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Study: Overheated grizzly bears, particularly pregnant ones, love a cold bath

Overheated grizzly bears, particularly pregnant ones, love a cold bath.

Those are the findings from a study led by University of Idaho graduate student Savannah Rogers and associate professor of wildlife sciences Ryan Long. Their research, published in Functional Ecology, shows that grizzly bears in Yellowstone National Park bathe in cool water to prevent overheating.

“We show that behavior is already an important strategy for grizzly bears to avoid heat stress and will only become more important as temperatures rise,” said Rogers in an email.

The conclusion, while intuitive, sheds light on grizzly bear behavior made famous by National Geographic cameras in 2016. The study provides a glimmer of hope for a famously heat-sensitive species staring down the overheated barrel of climate change.

“The story isn’t so much that heat is hard on lactating bears and it’s only going to get harder as it warms up,” Long said. “Those two things are true, but the real punch line is they’ve figured out a way to overcome that.”

Taking a cool bath is no minor benefit, particularly for pregnant bears. In fact, the cool baths “increased the number of hours during which lactating females could be active by up to 60% under current climatic conditions and by up to 43% in the future climate scenario,” according to the study.

That’s a significant advantage, especially for a large mammal like a grizzly bear.

“Large-bodied animals like grizzly bears are really well adapted to cold temperatures, but they don’t do well with the heat,” Long said. “They have a really hard time dumping heat.”

Researchers gathered the biometric data – including body mass, fur depth and density – from captive bears at Washington State University’s Bear Center. They looked at habitat information – forage cover, humidity, temperature precipitation and topography – for wild bears in Yellowstone.

Using a mathematical model, researchers combined these variables to see “what the heat balance looks like for the bear under different conditions,” Long said.

“Bears are nothing if not behaviorally flexible,” Long said. “This is a pretty interesting strategy to overcome what would be a pretty significant obstacle.”

Because female grizzly bears are the primary driver for robust grizzly bear populations, any behavioral adaptation that allows them to survive warmer summers is important information for wildlife managers, Rogers said.

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