Testing proximate causes and ultimate explanations of social cue use for habitat selection by songbirds

For many animals, breeding habitat selection is important because of its direct effects on fitness. There is growing evidence that songbirds select habitat using social cues emitted from individuals present in the habitat. Using the Yellow Warbler (Setophaga petechia), I designed multiple playback experiments to test what types of social cues animals use for habitat selection, what fitness benefits individuals. I first examined whether Yellow Warblers discriminate between conspecific song categories social cues with different information about habitat quality. Second-category song broadcast attracted more Yellow Warblers to breeding habitat than first-category song did, highlighting that yellow warblers prefer to use social cues linked to pairing status (e.g., second-category song) over other social cues available (e.g., first-category song). I also evaluated if Yellow Warblers and heterospecific Willow Flycatchers (Empidonax traillii) assess apparent warbler density (a function of the number of social cues present) when selecting habitat. Yellow Warblers did not make their settlement decisions based on apparent conspecific density, but individuals clustered territories more closely where apparent conspecific density was highest. In contrast heterospecific attraction by Willow Flycatchers did occur, with Willow Flycatchers being most abundant at high apparent Yellow Warbler density treatments. Finally, I tested for reproductive benefits of using social cues for habitat selection to investigate fitness benefit of conspecific attraction (i.e., settling near conspecifics), therefore providing an ultimate explanation for why conspecific attraction occurs. Results from an experiment with Brown-headed Cowbird models (Molothrus ater; a brood parasite that reduces reproductive success) revealed that Yellow Warblers behaved more aggressively towards cowbirds when apparent conspecific density was high. Results from these studies provide insight as to when, where, and in what species to expect social cue use for habitat selection