Molt in the Adelie Penguin

Abstract

RICHDALE (1957: 175-176) and Murphy (1936: 402-403) had to rely on the fragmentary accounts of early Antarctic explorers and biologists for information on the molt of Adelie Penguins (Pygoscelis adeliae). They had encountered molting birds on land and in the pack-ice during February and March at the close of the breeding season and noted that the birds did not enter the water or feed during the molt (Clarke, 1906; Wilson, 1907; Gain, 1914). On the basis of his own observations and a review of the literature, Sladen (1958: 65) concluded that the majority of Adelie Penguins molt while on ice floes in the pack and that the number which molt on land in different areas varies from year to year according to prevailing ice conditions. Taylor (1962: 196-198) found that about one-third of the birds which molted in the vicinity of his study rookery at Cape Royds (the most southerly Adelie Penguin rookery) were local breeders and the rest, non-breeders. Wilson (1907: 54-58) simply stated that the length of molt was two weeks and Gain (1914: 31) gave 20 days. Cendron (1953) studied the complete molt on three birds and these took 9, 15, and 17 days to replace their old plumage. Taylor (1962: 196-198) noted the duration of molt as being about two weeks, after which the birds departed to sea. Clarke (1906: 162) found that birds which had recently completed the molt (in April) weighed about 30 per cent less than those at the beginning of the breeding season (in October). Cendron (1953) weighed 25 Adelie Penguins at the beginning of molt and 12 at the end and obtained an average weight loss of 40 per cent. My observations on molting birds were made at Wilkes Station, Ant-arctica (66 ø 15' S lat., 110 ø 32' E long.), at the end of the 1958-59 and 1959-60 breeding seasons and represent part of an intensive study of Adelie Penguin behavior during a two-year period at the same location (Penney, in press). METIIODS In the study rookery containing approximately 2,700 breeding birds, molting was observed systematically in 248 adults and 59 juveniles. (Adults are at least two years old and are characterized by a black chin before the observed molt; juveniles, hatched the previous season, have a white chin.) Molting birds under study were flipper-banded (Sladen and Penney, 1960) as were about 1,000 other birds being studied for territorial and social behavior. The total number of birds molting in the area of the rookery was about one-fifth the estimated total breeding population. The majority of the molting Adelie Penguins were banded at the end of the 61 The Auk, 84: 61-71.