Effects of Wind and Illumination on Behavior and Metabolic Rate of American Goldfinches (Carduelis tristis)

We measured the metabolic rate of active-phase American Goldfinches (Carduelis tristis) with and without illumination at 10°C and four wind speeds. We observed the birds via closed-circuit television. Illumination alone increased metabolism 37%. Metabolic rate increased linearly with activity and wind speed. A decrease in activity as wind speed increased tended to counteract the increase in thermoregulatory metabolism caused by convection, and reduced the slope of metabolism-vs.-wind-speed plots. The increase of metabolism with activity was reduced by the presence of illumination, which suggests relatively more compensation for thermoregulatory metabolism by activity metabolism when illumination is present. Stepwise linear regression was used to correct for nonthermal effects of illumination and wind to improve estimates of their purely thermal effects.