Beak of the Week – Bay-breasted Warbler

Bay-breasted Warbler (Setophaga castanea)
Family: Parulidae

When in doubt…look at the feet? Or at least that’s what you do when you are in doubt as to whether you are looking at a non-breeding female/young Bay-breasted or a Blackpoll warbler. Because these two can look very similar, biologists will use the distinctive blue-grey color of the soles to confirm the identities of Bay-breasted Warblers. Adult breeding males are dark grey on the top, with a white/cream-colored underside, and nape, white wingbars, and a reddish-brown crown, throat, and flanks. Adult breeding female Bay-breasted Warblers are less dark and have just a wash of the chestnut coloring.

Bay-breasted Warblers are mainly insectivorous, with a large portion of their diet consisting of spruce budworm. Since spruce budworms make up a large portion of the Bay-breasted Warbler’s diet, the prevalence of spruce budworm directly impacts Bay-breasted Warbler population sizes from year to year. Cape May, Blackpoll, and Blackburnian Warblers also feed on spruce budworms, but at different heights within the canopy, helping to reduce competition for food.

The fall migration path that a Bay-breasted Warbler takes, is often influenced by age. Adult birds will tend to migrate more on the western side of the migration route, while more immature birds will migrate more to the east. During migration, Bay-breasted Warblers use a wide variety of habitat types that differ from their preferred breeding habitat of boreal forest. Bay-breasted Warblers are at the tail end of their migration through the Upper Texas Coast on their way to the breeding grounds.

By Sarah Lefoley, Conservation Technician, Houston Audubon

Photos by Greg Lavaty

Visit our Bird Gallery to learn about other Texas birds. 

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