Energetics of East African Pycnonotids 1

Rate of oxygen consumption was measured in five bulbuls (Family Pycnonotidae) from western Uganda to evaluate whether this group is indeed characterized by the very low basal rates of metabolism previously reported. For three of these species, body temperature and rate of metabolism were measured as a function of ambient temperature from 10°C to 35°C. In these species body temperature was highly variable, and declined with ambient temperature in Andropadus virens. Such variation, in conjunction with behavioral adjustments, may reduce heat loss at low ambient temperatures. Body mass accounted for 98 percent of the variation in the basal rates of metabolism presented here. Basal rates in these species ranged from 81 to 90 percent of values predicted by the Aschoff–Pohl relationship for passerines, whereas previous measurements ranged from 56 to 72 percent of predicted values. This difference may reflect differences in species or measurement techniques, which, if the latter, suggests that the reduction in metabolic rate in this family may be less than originally thought. These data underline the importance of continued data collection on the metabolism of tropical birds, few of which have been measured to date.