Postfledging occupancy of breeding sites by female Common Murres (Uria aalge)

Virtually all female Common Murres (Uria aalge) continued to visit the colony after their mate had taken the chick to sea. There were significant differences among years, but the average time between a chick fledging find a female last being seen at the colony was 13 days (range 0-36). In over 99% of instances, the female was at her breeding site. On N ~5% of days she was joined by another male, and in a few cases (8% of those days) copulation was observed. None of those transient matings persisted into the next season, even when the original male did not return; thus, we found no support for the hypothesis that females might be looking for replacement mates in case they were widowed. The most successful females (in terms of breeding output over several years) tended to have the longest periods of postfledging visiting, apparently because such birds fledged their chicks early in the season, but there was no difference in daily frequency of attendance. We conclude that successful males and females were maximizing time spent occupying the best breeding sites, even to the extent that only one adult took the chick to sea to complete its development. Received 2 February 2002, accepted 14 August 2002.