Arctic reindeer threw the clock out the window
Animals in the extreme north no longer follow circadian rhythms due to the abnormality of the light they receive. Midwinter brings round-theclock darkness, and in summer the Sun doesn’t set. While this happens predictably every year, daily rhythms get lost in the constant light conditions. Polar animals can’t rely on regular changes in light cues to dictate what time to get up and go back to sleep, so instead they have simply given up following a body clock at all.
Reindeer in northern Norway have been found to forage around the clock and take short naps in between grazing whether they are in blazing sunshine or complete darkness.
Knowing the time of day may not be important to reindeer, but they still need to keep track of the seasons in order to synchronise the herd’s breeding to ensure enough food availability for nursing mothers. It’s still a mystery as to how reindeer know when to reproduce, but it’s possible that fluctuations in the sleep hormone melatonin kick in during autumn and spring.
Arctic reindeer mainly eat lichen and moss, but they are also known to feed on lemmings, Arctic char fish and eggs