IDENTIFICATION OF SEX OF ADELIE PENGUINS FROM OBSERVATIONS OF INCUBATING BIRDS

The suggestion that sex of Adelie penguins, Pygoscelis adeliae, might be assigned by observing which member of the pair (the male) takes the first long incubation shift (Anon. 1991) was examined for each of the 1990-91, 1991-92 and 1992-93 breeding seasons. There was an 8- or 9-d ay period when more than 90% of the incubating birds were male and a 6 - or 7-day period when more than 90% of the birds were female. The dat es of these peak periods of male or female presence overlapped by only 2-5 days between the three seasons but were constant to within 2 days relative to the commencement of egg laying. Peak presence of males oc curred 15-21 days after the appearance of the first egg in the colony and peak presence of females after 33-36 days from this date. In all t hree seasons male birds could be identified with 91.8-98.6% accuracy w ithin 15-21 days after the first sighting of an egg. The method provid es, therefore, a means of identifying the sex of Adelie penguins with an accuracy greater than 90% and is applicable to whole colonies conta ining several hundred pairs without recourse to continuous observation s or capturing the birds.