Female_data_code.R

Many bird species are negatively impacted by obligate avian brood parasites, which lay their eggs in the nests of host species. The Yellow Warbler (<i>Setophaga petechia</i>), which is host to the brood-parasitic Brown-headed Cowbird (<i>Molothrus</i> <i>ater</i>), represents one of the best-replicated study systems assessing antiparasitic host defenses. Over 15 prior studies on Yellow Warblers have used model presentation experiments, where breeding hosts are exposed to models of Brown-headed Cowbirds and other nest threats, to test for defenses unique to this species. Here we present results from our own quasi-replication study of the Yellow Warbler/Brown-headed Cowbird system, which used a novel design compared to previous experiments by conducting acoustic playback treatments only rather than presenting visual models with or without calls. We exposed active Yellow Warbler nests to playbacks of Brown-headed Cowbird chatters, Blue Jay calls (<i>Cyanocitta cristata</i>; nest predator), conspecific “seet” calls (a referential alarm call for brood parasitism risk), conspecific “chip” calls (a generic alarm call), and control Wood Thrush (<i>Hylocichla mustelina</i>) songs during the incubation stage. Similar to previous studies, we found that female warblers seet called more frequently in response to playback of brood parasitic chatter calls and conspecific seet calls but produced more chip calls in response to playback of nest predator calls. However, female Yellow Warblers approached all playbacks to similar distances, which was different from the patterns seen in previous studies. Our study demonstrates the importance of both replicating and also pivoting experimental studies on nest defense behavior, as slight differences in experimental design can elicit novel behavioral responses in the same species.