Abstract:
Basal metabolic rate (BMR) is one of the most widely used
metabolic variables in endotherm ecological and evolutionary
physiology. Surprisingly few studies have investigated howBMR
is influenced by experimental and analytical variables over and
above the standardized conditions required for minimum normothermic
resting metabolism. We tested whether avian BMR
is affected by habituation to the conditions experienced during
laboratory gas exchange measurements by measuring BMR five
times in succession in budgerigars (Melopsittacus undulatus)
housed under constant temperature and photoperiod. Both the
magnitude and the variability of BMR decreased significantly
with repeated measurements, from 0.410 0.092 W (n p 9)
during the first measurement to 0.285 0.042 W (n p 9)
during the fifth measurement. Thus, estimated BMR decreased
by ∼30% within individuals solely on account of the number
of times they had previously experienced the experimental conditions.
The most likely explanation for these results is an attenuation
with repeated exposure of the acute stress response
induced by birds being handled and placed in respirometry
chambers. Our data suggest that habituation to experimental
conditions is potentially an important determinant of observed
BMR, and this source of variation needs to be taken into account
in future studies of metabolic variation among individuals,
populations, and species.
