There are three main seasons in the life of a bear: the active season, beginning in May, a period of intense eating, in late September, and hibernation, from January till spring. Physiologically, the hibernation period is puzzling to researchers. When a bear hibernates, their metabolic rates, as well as the heart rate, drop considerably. It does not urinate or defecate. The quantity of nitrogen in its blood increases sharply, without damaging the liver or kidneys. The animal becomes resistant to insulin but does not experience any fluctuations in its blood sugar levels.
A human experiencing these conditions every year for many months at a time can easily end up with obesity, diabetes, atrophied muscles, or worse, bone loss. However, each spring bears emerge no worse for wear, although a little groggy. “Even when they are very fat, it’s healthy obesity,” said Brian Barnes, who studies black bear hibernation in Alaska. “They don’t suffer from the same kinds of pathologies that occur in people.” A team of Washington State University researchers recently published a study that sought to decipher the underlying process in the cells of hibernating grizzly bears. Researchers took samples from the liver, muscle, and fat of six captive grizzly bears around three times during the year. In the lab, a group of researchers analyzed the DNA to know the changes that occur in the cells throughout the year. “The effect of hibernation on each tissue is different,” said one of the authors of the paper, Joanna Kelley, Evolutionary Biologist, Washington State University. “Hibernation is not just as simple as hibernating and not hibernating. There are transitional things happening throughout the year.” The team of researchers found that the bears’ fatty tissues got changed during hibernation, while the muscle tissue barely changed at all. The muscle cells remained active during the hibernation period.
Hibernation may be something that humans learn to master, fully, or even in part. Meanwhile, wildlife researchers are keen to explore the importance of hibernation for the survival of the animals that already do it.