NEST DESERTION AND APPARENT NEST PROTECTION BEHAVIOR BY BELL'S VIREOS IN RESPONSE TO COWBIRD PARASITISM

Abstract

Abstract Bell's Vireos (Vireo bellii) deserted 51% of nests parasitized by Brown-headed Cowbirds (Molothrus ater) in central Missouri from 1996–1998. Deserting vireo pairs fledged more host young within a season than pairs that accepted cowbird eggs when only successful nests were considered; parasitized acceptor nests never fledged any vireo young. Vireo pairs that deserted did not always desert parasitized nests. We observed five encounters between female cowbirds and Bell's Vireos at four nests. In one observation the female vireo used nest-protection behavior, which resulted in the cowbird egg appearing beneath the nest; this nest was not deserted. We found a total of eight nests where cowbird eggs remained on the ground below nests, five of which were abandoned. Nest desertion appears to benefit Bell's Vireos by allowing for unparasitized renests, but the stimuli eliciting nest desertion by Bell's Vireos remain in need of further study. Desercion de Nidos y Aparente Comportamiento Protector de Vireo ...