PARIS • If Santa is recruiting helpers to haul Christmas presents around the world this year, he had better take a few extra. That is because, researchers warn, reindeer are shrinking.

Over the past 16 years, the weight of adult reindeer in Svalbard in the Norwegian Arctic has dropped by 12 per cent, likely due to global warming, according to findings presented to a meeting of the British Ecological Society (BES) in Liverpool yesterday.

By the time they reached adulthood, reindeer born in 2010 weighed just over 48kg, compared to 55kg for those born in 1994.

"Twelve per cent may not sound very much, but given how important body weight is to reproduction and survival, it's potentially huge," said study leader Steve Albon of the James Hutton Institute in Scotland.

Previous research showed that when the average adult weight in April is less than 50kg, the population as a whole declines, he added.

Professor Albon and his fellow researchers blame climate change. Scientists say land surface temperatures in the Arctic were about 2.8 deg C higher last year than when record-keeping began a century earlier.

Warmer winters mean more rain, which falls on snow and freezes, the BES study says.

The ice prevents reindeer from getting to the lichen which is the bulk of their winter diet and for which they forage in the snow. Lichen are complex organisms comprised of a fungus living in symbiosis with an alga or bacterium.

"The reindeer starve, aborting their calves or giving birth to much lighter young," said the BES.

Reindeer numbers have risen in the past two decades, so greater competition for food likely also contributed to their smaller size. This meant there could be more but smaller reindeer in the decades to come, "possibly at risk of catastrophic die-offs because of increased ice on the ground".

The team has tracked Arctic reindeer since 1994.

AGENCE FRANCE-PRESSE