Townsend's Warbler

Photo by Herbert Clarke/CLO
from the Cornell Lab of Ornithology's Visual Services

Cool Fact: Exclusively insectivorous on their breeding grounds, Townsend's Warblers wintering in Central American cloud forests feed on honeydew, a sugary liquid excreted by insects.

Vocalization of Townsend's Warbler temporarily unavailable during the move to our new building. Please check back in April 2003.

Strikingly arrayed in black, yellow, white, and olive-green, Townsend's Warblers are arguably among the most beautiful birds of western North America. In winter, they are relatively common and easily seen on the coasts of Oregon and especially California. Despite their familiarity, however, Townsend's Warblers remain something of a biological enigma, as many aspects of their behavior and population dynamics remain undescribed.

Townsend's Warblers breed in mature coniferous and mixed forests. The breeding range of the species extends from east-central, south-central, and southern Alaska south through much of British Columbia to the Olympic Peninsula in Washington, and to the mountains of western Montana, the Idaho panhandle, and northeast Oregon.

Townsend's Warblers have two separate winter ranges. Those that breed on the Queen Charlotte Islands winter on the Pacific coast from British Columbia to southern California. Other Townsend's Warblers migrate to southeast Arizona and southwest Texas, extensive stretches of montane habitat in Mexico, and parts of Guatemala, Nicaragua, Honduras, and Costa Rica. Those individuals that winter on the Pacific coast have shorter wings than those wintering in Arizona, Texas, Mexico and Central America. This difference raises the possibility that the two groups should be considered distinct subspecies.

Townsend's and Hermit warblers are very closely related; they often hybridize in the narrow zones where their ranges overlap. Researchers believe that Townsend's Warblers are displacing Hermit Warblers in these zones, in part because male Townsend's Warblers show greater aggression, maintain their territories more effectively, and attract females more readily than Hermit Warblers. Townsend's Warblers also lay more eggs per clutch than Hermit Warblers in the hybrid zone; this difference may be another selective advantage for Townsend's.

Townsend's Warblers feed primarily on insects in their breeding range, usually gleaning from tree branches and foliage, and occasionally foraging in flight. In localized parts of their winter range, they also feed on honeydew right as the sweet liquid emerges from the long excretory tubes of scale insects.

Relatively little is known about the breeding biology and population dynamics of the species. Clutch sizes in a sample of 15 nests in south-central Alaska ranged from 5 to 7 eggs, while 10 of 11 nests in Washington and Oregon had exactly 5 eggs. Evidently, in all parts of the species' breeding range, only females build nests, incubate eggs, and brood nestlings.

Description: Townsend's Warblers are medium-sized wood-warblers, measuring about 5 inches in length. Adult males are strikingly patterned, with broad yellow eyebrow and mustache stripes, set off against a black crown, ear patch, and throat. Short arcs along the bottom of each eye are also bright yellow. Lower breast is yellow, belly is white, with black stripes along the sides and flanks. The male's back is olive-green. Each wing has two white bars. Tail has white outer feathers, which may be conspicuous in flight. Females and immature males resemble adult males, but are duller overall, with olive-green markings on the head and face, instead of black, and yellow throat with variable amounts of black.

Voice: Only male Townsend's Warblers sing. Songs are variable within and between populations, with high, buzzy, often rising notes.