In late summer the females and weaned young moved back to the south. These bats may be highly gregarious. Lekagul and McNeely stated that the typical roosting group of M. australis consists of only one male and six females and that such groups are transitory, breaking up when the bats go out to feed. Males were found to disappear from the colony by December, when the young were born. In Europe mating occurs in August and September, fertilization occurs shortly thereafter, embryonic development is retarded through hibernation, and the young are not born until spring.
Females are ready for breeding again after the young are weaned.
In M. australis mating was in August, implantation occurred by mid-September with little or no delay, and births took place in December. The longevity record in the genus is nine years. Several colonies that formerly contained thousands of individuals have almost or entirely disappeared. This species is very sensitive and may be eliminated if its roosts in caves and mines are disturbed by human workers or tourists.