Biological rhythms in reindeer

Abstract

Reindeer display numerous biological rhythms that prepare them for predictable changes in their environment. This form of biological timing generally results from an interplay between endogenous clocks and ambient signals of which the daily light-dark cycle is the most pronounced. Living at high latitudes, reindeer are exposed to extreme photic conditions throughout the year. As a consequence, they seem to have developed a form of biological timing which involves a reduction in the activity of endogenous clock mechanisms.