Thermoregulation under semi-natural conditions in speckled mousebirds: the role of communal roosting

<p>Mousebirds (Coliiformes) exhibit well-developed communal roosting behaviour as well as a pronounced capacity for facultative hypothermic responses. We recorded body temperature (T_b)) in speckled mousebirds (<i>Colius striatus</i>) under semi-natural conditions in outdoor aviaries, and examined interactions between behavioural and metabolic thermoregulation by experimentally manipulating food availability and communal roosting behaviour. When food was available <i>ad libitum</i>, mousebirds roosting in a cluster maintained approximately constant rest-phase T_b, with 32°C < T_b < 42°C. By contrast, rest-phase T_b in single mousebirds decreased at 0.5°C/hr and minimum rest-phase T_b was significantly lower than when clustering. When food availability was restricted, the mousebirds exhibited facultative hypothermic responses that were less pronounced in clustering groups (minimum rest-phase T_b = 33.3°C, circadian amplitude of T_b = 9.5°C) compared to single birds (minimum rest-phase T_b = 30.7°C, circadian amplitude of T_b = 11.8°C). When clustering, rest-phase T_b was highly synchronized among individuals. Our data reveal that communal roosting has profound consequences for rest-phase thermoregulation in <i>C. striatus</i>, and provide further insights into the potential role of physiological constraints in the evolution of avian sociality.</p>