Rubba-Dub Dub

Cooling Baths Help Grizzlies
Avoid Stress Caused by Heat

Taking a bath to relieve stress isn’t unique to humans. Bears do it too, and although they appear to luxuriate in taking a dip, it likely functions to help them cool down and conserve energy, researchers at the University of Idaho learned.

As the climate warms … access to cool water will likely become increasingly important.Ryan Long, Ph.D.,
associate professor
of wildlife sciences

In a study led by U of I graduate student Savannah Rogers and Associate Professor of Wildlife Sciences Ryan Long, researchers found that grizzly bears in Yellowstone National Park take cool water “baths” to help prevent overheating.

“Because body temperature of mammals rises during lactation, bath-taking by female grizzly bears in the park may help enable increased milk production and ensure offspring survival,” according to the findings published in Functional Ecology, a journal of the British Ecological Society.

A team of researchers from U of I, Washington State University, the University of Wisconsin-Madison and U.S. Geological Survey studied how the risk of heat stress was influenced by activity and milk production in grizzly bears. The team also evaluated the importance of bath-taking, or submerging in cool water, for alleviating heat stress.

“We found that the activity level of lactating female grizzly bears was much more limited by heat than the activity of non-lactating females,” Long said. “This disparity increased in a warmer climate scenario.”

Scientists have known that bears, including grizzlies and black bears, like to submerge in cool water on hot days. Using Yellowstone National Park as an outdoor laboratory, National Park Service researchers observed bath taking on trail cameras at spring-fed sink holes in the park.

Rogers, who earned her master’s degree in bioinformatics and computational biology, saw the images taken by park service scientists and had an aha moment.

What if there is more to bear baths than just a bunch of grizzlies having a pool party?

Rogers constructed computer models to solve the question. She found grizzlies use baths to cool down in times of heat stress from activities such as foraging and raising cubs.

Then, using computer models, the researchers sought to predict the potential effects of a warming climate on female grizzlies with cubs.

“We found that the use of ‘bathtubs’ by female bears to cool could help them overcome constraints on activity and milk production imposed by heat, even in a warmer climate,” Rogers said.

The “bathtubs” in the park are natural depressions containing water that are deeper than wallows commonly used by elk. The tubs allow bears to fully submerge.

“Our research suggests that as the climate warms, grizzly bears can avoid heat stress through behaviors such as ‘bath taking,’ and thus access to cool water will likely become increasingly important,” Long said.

The research doesn’t make assumptions about the importance of cool water baths for perpetuating the species, but the implications are real.

“We know that females with cubs are drivers of population dynamics, and so we know the impact of climate on females with cubs is really important,” Rogers said. “Looking at this population going forward, we don’t know exactly what it will mean if temperatures get warmer or how else bears might have to change their behavior to offset that extra heat.”

Article by Ralph Bartholdt, University Communications and Marketing.

Photo by National Park Service.

Published in March 2021.