The foraging behaviour of 20 Chinstrap Penguins Pygoscelis antarctica breeding at Ardley Island, King George Island, Antarctica was studied during the austral summers of 1991/2 and 1995/6 using stomach temperature loggers (to determine feeding patterns), depth recorders and multiple channel loggers. The multiple channel loggers recorded dive depth, swim speed and swim heading which could be integrated using vectors to determine the foraging tracks. Half the birds left the island to forage between 02h00 and 10h00.
Mean time at sea was 10.6 h. Birds generally executed a looping type course with most individuals foraging within 20 km of the island. Maximum foraging range was 33.5 km. Maximum dive depth was 100.7 m although 80% of all dives had depth maxima less than 30 m. The following dive parameters were positively related to maximum depth reached during the dive: total dive duration, descent duration, duration at the bottom of the dive, ascent duration, descent angle, ascent angle, rate of change of depth during descent and rate of change of depth during ascent. Swim speed was unrelated to maximum dive depth and had mean values of 2.6, 2.5 and 2.2 m/s for the descent, bottom and ascent phases of the dive. The sequence of maximum depths reached in a dive series was not random, tending to be concentrated at a particular depth, irrespective of whether the penguins were feeding at that depth or not. Generally, sequential dives to a specific depth were abruptly terminated by a single dive to another depth which was characteristic in having no bottom phase and unusually steep descent and ascent angles. The maximum depth reached during this dive was then adhered to in the next dive sequence. There were peaks in feeding activity between 06h00 and 09h00 and 14h00 and 22h00. Although foraging effort and relative success decreased around midnight when light intensity was lowest, birds did dive up to 22 m at this time, considerably deeper than sympatric Adélie P. adeliae or Gentoo P. papua Penguins. These findings indicate that, in accordance with their small body size, Chinstrap Penguins forage inshore close to the surface during the chick-rearing phase. Apparent short-comings in the volume of water searched compared to sympatric congeners can be made good by intense diving activity during the period at sea, with no inter-bout rests, higher swim speeds and an apparent ability to be able to forage at lower light intensities which enables Chinstrap Penguins to forage better under twilight conditions
