Leopard seal study at Palmer Station

ROBERT J . HOFMAN

Department of Ecology and BehaviorUniversity of Minnesota

During the austral summer 1972-1973, researchersfrom the University of Minnesota and Utah State Uni-versity cooperated on an integrated study of the inter-relationships of leopard seals and Adélie penguins in thevicinity of Palmer Station on the Antarctic Peninsula.Messrs. James Schmidt and Bruce Goforth were fieldrepresentatives of Dr. Dietland Müller-Schwarze, UtahState University, and Messrs. Richard Reichle and RobertHofman were field representatives of Dr. D. B. Siniff,University of Minnesota.

The field party was established at old Palmer Stationon December 6, 1972, by which time all sea ice had dis-appeared from Arthur Harbor and surrounding areas.The study area was selected to provide contrast with siteson Ross Island, where most penguin-leopard seal inter-actions have been observed. Adélie penguins were knownto breed on Humble, Torgersen, and Litchfield Islands,and previous seal censuses in this area had indicated thatleopard seals were sometimes abundant. During the aus-

tral summer 1971-1972, Dr. Miiller-Schwarze visited thearea and noted that leopard seal predation on Adéliepenguins appeared to be less than might have been an-ticipated (Müller-Schwarze and Müller-Schwarze, inpress).

Visual observation and radio telemetry were the prin-cipal research techniques. An attempt to get underwaterphotographs of leopard seal-penguin interactions withunderwater television and 16 mm movies was unproduc-tive. Observation and antennae sights were established atold Palmer Station, Litchfield Island and Norsel Point(fig.). From these areas, Loudwater Cove, parts of WylieBay, and most of Arthur Harbor could he observed,and radio fixes could be taken to triangulate positionsof radio-tagged animals.

The Adélie penguin colonies on Torgersen, Humble,and Litchfield Islands were censused to determine thenumber of penguins available as a potential food sourcefor resident leopard seals. Penguins leaving and return-ing to the major beach on Humble Island were talliedat different times of the day to determine the activitypattern and thus the availability to predation sincepenguins are vulnerable only when they are in the water.

Nineteen leopard seals (nine males and ten females)were successfully immobilized with drugs (sernylan andvalium), tagged with three different tags, radio-marked,and released. Three additional leopard seals were marked

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tion and antenna sites.

196 ANTARCTIC JOURNAL

with barbed streamer tags, without prior immobilization,to provide behavioral comparison between drugged andundrugged animals. Some of the drugged animals weredyed with a large identifying number on the back sothat they could easily be identified in the water. Standardmeasurements, a blood sample, and a toenail were takenfrom most immobilized specimens. Four animals (twomales and two females) were drug-related fatalities, andskulls, reproductive tracts, and stomachs were collectedfor further analysis.

Leopard seals were frequently seen patroling areasinhabited by penguins, but only two kills and threeunsuccessful attempts were observed. Fecal analysis sug-gested that the primary food source of most of theseleopard seals was krill. The early arrival of UNS Mirfak(February 6) resulted in the premature termination ofthe project before Adélie fledglings entered the water.Predation may have increased when young birds left therookeries, but the actuality remains an unknown.

This work was supported by National Science Foun-dation grant GV-24327.

Reference

MüIIer-Schwarze, C., and Mü!!er-Schwarze, D. E. In press.Symposium on the Biology of the Seal, Guelph, Ontario,Canada. August 1972.

Sympathetic control of nonshiveringthermogenesis in south polar skua chicks

DAVID E. MURRISH and CHARLES L. GUARD

Department of BiologyCase JVesten Reserve University

Chicks of the south polar skua Catharacta skna mc-cormicki acquire the ability to maintain a constant bodytemperature within several days after hatching (Speller-berg, 1969). The maintenance of homeothermy by neo-nate mammals is well established, but it is only poorlyunderstood in newly hatched precocial birds. Youngmammals are able to produce heat without shivering(Brück and Wunnenberg, 1965). As they mature, thenonshivering thermogenesis is replaced gradually byshivering thermogenesis. The nonshivering heat pro-duction is dependent upon endogenous catecholamines,especially norepinephrine. Young domestic chicks dem-onstrate a nonshivering thermogenic response to coldthat is apparently under the control of beta-activatingcatecholamines (Wekstein and Zolman, 1968).

To determine if newly hatched skuas exhibit a similar

sympathetic neural response to cold stress, the effects ofseveral adrenergic blocking agents on the maintenance ofbody temperatures were studied.

Birds were removed from the nest on 1, 3, and 5 daysafter hatching. Mean body weights were 64.6, 75.8,91.1 grams, respectively. If there was a pair of chicks inthe nest, only one was taken. All chicks were returnedto the nest within 6 hours, and no chick was used twice.All but two birds completely recovered and appeared tobe healthy several days after their return to the nest.

Body temperatures were recorded from a telether-mometer connected to a thermistor probe inserted 2.5.centimeters in the cloaca. Birds were put in paper boxesand then placed in a 30° C. incubator until the bodytemperature stabilized. Finally, the chicks were injectedand 30 minutes later placed in a refrigerator regulatedat 10 :1: 1.0 0 C.

Birds of the three ages were injected, I.P., with either(a) 0.9 percent saline solution, (b) 10 milligrams perkilogram body weight propranolol, a beta-adrenergicblocker; (c) 5 milligrams per kilogram phenoxybenza-mine, an alpha-adrenergic blocker or (d) a combinationof propranolol and 2 milligrams per kilogram isoproter-enol, a beta-activating amine.

Skua chicks can regulate their body temperature withinrather narrow limits (36.9 ± 0.5° C., SD) from theirfirst day without apparent shivering in an air temperatureof 10°C. (fig. 1).

Propranol, a beta-adrenergic blocker, hinders the abil-ity of day-1 chicks to thermoregulate and their body

PropranoIoNI51l.-.- .__.--1l

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Figure 1. Effect of 10 milligrams per kilogram propranolol on thebody temperature of skua chicks, exposed to 100 centigrade, 1,2, and 5 days after hatching. Saline injected controls for days3 and 5 chicks are not shown; their body temperatures wereindistinguishable from 5-day chicks injected with propranolol.

July-August 1973 197