Seasonal activity patterns of bats in North Sydney, New South Wales: implications for urban bat monitoring programs

Abstract

Behavioural and physiological traits of bats may influence seasonal bat activity in urban areas. To examine this, we used acoustic surveys to monitor insectivorous bat activity in urban bushland and at two day-roosts of Miniopterus orianae oceanensis between September 2013 and August 2014. Day-roosts were also assessed for potential as swarming sites and monthly estimates of colony size were made at one of these, while radio-tracking was used to identify additional roosts. Acoustic surveys identified seven species, with Mi. o. oceanensis and Chalinolobus gouldii most commonly recorded. Nightly species richness was lower in winter than in other seasons, while total bat activity was greatest in autumn, reflecting increased activity by C. gouldii and Mi. o. oceanensis in this season. One Mi. o. oceanensis day-roost was used from autumn to early spring, with numbers of bats increasing from ~50 to 300 and high fidelity shown to this site by radio-tagged bats in autumn, while nightly activity at another day-roost was suggestive of swarming. Seasonal differences in bat activity were species-specific and, for Mi. o. oceanensis, corresponded to changes in population size as bats migrated to and from Sydney to meet reproductive and overwintering requirements. We recommend urban bat monitoring programs sample multiple seasons to adequately document trends in activity for all bat species.