Behaviour and thermal biology of mammals and birds: a laboratory-field comparison

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Studies on the behaviour and function of mammals and birds most often are conducted in the laboratory and it is generally assumed that they are representative of free-ranging animals. We compared whether and how behaviour and thermal biology of several species differ between the laboratory and field. Our comparison shows that in many species timing of activity and thermoregulation in the laboratory diverge substantially from those in the field. In captivity, even when held outdoors, small marsupials tend to be largely nocturnal independent of the weather, whereas in the field many are partially diurnal and adjust activity to the prevailing environmental conditions. Normothermic captive sugar gliders (Petaurus breviceps) have a constant body temperature (Tb) that is unaffected by ambient temperature (Ta), whereas in free-ranging gliders Tb is correlated with Ta. The most pronounced differences have been observed for patterns and variables of torpor. Captive and freeranging animals often show differences with regard to the timing of torpor and the duration of torpor bouts, which are usually shorter and shallower (higher Tb and metabolism) in captivity. Moreover, torpor is often used more frequently in the field than in captivity and in extreme cases some species, such as Tawny frogmouths (Podargus strigoides) and kookaburras (Dacelo novaeguineae) that use torpor in the field totally refuse to do so in captivity. In contrast, mouse birds (Colius colius), which enter torpor in captivity as individuals do not do so in the wild, most likely because they cluster and use social thermoregulation and slight decreases in Tb instead. Our comparison suggests that laboratory studies often do not provide representative data on behaviour and thermal biology of animals and underestimate how their flexibility will affect energy expenditure and survival in the wild.

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