Body temperature patterns in two syntopic elephant shrew species during winter

We measured body temperature (T(b)) in free-ranging individuals of two species of elephant shrews, namely western rock elephant shrews (Elephantulus rupestris) and Cape rock elephant shrews (E. edwardii), during winter in a winter-rainfall region of western South Africa. These syntopic species have similar ecologies and morphologies and thus potential for large overlaps in diet and habitat use. Unexpectedly, they displayed different T(b) patterns. Western rock elephant shrews were heterothermic, with all individuals decreasing T(b) below 30°C on at least 34% of nights. The level of heterothermy expressed was similar to other species traditionally defined as daily heterotherms and was inversely related to T(a), as is commonly seen in small heterothermic endotherms. In contrast, Cape rock elephant shrews rarely allowed their T(b) to decrease below 30°C. The level of heterothermy was similar to species traditionally defined as homeotherms and there was no relationship between the level of heterothermy expressed and T(a). In both species, the minimum daily T(b) was recorded almost exclusively at night, often shortly before sunrise, although in some individuals minimum T(b) occasionally occurred during the day. The interspecific variation in T(b) patterns among Elephantulus species recorded to date reiterates the importance of ecological determinants of heterothermy that interact with factors such as body mass and phylogeny.