Position of the pinnae and thermoregulatory status in brown long-eared bats ( Plecotus auritus)

Abstract

The relationship between position of the pinnae and thermoregulatory status was investigated in 13 captive brown long-eared bats ( Plecotus auritus L.). Bats with body temperature ( T b) in excess of 28°C were endothermic, and those at lower T b were torpid. The pinnae of torpid bats were generally tightly folded below the forearms, whilst those of endothermic bats were, to a varying degree, erected. There was a significant positive relationship between T b and degree of erection of the pinnae, ranked on a scale 0–5. A fitted regression, however, only explained 9.3% of the variability in T b. There was also no significant relationship between the elevation of T b above the ambient temperature ( T a) and the degree of erection of the pinnae, for both endothermic and torpid bats. The absence of a precise relationship between both T b- T a and T b, with pinnae erection, in addition to a significant association between pinnae erection and thermoregulatory status suggests that pinnae erection and thermoregulatory status are not functionally related. Folding the pinnae below the forearms is probably incompatible with other behaviours, such as grooming, which involve considerable movement of the forearms. These behaviours occur predominantly during endothermy and it is more likely therefore pinnae would be unfolded during endothermic periods. This latter hypothesis is supported by longitudinal measurements of both T b and ear position in individual bats at a relatively constant T a. Pinnae position cannot be used to reliably assess thermoregulatory status of individual brown long-eared bats through time.