If global warming continues, some reindeer may go down in history — and never come back. An archaeologist at the University of Washington, Donald Grayson, believes those...

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If global warming continues, some reindeer may go down in history — and never come back.

An archaeologist at the University of Washington, Donald Grayson, believes those reindeer, or caribou as they’re also known in North America, could disappear from the southern borders of their habitat. On this continent, that could spell the end for herds roaming mountains in Washington, Idaho, southern British Columbia and Alberta.

The woodland caribou, which lives in the mountains in small herds, is considered the most endangered large mammal in the Lower 48 states and can be found only in the Selkirk Mountains in northeastern Washington and northern Idaho. In the 1980s, their numbers fell below 30; the Washington state Department of Fish and Wildlife has since transplanted 60 caribou into the mountains.

“With global warming, those animals are going to be in real trouble,” Grayson says.

The study, which he wrote with paleontologist Françoise Delpech, is expected to run in the April issue of Conservation Biology, an academic journal.

Grayson is not too worried about the survival of other reindeer species closer to the North Pole in such places as Scandinavia, Russia and Canada. Those species, unlike the ones in Washington state, live on barren ground and migrate in big herds.

“The elves and Santa should be fine,” he said. “But if Santa were drawing a sleigh from the southern edges, he’d have to look a lot farther north.”

Grayson based the study on his discovery that reindeer disappeared from southwest France 11,000 years ago because of rising summer temperatures.

Grayson studied reindeer remains excavated in Grotte XVI, or Cave 16, in southwest France. Modern humans, and Neandertals before them, inhabited the cave. Based on the reindeer they hunted and brought back to the cave, he tracked the population count.

He found the reindeer disappeared twice from southern Europe, where they lived in Italy, France and Spain. They became extinct the first time 125,000 years ago after an ice age ended. But they returned to the area 16,000 years ago when another ice age began, and disappeared again 11,000 years ago.

In North America, reindeer lived as far south as what is now Mississippi during that time period.

Grayson originally looked at the bones to compare the hunting and eating habits of Neandertals and modern humans. Archaeologists have been digging through Grotte XVI for the past 20 years. In 9 feet of earth, history stretches back 40,000 years.

It was previously believed that modern humans replaced Neandertals because they were more sophisticated hunters. If so, the Neandertals would have eaten smaller mammals that were easier to catch.

However, Grayson found the fossils didn’t show significant changes. The Neandertals ate reindeer just like the modern humans did, and their butchering techniques were quite similar.

So Grayson turned to the weather. He found climate data from a separate study on pollen, in which scientists reconstructed weather conditions tens of thousands of years ago by studying layers of pollen that had collected at a lake bottom.

It became clear that global warming had directly affected reindeer population, he said.

When summers heated up, reindeer population decreased. When summers cooled, the reindeer population increased.

About 11,000 years ago, the reindeer disappeared from the cave. Grayson expects the same thing would happen to reindeer in the southern edge of its North American habitat as summer temperatures rise.

Perhaps it’s because reindeer have very few sweat glands, or maybe because they don’t shed their heavy pelts during the summer. Grayson isn’t sure. He hopes biologists will study those possibilities.

While his research concerns reindeer living to the south, previous studies indicate global warming has hurt reindeer population in the north as well. As the winters heat up, snow thaws and refreezes, forming ice crusts the animals must dig through to find food.

It’s always possible if the reindeer become locally extinct, they could come back when the next ice age begins, Grayson says.

After all, the reindeer did return to southwest France after a 109,000-year extinction. And it’s only been 11,000 years.

Sharon Pian Chan: 206-464-2958 or schan@seattletimes.com