SUMMARY
Hibernation is a strategy allowing bats to save energy when food availability and ambient temperature are low. Four decades ago, an altitudinal migration of the bat Myotis velifer to a hibernating site was registered in Mexico. However, no records or characterization of the sites used by this species to hibernate in the country are virtually known. Our main objective was to describe and characterize a hibernating colony of Myotis velifer in a tunnel located at 3,600 meters above sea level in La Malinche National Park, a mountain ecosystem of central Mexico. From June 2015 to May 2016, we visited the tunnel each month. In each visit, we looked for bats and made a one-time measurement of ambient temperature and relative humidity. During the first visit to the tunnel, we randomly captured and measured (i. e., sex, length of the forearm, body mass, and reproductive condition) seven individuals for information purposes. These individuals were released at the end of procedures. In mid September 2015, we found 14 M. velifer hibernating in clusters of different sizes. By mid January, the colony reached 81 individuals. We not longer found bats when we visited the tunnel in middle March. Ambient mean temperature and humidity were 7.5 ± 1.5 ºC and 70 ± 8.3 % respectively. Our new record of the hibernating colony of M. velifer exemplifies the specificity of hibernacula used by this species in central Mexico. The six-month period of hibernation and environmental variables we recorded match with the interval that M. velifer has been reported hibernating at other latitudes. Currently, characterizing the environmental requirements of bats to hibernate is of relevance to promote specific conservation strategies for this group of vertebrates.