Climate Change Is Screwing With The Diet Of Yellowstone's Grizzly Bears


Tom Hale

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

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Grizzly bears photographed by a camera trap in Cooke City Basin, Montana. US Forest Service via UC San Diego

Climate change is transforming the environment of Yellowstone National Park, a place that has stood strong for millennia and remained relatively unchanged for centuries. As the environment shifts, it brings new challenges for its inhabitants, especially its iconic grizzly bears.

A study in the journal PLOS ONE by the University of California San Diego and Unity College has been looking at the diets of grizzlies living around the Cooke City Basin in Montana to see how it's reshaping as Yellowstone's average temperature increases. 


They discovered that many grizzlies continue to rely on whitebark pine seeds as a staple of their diet. Unfortunately, this critical source of food is dramatically declining in the region. Shorter and milder winters are meaning that beetle infestations are becoming more and more common. Rising temperatures are also taking their toll on the region’s cutthroat trout and deer, another primary source of food for the grizzly.

“Whitebark pine trees have declined due to an introduced fungal disease called blister rust, and, more recently, to increased infestation by the mountain pine beetle, which is exacerbated by climate change," study co-author Carolyn Kurle, of UC San Diego, said in a statement. "Such declines further highlight the need to monitor diets of grizzlies as the environment continues to change."

They studied what the bears had been eating by looking at their hair. They used stable isotope analysis, a method often used in conservation and archaeology, which identifies the distribution of certain stable isotopes and chemical elements within chemical compounds of an individual's tissue or bone, making it possible to draw conclusions about their diet and lifestyle.

"Instead of investigating the diets of animals based on what's eliminated (feces), we estimate the importance of major food sources to animals based on what's assimilated into their tissues," said lead author Jack Hopkins. 


Although it showed many bears continue to munch on the dwindling whitebark pine, the evidence suggests that some of the bears are already responding to these new pressures already. Namely, the females are eating more berries and the males eating more meat when they can.

While it seems positive the bears have found a way to acclimatize, it's unclear how this new scenario will pan out. The grizzly bears of Yellowstone have been a source of disagreement among conservationists and politicians, in regards to whether they remain federally protected. One of the reasons grizzlies have remained protected for decades is because it has not been clear how declines in whitebark pine trees impact population trends over the long term.

To reveal the fate of the grizzly bear, scientists simply need to keep their ear to the ground and carry out more research.

Whitebark pine (Pinus albicaulis) in Yellowstone National Park. SueSmith/Shutterstock


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