title: Avian torpor or alternative thermoregulatory strategies for overwintering?
abstract: It is unclear whether torpor really is uncommon amongst passerine birds. We therefore examined body temperature and thermoregulatory strategies of an Austral passerine, the white-browed babbler (Pomatostomus superciliosus), which has characteristics related to a high probability of torpor use; it is a sedentary, insectivorous, cooperative breeding species, which we studied during winter in a temperate habitat. Wild, free-living babblers maintained normothermy overnight, even at sub-zero ambient temperatures, with a mean minimum body temperature of 38.5±0.04°C that was independent of minimum black bulb temperature. Physiological variables measured in the laboratory revealed that babblers had a low basal metabolic rate and evaporative water loss, but their body temperature and thermal conductance were typical of those of other birds and they had a typical endothermic response to low ambient temperature. Huddling yielded significant energy savings at low temperatures and a roost nest created a microclimate that buffered against low temperatures. Low basal energy requirements, communal roosting and the insulation of a roost nest confer sufficient energetic benefits, allowing babblers to meet energy requirements without resorting to heterothermia, even in their depauperate, low-productivity landscape, suggesting that passerine birds use alternatives to torpor to balance their energy budgets when possible.
authors.affiliation: Department of Environment and Agriculture, Curtin University, Bentley, WA 6845, Australia.
authors.forename: Tegan K
authors.initials: TK
authors.lastname: Douglas
authors.affiliation: Department of Environment and Agriculture, Curtin University, Bentley, WA 6845, Australia C.Cooper@curtin.edu.au.|School of Animal Biology, University of Western Australia, Crawley, WA 6009, Australia.
authors.forename: Christine E
authors.identifier: 0000-0001-6225-2324
authors.initials: CE
authors.lastname: Cooper
authors.affiliation: Department of Environment and Agriculture, Curtin University, Bentley, WA 6845, Australia.|School of Animal Biology, University of Western Australia, Crawley, WA 6009, Australia.
authors.forename: Philip C
authors.initials: PC
authors.lastname: Withers
mesh_terms: D000818:Animals; D001481:Basal Metabolism; D001831:Body Temperature; D001833:Body Temperature Regulation; D046109:Passeriformes / Q000502:physiology*; D012621:Seasons; D064348:Torpor
keywords: Body temperature; Evaporative water loss; Heterothermia; Metabolic rate; Respirometry; Temperature telemetry