Energetics of communal roosting in chestnut-crowned babblers: implications for group dynamics and breeding phenology.
For many endotherms, communal roosting saves energy in cold conditions, but how this might affect social dynamics or breeding phenology is not well understood. Using chestnut-crowned babblers (Pomatostomus ruficeps), we studied the effects of nest use and group size on roosting energy costs. These 50 g cooperatively breeding passerine birds of outback Australia breed from late winter to early summer and roost in huddles of up to 20 in single-chambered nests. We measured babbler metabolism at three ecologically relevant temperatures: 5°C (similar to minimum nighttime temperatures during early breeding), 15°C (similar to nighttime temperatures during late breeding) and 28°C (thermal neutrality). Nest use alone had modest effects: even for solitary babblers at 5°C, it reduced nighttime energy expenditures by <15%. However, group-size effects were substantial, with savings of up to 60% in large groups at low temperatures. Babblers roosting in groups of seven or more at 5°C, and five or more at 15°C, did not need to elevate metabolic rates above basal levels. Furthermore, even at 28°C (thermoneutral for solitary babblers), individuals in groups of four or more had 15% lower basal metabolic rate than single birds, hinting that roosting in small groups is stressful. We suggest that the substantial energy savings of communal roosting at low temperatures help explain why early breeding is initiated in large groups and why breeding females, which roost alone and consequently expend 120% more energy overnight than other group members, suffer relatively higher mortality than communally roosting group mates.
Department of Biology, University of California, Riverside, Riverside, CA 92521, USA chappell@ucr.edu.
Mark A
0000-0002-3776-5088
MA
Chappell
School of Biological Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia.|Centre for Integrative Ecology, Deakin University, Geelong, Victoria 3217, Australia.
William A
WA
Buttemer
Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn, Cornwall TR10 9FE, UK.|Fowlers Gap Arid Zone Research Station, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia.
Andrew F
AF
Russell
D000818:Animals; D001481:Basal Metabolism / Q000502:physiology; D001947:Breeding; D003299:Cooperative Behavior; D003624:Darkness; D004734:Energy Metabolism / Q000502:physiology*; D009425:Nesting Behavior / Q000502:physiology*; D009517:New South Wales; D010101:Oxygen Consumption / Q000502:physiology; D046109:Passeriformes / Q000502:physiology*; D013696:Temperature
Cooperative breeding; Energy expenditure; Group size; Metabolic rate; Oxygen consumption; Thermoregulatory costs