Natalus stramineus is a cavedwelling bat broadly spread in Mexico but with scarce information about its natural history. In this work, we reported the associated bat species and roosting sites of N. stramineus in Mexico. Also we observed roosting habits and recorded monthly air temperature and relative humidity throughout one year in a roost of this bat, located in the state of Colima, Mexico. It has been found in 108 roosting sites most of which are caves and mines. These roosts were located in a wide range of elevations, vegetation and climates, however most were located below 400 m asl, in tropical deciduous forest and hotsubhumid conditions. We were unable to find this species in some previously recorded caves. In El Salitre Cave, temperature and relative humidity in their roosting sites were stable throughout the year. The former variable fluctuates from 25.8 to 26.9°C and the latter variable from 92.1 to 100%. Individuals of N. stramineus usually hang in the lower parts of walls and rocky ceilings, occupying cavities and crevices occasionally. They hang individually without contact to each other, keeping a distance of 550 cm between themselves. Fortyfive bat species have been found associated with this natalid, but more frequently Pteronotus parnellii, Mormoops megalophylla, Glossophaga soricina y Desmodus rotundus. This bat prefers to occupy warm and humid parts of the roosts, because these conditions are ideal to conserve the body heat and to maintain their wings in good conditions. Its great tendency to be associated with mormopids and some phyllostomids is explained partly by their similar microclimatic requirements in their refuges, as well as by the thermal benefits associated with clustering in colonies. N. stramineus depends heavily on hot caves for their survivorship and occupies mines with similar microclimatic conditions in an opportunistic way.
