The world's largest reindeer herd is dying off at an alarming rate

Here's some cheerful Christmas news — the world's largest wild reindeer herd is experiencing a sharp decline, dropping 40% since 2000, the BBC reported on Tuesday. At its peak in 2000, the herd, which inhabits Russia's northern Taimyr Peninsula, numbered a million. Now, it's down to just around 600,000, according to new research.

The herd is being affected by both increasing human development in the area and rising temperatures, the BBC reported, which are forcing the herd to travel farther than ever in its yearly migration to cooler spots.

"They now have to travel much longer distances to reach those areas with their newborn calves, and that means there is an increase in calf mortality," Andrey Petrov, of the University of Northern Iowa's Arctic Center, told the BBC.

Petrov also said that rivers in the herd's home territory are growing, making them harder and more dangerous for the reindeer to cross. And the problem isn't just limited to the herd in the Taimyr Peninsula. "We are also seeing this with other wild reindeer declining rapidly in other parts of the world," Petrov said.

And the decline in reindeer populations isn't just sad news for Santa — reindeer are actually a vital part of the Arctic ecosystem and vital to the survival of the humans who rely on them for their livelihood.

"Thousands and thousands of people rely on wild reindeer," Petrov said. "It is the basis of their subsistence economy. So it's about human sustainability too."