Breeding biology of Australian owlet-nightjars Aegotheles cristatus in eucalypt woodland

Although the Australian Owlet-nightjar Aegotheles cristatus is probably the most abundant and one of the most widespread nocturnal birds in Australia, the majority of information published about its ecology, behaviour 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, fledging success, fledgling behaviour and roost site use for a population breeding 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 more common than the three (four versus two nests) reported in the literature. Chick growth rates were fast, suggesting that adult size is reached approximately 13 days post-hatching. Contradicting the literature, we found that only one adult, presumably the female, incubated and brooded. When approached, this individual usually flushed from the nest, which also differs from descriptions in the literature. Brooding ended 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 for at least 14 days post-fledging or that it roosted in sites used before or after by other Australian Owlet-nightjars. Both nests and adults suffered high rates of predation, which indicated that this was the most likely factor regulating the population of this species.