Influence of weather on long-tailed bat detection in a North Island exotic forest

Accurate surveys and monitoring are required to guide the conservation and management of threatened species. Some fauna species that are cryptic or difficult to observe because they are nocturnal, mimic other species, conceal themselves, or can be incredibly hard to survey. Emergence and activity of these species may be related to complex environmental cues including weather and atmospheric conditions. The conservation status of New Zealand’s long-tailed bat (Chalinolobus tuberculatus) is Threatened-Nationally Critical. Occurrence and activity of long-tailed bats is commonly monitored with acoustic bat detectors. However, even in locations where long-tailed bats are known to be present, they may only be detected on a subset of nights meaning that detection with acoustic detectors is imperfect. We analysed long-tailed bat detection data collected in Kinleith Forest, central North Island, New Zealand in 2006 and 2007 using zero-inflated generalised linear (mixed) effect models. We found relationships between bat detection and several environmental variables. Results suggest that bat surveys would be most effective at detecting bats when undertaken one to four hours after sunset, on nights when the temperature at sunset is above 8ºC, and preferably when the temperature stays in the 8 and 17°C range during the night. Higher humidity and a light breeze may also be a desirable condition for monitoring. A night that is similar to, or slightly warmer, than recent nights may be favourable. Caution should be taken extrapolating these results to elsewhere because bats in other regions may respond differently to temperatures out of necessity. High site-specific variation in bat counts at higher temperatures and humidity occurred with zero activity often recorded. Therefore, we caution against assuming bats are absent because they have not been detected by surveys undertaken during higher temperatures and humidity conditions unless surveys have been run for multiple nights in suitable conditions.