Worm-eating Warbler (Helmitheros vermivorum)
By Carrie Chapin, Houston Audubon Conservation Technician
One member of the great menagerie of warblers to visit the Texas coast during spring migration is the secretive Worm-eating Warbler. Previously placed in the same genus as Swainson’s Warbler, this small passerine frequents forest understories and can be difficult to find in the dense shrubs and vegetation it prefers. Its name refers to the many species of caterpillars it consumes (though most warblers eat plenty of caterpillars too). Both sexes of Worm-eating Warblers can be identified by their prominent black streaks on an orange head with a long, pointed bill. The wings are dull olive and lack wingbars, and the breast is unmarked. Following their insect-like trill (similar to that of a Chipping Sparrow) or sharp tseet call is the most reliable method of locating hidden individuals.
Worm-eating Warblers breed in the eastern and central United States and overwinter in Mexico, Central America, and the Caribbean. They prefer to nest in dense, large stands of trees with lots of understory vegetation. The nest is a simple open cup placed on the ground and hidden by dead leaves and vegetation. After the nest is constructed by the female, she lays between four and six eggs and incubates them for eleven to seventeen days. Both parents feed the offspring, and the male defends a large territory from thrushes and conspecifics. After ten days, the young leave the nest and the male stops defending the territory.
Worm-eating Warblers are sensitive to habitat fragmentation and need over 52 acres of forest to nest. Nests placed along the edges or in fragmented habitats are frequently parasitized by Brown-headed Cowbirds. Unfortunately, insecticides used to control spongy moths can cause a decline in their populations. Interestingly, Worm-eating Warblers appear tolerant of clear-cutting and may move back into a nest three years after a disturbance. As with many other nocturnally migrating bird species, Worm-eating Warblers face additional mortality from window strikes and feral cats.
This species migrates across the Texas coast from late March through early May. Some of the bests spots to catch a glimpse are in the Smith Oaks or Boy Scout Woods Sanctuaries in High Island, Texas, or in the Edith L. Moore Sanctuary in Houston. Be sure to identify this small bird in the bushes, you might be pleasantly surprised!
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