This colorful 5-inch-long warbler may be seen in New Mexico during spring and fall migrations. The males have black crown, throat, and eye patches, with bright yellow streaks separating them. The breast is yellow streaked with black and the back is olive. There are two white wing bars. Females are less distinctively colored, the crown and eye patches being light brown with less streaking on the breast, and a yellow throat.
Townsend’s warblers breed in mature spruce and hemlock forests of the northern Rocky mountains and Cascades, extending up through British Columbia and into Alaska. They migrate in spring and fall across the western U.S., to wintering forests of pines and hardwoods in Mexico and along the Pacific Coast.
They forage for insects in the forest canopy, picking them off of leaves or bark as they flit about or hover, or else flying out to capture them on the wing. They will also take spiders and possibly other arthropods, as well as some seeds and berries during the winter. They also feed on nectar in their winter habitats, including the so-called sugary “honeydew” produced by scale insects, a substance produced from the sticky sap the insects have sucked from tree leaves and bark.
Townsend’s warbler nests are cup-shaped and constructed of grass, moss, bark and twigs, and lined with softer materials like feathers or hair. Nestlings fledge less than a week after hatching.
Townsend’s warblers are known to interbreed with Hermit warblers where their ranges overlap in Oregon and Washington, producing hybrids. The Townsend’s warbler is the more aggressive species and is slowly replacing the Hermit warbler populations. Hermit warblers show similar markings, with a yellow head and dark crown and throat patches, but lacking the dark eye streaks of the Townsend’s. Taxonomists debate whether the two populations actually constitute a single species, since they are able to interbreed and produce viable hybrids in areas where populations occur together.
The Audubon Society states that the population of Townsend’s warblers is currently stable and common, at about 20 million birds, but predicts losses of breeding habitat in the southern parts of the range in the northwestern U.S. as global warming shifts cooler forests northward.