regurgitated kril-water content(g H20/g dry)

of Na per milliliter (tmo1 Na/mL) free water in food], regard-less of the size of the chick, but the food—water content andisotopically measured mass-specific water intake rate are sig-nificantly higher in small chicks than in large chicks (figure 3).Although, based solely on our data from this study, we cannotrule out physiological changes that may occur as chicks devel-op, we hypothesize that the relatively lower water intake oflarge chicks creates a higher demand for use of the salt glandsto excrete a salt load. The salt glands can excrete largeamounts of salt with very little concomitant water loss. Smallchicks are less water limited and use their kidneys to excretemore of the salt load than do larger chicks.

This research was supported primarily by National Sci-ence Foundation grant OPP 89-17066. We are very grateful tothe Palmer Station staff for their invaluable assistance at vari-ous stages of our work. We especially thank Mark Melcon andJim Close, who often worked long hours to meet our con-struction and boating needs.

References

Schmidt-Nielsen, K., C.B. Jorgensen, and H. Osaki. 1958. Extrarenalsalt excretion in birds. American Journal of Physiology, 193(1),101-107.

Volkman, N.J., P. Presler, and W.Z. Trivelpiece. 1980. Diets ofpygoscelid penguins at King George Island, Antarctica. Condor,82(4),373-378.

01000200030004000

01000200030004000chick mass (grams)

Figure 3. Relationship between food-water content and the mass ofthe Adélie penguin chicks being fed that food, and the relationshipbetween isotopically measured water influx and body mass inAdélie penguin chicks at Palmer Station, Antarctica.

1000

800field H20 influx

(ml/kg day) 600

400

200

Continuing studies of the demography andforaging behavior of the Pygoscelis penguins

D.F. MCCORMICK, S.D. EMSLIE, N.J. KARNOVSKY, L.W. KEITH, S.G. TRIVELPIECE, andW.Z. TRIVELPIECE,Department of Biology, Montana State University, Bozeman, Montana 59717

We were at Copacabana Field Station, Admiralty Bay,King George Island, from mid-October 1992 to the end

of February 1993. The bay and surrounding waters were icefree upon our arrival and had been for most of the winter (X\TIPolish Expedition members personal communication). Polishscientists at nearby Arctowski Station reported that the winterhad been mild and that most of the snow and ice in evidenceat the time of our arrival was from recent storms.

Our research consisted of three interrelated projects: thecontinuation of the previous years' demographic study on theAdélie, gentoo, and chinstrap penguin populations; a study ofAdélie foraging behavior; and a study examining penguinband loss using implanted transponders. Adélies reoccupiedtheir colonies in early October and began laying eggs shortlyafter our arrival. A severe snow storm in late October deposit-ed several feet of heavy snow on the nesting Addlies, resultingin large egg losses throughout the rookery. Gentoos and chin-

straps, which began egg laying in mid to late November, wereunaffected by the storm.

The demographic study followed the methodology ofprevious years. A random sample of 200 breeders of eachspecies, as well as all known-age birds, were followedthroughout the reproductive season. Adélies fledged less thanone chick per pair, about average for Addlies; however, gen-toos and chinstraps fledged well over one chick per pair.These results suggest that food availability was high in the1992-1993 season and that all three species would have hadhigh reproductive success if not for the adverse effect of envi-ronmental factors on the Adélies.

The Adélie foraging behavior study involved epoxyingradio transmitters to the back feathers of 20 adults withchicks. The transmitters were left on for 4 weeks, from mid-December 1992 to mid-January 1993. A data logger, hookedup to a receiver, automatically recorded the times on land

ANTARCTIC JOURNAL - REVIEW 1993151

(signal present) and at sea (signal absent). The data collectedare under analysis and will be compared with previous years'foraging trip durations. The amounts of food brought back tofeed the chicks averaged over 600 grams per trip by adults,which is comparable to food load sizes delivered to chicks inprevious seasons.

A study on band loss was begun with Adélies and gen-toos. Transponder implants were injected under the skin ofthe penguins, enabling us, with the aid of a hand-held scan-ner, to identify individual birds without bands. Three differ-ent groups of Adélie males were set up: banded only, implant-ed only, and banded and implanted. Since Adélie males are 99percent nest-site faithful if they survive the winter (Trivel-piece and Trivelpiece 1990), we will be able to determine nextseason if band loss is significant and if bands contribute tomortality. A small sample of gentoos was also implanted, inhopes that we would get some idea on band loss and band-induced mortality in the largest of the three species.

