Diet of Swainson's Warblers on the Breeding Grounds

Abstract

ABSTRACT SAVAGE, AMELIA LEE. Diet of Swainson’s Warblers on the Breeding Grounds. (Under the direction of Dr. Christopher Moorman).

Swainson’s Warbler (SWWA), Limnothlypis swainsonii, is a migratory songbird that breeds in bottomland hardwood forests across the southeastern United States. It is believed to be one of the least abundant breeding songbird species in the region. While nest-site selection has been well studied, little is known about SWWA foraging habits except that the species is insectivorous with a large bill used to flip fallen leaves on the forest floor. We captured and crop-flushed SWWA to determine diet, and sampled leaf litter arthropods and vegetation at each SWWA capture location. We compared the proportion of arthropod orders detected in crop-flush samples to the proportion of arthropods collected in the leaf litter to determine which orders were eaten by SWWA more or less than their proportional availability. Although Acari (mites and ticks) and Chilopoda (centipedes) were the most abundant arthropods recorded in the leaf litter samples (51% and 18%, respectively), these orders rarely occurred in crop flush samples. Conversely, Araneae (spiders) and Coleoptera (beetles) were uncommon in leaf litter samples (2% and 5%, respectively) but were the most abundant arthropod orders in SWWA crop flush samples. We conducted binary logistic regressions with the presence or absence of Aranids as the dependent variable and habitat measures as the independent variables. The probability that spiders were present in the leaf litter increased as leaf litter depth increased. Leaf litter depth should be preserved by maintaining closed canopy forests and natural flooding regimes to promote SWWA foraging habitat.