Reindeer cope in Arctic dark

22 December 2005

In the Arctic's winter wonderland, animals face constant darkness. We switch on the lights to kick-start our body clocks, but how do polar animals manage without? Reindeer-stalking scientists now know how Santa's friends keep spirits bright.

Antenna investigates...

This story was published in Nature on 22 December 2005.

Image: Nicholas Tyler

Got the winter blues? Spare a thought for the reindeer of the Arctic Circle, where in winter the night never ends. Scientists are just back from a long mission to snowy Svalbard to find out how the reindeer cope.

Winter days are gloomy in the Arctic Circle.

Image: Nicholas Tyler

Where is Svalbard?
Tucked above the Arctic Circle, Svalbard is a group of islands in the Arctic Ocean. Scientists armed with monitoring equipment tracked the reindeer to their home to investigate how they deal with the daytime darkness of the polar winter.
Imagine trying to get close enough to a wild reindeer to attach a collar around its neck. Karl-Arne Stokkan and his team found shooting a sedative dart at each animal was the only way they could strap a monitoring device to six Svalbard reindeer.
The small gadget, called an Actiwatch, measures movement - distinguishing stationary sleep time from active periods.

The scientists attach brightly coloured collars so they can spot the reindeer from a distance.

Image: Nicholas Tyler

Karl-Arne Stokkan, Arctic biology expert, University of Tromso, Norway.

'We sometimes walk for days to reach the right reindeer. To get close enough to fire the darts we have to know how to behave around the animals. Once the Actiwatch is fitted we give an antidote and the animal gets up and walks away.'
Karl-Arne Stokkan, Arctic biology expert, University of Tromso, Norway
After analysing the activity patterns of 'Rudolf' and friends for a year, the scientists made an astonishing discovery. Your timetable for activity and rest is controlled by your body clock, which resets every morning when it gets light. But these reindeer can ignore their internal clock when it suits them.
'The reindeer don't sleep right through the night like we do but have infrequent patches of activity and rest, sometimes with naps. In seasons where it's either permanently dark or light this pattern continues around the clock. We think the reindeer body clock is idling during midsummer and midwinter.'
Karl-Arne Stokkan

During the Arctic summer (top) the Sun never sets. But in winter (bottom) it never rises above the horizon, so animals must live in constant darkness.

Image: Nicholas Tyler

Now we know how Santa's friends keep dashing through the snow in the dark days of a polar winter - but what about Santa himself? The latest sleep research is exploring what keeps human body clocks ticking.
'Human body clocks run on a cycle lasting slightly over 24 hours - 24.4 hours in fact. Light trains this body clock, keeping time with day and night.'
Simon Archer, sleep expert, University of Surrey

Simon Archer, sleep expert, University of Surrey

Image: FreeFoto.com

The rising sun can set your clock each morning, but any artificial ray of light will do it too. Even flicking the switch on a midnight stumble to the bathroom will reset your internal ticker and leave you feeling fatigued.
How does it work? 'One of the main things light does is suppress your body's production of melatonin, the hormone that helps you sleep.'
Simon Archer
But how would you cope visiting Santa during the dark polar winter, when there might not be any light for months? Unlike his reindeer, you'd struggle without artificial light.
'Humans evolved close to the equator, so they've got no evolutionary history of coping with constant darkness. People in polar environments create light-dark cycles all year round using artificial light in the winter and by closing the shutters to block out the light on summer nights.'
Dirk-Jan Dijk, sleep expert, University of Surrey

Dirk-Jan Dijk, Professor of sleep and physiology, University of Surrey

'With reindeer, as the days get dark, their body-clock activity fades. It comes back as soon as the reindeer experience dusk in the springtime.'
Karl-Arne Stokkan
If reindeers' biological clocks take a winter break, perhaps this explains how Santa's friends stay on flying form despite the dark.

Svalbard reindeer are different from the reindeer we're used to. They're shorter and chubbier and grow luxuriously thick winter coats.

Image: Nicholas Tyler

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