Hungry Grizzly Bears Are About To Start Waking Up in Yellowstone

Hungry grizzly bears in Yellowstone National Park are about to emerge from hibernation and attention is now focused on spotting the first individuals to emerge from their dens.

Grizzly bears spend much of the winter in dens, slowing their metabolism down so they can survive with little activity during the seasonal shortage of prey.

"Grizzly bears are true hibernators and stay in a winter den for five to six months," Frank T. van Manen, a supervisory research wildlife biologist with the U.S. Geological Survey told Newsweek. "During hibernation, they reduce their metabolism to about 25 percent of active metabolism and heart rate by 20 percent to 45 percent during denning. However, the decrease in body temperature is only moderate (36 to 46 degrees Fahrenheit)."

When they emerge from this deep sleep, bears are hungry and typically head for low ground as they look food to replenish their dwindling body mass.

"There is not much food available upon emergence from the winter den so they initially look for easy food sources such as winter-killed ungulates [like elk]," van Manen said. "Many bears still rely on their fat reserves upon den emergence, and only start gaining weight again when more foods become available later in the spring."

Male grizzlies in Yellowstone tend to emerge in March. Last year, the first Yellowstone grizzly of spring was spotted on March 16. In 2020 the first was seen on March 7. Female grizzly bears with cubs usually emerge around April when their cubs are sufficiently grown.

The latest count of grizzly bears in 2019 showed there were 728 individuals living in the greater Yellowstone ecosystem.

Grizzly bears dig or use natural features like caves for their winter dens, which are insulated by snowfall found at the higher altitudes. Climate change however is causing reduced snowfall in Yellowstone and throughout much of grizzly bear range in North America, impacting their winter and spring habits.

Restrictions on visiting some areas of the park where deer and elk carcasses are most likely to attract grizzlies in spring are enforced from March 10. Park authorities say they hope to minimize interactions between bears and people this way.

Park officials say visitors should carry bear spray and keep at least 100 yards away from any bears they encounter.

"When in grizzly bear country, people should always be aware of bear activity and be prepared to reduce the chance of an encounter, and know how to respond when an encounter does occur," van Manen said. "The risk of encounter is actually a little less during this time of year because bears emerge from their dens over an extended time period and do not move around as much as later in the season; females with new-born cubs fourth week of April, other females third week of April; and males fourth week of March."