Energetic Relationships of a Very Small Passerine Bird

Abstract

The oxygen consumption of postabsorptive Black-rumped Waxbills (Estrilda troglodytes) ranged from 3.5 to 3.9 cc. Oa/gm./hr. in the zone of thermal neutrality (approximately 28” to 35” C.), to 14.5 cc. Oa/gm./hr. at 1.8” C. The thermal con- ductance value of 0.40 cc. 0s (gm./hr./°C.)-l is among the highest recorded to date, as would be expected for a bird this small (average postabsorptive weight, 6.1 gm.). Evaporative water loss increased with increasing ambient temperatures, with values ranging from 1.6(?) to 18.4 mg. HsO,/gm./hr. at temperatures of 5.8 to 38.6’ C., re- spectively. Maximum recorded water loss values were equivalent to a loss of 44 per cent of the body weight per 24 hours. The Black-rumped Waxbill is unable to dissipate more than 50 per cent of its metabolic heat through evaporative cooling in the temperature interval studied. Heart rates of 500 to 540 beats per minute, and breathing rates of 135 to 140 breaths per minute, in the thermoneutral zone, are consistent with similar measurements from other small birds and mammals.