Ecologists have found that reindeer are shrinking due to the impact of climate change on their food supplies.

Speaking at the British Ecological Society annual meeting in Liverpool on Dec. 12, Professor Steve Albon discussed a study published earlier this year in Global Change Biology that followed reindeer on Svalbard over the course of 20 years.

The study shows that adult reindeers’ weight has declined by 12%. Albon believes there are three factors playing into this all influenced by climate change.

Warmer springs mean more abundant food supply, but more rain in the winters leads to a frozen layer blocking reindeer from food in colder months. This leads to female reindeer having lighter calves or not being able to birth the calves at all. In addition, reindeer numbers have doubled over the past 20 years, so there is now more competition for food.

Albon believes this could be dangerous for the species in the future. Despite the fact there will be more reindeer, the species could possibly be “at risk of catastrophic die-offs because of increased ice on the ground.”

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