What mother doesn’t love a bath after a hot day with the kids?
Even grizzly bear sows seek out a soak, especially when nursing cubs of the year. A new study by University of Idaho graduate student Savannah Rogers and Associate Professor of Wildlife Sciences Ryan Long documented the bears’ use of ponds and pools in Yellowstone National Park.
“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. Those “bathtubs” include natural depressions containing water that are deeper than the wallows commonly used by ungulates such as elk. Bears appear to prefer watering holes where they can fully submerge.
Their study was published in Functional Ecology, a journal of the British Ecological Society, and involved a collaborative team of researchers from the U of I, Washington State University, the University of Wisconsin-Madison and the U.S. Geological Survey. It looked at how the risk of heat stress from a warming climate might affect milk production in grizzly bears. It also investigated how bears respond, including their use of soaking pools.
“We found that the activity level of lactating female grizzly bears was much more limited by heat than the activity of non-lactating females, and that this disparity increased in a warmer climate scenario,” Long said. Nursing mammals’ body temperatures tend to be higher than that of females without young. Finding ways to cool off could increase milk production in bears and improve the chances their cubs survive, he said.
Using computer models, the researchers sought to predict the potential effects of a changing climate on female grizzlies with versus without cubs. They found that although heat was not the most important factor influencing the distribution of bears across the Yellowstone landscape — elevation and distance to roads were most important — it had a greater effect on the behavior of lactating than non-lactating females, and access to pools of cool water was an important mechanism for relieving heat stress.
“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.