Reproductive success was below average for both thebrown and south polar skuas. There were many non-weather-related losses of both eggs and chicks. This was probably due

to poor food availability in the study area, particularly a lackof the antarctic silverfish in diet samples. This leads tomarauding by failed breeders and nonbreeders, resulting inincreased chick mortality among pairs that were successful.The other flying birds breeding in the area seemed to have anaverage summer.

As in past seasons, we were visited by a few nonresidentincidentals. Several macaroni penguins and arctic terns wereseen, and a black-necked swan was sighted in the bay inDecember.

We thank the crew of the RIV Polar Duke and the U.S.Antarctic Program for logistical support, and the members ofthe XVI and X\TII Polish Antarctic Expeditions for their hospi-tality and assistance. This research was supported by NationalScience Foundation grant OPP 91-21952.

ReferencesTrivelpiece, W.Z., and S.G. Trivelpiece. 1990. Courtship period of

Adélie, gentoo, and chinstrap penguins. In L.S. Davis and J.T.Darby (Eds.), Penguin biology. San Diego: Academic Press.

XVI Polish Expedition. 1992. Personal communication.

Splenic contraction, blood volume, and musclesaturation of free-diving Weddell seals

WILLIAM E. HURFORD, GREGORY P. GUYrON, WARREN M. ZAPOL, ROBERT C. SCHNEIDER, KEVIN STANEK, and DAVID G.ZAPOL, Department ofAnesthesia, Massachusetts General Hospital, Boston, Massachusetts 02114

PETER W. HOCHACHKA, Department ofZoology, University of British Columbia, Vancouver, British Columbia, V6T2A9, CanadaGRAHAM C. LIGGINS, Postgraduate School of Obstetrics and Gynecology, National Women's Hospital, Auckland 3, New Zealand

The Weddell seal (Leptonychotes weddellii) is capable ofdives of over 1 hour (h) to depths greater than 500 meters

(m). Common dives of up to 20 minutes (mm) duration usual-ly take place under aerobic conditions, suggesting that highlyrefined strategies control the usual storage and utilization ofoxygen (Kooyman 1981). Because the seal's lungs collapseduring diving, oxygen storage during diving is limited to thatstored in the blood and myoglobin (Falke et al. 1985). Wesought to explore the behavior of these oxygen stores duringdiving. Weddell seals increase their circulating hemoglobinconcentration by 60 percent during the first 10-12 min of adive (Qvist et al. 1986). We hypothesized that the spleen of theWeddell seal would contract, similar to the contractionobserved in exercising thoroughbreds (Persson et al. 1973),and inject erythrocytes into the peripheral circulation duringdiving. Because Weddell seals have a very large spleen,approximately two-thirds of the seal's erythrocytes might besequestered in the spleen at rest (Qvist et al. 1986). To test thishypothesis, splenic dimensions were measured by ultrasoundduring recovery from diving and correlated with changes ofvenous hemoglobin concentration and hematocrit.

Oxygen may also be stored as oxymyoglobin (Mb0 2) inmuscle and utilized during exercise. The evidence for this islargely indirect. Arterial lactate concentrations remain lowduring dives of less than 20 min duration in the Weddell seal(Kooyman et al. 1980). It is possible that swimming musclesremain sufficiently perfused to permit aerobic metabolismduring diving. It is also possible that the circulation to exercis-ing muscle dilates periodically to allow resaturation ofoxymyoglobin stores (Eisner et al. 1985; Kooyman 1989). Weemployed laser spectrophotometry in this study to measurechanges of Mb02 stored in the swimming muscle of unre-strained diving seals. Rates of Mb02 utilization could then becorrelated with dive duration and swimming velocity. In addi-tion, the pattern of perfusion (pulsatile vs. continuous) couldbe ascertained.

During November and December 1992, five subadultmale Weddell seals [estimated body weight 365±50 kilograms(kg), mean ± standard deviation (SD)] were captured nearRoss Island, Antarctica (77.8 0S 168°E), and sledged to a fieldcamp constructed for isolated hole diving (Kooyman et al.1980; Qvist et al. 1986). Epidural venous sinus catheters were

ANTARCTIC JOURNAL - REVIEW 1993152