WORM-EATING WARBLER

© Larry Master
Photographer: Larry Master

SCIENTIFIC NAME: Helmitheros vermivorus (Gmelin)

OTHER NAMES: Worm-eater, Worm-eating Swamp Warbler (Terres 1980).

DESCRIPTION: Sparrow-sized (13-14 cm [5-5.5 in.]), with distinctive broad black stripes on a buff-colored head. Remaining upperparts brownish olive, and underparts dark to pale buff. Legs flesh-colored, and robust bill brownish black above and horn to pink below. Sexes similar. Song a simple high-pitched trill, che-e-e-e-e-e-e, lasting about two seconds; sharp, strident chip call also given. No recognized subspecies (Terres 1980, Hanners and Patton 1998).

DISTRIBUTION: Breeding distribution discontinuous from northeastern Kansas and southeastern Nebraska east across southern Great Lakes region to southern New England, south to northeastern Texas, south-central Alabama, northwestern Florida, and South Carolina (AOU 1998). Winters from sea level to 1,500 meters (4,500 feet) in southern Mexico and on the Atlantic and Pacific slopes of Central America south to central Panama. Also winters on Bermuda and in the West Indies (Bahamas, Greater Antilles, Virgin Islands, Cayman Islands) (Hanners and Patton 1998). In Alabama, uncommon in spring, summer, and fall in Tennessee Valley and Mountain Regions. In the Inland Coastal Plain Region, uncommon in spring and fall, and rare in summer. In the Gulf Coast Region, fairly common in spring, uncommon in fall, and rare in late summer (Jackson 2001a).

HABITAT: Breeds in large tracts of deciduous and mixed forest, particularly those with moderate to steep slopes and patches of dense understory shrubs, although breeding populations also occur in low-elevation coastal forests (Hanners and Patton 1998). In migration, occurs in various forest, woodland, scrub, and thicket habitats. In winter, inhabits shrub and subcanopy layers of a variety of forest types (Patton et al. 1998).

LIFE HISTORY AND ECOLOGY: Returns to breeding grounds in April and May. Males establish territories and monogamous pair bonds formed soon thereafter. Female builds well-concealed nest on ground, usually on a hillside or bank. Nest of dead leaves constructed, with lining often consisting of hair-like moss setae and mammal hair. Clutch consists of four to six whitish eggs, lightly speckled with brown. Although single-brooded, replacement clutches produced if earlier nest attempts fail. Female incubates eggs for 12-13 days; young leave nest nine to 10 days post-hatching. Both parents feed young, which become independent about three weeks post-fledging. Subjected to brood parasitism by brown-headed cowbird (Hanners and Patton 1998). Noted for habit of probing suspended dead leaves for food. Diet consists mostly of caterpillars, other insects, spiders, and slugs (Hanners and Patton 1998).

BASIS FOR STATUS CLASSIFICATION: Highly vulnerable to population decreases because of dependency on large tracts of unfragmented forest for nesting (Patton et al. 1998). Probably requires large (300-1,000 hectares [720-2,400 acres]) tracts of deciduous forest for successful reproduction and high productivity (Patton et al. 1998). Large contiguous areas with a minimum of nonforested edge produce the highest densities of breeding individuals and increase reproductive success by decreasing nest parasitism and predation (Hanners and Patton 1998). Also, has relatively narrow nonbreeding distribution, and nonbreeding populations are threatened because human alteration of tropical, broadleaved forests is expected (PIF 2002). Severe deterioration in future suitability of breeding conditions expected in Central Hardwoods Bird Conservation Region. Breeding Bird Survey data demonstrate a possible or moderate population decrease in the Appalachian Mountains. Additionally, Breeding Area Importance scores indicate species is present in highest relative abundance, and in high relative abundance, for the Appalachian Mountains and Central Hardwoods, and Southeastern Coastal Plain Bird Conservation Regions, respectively (PIF 2002). Priority designation assigned in Alabama based on Partners In Flight (PIF) scores for three factors: relative abundance, distribution of nonbreeding populations, and threats to nonbreeding populations. For all PIF Bird Conservation Regions found in Alabama (Appalachian Mountains, Central Hardwoods, Piedmont, Southeastern Coastal Plain), species occurs in low relative abundance and populations appear to be patchily distributed (PIF 2002).

Author: Paul D. Kittle