Testing multichambered bat box designs in a habitat-offset area in eastern Australia: influence of material, colour, size and box host

Bat boxes are frequently used as conservation and habitat-offset measures, yet their effectiveness is equivocal, particularly in Australia. Boxes used in Australia are largely voluminous-type boxes with Chalinolobus gouldii (Gould’s wattled bat) frequently dominating their use. We tested multichambered boxes comprising fissure-type cavities made from either plywood (~20 000 cm3) or woodcement (~7400 cm3). We investigated whether occupancy was influenced by box colour (white boxes facing morning sun versus black boxes facing afternoon sun), box material/size, chamber width (15 mm versus 20 mm) and box host (tree versus pole). Boxes were monitored over 1.8 years. Overall, 245 bat observations were recorded. Boxes were frequently used (15% of 1088 box checks) by Nyctophilus geoffroyi (lesser long-eared bat), a species uncommonly reported to use boxes, which used 50 of the 64 boxes (78%), including for maternity roosting (n = 6). In comparison, C. gouldii was rarely detected (1% of box checks). Two other species were also found in boxes at low frequencies. Modelling showed a preference by N. geoffroyi for black boxes, the larger plywood box and boxes installed on poles. Fissure-type boxes appear to meet the roost requirements of N. geoffroyi but not that of C. gouldii, the species principally detected in voluminous-type boxes and postulated to gain a competitive advantage. The black woodcement box was the second most frequently used design, demonstrating that this long-lasting box material can be a suitable alternative to the less durable plywood material. Given that just one species commonly used boxes, there is a need for further research on box designs.