As late fall turns into winter and winter drags endlessly on, what are our furry, feathery, and scaly friends up to? Some may migrate to warmer places, some adapt to the changing environment and brave the cold, while others hibernate. Bears have often been misidentified as hibernators for a very long time, when in fact their winter sleep practice falls into another category called torpor. Unlike hibernation, animals that practice torpor can wake from their sleep easily if they feel threatened; or in the case of bears, if they need to give birth to their young. Bears in torpor have slightly decreased body temperatures, heart rates, and breathing rates. Contrary to popular belief bears do not HAVE to hibernate, but rather involuntarily fall into this state of torpor as their environmental conditions dictate. As long as there is enough food, there will be active bears. Because of this, the following timeline may vary depending on bear species, geographic location, food availability, and winter weather patterns.
Female bears wake to give birth to their cubs. Females can have up to four cubs, but the average litter size is two. The newborn cubs will weigh less than half a pound each, roughly one four-hundredth as much as their mother weighs. Bear cubs are one of the smallest newborn mammals relative to their mother’s size in the world. After their first meal, the blind cubs snuggle up next to their warm mother and rest.
Sleep and care for the new cubs continues.
Snow starts to melt and male bears are the first ones out of their dens. On the search for food, many of the bears will wander and roam for the next month. Mothers with cubs will come out of their dens last, either in late April or into May. A bear’s metabolic process will begin to adjust to more normal levels at this time.
The landscape is beginning to green with new growth and more food. Bears slowly start to gain weight after the long, famished winter months. Cubs are still nursing and growing, weighing between 4-10 pounds.
Bears’ diets will consist mostly of insects and berries during this time in the summer. Mating season begins and male bears will be in search for females without cubs. Cubs will begin to eat solid foods in preparation for denning up again with their mother.
Bears begin hyperphagia, a time period in which they gorge themselves on as many calories as possible in preparation for winter. A bear with unlimited resources could consume up to 6,000 calories a day during this time.
Bears become more lethargic and food is becoming scarce. By now they will be at their largest body size and coats will more than double in insulation value.
Most bears will have entered their dens by now. Dens are not always found in caves; bears can den under fallen trees, brush piles, and inside hollow logs. The opening to a bear’s den is usually quite small, making it hard to believe that they can fit at all! But this provides protection and extra insulation during their sleep.
The state of sleep deepens. Heart and breathing rates slow.
Torpor is taking place in its full extent! Bears are warm and asleep in their well-constructed dens until spring.