BREEDING BIOLOGY OF AUSTRALIAN OWLET-NIGHTJARS AEGOTHELES CRISTATUS IN EUCALYPT WOODLAND

Although the Australian Owlet-nightjar Aegotheles cristatus is probabl y the most abundant and one of the most widespread nocturnal birds in Australia, the majority of information published about its ecology, be haviour and especially reproductive biology is anecdotal. Based on six observed nesting attempts, we report data on breeding season, clutch size, incubation and brooding behaviour, nestling growth rates, fledgi ng success, fledgling behaviour and roost site use for a population br eeding near Armidale, New South Wales, during 1996-97. Chicks fledged from two of the six nests and we found a clutch size of four to be mor e common than the three (four versus two nests) reported in the litera ture. Chick growth rates were fast, suggesting that adult size is reac hed approximately 13 days post-hatching. Contradicting the literature, we found that only one adult, presumably the female, incubated and br ooded. When approached, this individual usually flushed from the nest, which also differs from descriptions in the literature. Brooding ende d on day 8 post-hatching, not 11, as has been reported. For one radio- tagged chick, there was no evidence that it roosted with adult birds f or at least 14 days post-fledging or that it roosted in sites used bef ore or after by other Australian Owlet-nightjars. Both nests and adult s suffered high rates of predation, which indicated that this was the most likely factor regulating the population of this species.