Thermoregulation in two free-ranging subtropical insectivorous bat species: <i>Scotophilus</i> species (Vespertilionidae)

Abstract

Little is known about the thermal regulatory behaviour of free-ranging subtropical bats. We studied torpor use in two free-ranging subtropical sibling species of insectivorous bat, Scotophilus dinganii (A. Smith, 1833) and Scotophilus mhlanganii , during the austral autumn. All S. dinganii (mass 28.9 ± 2.6 g (mean ± SD)) roosted in buildings, whereas all S. mhlanganii (28.0 ± 0.4 g) roosted in the foliage of trees or in a tree cavity. Contrary to what has been seen in other subtropical species, both Scotophilus species used only one bout of torpor per day. Bats entered torpor 2 h after returning from foraging and aroused passively as the roost was heated by the sun the following day. There was a negative correlation between duration of foraging and duration of torpor, probably because bats that foraged longer had less time for torpor. Despite physical differences between roosts, foliage and building roosts appeared equally thermally labile, resulting in torpor bouts of similar depth and duration between individuals of the two species that used such roosts. Cavity-roosting female S. mhlanganii, on the other hand, used torpor bouts that were longer and shallower than those used by its female conspecifics in foliage roosts and female S. dinganii in buildings. Thus, thermal regulatory behaviour was determined more by the type of roost used than by interspecific differences in physiology.