Variation in primary molt in the least auklet

Along with breeding and migration, molt is one of the most energetically expensive components of a bird's annual cycle. Auklets (tribe Aethiini) are apparently unique among the Alcidae in that flight-feather molt and breeding overlap. We compared the degree of overlap of primary molt with breeding in the Least Auklet (Aethia pusilla) at four colonies in varying oceanographic environments: Kiska Island (Aleutian Islands, Alaska, 52°N), St. George Island (Pribilof Islands, Alaska, 56°N), St. Paul Island (Pribilof Islands, 57°N), and Cape Ulyakhpen (Chukotka Peninsula, Russia, 64°N). We hypothesized that the onset and speed of feather replacement should be related to latitude or sea-ice dynamics. Flight-feather molt commenced during incubation with up to four primaries replaced by the end of chick rearing. At Kiska, we found no difference in molt rate between adult breeders and nonbreeders, but subadults started molt after adults and were more variable in when they started primary molt. At higher latitudes adult auklets replaced their first four primaries faster and initiated molt later although the length of the breeding season was similar. The increased energetic requirements of Least Auklets breeding and molting at higher latitudes are supported by the cold Anadyr Current, which advects lipid-rich oceanic copepods (Neocalanus spp.). In the Least Auklet and other members of the Aethiini, sequential primary molt, rather than the simultaneous molt typical of other alcids, may be possible because of auklets' lower body mass, lower wing loading, mass loss at hatching, and foraging on highly abundant prey.