ANNUAL CYCLE OF SEX STEROIDS IN THE YELLOW-EYED PENGUIN (MEGADYPTES ANTIPODES) ON SOUTH-ISLAND, NEW-ZEALAND

The yellow-eyed penguin (Megadyptes antipodes) is a rare penguin restr icted to the South Island and some offshore islands of New Zealand. It is the least colonial of the penguins but shares with many other peng uins a distinct breeding season with a short, synchronised period of e gg-laying. Blood samples were collected throughout the year from yello w-eyed penguins on the Otago Peninsula, South Island in order to chara cterise relationships between steroid hormone levels and events of the breeding cycle. Testosterone levels in male penguins were high during the pre-egg phase, dropped dramatically to low levels during incubati on, and remained low during the guard and postguard phases of the bree ding cycle. Testosterone levels in females showed a similar pattern. M ale testosterone levels were significantly higher than female levels d uring the pre-egg phase. The patterns of changes in estradiol levels w ere similar to those for testosterone. Estradiol levels were significa ntly higher in females than males during the pre-egg phase. There was a clear annual cycle of testosterone levels in yellow-eyed penguins, w ith levels low from January (midsummer) until July. They then rose mar kedly in August (the time of increased activity around nest sites) and reached a peak in September, followed by a steep decline to low level s again in October. There was also an annual cycle of estradiol levels with a peak that coincided with the testosterone peak. Progesterone l evels varied during the year, being elevated in late summer and autumn (February-May) and lower during the remainder of the year. The annual cycles of testosterone and estradiol in the yellow-eyed penguin close ly resemble those of other penguins that also have a short egg-laying period, despite the sedentary nature and solitary rather than colonial nesting behaviour of the yellow-eyed penguin. (C) 1994 Academic Press , Inc.