feeding patterns of emperor penguins ... emperor penguin with a prototype microprocessor time/depth

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  • Feeding patterns of emperor penguins GERALD L. KOOYMAN and DONALD A. CROLL

    Scripps Institution of Oceanography University of California at San Diego

    La Jolla, California 92093

    King, Aptenodytes patagonicus, and emperor penguins, A. for- steri, are the largest diving birds. They have many similarities in body form, breeding habits, and prey selection, and they oc- cupy adjacent, but geographically separated, habitats (i.e., the king penguin is subantarctic and the emperor penguin is high polar). Because of these features, a comparative study of forag- ing behavior was begun in 1985 to measure the sea-cycle times, food habits, dive behavior, and energetics of the sea-cycle. The results of this study should answer basic questions about the similarities and differences in preferred dive depths, prey type and distribution, and energy expenditure of the foraging cycles. These, in turn, should provide insight about environmental factors that influence the feeding characteristics of these two species.

    In 1985 field studies were carried out on the king penguin at St. Andrews Bay, South Georgia (Kooyman and Thorson 1985). This past season the second part of the study was completed with an investigation of the hunting behavior of emperor pen- guins at Cape Washington, Antarctica. Several types of experi- ments and observations were made after our 26 October arrival at Cape Washington.

    Due to the remoteness of the colony we were airlifted by LC-130 to Priestley Glacier on 22 October. From there we tra- versed Browning Pass, Campbell Glacier, and Terra Nova Bay. We remained at the colony until 6 January when we were picked up by the U.S. Coast Guard icebreaker Polar Sea.

    Soon after our arrival we counted 1,859 dead chicks and 193 abandoned eggs. Because there had been no scavenging by other animals, this was about the total loss through the winter and up to the time of the count, except for some eggs and chicks that had been buried by drifting snow. The mortality was less than 10 percent of all chicks at the colony and is remarkably low in comparison to observations made elsewhere (Jouventin 1975).

    Food habits were determined by stomach lavage of birds recently returned from sea. Most of the food found in the samples was partially digested fish, but krill was also found in some samples. The fish species consumed is unknown. The food appeared to have a high oil content and therefore, on a per-weight basis, it was probably high in energy. Calorimetric analyses are in progress.

    Dive behavior and preferred depths were determined with depth histogram recorders (Kooyman, Billups, and Farwell 1983), and a prototype time/depth recorder. The data acquisition of the latter recorder was controlled by a microprocessor. The unit weighed about 200 grams. All recorders and radios were strapped and glued to the dorsal feathers (figure).

    The frequency distribution of dive depths was bimodal, sim- ilar to the king penguin, but deeper. The shallow depth peak was between 25 and 50 meters if dives less than 25 meters are not included. The deep dive peak was between 150 and 200 meters. For the first time in a bird time/depth profile, dive durations and patterning of dive bouts were obtained. The

    Emperor penguin with a prototype microprocessor time/depth rec- order. (Photo by D.A. Cr011.)

    record from one bird shows that they will hunt between 150 and 200 meters for several hours while making 7-8 minute dives. Most dive durations fall between 2 and 8 minutes. The rapid sequencing of dives to depths greater than 100 meters for such long durations raises several physiological problems about management of oxygen stores and avoidance of decompression sickness, which had not been appreciated before these record- ings. Some of the physiological questions will be the subject of study in the forthcoming season.

    This project was supported by National Science Foundation grant DPP 83-16963. We would like to acknowledge the enthusi- astic support of Commander J . Mazza and his VXE-6 Squadron; National Science Foundation project directors, especially Eric Chiang, who guided the planning of the projects deployment; the ITT/Antarctic Services, Inc., support personnel; the Polar Sea for a timely pickup; C. Vallone, the Italian Antarctic Program director for his hospitality; and finally, M. Boone for prepara- tion of the depth histogram recorders, E. Ponganis for design and construction of the microprocessor recorders, and S. Stone and S. Smith for getting us across the glacier and assisting us in the field.

    References

    Jouventin, P. 1975. Mortality parameters in Emperor penguins Ap- tenodytesforsteri. In B. Stonehouse (Ed.), The biology of penguins. Lond- on: Macmillian Press.

    Kooyman, CL., and P.H. Thorson. 1985. Foraging characteristics of king penguins from Saint Andrews Bay, South Georgia. Antarctic Journal of the U.S. 19(5), 172-173.

    Kooyman, CL., JO. Billups, and W.D. Farwell. 1983. Two recently developed recorders for monitoring diving activity of marine birds and mammals. In A.G. MacDonald and I.G. Priede (Eds.), Experunen- tal Biology at Sea. New York: Academic Press.

    1987 REVIEW 221

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