The worm-eating warbler (Helmitheros vermivorum) is a small New World warbler that breeds in the Eastern United States and migrates to southern Mexico, the Caribbean, and Central America for the winter. Taxonomy The worm-eating warbler is the only species currently classified in the genus Helmitheros. However, Swainson's warbler has previously been in this genus as H. swainsonii. Description The worm-eating warbler is a small New World warbler. Measurements: Length: 4.4-5.2 in (11.2-13.1 cm) Weight: 0.4-0.5 oz (12-14 g) Wingspan: 7.9-8.7 in (20-22 cm) It is relatively plain with olive-brown upperparts and light-coloured underparts, but has black and light brown stripes on its head. It has a slim pointed bill and pink legs. In immature birds, the head stripes are brownish. The male's song is a short high-pitched trill. This bird's call is a chip or . Worm-eating warblers are sexually monomorphic. Males and females can only reliably be sexed during the breeding season by the presence of a brood patch in females or a cloacal protuberance in males. These birds are also difficult to age. Hatch year/second year birds have rusty tips on tertials that wear off by March of the following year. Juveniles can be distinguished by duskier head markings, and cinnamon wingbars. Reproduction This bird breeds in dense deciduous forests in the eastern United States, usually on wooded slopes. The nest is an open cup placed on the ground, hidden among dead leaves. It is one of several species of new-world warblers that nests on the ground including the black-and-white warbler (Mniotilta varia), the ovenbird (Seiurus aurocapilla), the northern waterthrush (Parkesia noveboracensis), Louisiana waterthrush (Parkesia motacilla), palm warbler (Setophaga palmarum), and the Kentucky warbler (Geothlypis formosa). The female lays four or five eggs. Both parents feed the young; they may try to distract predators near the nest by pretending to be injured. Worm-eating warblers are often parasitized by brown-headed cowbirds (Molothrus ater) where forest fragmentation occurs. Reducing forest fragmentation may prove vital if populations of worm-eating warblers suffer large declines. Habitat and distribution These birds breed in the Eastern United States. Their selected habitats vary significantly between populations. In much of their range, worm-eating warblers are associated with mature hardwood forests on steep slopes. However, recent attention has been focused on coastal breeding populations, as little is known about their ecology or status. Historically, coastal populations would select for pocosin ecosystems. More recently, however, these populations have shifted