Journal
JOURNAL OF EXPERIMENTAL BIOLOGY
Volume 220, Issue 7, Pages 1341-1349Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jeb.154633
Keywords
Temperature telemetry; Heterothermia; Body temperature; Respirometry; Metabolic rate; Evaporative water loss
Categories
Funding
- Holsworth Wildlife Research Endowment
- BirdLife Australia's Stuart Leslie Bird Research Award
- Australian Bird Study Association Fund for Avian Research
- Australian Postgraduate Award
- Curtin Research Scholarship
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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 degrees C that was independent of minimum black bulb temperature. Physiological variables measured in the laboratory revealed that babblers had a lowbasalmetabolic 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 tomeet 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.
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