The rising temperature was cited as the culprit behind the reduced size of reindeers. Based on 16-year survey on the arctic island of Svalbard in Norway, the reindeers inhabiting the area have declined in weight by 12%.

The research, presented at a meeting of the British Ecological Society in Liverpool, explained how the rise in temperatures deprive female reindeers of nutrients during the gestation phases.

The Svalbard ground is typically covered in snow for eight months during the year, thus limiting grass growth to June and July.

As summer temperatures increased, pastures have become more productive. This allows female reindeers to gain more weight by the autumn and therefore to conceive more calves.

However, global warming has resulted to warmer winters, bringing greater rainfall which then freezes when it settles on the snow. This causes the reindeers' food to be locked below. Although reindeers can clear the snow using their antlers in order to access the food below, they cannot break through hard ice.

As a consequence, female reindeers are starved, causing them to abort their calves or give birth to much lighter young.

When the survey began in 1994, the adult reindeers recorded an average mass of 55 kg. However, by 2010, it had dropped to 48 kg.

"The implications are that there may well be smaller reindeer in the Arctic in the coming decades, but possibly at risk of catastrophic die-offs because of increased ice on the ground," said Professor Steve Albon, an ecologist at the James Hatton Institute in Aberdeen.

He said his research shows some critical changes facing the Arctic species. He added that mammals are particularly energy efficient since they have a relatively high surface-area-to-volume ratio.

"While I doubt we will see the extinction of reindeer across their circumpolar range, Santa may need more to pull the laden sleigh," he joked.