The effects of genetic relatedness on mate choice and territorial intrusions in a monogamous raptor

Abstract

Kin recognition has been shown in some bird species, suggesting that birds might be able to actively avoid inbreeding through mate choice. However, the evidence for such behaviour in wild bird populations is scarce. Intrusions performed by conspecifics could be part of the breeding strategy of a territorial bird species: an intruder might find the opportunity to replace a resident individual and acquire its territory. If intruders seek the opportunity to breed, their relatedness to the opposite-sex resident could influence their nest site intrusions similarly to mate choice. Observations of intrusions also revealed that vagrant juveniles of long-lived raptors repeatedly visit their natal population before maturation. The present study focused on the White-tailed Eagle (Haliaeetus albicilla): a territorial, long-lived, monogamous raptor species. We investigated whether (1) relatedness is considered in mate choice in this species, based on noninvasively collected DNA samples. (2) We furthermore addressed whether nest site intrusions could be explained by any of the following three nonexclusive hypotheses: (i) finding a mate, (ii) acquiring a good-quality territory, or (iii) visiting the natal area. Our results suggest that White-tailed Eagles avoid kin in mate choice. Although a considerable proportion of the intruders were juveniles, none of them was likely to be offspring of resident pairs of the study population. We found a nonsignificant trend towards lower relatedness than expected from random intrusions in both sexes. The revealed intrusion events suggest a sex bias: males seem to prefer better-quality territories more than females do.