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Literature Review

Yellow warbler

Dendroica petechia brewsteri

USFWS: No status
CDFG: Species of Special Concern

Background

Distribution, Abundance and Trends. The yellow warbler occurs in riparian areas throughout Alaska, Canada, the United States, and parts of Mexico. A tropical subspecies occurs in Central and South America. The yellow warbler prefers wetlands and mature riparian woodlands dominated by cottonwoods, alders, and willows. It also uses well watered, second growth woodlands and gardens. The yellow warbler winters south to the Bahamas, Central America and South America to Peru, Bolivia, and Brazil. The species breeds throughout the United States and Canada. The population is fluctuating in North America: declining in some areas and increasing in others. It was once a common to locally abundant summer resident in riparian areas throughout California. Currently, populations are reduced and locally extirpated (e.g., Sacramento Valley and San Joaquin Valley). Once a common resident in San Francisco, there are no recent breeding records for this area. Breeding populations in Marin County have declined, but the species is still common in Santa Cruz County. Numbers have also declined in Siskiyou County, but are steady in some areas of the Sierra Nevada. Yellow warblers are common along streams below about 8,000 feet in the eastern Sierra. The yellow warbler has declined significantly as a breeding bird in the coastal lowlands of southern California and is believed to be extirpated from the Colorado River. Destruction of riparian habitats and cowbird parasitism are the major causes of the decline.

The yellow warbler is known or believed to occur as a breeding bird at Whitewater Canyon, Mission Creek, Chino Canyon, Andreas Canyon, in the Whitewater River near the Salton Sea, and at Cottonwood Spring in Joshua Tree National Park. Many yellow warblers also migrate through the Plan area en route to other breeding areas. In migration, the yellow warbler may use desert fan palm oasis woodland, mesquite hummocks, mesquite bosque, arrowweed scrub, desert dry wash woodland, desert sink scrub, desert saltbush scrub, southern sycamore-alder riparian woodland, Sonoran cottonwood-willow riparian forest, valley freshwater marsh, and cismontane alkali marsh in the plan area. The species would also use urban areas in migration. No conservation measures are proposed in urban areas; however, it is anticipated that suitable landscape trees and shrubs will continue to thrive in urban areas.

The yellow warbler typically arrives from their wintering areas from late March to May. It tends to nest in locations of intermediate height and shrub density. The nest is built in an upright fork or crotch of a large tree, or sometimes a sapling or bush, generally 6 to 8 feet above the ground. The nest is a well-formed cup of interwoven plant fibers and down, fine grasses, lichens, mosses, spider's silk, hairs, etc. Usually 4 to 5 eggs are laid in spring or early summer. Incubation is 11 days, and the young leave the nest at 9 to 12 days old. The yellow warbler feeds on caterpillars, cankerworms, moth larvae, bark beetles, borers, weevils, small moths, aphids, grasshoppers, and spiders, and occasionally feeds on a few species of berries.

Threats and Limiting Factors. The primary threats to the yellow warbler in the Plan area are cowbird parasitism and destruction or degradation of habitat from flood control and other human activities. Cowbird parasitism is well documented, and the yellow warbler is one of the most common hosts. One cowbird may lay an egg in up to 12 different nests in a breeding season, and yellow warblers lay a single clutch per season. Human activities, including golf courses and agriculture, attract cowbirds, thereby increasing the threat to yellow warblers.

Special Considerations. Effective control of cowbirds may be difficult because of the number of golf courses and agricultural areas in the Coachella Valley, which provide habitat for the cowbird.