The small bent-winged bat Miniopterus australis was studied at low tropical latitudes north of the equator, principally in Subis cave, Niah, Sarawak, East Malaysia. During the course of field-work in 1957–58, most specimens were captured at roost in concavities in the cave ceiling, here termed “cupolas”. At all months of observation, roosting groups varied from one to seven bats. Solitary bats were predominantly males, and multiple groups rarely included more than one male. It is suggested that the sexes differ in their response to a potential or familiar roosting site, depending on the prior occupation by other bats. Roosting behaviour did not vary with the progress of the reproductive cycle and seemed to have no epigamic function.
Observations of reproductive biology in 1957–58, supported by specimens captured in 1959–60, demonstrated that the species is monoestrous, with a brief annually recurrent breeding season in November-December. Copulation was observed in early November and preceded ovulation. In unovulated females taken in early December the right uterine horn was distended with spermatozoa. The single embryo subsequently implanted in the right horn, although in the three females examined the fertilized ovum derived from the left ovary.
Parturition occurred in late April and early May after a gestation period of 4 1/2–5 months. This period is considerably longer than the presumed species-specific minimum, observed at latitude 15d̀ S. The prolonged gestation period is regarded as an adaptation to perennially low and variable food resources in an otherwise favourable environment, and there is evidence that the months of gestation and birth coincide with a period of limited seasonal increase in abundance of insect prey.