Foraging patterns in the Antarctic shag (Phalacrocorax bransfieldensis) at Harmony Point, Antarctica

During the 1995/96 and 1996/97 summer seasons the foraging pattern of the Antarctic Shag Phalacrocorax bransfieldensis was studied by direct observation on individuals breeding at Harmony Point, Nelson Island, South Shetland Islands. During pre-laying and incubation individuals of both sexes usually foraged once a day; females early in the morning and males when their partners returned to the nests. During the rearing period the parents incremented the number of daily foraging trips usually alternating the time at sea. Compared to the incubating period, when rearing chicks individuals of both sexes reduce the extension of the foraging trips which in years of scarce food availability may no result in reducing the daily total time spent foraging due to the marked increment in the number of trips required to cover the demands at the nest. Rearing individuals respond to increasing energy requirements at the nest (i.e. as chick grew older or at increasing number of chicks at the nests) by incrementing the number of daily foraging trips and the time spent foraging. The information obtained suggest that the Antarctic Shag display mechanisms tending to buffer variable food abundance or energy requirements at the nest. The possibility of using the foraging parameters considered in this study in monitoring programmes is discussed.