Variation in antiparasitic behaviors of Red-winged Blackbirds in response to simulated Brown-headed Cowbirds

Abstract

ABSTRACT Red-winged Blackbirds (Agelaius phoeniceus) are a frequently parasitized host species of obligate brood parasitic Brown-headed Cowbirds (Molothrus ater). Yet, this common host does not reject parasite eggs or young. A hypothesis to explain the lack of cowbird egg and nestling rejection is that redwings frontload their responses by investing into antiparasitic nest defense behaviors toward female cowbirds, relative to non-laying male cowbirds and non-threatening other species. A review of prior studies using cowbird-mount presentations with or without acoustic playbacks supported some but not all predictions of this hypothesis. We conducted a new study at two geographically separate sites, in New York City, NY and in Ithaca, NY, USA, where Red-winged Blackbirds were presented with taxidermic models on a tripod and species- and sex-specific vocalization playbacks of female or male Brown-headed Cowbirds, female Northern Cardinals (Cardinalis cardinalis), or a tripod and silence (control). Reactions ...