Effects of short-term acclimation on thermoregulatory responses of the rock kestrel, Falco rupicolus

The effects of a short-term acclimation period on basal metabolic rate (BMR) and resting metabolic rate (RMR) were measured in captive-bred Rock Kestrels (Falco rupicolus). Birds were exposed to winter conditions (pre-acclimation) in a semi-natural environment before they were acclimated for a period of 3 weeks at a constant temperature of 25 °C and a constant light:dark cycle (12:12 h) (post-acclimation). After acclimation the kestrels showed changes in RMR, BMR and the width of the thermoneutral zone. There was inter- and intra-individual phenotypic plasticity in BMR and RMR both pre- and post-acclimation. However, more inter-individual variation was seen after acclimation. This study concurs with recent suggestions that phenotypic plasticity in BMR is prevalent in avian physiology, and thus a single-species-specific BMR value may not be representative. Furthermore, comparative avian studies of BMR need to account for phenotypic plasticity.