Cool gleaners: Thermoregulation in sympatric bat species

Abstract

Thermoregulatory behavior in temperate bats is influenced by gender, food availability, ambient temperature and reproduction. Ecologically and morphologically similar bat species (Myotis bechsteinii, M. nattereri, and Plecotus auritus; Vespertilionidae) facing similar diurnal conditions should therefore not differ in their thermoregulatory behavior. Identified day roosts (n=23) of radio-tagged bats (n=30) were spread over an area of 33.1ha, but ambient temperature did not differ between roosting sites. Furthermore, there was no significant difference in cardinal direction, roost height, canopy coverage, and breast height diameter between day roosts used by the three species. Minimum roost temperatures and isolation values, however, differed significantly between our species with lowest values in P. auritus. The range of skin temperatures (min–max) recorded by temperature-sensitive transmitters was not species-specific with the lowest ranges in late pregnancy (mean±SD: 7.1±1.1°C) and highest in post-lactation (mean±SD: 13.1±1.1°C). The minimum skin temperature, however, was species-specific with the lowest values in P. auritus (mean±SD: 20.2±1.1°C), intermediate in M. nattereri (mean±SD: 23.4±1.0°C), and the highest in M. bechsteinii (mean±SD: 26.8±1.0°C). Species-specific usage of energy-saving mechanisms might represent an important niche differentiation of species. Different mechanisms might allow, e.g. one species to occupy colder roosts with higher temperature variations or to shorten foraging times due to distinct thermoregulatory behavior.