Fluctuation of Adelie penguin populations in two small rookeries of the Syowa Station area, Antarctica

Abstract

The fluctuation of the Adelie penguin population was investigated at the Ongulkalven rookery (69°01'S, 39°26'E) and the Mame-zima rookery (69°01'S, 39°29'E) near Syowa Station (69°00'S, 39°35'E), Antarctica. Number of bird in the Ongulkalven rookery was 110,103 and 156 in the breeding seasons of 1961-62,1966-67 and 1970-71,respectively. From 1971-72 season, the population of penguin began to decrease and in 1975-76 season it reached about one-third of that of 1970-71 season. Thereafter, the reduction of population became gradual. The same tendency in population fluctuation as mentioned above was also observed at the Mame-zima rookery. The disturbance by the expedition members seemed to be little because of the low frequency of their penguin watching. A possible relation between the penguin populations in two rookeries and the sea ice condition in the breeding season was observed. Since Japanese Antarctic Relief Ship, Icebreaker FUJI, succeeded to approach Syowa Station from 1965-66 to 1970-71 seasons but failed after 1971-72 except 1977-78 summer, the ice condition between 1965-66 and 1970-71 breeding seasons seemed to be advantageous to the Adelie penguin but to become unfavorable after 1971-72 season.