How do reindeer spend the winter school night?

In the far north, at the Arctic Circle, the sun shines during the six months of summer and dives throughout the six months of winter, creating days of 24 hours full of sunshine or completely darkness. The reindeer abandoned the familiar 24-hour biological rhythm to accommodate it.

Conventional dynamics and plants set biological alarm clocks according to the sun's rise and sunset. In humans, this endogenous cycle begins when we wake up, lasts when we are active and closed when sleep comes.

Many animals can maintain their biological rhythms from sudden changes, such as when a migratory bird flies to the region with longer hours of sunshine per day. But very few species keep the rhythm when the sun shuts off or fades, like when the season changes on the North Pole.

" Maintaining a rhythm requires a 'strong' biological clock - the watch can run independently from the outside, " said Karl-Arne Stokkan from Tromsø University, Norway. " We think reindeer, like other Arctic animals, possesses a weak watch ."

What did reindeer do?

Stokkan's group monitored the daily behavior and feeding of two reindeer species living at two different latitudes: Rangifer reindeer species tarandus tarandus on the Norwegian continent (70 degrees north latitude) and Svalbard R reindeer .t. platyrhynchus at 78 degrees north latitude.

At these latitudes, reindeer always experiences winter in the twilight, and the sun never dives in the summer. In spring and autumn, the transition between these two types lasts several weeks, with about 18 weeks each year having distinct day / night cycles.

In those few weeks, both species follow the rhythm 24 hours a day, Stokkan said. But in the summer, they lose the rhythm of day and night. The Svalbard reindeer lacks the rhythm in winter.

Because there is no body alarm every day, Stokkan assumes that they sometimes take a nap (though very rare) alternating between stressful activities.

In this case, owning a weak biological clock seems to benefit them.

According to Stokkan, running in the winter and summer seems to be dominated by the digestive system rather than the sun, and caribou eating whenever the weather permits. This free diet is best suited to the type of digestion that supports the bacteria of reindeer and other nail species.

Measures to reduce the effect of the biological clock may also increase the ability to respond and speed up adaptation to animal changes in the morning / evening cycle. It may also play an important role for migratory birds and hibernating animals.