Birds in Winter

AMONG THE MOST SIGNIFICANT seasonal changes birds face in winter is the amount of daylight. Only a few birds, such as Arctic Terns (Sterna paradisaea) and the austral seabirds that migrate over oceans to spend their summer and winter at similar latitudes, enjoy days of equal length most of the year. For birds remaining at high latitudes, the hours of light are vastly reduced for several months, and even the birds wintering near the equator, with a constant maximum of 12 hours of light, see less of the sun than in their breeding range. Birds must adjust their time budget... (pp 149-166)