CIRCADIAN METABOLIC AND THERMOREGULATORY PATTERNS OF RED-BILLED WOODHOOPOES (PHOENICULUS-PURPUREUS) - THE INFLUENCE OF HUDDLING

Circadian rhythms of metabolic rate and body temperature were measured in groups of huddling and solitary red-billed woodhoopoes (Phoeniculu s purpureus) as a function of ambient temperature. Basal metabolic rat es were 30-60% lower than those of similar-sized birds of other specie s. As a consequence, circadian amplitudes of T-b and VO2 fluctuation b etween the rest and activity phases of non-huddling birds were also la rger than expected. Circadian rhythms of metabolism save huddling and non-huddling woodhoopoes 19-34% of their potential daily energy expend iture. Birds huddling in groups conserved 12-29% of the daily energy e xpenditure of non-huddling birds at ambient temperatures of 20 degrees C and below. However, at 30 degrees C huddling birds used c. 12% more energy than non-huddling birds. The various avenues of energy conserv ation employed by woodhoopoes are suggested to be beneficial in: a) au gmenting the proximate benefits of cooperative breeding; and b) optimi zing fitness in the drought-prone sub-Saharan savannahs which are heav ily influenced by the El Nino Southern Oscillations.