Feeding patterns of emperor penguinsGERALD L. KOOYMAN and DONALD A. CROLL

Scripps Institution of OceanographyUniversity 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 inbody form, breeding habits, and prey selection, and they oc-cupy adjacent, but geographically separated, habitats (i.e., theking penguin is subantarctic and the emperor penguin is highpolar). 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. Theresults of this study should answer basic questions about thesimilarities and differences in preferred dive depths, prey typeand distribution, and energy expenditure of the foraging cycles.These, in turn, should provide insight about environmentalfactors that influence the feeding characteristics of these twospecies.

In 1985 field studies were carried out on the king penguin atSt. Andrews Bay, South Georgia (Kooyman and Thorson 1985).This past season the second part of the study was completedwith 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 arrivalat Cape Washington.

Due to the remoteness of the colony we were airlifted byLC-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 pickedup by the U.S. Coast Guard icebreaker Polar Sea.

Soon after our arrival we counted 1,859 dead chicks and 193abandoned eggs. Because there had been no scavenging byother animals, this was about the total loss through the winterand up to the time of the count, except for some eggs and chicksthat had been buried by drifting snow. The mortality was lessthan 10 percent of all chicks at the colony and is remarkably lowin comparison to observations made elsewhere (Jouventin1975).

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

Dive behavior and preferred depths were determined withdepth histogram recorders (Kooyman, Billups, and Farwell1983), and a prototype time/depth recorder. The data acquisitionof the latter recorder was controlled by a microprocessor. Theunit weighed about 200 grams. All recorders and radios werestrapped 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 peakwas between 25 and 50 meters if dives less than 25 meters arenot included. The deep dive peak was between 150 and 200meters. For the first time in a bird time/depth profile, divedurations 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 and200 meters for several hours while making 7-8 minute dives.Most dive durations fall between 2 and 8 minutes. The rapidsequencing of dives to depths greater than 100 meters for suchlong durations raises several physiological problems aboutmanagement of oxygen stores and avoidance of decompressionsickness, which had not been appreciated before these record-ings. Some of the physiological questions will be the subject ofstudy in the forthcoming season.

This project was supported by National Science Foundationgrant 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 EricChiang, who guided the planning of the projects deployment;the ITT/Antarctic Services, Inc., support personnel; the Polar Seafor a timely pickup; C. Vallone, the Italian Antarctic Programdirector for his hospitality; and finally, M. Boone for prepara-tion of the depth histogram recorders, E. Ponganis for designand construction of the microprocessor recorders, and S. Stoneand S. Smith for getting us across the glacier and assisting us inthe 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 ofking penguins from Saint Andrews Bay, South Georgia. AntarcticJournal of the U.S. 19(5), 172-173.

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

1987 REVIEW 221