Off-territory movement of male American Redstarts (Setophaga ruticilla) in a fragmented agricultural landscape is related to song rate, mating status and access to females

Abstract

Male songbirds often move off-territory to pursue extra-pair fertilizations. This movement represents a trade-off between paternity gain and loss and can be influenced by male quality and access to fertile females. Access to females could be reduced in fragmented landscapes that have small patches and low connectedness. We studied movement and extra-pair fertilization success of radio-tracked male American Redstarts (Setophaga ruticilla) in forest patches in an agricultural landscape in Alberta, Canada, over 2 years. Males spent an average of 18% of their time off-territory, mostly intruding onto adjacent territories and rarely moving between patches. They averaged 0.8 trips/h, with mean trip duration of 17 min and mean trip distance of 104 m. Less time was spent off-territory when their mate was nest-building and males intruded most often onto territories with nest-building females. Males with higher song rates and more nearby females intruded most onto other territories. Monogamous males in better condition with higher song rates spent the most time off-territory. However, males with more nearby females and higher local breeding synchrony spent the least time off-territory, suggesting these males face a trade-off between seeking extra-pair fertilizations and protecting against cuckoldry. Forest cover was not an important predictor of movement. Investment in off-territory movement did not predict extra-pair fertilization success or probability of cuckoldry. However, few tracked males achieved extra-pair fertilizations (1/22 tracked males vs 18/57 non-tracked males), possibly an artefact of low sample size or the effect of radio transmitters on female choice.