To face the cold and food scarcity of the winter in the northern hemisphere, they take the team out of the field, spending time without drinking, eating, urinating and defecating. In the case of black bears, this period varies between five and seven months a year. According to a survey by the University of Alaska released in February, the metabolism of this species is reduced to 25% of its capacity, the body temperature drops by an average of 6ºC and the heart rate drops from 55 to just nine beats per minute! Burning stored fat in the body releases the water and few calories it needs to survive. There is also a recycling of nitrous components, such as urea. Combined with the glycerin resulting from the use of fat, these wastes form amino acids that help maintain body proteins.
Nap time
Learn how the animal prepares to disappear from the map for up to seven months
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NORMAL ACTIVITY
This is the “quiet” period, when the weather is favorable, food is available and the animal’s metabolism is running at 100% capacity. In general, it begins at the end of the first month of spring and lasts until mid-summer.
HYPERPHAGIA
The name says it all: it’s time to eat a lot! From mid-summer to a little more than mid-autumn, black bears with unlimited access to food drink at least 30 liters of water a day and store calories (while caloric expenditure remains the same as before).
AUTUMN TRANSITION
Begin to slow metabolism for hibernation. They eat less than in hyperphagia, but water consumption and urination are still high. Your heart rate drops from about 80 per minute to about 50 (and during your 22 hours of sleep a day, it drops to 22 per minute).
HIBERNATION
It can take up to seven months. During the period, the consumption of daily calories, extracted from the fat accumulated in hyperphagia, drops to between 4 and 6 thousand. Metabolism is reduced to 25%. Even the intake of oxygen is greatly reduced: in general, the bear breathes only once every 45 seconds
WALKING HIBERNATION
You know when you wake up and you’re still a little groggy? Imagine after sleeping for months! For about 20 days, bears keep their metabolism below full capacity, even though their body temperature has already returned to normal. It is the adjustment period before returning to regular life.
– (North American Bear Center/Disclosure)
CAFOFO ANIMAL
They overwinter under the roots or at the base of a large tree, under a rock or in a burrow they dig in the ground, at least 0.5 m high and almost 1 m long. The ground and background are lined with branches of vegetation. In very cold regions, they set up the burrow at a point where a lot of snow falls to increase thermal insulation. And they tend to return to the same shelter every winter.
– (North American Bear Center/Disclosure)
EVERY MAN FOR HIMSELF
Bears are essentially solitary, except in the mating season. Or when pregnant bears give birth, usually during hibernation. They stay in the den with the young (between three and six) throughout the winter, nursing them. After hibernation, care for them until they are 2 years old. After that, the little ones have to fend for themselves to get food and set up their own shelter.
WHAT ABOUT THE ZOO?
Far from the natural habitat, the animal loses its cycle
Bears in captivity rarely hibernate, since, depending on the place, it is not cold and food is always available. Incidentally, for this very reason, the panda does not hibernate even in nature: its bamboo shoots do not become scarce with the change of seasons. And, as they live high up in the mountains, if the cold sets in, just look for a milder temperature at lower altitudes.
• Other animals that hibernate: squirrels, groundhogs, bats, hamsters, voles and hedgehogs.
SOURCES Carlos C. Alberts, professor of biological sciences at Unesp de Assis, website of the North American Bear Center (www.bear.org) and research Hibernation in Black Bears: Independence of Metabolic Suppression from Body Temperature, from the University of Alaska, published in the magazine Science PHOTOS Press Release/North American Bear Center