western Birds 1. Western Field Ornithologists, Camarillo, California, and California Department of Fish and Game, Sacramento. Studies of Western Birds No. 1 YELLOW WARBLER (Dendroica petechia) Sacha K. Heath Criteria Scores Population Trend 15 Range Trend 5 Population Size 2.5 Range Size 0 Endemism 0 Population Concentration 0 Threats 5 Current Breeding Range Historic Breeding Range County Boundaries Water Bodies Kilometers 100 50 0 100 Current and historic (ca. 1944) breeding range of the Yellow Warbler in California; occurs much more widely in migration. Breeding numbers have declined greatly, particularly in lowland areas west of the Cascade–Sierra Nevada axis, and the range has retracted broadly in the Central Valley and locally in the Owens Valley. 332 Studies of Western Birds 1:332–339, 2008 Species Accounts California Bird Species of Special Concern SPECIAL CONCERN PRIORITY Mojave River) and all of the Colorado Desert. Known elevational limits of breeding were 7000 ft Currently considered a Bird Species of Special (2134 m) on the western and 8500 ft (2591 m) on Concern (breeding), priority 2. Included on both the eastern flank of the Sierra Nevada. With few prior special concern lists (Remsen 1978, 2nd exceptions, Grinnell and Miller (1944) mapped priority; CDFG 1992). locations of individuals reported or collected dur- ing the breeding season in every county within GENERAL RANGE AND ABUNDANCE this general range. Quantitative estimates of his- Breeding widely in the New World, the Yellow toric breeding abundance are scant and mostly Warbler comprises three subspecies groups: aestiva unreliable. For example, estimates of 10 birds (continental North America), petechia (extreme per 3 river mi (4.8 km) in the Sacramento Valley southern Florida and Caribbean), and erithacho- region (Grinnell et al. 1930) did not discern rides (coastal Mexico to northern South America; between singing migrants and breeders, both of Lowther et al. 1999). The aestiva group migrates which likely occurred during the late May surveys to winter mainly from northern Mexico south to (T. Manolis in litt.). central South America. Overall considered one of the most abundant warblers in North America; RECENT RANGE AND ABUNDANCE published breeding density estimates range from IN CALIFORNIA 0.7 to 14.4 pairs per ha (Lowther et al. 1999). Despite many local declines, Yellow Warblers Four subspecies of the aestiva group have pre- currently occupy much of their former breeding viously been considered to occur in California: range, except in the Central Valley, where they are breeding D. p. brewsteri, D. p. morcomi, and D. p. close to extirpation (see map). Broad-scale signifi- sonorana, and transient D. p. rubiginosa (Grinnell cant declines have been documented for the U.S. and Miller 1944). Because D. p. brewsteri and D. Pacific Northwest region (1979–1999, Ballard et p. morcomi are not consistently distinguishable al. 2003) and declines approaching significance in (Patten et al. 2003), brewsteri is best considered California (1968–2004, Sauer et al. 2005). Both synonymous with morcomi (P. Unitt pers. comm.). local abundance and long-term trends, however, Sonorana, found only along the lower Colorado vary greatly by region. River and ranked independently as a species of Northwestern California. This species breeds special concern (see relevant account), is not con- locally throughout Del Norte, western Siskiyou, sidered further here. Humboldt, Trinity, Mendocino, and Sonoma counties, except at lower elevations along the SEASONAL STATUS IN CALIFORNIA coast in Mendocino and Sonoma (Bolander and Occurs principally as a migrant and summer Parmeter 2000, Harris 2005, Hunter et al. 2005, resident from late March through early October; D. Tobkin pers. comm.). Breeding Bird Survey breeds from April to late July (Dunn and Garrett (BBS) averages vary widely, from 1.00 birds per 1997). route at Bartlett Springs, Lake County, to 71.89 birds per route at Horse Creek, Siskiyou County HISTORIC RANGE AND ABUNDANCE (Sauer et al. 2003). Breeding density was only 0.26 pair per ha at Clear Creek, Shasta County, in the IN CALIFORNIA northern interior Coast Ranges (PRBO unpubl. Grinnell and Miller (1944) described the Yellow data). Breeding bird atlases found Yellow Warblers Warbler as a “common” to “locally abundant” in 16% of blocks (66 of 425, 6 confirmed) in breeder throughout California, except for most Humboldt County (Hunter et al. 2005) and in of the Mojave Desert (it occurred locally only in 43% of blocks (34 of 79, 11 confirmed) in Napa the Panamint and Grapevine mountains and the County (1989–1993; Berner et al. 2003). Recent BREEDING BIRD SURVEY STATISTICS FOR CALIFORNIA