Soon after, the bears enter artificial dens made of concrete and filled with hay for warmth and comfort. They do this when the weather starts turning cold in October, because in the wild, a declining supply of food is one factor that triggers hibernation. To study hibernation, the researchers begin by reducing the amount of food the animals get. “Often, we could show them what we wanted them to do just once, and they would get it from then on. They used dog-training techniques to teach the cubs how to sit, lie down, and tolerate medical tests. In their facility in Pullman, the researchers raised the animals. Two grizzly cubs play in a pool at the WSU Bear Center. Full-grown adult females weigh up to 450 pounds. Bears weigh about 5 pounds at that age, Nelson says. In 2001, Nelson and her colleagues decided to try a new approach: They adopted two 4-week-old captive female grizzlies, just as the cubs were starting to open their eyes. But these drugs slow the heart, among other effects, masking the animal’s natural state. Researchers have tried using anesthesia to sedate wild bears before collecting measurements. Wild grizzly bears, however, are not known for their cooperation skills. These kinds of tests require that an animal sit still for at least 20 minutes at a time. Previously, researchers had to trap the bears, put heart monitors on them, and attach tracking collars so they could retrieve the monitors later.īut to get more detailed information, today’s researchers need to monitor an animal’s heart with special equipment. ![]() Studying the hearts of hibernating wild grizzlies isn’t easy. “Why don’t the same kinds of stresses that would kill us affect these bears?” Nelson asks. In fact, a person with a heart rate that low would die. Such a slowly beating heart is a sign of major stress in a human. But how can a bear’s heart rate stay so low for so long without causing any permanent damage to the animal? It’s a question that scientists would like to answer. Scientists have long known that a grizzly’s heart rate drops to between about 5 bpm and 25 bpm during hibernation. Lynne Nelson and colleagues at the WSU Bear Research Center have trained grizzlies to cooperate in experiments. Over the winter, they lose about 30 percent of their body weight. They continue to move around, but move more slowly. During hibernation, the bears don’t sleep all the time but they do stop eating, drinking, and going to the bathroom. An average grizzly’s heart runs between 70 and 90 beats per minute (bpm)-but only in the summer.Īs winter approaches, grizzlies settle down in protected dens where they will hibernate for 4 to 6 months. An average human heart beats between 60 and 100 times per minute. Heart rate is one thing people have in common with grizzly bears. And other research with the eight or so captive grizzlies at WSU’s Bear Center might help scientists understand and protect bears in the wild. For years, she has been documenting some remarkable changes in the bears’ heart activity during hibernation.īecause bear hearts work like human hearts do, Nelson hopes her findings might one day help doctors better treat heart problems in people. Such odd, babylike behavior among adult bears is not the only thing that makes grizzlies so interesting, Nelson says. Now, years later, the grown-up captive bears still act the same way during hibernation, possibly because they feel safe and are free from the stress of having to defend themselves and hunt for food, as they would in the wild. ![]() “I didn’t know if they had forgotten us, if they would be fearful or hungry, or wonder why we didn’t bring a big load of food.”Īs soon as she and her colleagues walked into the den at WSU’s fenced-in Bear Center, however, they were surprised to find that the resting bears acted just like cubs: They licked the researchers’ faces and tried to sit in their laps. “I didn’t know what to expect,” says Nelson, a veterinarian and heart specialist at Washington State University (WSU) in Pullman. They weren’t fully grown, but they were definitely big enough to hurt her. And each young-adult animal weighed more than 150 pounds. The captive bears had known her since they were babies, but they hadn’t eaten in weeks. ![]() The first time Lynne Nelson entered a den of hibernating grizzly bears, she felt a little nervous.
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