Reindeer maintain circadian rhythm in dark months

Reindeer are able to maintain a 24-hour body clock during days of sustained light or darkness, according to a new research paper.

An international collaboration of scientists from the James Hutton Institute, the University of Veterinary Medicine in Vienna and two Norwegian research institutes measured heart rate, body temperature and activity of reindeer.

While previously it was believed that reindeer would switch to a “free-running mode” in sustained light or dark, researchers found that Svalbard reindeer maintain a circadian rhythm throughout the year, which is weakest when new forage is most plentiful through mid-June to mid-August.

Professor Steve Albon, honorary research fellow of the James Hutton Institute and co-author of the study, said: “Because of how the circadian rhythm is maintained by the night/day cycle, there has been considerable interest in what happens in 24 hours of total darkness during the Polar Night or 24 hours of light from the Midnight Sun.

“How polar animals cope with such extremes and recover from seasonal starvation is fascinating, especially given the impacts of rapid climate change in the Arctic.”

The team also discovered seasonal changes in reindeer heart rate and temperature, with a peak in the short summer growing season, allowing them to eat as much as possible while food is plentiful.

However, global warming is leading to more rain-on-snow events and ice-locked pastures in the Arctic, which cause starvation. Reindeer are essential for transport and food in the Arctic and are one of few species that can provide animal protein to people living in the far north.

The research paper, Circadian rhythmicity persist through the Polar night and midnight sun in Svalbard reindeer, was published in Scientific Reports.