Social cues are preferred over resource cues for breeding-site selection in Barn Swallows

Abstract

AbstractTo maximize fitness, animals choose habitats by using a combination of direct resource cues, such as the quality and quantity of safe breeding sites or food resources, and indirect social cues, such as the presence or breeding performance of conspecifics. Many reports show that nest predation leads to reduced fitness. However, it remains unclear how birds assess predation risk and how it affects breeding-site selection. In this study, we analyzed the relationship between predation risk and breeding-site selection in Barn Swallows (Hirundo rustica). We assessed the cues that swallows use in their selection. We used nest-site characteristics related to predation and foraging sites as direct resource cues, number of breeding pairs, and breeding success in the previous year as indirect social cues, and number of old and undamaged old nests as direct resource and/or indirect social cues. Breeding-site preference was assessed using the arrival date of males. We showed that only the number of undamaged old nests was used for breeding-site selection. When comparing effects at two spatial scales, nest-site and home-range, the effect of the number of undamaged old nests occurred at the home-range scale only, suggesting that these nests are used as an indirect social cue rather than a direct resource cue to reduce the energy or time-consuming costs of nest building. We suggest that undamaged old nests may indicate the presence and breeding performance of conspecifics for several previous years. Because Barn Swallows are migratory birds, undamaged old nests may be a reliable indirect social cue and may reduce the time required to sample information at breeding sites.