THE IMPORTANCE OF MATE RETENTION AND EXPERIENCE ON BREEDING SUCCESS IN CASSINS AUKLET (PTYCHORAMPHUS-ALEUTICUS)

We studied the relative effects of mate retention and breeding experience on reproductive success in Cassin's auklet (Ptychoramphus aleuticus) on Southeast Farallon Island, California, USA. Breeding success of banded birds was monitored from 1985 to 1990 and analyzed using linear and logistic regression. Breeding performance improved with experience and mate retention, but their relative effects differed. Hatching success improved with both female and male experience but declined with advanced experience in males, perhaps due to reproductive senescence. In males, but not in females, hatching success showed a quadratic relationship with length of the pair-bond when adjusted for experience, indicating a greater benefit to males for mate retention. Fledging and breeding success and weight at fledging also increased asymptotically with length of the pair-bond for both sexes. There was no correlation between mate switching and previous reproductive failure. An increase in weight at fledging with experience in females, but not in males, suggests that females either became more efficient at foraging or invested greater effort in chick rearing with experience than males.