Annual Variation of Primary Molt with Age and Sex in Cassin's Auklet

Abstract

In Cassin's Auklet (Ptychoramphus aleuticus) on Southeast Farallon Island, California, 1979-1984, we found significant annual and seasonal variation in timing and rate of primary molt in adult males, adult females, and subadults (1-2 years old). Except in 1979, adult males began to molt at least 10 days before adult females, and males molted at a slower rate. Subadult birds initiated molt later and molted faster, but showed less annual variation than adults. Timing of breeding and breeding success varied annually but were not correlated directly with molt. In years of extended breeding, molt rates were slower apparently in response to the energetic demands caused by the overlap of breeding and molt.