Feeding of the least, crested, and parakeet auklets around St. Lawrence Island, Alaska

Abstract

The feeding habits of three plankton-feeding Alcidae, the least, crested, and parakeet auklets were studied on St. Lawrence Island, Alaska, between 1964 and 1966. The crested and the least auklets (Aethia cristatella, A. pusilla) exhibit similar patterns of dependence upon the food resources: both have, during early summer, a diversified diet consisting of mysids, hyperiids, gammarids, etc., but restrict themselves largely to one principal prey during the chick-rearing period. Then, A. pusilla eats mostly Calanus sp. while A. cristatella eats Thysanoessa spp. In all years, hatching coincided closely with the appearance of these prey items (copepods and euphausids) in the environment and it is argued that the timing of the auklets' breeding season has been adjusted to their cyclical abundance. Cyclorrhynchus psittacula, the parakeet auklet, maintains a diversified diet throughout the summer: Parathemisto libellula, a pelagic amphipod, is the dominant prey in its diet.The three species are found feeding together and are presumed to use the same depth range. Segregation in feeding between A. cristatella and A. pusilla is achieved by difference in bill size. This difference is sufficient to impose obligatory feeding upon different resources. Segregation between two possible competitors, A. cristatella and Cyclorrhynchus, seems to rest upon innate preferences for different prey types, minor structural differences in the feeding apparatus, and differences in foraging habits: the relative importance of each of these factors remains to be established.As a whole, the amount of overlap in feeding between the three species studied is very small.