Yaks Climbing Higher Due to Climate Change

High on the Tibetan Plateau of Central Asia, you'll find the largest remaining population of wild yaks (Bos mutus). This long-horned, shaggy creature has persevered through more than a century of poaching, habitat loss, and competition with domestic yaks and their human herders.But now, these large black bovids are facing another challenge: climate change. The Tibetan Plateau (map) is experiencing an accelerated rate of rising temperatures—about double the rate seen in most of the rest of the world. And with that comes changes in precipitation patterns—including less snow, which is how the animals get their water

So in the winters of 2006 and 2012, scientists traveled to this region, sometimes called "the roof of the world," to see how male and female yaks are coping with the impacts of climate change at elevations over 15,000 feet (4,800 meters).

"Many people who are interested in climate change focus on how species will be redistributed in space and in time, where they'll go, but very few have studied potential mechanisms for change," said Joel Berger, lead author of the study and a senior scientist for the Wildlife Conservation Society.

"We focused on the two sexes and asked the question, Which of the two is more likely to be impacted?"

The short answer: Females, which are 20 times more likely to be found near snow patches than are males, according to the scientists' surveys of yak populations and their proximity to glaciers.

That's likely because females lactate through the winter, and have to drink more water from snow patches in order to produce their milk, said Berger, who is also a National Geographic grantee and professor at the University of Montana.

That means mothers may need to go to greater lengths to adapt—including climbing steeper and riskier mountains to find snow.

In the past, herds of both male and female yaks—which typically come together only to mate—could be found scattered across the region's valleys, flat areas, and mountain slopes. But this is not true of modern yaks, whose females live in higher elevations.
Berger suspects this is a legacy effect, or a leftover behavior from the days when poaching was so bad that it was dangerous for the yaks to graze in more easily accessible flatlands.

"There's some evidence for this in other species," said Berger. "Elephants are the particularly notable one, where decades after being poached they still show historic memory of being hunted."

It's still unclear why only the females seem to live the high life. However, it's possible that at one time males were also more likely to be found on steep slopes, but that they've somehow returned to their historic behavior more quickly.