Seasonal population dynamics and movement patterns of a critically endangered, cave-dwelling bat, Miniopterus orianae bassanii

Context: Seasonal migration and movements of bats have important implications for their conservation. The southern bent-winged bat (Miniopterus orianae bassanii), a critically endangered cave-dwelling taxon in Australia, has been described as undertaking regional-scale migration between maternity and non-breeding caves. Aims: To describe the seasonal cycle of movements by the southern bent-winged bat, including migration and congregation events of different sex- A nd age-classes in the population. Methods: We tagged a total of 2966 southern bent-winged bats with passive integrated transponder (PIT) tags. Antennas were used to detect bats in flight at a major maternity cave and a key non-breeding cave in south-east South Australia, from January 2016 to August 2019. We used capture-resight histories to visualise population patterns and model the daily encounter probability for each sex- A nd age-class at the respective roost sites. Key results: Bats congregated at the maternity cave for most of the year, with different seasonal patterns among sex- A nd age-classes. Seasonal movements were associated with behaviour over winter months: Most of the population dispersed from the maternity cave from May and a staged return occurred among population classes from July through September. A previously undescribed movement occurred in adult females and juveniles each year: These classes left the maternity cave in late summer, when juveniles became independent, and returned in early mid-autumn, later undertaking winter dispersal. Complex underlying movements of individuals occurred throughout the year, with individuals able to fly 72 km between roosting caves in just a few hours. Conclusions: Seasonal movements are a key aspect of the life history of this taxon. The newly reported movement of adult females and juveniles conforms to the maternal guidance hypothesis, whereby mothers guide their young to suitable non-breeding caves and hibernation sites. In addition to seasonal movements, some individuals moved 72 km between caves multiple times over short time periods, including on successive nights. This 72-km overnight flight distance more than doubles the previous distance used to inform management buffer zones. Extended congregation of bats at the maternity cave highlights resource limitation in the surrounding area as a potential threat to this population. Implications: The dynamic nature of the population has implications for the management of emerging risks, including mortality at windfarms and potential rapid spread of the exotic white-nose syndrome.