Tuatara: Volume 15, Issue 3, December 1967
Penguins in High Latitudes
Penguins in High Latitudes
Between 1961 And 1966 Canterbury University Antarctic Biology Unit undertook research on Adelie and Emperor penguins (Pygoscelis adeliae and Aptenodytes forsteri) at colonies in the south-western corner of the Ross Sea and McMurdo Sound. This paper reviews some of the results of the five-year study, parts of which have already been published (see References, p. 132). A further programme of penguin studies is now under way.
The unit began work at a small colony of Adelie penguins at Cape Royds (Ross Island) in October 1961. We originally intended to use the colony for experimental studies of behaviour, nesting success and microclimate, following earlier work in the 1959-60 season by Taylor (1962). This programme was abandoned when counts of nesting birds showed that the colony had declined seriously since 1956; instead we began a study of the breeding population, recruiting rates, and ecology of the colony, involving as little interference as possible. Birds banded by Taylor and others formed a valuable nucleus of known experienced breeders, and additional birds were banded each season to maintain a marked population of useful size.
The five seasons’ observations showed that the existence and continuing success of the colony (the southernmost in the world) depends on the annual formation of a polynya, or pool of ice-free water, in the sea ice close to Cape Royds from October onward (Stonehouse 1967b). Strong currents meeting off the Cape have been known to keep this area of the Sound open even in midwinter, when surrounding sea ice is 8-10ft thick. In November and December the polynya allows Cape Royds penguins to feed within a few miles of the colony during spells of relief from incubation and in the early stages of chick rearing, while the rest of McMurdo Sound is still ice-covered. A similar relation between polynyas and isolated high-latitude colonies has been noted elsewhere in Antarctica (Stonehouse 1964a, 1967b).
Adelies starve during courtship, living entirely on reserves of fat. In normal years at Cape Royds courtship takes about 11 days, and males continue fasting during the subsequent first incubation watch, which lasts 8-10 days in years when the polynya is present, but extends to two or three weeks when the ice remains firm. During courtship and incubation in warmer areas male Adelies expend energy at rates averaging some 20-25% higher than the theoretical page 130 standard metabolic rate for birds of their size; in the colder conditions of Cape Royds spring expenditure is of the order of 60-70% above standard. During the 20-day fast of a normal season Cape Royds males lose about 25% of their initial body weight (Stonehouse 1967a). When the fast is prolonged by the absence of the polynya, weight losses may approach 30-33%; i.e. the birds are subject to a physiological strain equivalent to that of the moult (as measured by percentage weight loss) but at a season of harsher climate, and with the additional strain of chick management still to come. Not surprisingly, many nests are abandoned in years when the polynya fails to form, and nesting success is reduced. The summer of 1962-1963 provided opportunities for studying breeding success in the colony under these conditions. (Sutherland: in press).
The area of ice-free water may determine the amount of food normally available and so control the maximum size of the colony. Numbers appear to have remained approximately constant at about 1500-2000 pairs between 1907 and 1956 (Taylor 1962), in spite of losses of eggs and adults during Shackleton's two expeditions in 1907 and 1916. A large U.S. permanent expedition base was established 17 miles from the colony in 1956, and from then numbers appear to have declined, at a mean total rate of 6%, to a total of just over 1000 pairs in 1962 and 1963. Strong circumstantial evidence suggests that the decline was due to disturbances by visitors, especially low-flying helicopters which landed — often several times daily during the breeding season — on a frozen lake less than 100 yards from the colony. The position was reported to the New Zealand Government in 1962, and in 1963 the U.S. Naval authorities invited our co-operation in drawing up regulations to protect the colony. The number of visits and visitors was drastically reduced, and in 1964 a slight increase of numbers of breeding birds was noted after the long decline.
Preliminary analysis of the five seasons’ counts suggests that the decline in breeding population was due to partial failure in recruiting rather than reduced nesting or breeding success. Disturbance is believed to have affected young birds, which visit the colony as non-breeders in December and January, and may be driven elsewhere by crowding or other conditions which inhibit territory holding.
