Bears Are Waking Up – And They're Hungry

As the bracing chill of winter subsides into spring, animals across the country are crawling out of hibernation, ready to eat.

The first grizzly bear in Yellowstone National Park to emerge was spotted on March 7, with thousands of other bears slowly following suit.

"Bears in Minnesota come out of the dens in late March and early April, but do not typically leave the den area until mid-April," Andrew N. Tri, the Forest Wildlife and Populations Research Group project leader at the Minnesota Department of Natural Resources, told Newsweek.

"Males and solitary bears seem to leave first. Females with cubs remain until the cubs are strong enough to climb. We don't know the mechanism as to why they leave the dens, but green-up doesn't typically happen until mid May, so there is some time in which bears do not have access to much food and continue to rely on their fat reserves," Tri said.

The end of hibernation is triggered by the warming of the air in the spring. Bears in the south tend to emerge earlier than those in the north as the temperature gets warmer first.

"The time of emergence is highly dependent on location," Øivind Tøien, a research assistant professor at the University of Alaska, Fairbanks Institute of Arctic Biology, told Newsweek. "For instance bears in interior Alaska are known to come out later than coastal bears. Black bears in the southern U.S. might just have a very short period of denning. Lactating sows with cubs born during hibernation might also come out a little later or at least stay in the denning area longer."

Hibernation is a period of torpor and low metabolic activity that many mammals undergo during the winter months. They experience low body temperature, slower breathing and a lower heart rate for several weeks.

"Hibernation in bears and also in smaller mammals is mostly about surviving through a period with low food availability," Tøien said. "The combination of accumulating fat reserves when food is available and then suppressing the metabolic rate during the winter allow them to survive through the winter on these limited fat reserves without burning protein and loosing muscle mass."

Before hibernation, the bears gorge themselves on food, with grizzly bears gaining up to 3 pounds in body weight each day.

"In Minnesota, bears really only have abundant foods for 3.5 months out of the year. After mid October, very little food remains on the landscape so bears head to dens. If there continued to be food out all year round, I would imagine that less bears would actually hibernate and only females that are pregnant would enter dens to give birth," Tri said.

It might be natural to assume that the bears would be ravenous when they emerge from their dens, but in reality, they actually act more sluggish as they wake up.

"So at the time they emerge from their dens, they are not in a fully recovered non-hibernating state," Tøien said. "Since we have been studying captive bears only here, it is hard to evaluate behavioral risks based on our observations. My experience is that they rather tend to spend a lot of time resting in this early phase after they emerge, which lines up with their metabolic state."

The bears tend to remain in their dens for a long time after they awaken, longer if they are females who have given birth to cubs over the winter.

"American black bear metabolism speeds up, they start to stretch their muscles, their heart begins beating regularly and they begin breathing normally," Tri said. "They do not wake up very hungry. For females with cubs, they remain at the den area until the cubs are old enough and strong enough to climb trees."

Therefore, the bears should not be any more dangerous than they are usually when the emerge.

"They are not inherently dangerous at all. It takes time for them to want to eat again, and they will start eating green vegetation (grass, clover, wetland plants) or whatever acorns lay on the ground and did not rot over winter. They will occasionally consume garbage or birdseed that humans fail to properly secure in the spring," Tri said.

With the effects of climate change encroaching on the U.S., experts worry that bear hibernation may be impacted.

"Climate could alter the time of emergence. In Alaska emergence might be related to the time when temperatures go above freezing," Tøien said. "Then melt water can enter the dens, making it uncomfortable and cause them to come out. This seems also to be the case in studies of European brown bears in Scandinavia. Theoretically if they are forced out of their dens earlier by warming climate, but green-up does not follow accordingly, they could get in trouble energetically, but we do not know if this happens."

However, bears are adaptable to changes in their environment, so there may not be any major impact on any of the U.S. species.

"We don't really know what will happen to bears with climate change, but it is important to remember that black bears are very adaptable," Tri said. "They exist from the edge of the tundra all the way into central Mexico across a wide varieties of climatic zones."

"They don't hibernate throughout their entire range, but pregnant females will den (not always underground) to give birth and raise the cubs. Some have hypothesized that bears out longer would increase human-bear conflict, but I'm not really sure if that would apply to all areas of bear range."

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