Abstract
Bat activity generally increases with temperature, so bat surveys are considered more effective in summer. Less is known about survey effectiveness at low temperatures and whether activity ceases under certain thresholds. Literature provides piecemeal information on winter activity of threatened New Zealand lesser short-tailed bats (Mystacina tuberculata) and long-tailed bats (Chalinolobus tuberculatus); no data exist on lower temperature thresholds below which activity is halted in some regions. We recorded bat echolocation calls over seven nights in winter 2021 to determine whether a lower temperature threshold exists where both species are inactive in the Pikiariki Ecological Area, Pureora Forest Park, central North Island, Aotearoa New Zealand. Long-tailed bat detection rates greatly reduced at <5 degrees C, ceasing at <2.6 degrees C; at edge sites, long-tailed bats had higher activity rates at higher temperatures, but this pattern did not hold in the forest interior. Lesser short-tailed bats were detected at all sampled temperatures (1 degrees C-10 degrees C), 56% of detections occurred at the forest edge; no lower temperature threshold beyond which activity ceased was found. While winter surveys may detect bats, rates are likely lower than in warmer months. Lesser short-tailed bat surveys could be worthwhile in winter due to their broader activity range, depending on the survey's objectives, but should be conducted over extended periods, and any conclusions about the presence or absence of bats should be made cautiously. Further research is needed to refine lower temperature thresholds and improve winter survey effectiveness.