Incidence of nest material kleptoparasitism involving Cerulean Warblers

We document 21 observations of interspecific stealing of nesting material involving Cerulean Warblers (Dendroica cerulea), Red-eyed Vireos (Vireo olivaceus), Blue-gray Gnatcatchers (Polioptila caerulea), Northern Parulas (Parula americana), Black-throated Green Warblers (D. virens), American Redstarts (Setophaga ruticilla), and Orchard Orioles (Icterus spurius) that occurred during studies of Cerulean Warbler breeding biology. These incidents involved a variety of combinations of nest owner and nest material thief suggesting that each of these species is both a perpetrator and recipient of this behavior in our study areas. Kleptoparasitic incidents occurred at all stages of the nesting cycle from nest-building through post-fledging. Two possible motivations for this behavior are related to saving time in finding nest materials and collecting this material for nest construction.