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Worm-eating Warbler
Helmitheros vermivorum
– Family
Authors: Hanners, Lise A., and Stephen R. Patton
Revisors: Vitz, Andrew C.

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Singing male Worm-eating Warbler, Vinton Co., OH, 1 May.
Figure 1. Distribution of the Worm-eating Warbler.

The sole member of the monotypic genus Helmitheros, the Worm-eating Warbler superficially resembles warblers of the genus Basileuterus, all of which are restricted to Central and South America. In eastern North America this species nests mainly where large tracts of deciduous and mixed forest overlap with moderate to steep slopes and patches of dense understory shrubs, although breeding populations are also found in low-elevation, coastal forests. It winters in forest and scrub habitats of the Greater Antilles and in moist forests of Central America, particularly along the Caribbean slope.

This is one of a suite of ground-nesting, forest songbirds of eastern North America that includes the Black-and-white Warbler (Mniotilta varia), the Ovenbird (Seiurus aurocapilla), the Northern (Parkesia noveboracensis) and Louisiana (P. motacilla) waterthrushes, and the Kentucky Warbler (Geothlypis formosus). The Worm-eating Warbler is perhaps best known for its habit of hopping through the understory and probing into suspended dead leaves for food—its primary foraging technique on the wintering grounds but also used on the breeding grounds, especially before leaves come out in spring. Worm-eating Warblers eat mostly caterpillars (once known as “worms”—hence this warbler’s name), other insects, and spiders.

The foraging behavior of the Worm-eating Warbler has been studied in both its summer and its winter habitats (e.g., Lack and Lack 1972, Greenberg 1987). Studies of forest birds conducted at sites in the Ozarks, southern Illinois, Tennessee, Ohio, and West Virginia have provided important information about its breeding biology, response to prescribed fire, and how it is affected by habitat fragmentation and forest management. A long-term study of the species’ demography and population ecology has been conducted at The Nature Conservancy’s Devil’s Den Preserve in southwestern Connecticut since 1991 (Gale et al. 1997). Most of the information on the post-fledging ecology of this species is from a study in southern Ohio (Vitz and Rodewald 2010, Vitz and Rodewald 2011). Unpublished data and observations are frequently provided herein.