Heterothermy in Mousebirds: Evidence of Avian Proto-torpor?

Abstract

Patterns of normothermy and heterothermy in two mousebird species differed in several respects from typical endothermic patterns. Primarily. heterothermic responses in Colius striatus lacked the entry and maintenance phases characteristic of typical torpor bouts. These observations suggest that mousebirds may exhibit "proto-torpor", a form of torpor intermediate between hypothesized ancestral wide-amplitude Th cycling and modern heterothermy. Clustering behaviour also formed an obligatory component of thermoregulation, and was necessary for the defence of a constant To during the rest-phase. The evolution of typical avian torpor appears to have been arrested in the mousebirds by the development of sociality and clustering.