Bird energetics: effects of artificial radiation.

Radiant energy reduces oxygen consumption in birds; this reduction is correlated with feather color, being greater in dark birds (26 percent reduction) than in white ones (6 percent reduction). With radiant energy (basking), the cow-bird effectively increased its insulation, thus shifting the lower end of the zone of thermal neutrality down by as much as 10 degrees C (35 degrees to 25 degrees C).