Yellow-rumped Warbler

The Yellow-rumped Warbler is one of the most abundant and adaptable warblers in North America, easily recognized in any plumage by its bright yellow rump patch, which gives rise to its popular nickname, 'butter-butt.' Breeding males are strikingly patterned in blue-gray, black, and white, with yellow patches on the crown, sides, and rump, while females and non-breeding birds are duller brown-gray with the yellow rump remaining a reliable identification clue.

Two well-known forms exist: the eastern 'Myrtle' Warbler, with a white throat, and the western 'Audubon's' Warbler, with a yellow throat; these were once considered separate species and some authorities still debate their taxonomic status. This warbler's unique ability to digest the waxy coating of bayberries and wax myrtle berries allows it to winter much farther north than most other warblers, which rely almost entirely on insects.

Key Field Marks

• Bright yellow rump patch, visible in all plumages and especially obvious in flight
• Yellow patches on the crown and sides of the breast in breeding plumage
• White throat ('Myrtle' form) or yellow throat ('Audubon's' form)
• Streaked gray-brown back and flanks with white wingbars
• Dull brownish-gray winter plumage retaining the diagnostic yellow rump

Similar Species

Magnolia Warbler also shows yellow on the rump but has a bold yellow underside with black streaking and a distinctive tail pattern, quite different from Yellow-rumped's mostly gray-brown body. Cape May Warbler has a yellow rump as well but shows a chestnut cheek patch (breeding male) and heavy breast streaking without the Yellow-rumped's white wingbars pattern. The combination of yellow rump plus yellow side patches is unique to the Yellow-rumped Warbler.

Habitat

Yellow-rumped Warblers breed in coniferous and mixed forests, especially spruce-fir and pine woodlands. Outside the breeding season, they use an exceptionally broad range of habitats, including deciduous woods, scrub, coastal dunes, and suburban gardens.

Range

This species breeds across Canada, Alaska, the northeastern United States, and mountainous parts of the West. It winters across the southern and coastal United States, Mexico, and Central America, forming large flocks.

Migration

Yellow-rumped Warblers are among the earliest warblers to arrive in spring and latest to depart in fall, owing largely to their unusual dietary flexibility, which lets them subsist on berries when insects are scarce.

Behavior

Highly social outside the breeding season, Yellow-rumped Warblers form large, active flocks that forage together in trees, shrubs, and even on the ground, often mixing with other species.

Voice

The song is a loose, warbling trill that rises or falls slightly in pitch. The call is a distinctive sharp, flat 'check' or 'chek,' often heard from flocks in flight.

Feeding

In the breeding season it gleans and sallies for insects, but in winter it switches heavily to fruit, particularly the waxy berries of wax myrtle and bayberry, which it can digest thanks to specialized bile salts, a rare trait among warblers.

Nesting & Breeding

The female builds a cup nest of twigs and grass, usually placed on a horizontal conifer branch well away from the trunk. She lays 4-5 eggs, and the species often raises two broods per season.