The western is the “default” breeding yellow-bellied kingbird across vast areas of the west (especially arid lowlands); but its distribution and habitat overlap with other yellow-bellied kingbirds (the Cassin’s, thick-billed, tropical, and Couch’s) as well as with the eastern and scissor-tailed flycatchers. From exposed perches on trees, shrubs, or wires, it chases and captures flying insects; it will also sally to vegetation or the ground and will take fruit during fall and winter. Monotypic. Length 8.1–9.6".
Adult: pale gray head; darker mask; concealed orange-red central crown patch. Pale grayish olive back. Plain brownish black wings, contrasting paler back. Square-tipped, black tail; white outer webs of outer pair of feathers. White throat subtly blends to pearly gray chest and yellow belly. Relatively small, black bill. Juvenile: duller, paler.
Typical tail pattern unmistakable, but individuals with worn or missing white outer tail feathers might be mistaken for other yellow-bellied species. The Cassin’s is overall much darker on chest, upperparts; has contrasting white chin, paler wings, gray tail tip. The tropical and Couch’s have heavier bills; olive-yellow chests; and dark brown, deeply notched tails. The Cassin’s, tropical, and Couch’s also have pale-edged upperwing coverts with a more scalloped appearance. The thick-billed has much heavier bill, darker upperparts, yellow central crown patch, paler underparts. (Juvenile’s underparts yellower, more western-like.) Superficially similar to juvenile or immature scissor-tailed, immature white-bellied kingbirds with tinge of yellow on underparts, Myiarchus, or say’s phoebe; but key field marks should still be apparent.
Call: single or repeated sharp kip notes; also a staccato trill. Dawn song: a repeated series of kip notes and long trills.
Status and Distribution
Common. Breeding: open country with scattered trees or shrubs; will nest on human-made structures (e.g., utility poles). Migration: mid-March–early June; late July–mid-September; scarce after early October, stragglers into November. Winter: central-western Mexico to Costa Rica; also southern Florida. Vagrant: in summer, casual/accidental to Alaska, central and northern Canada; in winter, rare/casual on Pacific coast to central California, on Gulf and Atlantic coasts, and to Panama, West Indies, and Bermuda.
Stable or increasing.
—From the National Geographic book Complete Birds of North America, 2006