METABOLIC-RATE AND BODY-TEMPERATURE OF AN AFRICAN SUNBIRD, NECTARINIA-CHALYBEA - DAILY RHYTHM AND THE EFFECT OF AMBIENT-TEMPERATURE

The oxygen consumption ((V) over dot O-2) of the lesser double-collare d sunbird, Nectarinia chalybea, was measured at ambient temperatures ( Ta) from 7 to 35 degrees C. The diel variation in body temperature (Tb ) and wet thermal conductance (C) was also determined. The sunbirds (m ean mass 8.36 g +/- S.E. 0.21 g) showed a pronounced diet cycle of (V) over dot O-2, with a mean reduction of 50% at night. Basal metabolic rate was estimated to be 3.23 mi O-2/g.h, which is 88% of the predicte d value for a passerine bird of this size. There was a mean reduction in Tb of 3.6 degrees C at night. Both day and night values of Tb decre ased with decreasing Ta, as did individual values of C. Winter breedin g in the south-west Cape is energetically stressful for lesser double- collared sunbirds, but they have the physiological capacity to reduce their energy expenditure substantially at night.