Abstract
Vocalisations of owlet-nightjars Aegotheles sp. are poorly known, with the exception of the Australian Owlet-nightjar A. cristatus. Among the vocalisations for the Australian Owlet-nightjar, hissing has been described as part of threat display in three first-hand early published reports (between 1848 and 1934). However, no reports of this behaviour have been published since 1934, despite a number of field studies on the breeding biology of the species, potentially casting doubt on the veracity of earlier reports. Here I describe an instance of hissing as part of a threat display (which also included flattening its body, with head up, swaying side to side and gape wide open) of an Australian Owlet-nightjar cornered in a nest box. I compare my observations to the few published occurrences, pose questions as to the circumstances and conditions for this behaviour, review vocalisations of other owlet-nightjar species and instances of hissing in Caprimulgiformes.