Circadian metabolic and thermoregulatory patterns of red-billed woodhoopoes (Phoeniculus purpureus): the influence of huddling

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Abstract
Circadian rhythms of metabolic rate and body temperature were measured in groups of huddling and solitary red‐billed woodhoopoes (Phoeniculus purpureus) as a function of ambient temperature. Basal metabolic rates were 30‐60% lower than those of similar‐sized birds of other species. As a consequence, circadian amplitudes of Tb and VO2 fluctuation between the rest and activity phases of non‐huddling birds were also larger than expected. Circadian rhythms of metabolism save huddling and non‐huddling woodhoopoes 19‐34% of their potential daily energy expenditure. Birds huddling in groups conserved 12‐29% of the daily energy expenditure of non‐huddling birds at ambient temperatures of 20°C and below. However, at 30°C huddling birds used c. 12% more energy than non‐huddling birds. The various avenues of energy conservation employed by woodhoopoes are suggested to be beneficial in: a) augmenting the proximate benefits of cooperative breeding; and b) optimizing fitness in the drought‐prone sub‐Saharan savannahs which are heavily influenced by the El Niño Southern Oscillations.

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