Roosting behaviour and the tree-hollow requirements of bats: Insights from the lesser long-eared bat (Nyctophilus geoffroyi) and Gould's wattled bat (Chalinolobus gouldii) in south-eastern Australia

Access to suitable roosts is critical for the conservation of tree-hollow roosting bats worldwide. Availability of roost sites is influenced by human land-use, but also by the roosting requirements and behaviour of species. We investigated roosting behaviour of the lesser long-eared bat (Nyctophilus geoffroyi) and Gould’s wattled bat (Chalinolobus gouldii) in a rural landscape in south-eastern Australia. Forty-five N. geoffroyi and 27 C. gouldii were fitted with radio-transmitters, resulting in the location of 139 and 89 roosts, respectively. Most (88%) roosts occupied by male N. geoffroyi contained only a single individual. During the breeding season female colonies were larger, with maternity roosts containing 18.3 ± 5.7 (s.e.) individuals. Mean colony sizes for C. gouldii were 8.7 ± 1.4 individuals. Both species shifted roosts frequently: on average, individual N. geoffroyi moved every 2.2 ± 0.23 days and C. gouldii every 2.2 ± 0.14 days. Notably, lactating female N. geoffroyi shifted roosts more frequently than non-breeding females. Individuals of both species roosted within a discrete area, with roosts typically <300 m apart; and consistently returned there from foraging up to 12 km distant. This roosting behaviour highlights three important requirements: (1) a relatively large overall number of hollows to support a population; (2) discrete roost areas with a high density of suitable hollows in close proximity; and (3) a range of hollow types to provide the specialised roosts required, particularly for breeding.