Prothonotary Warbler Nestlings Fledge From Mixed Broods Following Nest Takeovers By Tree Swallows

Interspecific nest-site competition among secondary cavity nesters can lead to nest-takeover events resulting in mixed broods. The nestlings of the smaller species in these mixed broods are usually unsuccessful. Among multiple takeover events occurring over 33 years of nest-monitoring records, we report 4 accounts of Protonotaria citrea (Prothonotary Warbler) fledging from mixed broods after Tachycineta bicolor (Tree Swallow) displaced Warblers from active nests. In each case, Prothonotary Warblers hatched earlier than their Tree Swallow nestmates, reducing the size discrepancy between species and enabling these nestlings to survive.