Breeding behaviour of colour-aberrant Adélie penguins (Pygoscelis adeliae) at Cape Crozier, Ross Island, Antarctica

Plumage colour variation occurs widely among bird species and is often associated with individual fitness. More specifically, colouration can affect thermoregulatory ability, mate selection and conspicuousness during foraging. Colour aberrations can be caused by genetic mutations, dietary imbalances, environmental conditions or disease and are rare. Plumage variations have previously been noted in Adelie penguins, although without any follow-up to measure implications for behaviour or fitness. To assess how this low-frequency condition affects breeding in Adelie penguins, we monitored the breeding of several colour-aberrant Adelie penguins during the 2019–2020 nesting season at the large Cape Crozier, Ross Island colony (> 300,000 pairs). In total, we found 12 individuals with unusual plumage for a frequency of 1:50,000 breeding penguins. There were seven dark brown Adelie penguins, three progressive greying Adelie penguins, one dilute Adelie penguin and one brown Adelie penguin, of which five were female, three male and four of unknown sex. Six colour aberrants initiated breeding with a normal-coloured mate, and five raised at least one chick to creche. The likelihood of breeding and breeding success of colour aberrants were similar to those of normal-coloured Adelie penguins, suggesting that colour aberrations do not negatively affect breeding.