Communal Cavity Roosting in Green Woodhoopoes: Consequences for Energy Expenditure and the Seasonal Pattern of Mortality

Green Woodhoopoes (Phoeniculus purpureus) roost in cavities in groups throughout the year. It has been proposed that the energy savings achieved by roosting with conspecifics in a cavity could enable birds in poor body condition to remain normothermic during inclement weather. We tested the hypothesis that woodhoopoes conserve energy by roosting with conspecifics in cavities and found that a woodhoopoe roosting with four conspecifics can reduce its nighttime energy expenditure by 30% or more when the minimum ambient temperature is about 5°C. In areas where nocturnal temperatures sometimes drop below freezing, such energy savings are associated with mortality patterns among adults during winter. Our data support the idea that energy considerations may have been important in the evolution and/or maintenance of sociality in this species.