Circannual rhythm

A Circannual rhythm is a biological rhythm that occurs on an annual basis, even in the abscence of environmental cues. So for example migratory birds kept in controlled conditions without seasonal cues still exhibit seasonal variations in behavior reflecting the underlying rhythm .

There are many different examples of circannual rhythms including:
 * Animal migration patterns eg butterflies, whales
 * breeding cycles of reproductive activity in ungulates
 * hibernation cycles in squirrels
 * pupation rhythm in carpet beetles

Species living outside of the equatorial zones employ the seasonal changes in the daily pattern of daylight/night, as the major synchronising signal for circannual rhythms.