Energy metabolism and body temperature in the Blue-naped Mousebird (Urocolius macrourus) during torpor

Abstract

Mousebirds (Coliiformes) respond to cold exposure and food limitation with nightly bouts of torpor . During torpor, metabolic rate and body temperature decrease markedly, which results in energy savings. The decrease in body temperature is a regulated phenomenon as is also the arousal which occurs spontaneously without external stimuli. During arousal, Blue-naped Mousebirds warm at a rate of 1 °C/min . This process requires significant amounts of energy . Our calculations show that the overall savings for the whole day are 30% at an ambient temperature of 15°C when daylength is 10 hours . Using glucose assays and RQ measurements, we found that during fasting, the birds switch to non-carbohydrate metabolism at an early phase of the day . This may be one of triggers eliciting torpor. By using cluster analysis of glucose levels we could clearly divide the night phase into a period of effective energy saving (high glucose levels) and arousal (low glucose levels) .