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In August, a lighting strike killed more than 300 of the animals in Norway, only a month after thousands of reindeer in Russia died from an anthrax epidemic. In 2013, around 61,000 reindeer starved to death on Russia's Yamal Peninsula after rare Arctic rains cut off their food supply.

Now scientists say reindeer are physically shrinking as climate change disrupts their diets of grasses, mosses and lichens.

Over the last 20 years, the weight of adult reindeer in Norway has declined by 12 percent, according to ecologists from the U.K.'s James Hutton Institute, the Norwegian Institute for Nature Research and the Norwegian University of Life Sciences.

Reindeer born in 1994 weighed 55 kilograms, or 121 pounds, once they reached adulthood, the ecologists found. But reindeer born in 2010 only weighed about 48 kilograms, or 106 pounds, as adults.

Researchers presented their findings Monday at the British Ecological Society's meeting in Liverpool, in an update to their paper published earlier this year in Global Change Biology.

The team had studied reindeer on Norway's Svalbard archipelago during a period of noticeable summer and winter warming in the Arctic.

Steve Albon, the study's leader and a professor at the James Hutton Institute, said he believed that several factors -- all connected to human-cased climate change -- may be responsible for making the reindeer lighter and smaller.

Warming winters mean Svalbard is getting more rain. When rain falls on the snow and freezes, reindeer can't push the snow aside and reach the grasses underneath. Snow typically covers the ground in Svalbard for eight months each year, meaning reindeer are increasingly cut off from their food supplies for longer stretches of time.

Reindeer populations are also rising due to warmer summers. In June and July, when grasses typically grow, the pastures are becoming more productive. Female reindeer start gaining weight in the autumn and conceiving more calves, boosting competition for food and further straining the food supply.

"The implications are that there may well be further smaller reindeer in the Arctic in the coming decades but possibly at risk of extensive die-offs because of increased ice on the ground," Albon said in a statement.