Low frequency of extra-pair paternity and high frequency of adoption in Black-legged Kittiwakes.

@enWe studied the timing and frequency of extra-pair copulations and extra-pair fertilizations in the Black-legged Kittiwake (Rissa tridactyla), a socially monogamous seabird that breeds in dense colonies. We recorded 313 copulations by 82 marked pairs in 25 000 nest-hr over three years. We recorded only two extra-pair copulations, both of which were obtained by opportunistic males that disrupted pair copulations in progress. Pairs performed a mean of 14 copulations per clutch suggesting that males may copulate relatively frequently for paternity assurance. Our parentage analysis based on eight microsatellite markers did not detect any extra-pair paternity in 119 offspring from 86 broods; however we did detect three cases of adoption caused by chicks moving to adjacent nests. The between-nest movement of a minimum of 8% of chicks suggests that escaping siblicide may be an adaptive strategy for some nestlings, despite the risk of falling into the sea and drowning (observed in 11 of 21 chicks).