Behavioral thermoregulation: orientation toward the sun in herring gulls.

Orientation toward the sun combined with postural changes minimized the net radiation gain on the adult herring gull during the breeding season. The decrease in absorbed solar radiation was due to reduced surface area exposed to direct sunlight and to reduced absorptivity since, when the bird orients toward the sun, the angle of incidence is such that only the white surfaces receive direct sunlight. At low wind velocities (0 to 0.6 meter per second) and ambient temperatures above the lower critical temperature, the birds rotated 180 degrees during the day, always facing the sun.