Baby in the bathwater: Should we abandon the use of body temperature thresholds to quantify expression of torpor?

Boyles et al. (this issue) argue against the use of body temperature (T-b) thresholds to quantify the expression of torpor in endotherms and our purpose is to provide a counterpoint argument. We contend that Tb thresholds provide valuable information about ecological factors influencing the evolution of thermoregulation. We also point out shortcomings of the so-called heterothermy index proposed as an alternative. However, to be clear, we do agree with Boyles et al. (this issue) that the use of torpor thresholds can limit some aspects of the study of thermoregulation and applaud the more widespread incorporation of theoretical underpinnings proposed by Boyles et al. (this issue) and others. (C) 2011 Elsevier Ltd. All rights reserved.