Thermal energetics of Nyctophilus geoffroyi (Chiroptera : Vespertilionidae) at the southern limits of its distribution

Abstract

The energetics of the lesser long-eared bat, Nyctophilus geoffroyi, at the southern limits of its distribution was examined to determine whether this species shows any latitudinal variation in this aspect of its physiological ecology. Estimates of metabolic rate were obtained from the oxygen consumption of adult bats in a non-reproductive condition. Values for the thermoneutral zone were similar but thermal conductance was lower than for bats from mainland of Australia. Euthermic body temperature was higher (37.4 ± 0.2°C) and the ambient temperature at which N. geoffroyi entered torpor has a downward shift of 10°C at the southern limits of its distribution. The basal metabolic rate (1.12 ± 0.14 mL O₂ g^–1 h^–1) also was lower than in lower latitudes. Thermal conductance of the bats in Tasmania was lower than that found in New South Wales or Western Australia (0.29 v. 0.38–0.39 mL O₂ g^–1 h^–1 °C^–1). All of these differences are apparently adaptations to a cooler environment.