Spring Tree Species Use by Migrating Yellow-Rumped Warblers in Relation to Phenology and Food Availability

Abstract

I examined the temporal pattern of migration and tree species preferences of Yellow-rumped Warblers (Dendroica coronata) in relation to tree and food phenology across three spring seasons (2001–2003) at a migration stopover site in east-central Illinois, USA. Foraging Yellow-rumped Warblers used tree species in relation to the date that trees initiated bud break and the date caterpillars were most abundant in trees. The first arrival date of Yellow–rumped Warblers at the stopover site varied with date of bud break; duration of migration through the stopover site ranged from 31 to 47 days. The earliest Yellow-rumped Warbler migrants observed arrived at the stopover site before appearance of many arthropods, and foraged on the temporarily abundant adult stage of the hackberry psyllid (Pachypsylla spp. [Fletcher] [Homoptera]). Later migrants switched to foraging for caterpillars. The proportions of foraging observations among tree species were similar across all 3 years and, each year, tree species used by Yellow-rumped Warblers diversified as spring progressed. Yellow-rumped Warblers are short-distance migrants (most winter in the southern United States); my results indicate these birds may have an advantage over long-distance migrants in view of global climate change as they can arrive early at stopover habitats and exploit resources when they are most available.