All data from 1968–2004 1968–1979 1980–2004 Sauer et al. (2005) Trend P n (95% CI) R.A. Trend P n Trend P n Credibility –1.4 0.14 128 –3.3, 0.4 1.81 –4.4 0.11 75 –2.0 0.10 112 High Yellow Warbler 333 Studies of Western Birds No. 1 efforts in Napa, however, failed to locate the spe- nests were located at Hospital Creek, Stanislaus cies at most of its historic breeding sites—most County, on the San Joaquin River NWR (PRBO notably at Napa River, Mill Creek, and Suisun unpubl. data), and in 2005 one nest and at least Creek—perhaps because of wine industry thin- three confirmed territories were found on San Luis ning of riparian habitat in the Napa Valley (R. NWR, Merced County (PRBO unpubl. data). Leong and B. Grummer pers. comm.). Cascade Range and Sierra Nevada. Yellow Northeastern California. The species breeds Warblers breed widely in this region in both widely in this region. In the Modoc National riparian habitat and chaparral shrub fields (CalPIF Forest, the Yellow Warbler was the most numerous 2003, J. Snowden and B. Williams in litt.). species detected on breeding season surveys (T. Abundance estimates ranged from 0.04 to 1.14 Ratcliff in litt.); it is also numerous throughout birds per ha among eight Sacramento River sites Shasta County (B. Yutzy in litt.). BBS averages above Shasta Dam (PRBO unpubl. data) and 0.83 ranged from 0.56 to 4.67 birds per route where to 0.97 pairs per ha at one site along Gurnsey the species was sampled on the Modoc Plateau, Creek, Tehama County (1998–1999; PRBO Surprise Valley, and Madeline Plain (Sauer et al. unpubl. data). A density of 0.95 birds per ha was 2003). The Susan River, Lassen County, held found in xeric montane shrub fields of Lassen 1.05 birds per ha (PRBO unpubl. data). On Volcanic National Park (PRBO unpubl. data). Atastra Creek in the Bodie Hills, Mono County, On the west slope of the Sierra Nevada, Yellow density was 0.26 birds per ha in 1979 (Weston Warblers breed from foothill woodlands up to the and Johnston 1980), but the species was absent mixed-conifer zone, and at select sites in the north in 2000–2003 (PRBO unpubl. data). At Mono they may be as abundant in montane chaparral as Lake, densities on the lower reaches of Rush and in riparian habitat (B. Williams, J. Steele in litt.). Lee Vining creeks have been as high as 2.74 and Verner and Boss (1980) considered them “fairly 1.71 pairs per ha, respectively, and are increasing common” summer residents in the late 1970s, and annually (PRBO unpubl. data), presumably as a Beedy and Granholm (1985) reported declining result of rewatering, removal of livestock grazing, numbers. They are increasing in postfire chaparral and riparian restoration. The Glass Mountain area in El Dorado County (E. Harper in litt.) and have and the White-Inyo Range hold small and local- averaged 12.4 birds per BBS route since the 1992 ized breeding populations (PRBO unpubl. data, fire (Sauer et al. 2003). In the southern Sierra, Johnson and Cicero 1991). mixed-conifer forests at 5600–6601 ft (1707– Central Valley. The Yellow Warbler is largely 2012 m) harbor small breeding populations (0.34 extirpated as a breeder in the Sacramento Valley. birds per ha; K. Purcell in litt.). Probable breeders Numbers were already low by the 1970s, when occur in meadows around 7000 ft (2134 m) on Gaines (1974) found the species at only 4 of Greenhorn Mountain, Kern County (J. Wilson 20 sites in the upper, and at none in the lower, in litt.). In the Kern River Valley, 142 males were Sacramento Valley. Intensive coverage along the counted on a valley-wide 10 July 1999 survey, Sacramento River in Glenn, Butte, and Tehama far exceeding the estimated 14 pairs for the counties from 1993 to 1999 found only five nests entire valley in 1985 (B. Barnes in litt.). Yellow of three pairs (PRBO unpubl. data, T. Manolis in Warblers have probably benefited from restora- litt.). In Placer County, individuals occur on the tion and Brown-headed Cowbird (Molothrus ater) valley floor during the breeding season (Webb trapping to aid Southwestern Willow Flycatcher 2003). Extensive surveys in 1998 and 1999, (Empidonax traillii exitmus) recovery in the area however, failed to locate breeding Yellow Warblers (B. Barnes and S. Laymon in litt.). along the Sacramento River and its lower tributar- On the east slope of the northern Sierra, ies in Colusa, Sutter, Yolo, and Sacramento coun- density was 0.29 pairs per ha in postfire chapar- ties, and no breeding records exist for Sacramento ral and regenerating conifers at Sagehen Field County as a whole (PRBO unpubl. data, T. Station, north of Truckee (Raphael et al. 1987); Manolis in litt.).
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