Abstract

Bridled Terns Sterna anaethetus on Penguin Island, near Perth, Western Australia, showed courtship behaviour during only 61% of 304 ten-minute observation periods before laying and most displays lasted less than five seconds. Head-nodding was the most frequent ground display during courtship. Egg laying was recorded from 16 November to 28 December in 1990, with most eggs laid in the first fortnight. Incubation lasted 27-33 days and shifts usually continued for the whole day with most changeovers at night. Hatching success averaged 72%, most egg losses resulting from desertion by the parents. It is estimated that about 84% of the chicks that hatched probably fledged.