Interspecific social information use in habitat selection decisions among migrant songbirds

Abstract

The presence of conspecifics is a social cue frequently used by songbirds in breeding-site selection. In migratory species, conspecific attraction is not possible for individuals that arrive first to breeding grounds, but these individuals may use information from ecologically similar heterospecifics. Resident tits (Paridae) are known to provide cues for migratory songbirds, however, the relevance of resident settlement decisions decreases as the season progresses. We investigated heterospecific attraction within migrant songbirds, and examined whether later arriving species use the presence of earlier arriving species as a cue for breeding habitat selection. We used a song playback experiment to test if wood warbler Phylloscopus sibilatrix settlement decisions are affected by chiffchaff Phylloscopus collybita and blackcap Sylvia atricapilla cues. Our results suggest that wood warblers used cues from heterospecifics when deciding where to breed. Wood warblers settled earlier and more numerously on plots with simulated presence of chiffchaffs, in contrast blackcap presence had a negative effect on settlement, suggesting heterospecific avoidance. Chiffchaffs and blackcaps were attracted to sites with simulated presence of conspecifics, which provides evidence for conspecific attraction in breeding-site selection of these species. Our experiment suggests that heterospecific attraction is not a phenomenon limited to resident-migrant interactions, but acts also between migrant species. Our results show an interplay of attraction and avoidance when using social cues for habitat selection decisions within a migrant songbird guild, and stress the importance of both positive and negative effects of social environment on settlement behaviour of individuals.