THE ADELIE PENGUIN PYGOSCELIS ADELIAE AT CAPE ROYDS

Abstract

SUMMARYThe Adelie Penguin rookery at Cape Royds, Ross Island, Antarctica, was kept under daily observation from 23 October 1959 to 26 February 1960.The rookery is described and its history given. The total area used for nesting has remained much the same over the last 50 years, but there has been a marked shift of nesting colonies into more sheltered positions.The adult population was counted every one or two days, and daily observations were made on 44 pairs of marked birds and 122 marked nests in which all eggs and chicks were individually marked.Considerable fluctuations occur in the numbers of adults and nests at the rookery during the breeding season, and their effect on methods used for assessing rookery size from counts made at odd times is discussed.Birds began to arrive at the rookery in mid‐October. The males usually arrived first and almost immediately began constructing nests. Eggs were laid during four weeks, from 4 November to 4 December; the usual clutch was two eggs, but in 65% of nests in which the first egg was lost soon after laying, a third was laid.Measurements and weights are given for 75 eggs. There is a decrease in size of successive eggs laid. The average interval between the laying of eggs in any one clutch was just over three days.The incubation period (day of laying to the day the chick finally emerged from the shell) of 150 eggs gave a mean period for first eggs of 34·8 (33–39) days, and for second eggs of 33·3 (30–37) days.Parental routine during incubation in 35 pairs of known sex is described; very few females took first turn at incubating the eggs. The fasting periods for Cape Royds birds are compared with those at the South Orkney Islands.The hatching, plumage, care and development of the chicks are described. The average length of the guard stage in 122 marked chicks was 22·4 days. The mean age of chicks when they left the rookery was 50·6 days; many chicks entered the water for short swims a day or so before they departed.Of 600 adults that returned to moult at the rookery during February, probably two‐thirds were non‐breeding birds.Mortality of adults at the breeding grounds was slight. Most egg losses were due to eggs being displaced from nests, or the abandoning of nests and eggs. A study of marked nests showed that 67% of all chick losses were directly due to Antarctic Skua predation, other mortality factors being desertion and exposure. Of the eggs 66% hatched and 75% of the chicks survived to leave for sea.The breeding season at Cape Royds (77° 30′S.) is compared with that in the South Orkney Islands (61° S.). The availability of food is probably the most important factor determining the length of the breeding seasons at different rookeries.