Seasonal Foraging Specialization in the Worm-Eating Warbler

Abstract

Abstract. The foraging behavior of Worm-eating Warblers (Helmitheros vermivorus) was studied in Maryland during the breeding season and in Jamaica, Dominican RepubUc, and Belize during the nonbreeding season. Over 75% of the foraging maneuvers recorded from May to early August in Maryland were directed towards live foliage, whereas over 75% of the maneuvers were directed towards dead curled leaves in the understory of tropical forest in the temperate zone winter. Sampling of the relative abundance of arthropods associated with dead and live foliage showed that although the ratio of total numbers in dead and live leaves was similar in the temperate and tropical sites, the overall ratio of estimated biomass was considerably greater in the tropical sites. This is because large arthropods commonly use dead curled leaves as daytime roosts in tropical forests. However, the largest temperatezone arthropods are generally found on leaf surfaces during the day. The winter-foraging specialization on dead leaf arthropods apparently is the more demanding; the most specialized search and attack behaviors are associated with feeding at dead and hve curled leaves. I revisited the Belize study sites in September, when Worm-eating Warblers were presumably arriving and found an intermediate use of dead and live leaves. Relative abundances of arthropods on dead and live leaves were similar to those found in the winter period at the same sites. This suggests a period of transition which is consistent with the trial and error learning hypothesis for the development of seasonal foraging specializations in this species.

Characterization of Worm-eating Warbler (Helmitheros vermivorum) breeding habitat at the landscape level and nest scale

“…This difference in litter composition could influence the nesting appeal for ground-nesting species such as Worm-eating Warbler. In addition, during the nesting portion of the breeding season in Maryland, 80% of Worm-eating Warbler foraging efforts were directed toward leaf gleaning in chestnut oak (Quercus montana;Greenberg 1987). Thus, it is possible that foraging preference (i.e., selecting sites with a prevalence of xeric oak species), rather than nesting microhabitat on the forest floor, may be driving the association of Worm-eating Warbler nest sites with SW-facing slopes.…”

“…Similarly, structural characteristics, such as the presence of dense understory vegetation, thick leaf-litter layer, or steep slope at the nest site, could be important variables influencing nest success (Vitz et al 2013). Previous research has described a preference of Worm-eating Warblers to forage in chestnut oaks during the early breeding season (Greenberg 1987). Thus, tree species composition in the nesting area could potentially influence foraging efficiency during the nestling stage.…”

Bird behaviour on and entanglement in invasive burdock (<em>Arctium</em> spp.) plants in Winnipeg, Manitoba

“…In both temperate and tropical forests, dried leaves contain a larger number and higher biomass of arthropods than live green leaves (Greenberg 1987). Foraging in dead leaves is a specialized niche used mainly during the nonbreeding season by several neotropical resident and migrant songbirds (remsen and Parker 1984;Greenberg 1987;remsen et al 1989). Four species of neotropical migrant warblers in the former genus Vermivora, including orange-crowned Warblers, have been reported to specialize in this foraging behaviour in winter.…”

Assessment of indirect pesticide effects on worm‐eating warbler populations in a managed forest ecosystem

“…Bacillus thuringiensis kurstaki is not harmful to most nontarget organisms because the bacterium directly affects only lepidopteran larvae (caterpillars). Although it poses no fatal threat to birds at the recommended application rate, Btk targets a major source of prey items for worm-eating warblers (Helmitheros vermivorus) during the late spring and summer, when the insectivorous songbirds are breeding [8]. Worm-eating warblers feed primarily on caterpillars during the chick-raising portion of the breeding cycle [8] and have demonstrated lower foraging plasticity than other sympatric songbird species [9].…”

“…Although it poses no fatal threat to birds at the recommended application rate, Btk targets a major source of prey items for worm-eating warblers (Helmitheros vermivorus) during the late spring and summer, when the insectivorous songbirds are breeding [8]. Worm-eating warblers feed primarily on caterpillars during the chick-raising portion of the breeding cycle [8] and have demonstrated lower foraging plasticity than other sympatric songbird species [9]. Therefore, the worm-eating warbler might exhibit a more dramatic response to Btk applications because of its fairly specialized diet and provides a case study of potential population effects of pesticide application in a forest ecosystem.…”