Banded birds gave insight into colony organisation. Males returning at the start of a season usually headed for a particular site, some 80% returning to sites where they were known to have bred before. Females were less determinate, usually wandering in the colonies and attaching to particular males (often a former mate) rather than sites of previous breeding. Males tended to return before their mates, spending on average nearly four days longer on the colony before the eggs appeared. About one third of the birds page 131 entering the colony in 1961 failed to breed. Rate of failure to breed among banded birds (which were known to have bred before) was very, much lower and confined to those which arrived late in the season. Practically all of the eggs were laid between November 7 and 30, a span since found to be remarkably constant for the colony each year. Details of breeding in the 1961 season have been published (Stonehouse 1963) and accounts of subsequent seasons are in preparation (Stonehouse, Yeates).
Toward the end of November numbers on a colony stabilize and bear a simple relation to the peak number of nests. Aerial photographs taken at this time of the year can thus be interpreted to give a reasonable estimate of colony size, allowing rapid counts to be made in outlying colonies which cannot readily be visited on the ground. This technique has been used to count Adelie colonies at Cape Bird, Beaufort Island, Franklin Island and Inexpressible Island in successive years during the study period (Stonehouse 1966). Flights especially arranged for this purpose by the U.S. Navy have also revealed colonies of Emperor penguins at Beaufort and Franklin Islands, and allowed us to estimate their size and success. (Stonehouse 1965 and in press).
Special helicopter flights were made each year, as closely as possible to the end of November, to count Emperor penguins at the historic Cape Crozier colony. Emperors lay a single egg, incubating on their feet through winter and early spring, and carrying their chicks in the same brood cavity. By October the chicks are too large to be carried, and form creches on the sea ice close to the cliffs of the Ross Ice Shelf. By late November they are sturdy enough to be shepherded and counted. Census taken each year since 1961 have shown that the colony now has a breeding strength of about 1500 pairs, i.e. between four and five times as many as were recorded during Scott's expeditions of 1902 and 1911. The difference is due to changes in the face of the Ross Barrier; during the early years of the century the colony formed in an enclave facing the open sea, but for the past few years has assembled in deep V-shaped rifts behind the main Barrier cliff. Where previously the northerly swells of winter exposed the breeding birds to constant hazard, they are now protected from the danger of being washed or carried away until the ice breaks out in late December or January (Stonehouse 1964).
Some aspects of relations between Adelie penguins and McCormick skuas (Catheracta maccormicki) at Cape Royds were studied by Spellerberg (1967 and in press) as part of a general ecological account of the McMurdo Sound skua population.
I thank Professor G. A. Knox, the University Grants Committee, Antarctic Division of D.S.I.R., Operation Deepfreeze of the U.S. Navy, and my colleagues of the Unit. All have contributed to the results which this paper summarises.
Spellerberg, I. F., 1967. Ecology of the McCormick Skua Catharacta maccormicki (Saunders) in Southern McMurdo Sound. M.Sc. thesis of Canterbury University, Christchurch, New Zealand.
Stonehouse, B., 1963. Observations on Adelie penguins Pygoscelis adeliae at Cape Royds, Antarctica. Proceedings 13th Internat. Ornith. Congress, 766-779.
—— 1964a. Bird life. Chapter 13 in Antarctic Research: A review of British scientific achievement in Antarctica. London, Butterworth, 219-239.
—— 1964b. Emperor penguins at Cape Crozier. Nature 203 (4947): 849-851.
—— 1965. Counting Antarctic animals. New Scientist 27 (454): 273-276.
—— 1966. Emperor penguin colony at Beaufort Island, Ross Sea, Antarctica. Nature 210 (5039): 925-926.
—— 1967a. The general biology and thermal balance of penguins. In Advances in Ecological Research 4: 131-196. Academic Press, London and New York.
—— 1967b. Open water in McMurdo Sound during winter and early spring. Polar Record 13 (86): in press.
Taylor, R. H., 1962. The Adelie penguin Pygoscelis adeliae at Cape Royds. Ibis 104 (2): 176-204.