Helmitheros vermivorus
The name “Worm-eating” was given to this warbler because its diet includes caterpillars, once referred to as “worms.” The species has not been reported to pull earthworms from the soil as American Robins (Turdus migratorius) do. Instead this insectivore gleans its diet (insects and their larvae as well as spiders) from foliage. This warbler uses tactics such as probing curled live or dead leaves for hidden prey while hanging from a twig or small branch, probing crevices, sallying to grab flying prey and picking off slow-moving insects from open leaves and young twigs (Hanners and Patton 1998).
The Worm-eating Warbler is the only member of its genus, has no recognized subspecies and is not closely related to any other species (Hanners and Patton 1998).
DISTRIBUTION. During the 1987-1992 field work seasons of the TBBA project, volunteers found 2 confirmed breeding records for Worm-eating Warbler (31094-C2 and 30095-E2), 6 probable records (30095-D1, E1, E2 & E3, 30094-F6 and 31095-D2 and 3 possible records (30095-E2 & E3 and 33094-G2). Except for the last location, all these are northeast of Houston in the southern Pineywoods region and mostly (7) in latilong 30095.
The breeding range of this warbler extends northeast from Texas and Oklahoma (where this warbler is limited to the southeast corner of the state [Kuhnert 2004]) to southern New England and extending east to the Atlantic Coast from the Carolinas northward. In winter the species occurs from northeast Mexico south at lower elevation to Panama and on Bermuda, the Bahamas and the Greaten Antilles (Howell and Webb 1995, Am. Ornithol. Union 1998, Hanners and Patton 1998, Sauer et al. 2005).
SEASONAL OCCURRENCE. In spring Worm-eating Warblers arrive in Texas from late March to early May and probably breed from April to June. Southbound migrants are present from late August to early October. In migration this warbler is uncommon to common, primarily along the coast (Oberholser 1974, Lockwood and Freeman 2004).
BREEDING HABITAT. Worm-eating Warblers mainly breed in large tracts of deciduous or mixed deciduous-coniferous forests on moderate or steep slopes with patches of dense understory. In Texas they are found breeding in dense woodlands associated with bay-gallberry holly bogs (Hanners and Paton 1998, Lockwood and Freeman 2004).
The female selects the site within a pair’s territory. She builds the nest on the ground, usually on the side of a ravine, commonly near water and well-hidden under dead leaves blown into a drift against a small tree, roots of a shrub or tree, beside a rock ledge or outcrop, or under dense low shrubs such as huckleberry or blueberry. The female forms a cup of partly decomposed leaves, often using damp material . The cup is lined with fungal sporophyte stems (Hanners and Patton 1998).
The usual first clutch contains about 5 (range 4-6) smooth, white to flesh pink eggs, speckled with various shades of brown. Incubation lasts approximately 13 days (range 11-17 days) and the nestling stage lasts about 10 days. After leaving the nest the brood is split by the parents and each parent remains with 2-3 chicks for about 3 weeks. Rates of brood parasitism by Brown-headed Cowbirds (Molothrus ater) are highest in fragmented woodlands (up to 75%; Hanners and Patton 1998).
STATUS. Worm-eating Warblers are rare to uncommon summer residents in the central and southern Pineywoods.(Lockwood and Freeman 2004). The breeding symbols on the TBBA map do not go as far north and west. as the breeding and summer observations on the map in Oberholser (1974). The breeding range may have shrunk. Only 4 North American Breeding Bird Survey (BBS) routes in Texas detected this warbler and only at relative abundances <1, making trend data for Texas of little value. Data from 358 routes across the breeding range suggest a +1.1% annual population change for the years 1980-2005 (Sauer et al. 2005). Loss of habitat in the breeding range of this inhabitant of woodland interiors is probably the major threat to its future as a breeding species in Texas. Text by Robert C. Tweit (2007)
Literature cited.
American Ornithologists’ Union. 1998. Checklist of North American birds, 7th ed. Am, Ornithol. Union, Washington, DC.
Hanners, L. A. and S. R. Patton. 1998.Worm-eating Warbler (Helmitheros vermivorus). InThe birds of North America, No. 367 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.