Census of the endangered Mexican long-nosed bat Leptonycteris nivalis in Texas, USA, using thermal imaging

Emory Cave in west Texas, USA is one of the few natural roost sites used by the endangered Mexican long-nosed bat Leptonycteris nivalis in the United States. Despite concern over declines in population size, no reliable methods have been developed for censusing colonies of this species that are both accurate and minimize disruption to the colony. The objective of this study was to use non-invasive thermal infrared imaging to census L. nivalis as individuals emerge from Emory Cave and to evaluate the success of this method for future monitoring efforts. We recorded 6 emergences of bats from Emory Cave (4 and 5 June, 4 and 5 July, 4 and 5 August 2005) using thermal infrared cameras. Recordings were manually reviewed, and peak emergence rate was determined to be 54, 159, and 61 bats min–1 in June, July and August, respectively. The greatest number of L. nivalis (at least 2742 to 2874) was present in July. Overall, our data suggest that thermal infrared imaging provides a more reliable and accurate estimate of the number of L. nivalis at Emory Cave than has previously been possible using extrapolation from surface area of the cave ceiling covered by bats.