Do Black Bears Hibernate?
Black bears are not true hibernators. Instead, they experience what is often called denning, ursid hibernation or carnivore lethargy.
This period of reduced activity occurs in all black bear populations. Winter lethargy is brought on by many factors, including reproductive status, food availability, amount of daylight, and temperature change.
However, it is notable that bears in southern states den for shorter periods and sleep less deeply than bears in colder climates. While denned bears in northern states are very lethargic and less responsive to people, bears in the South readily run away when people come close to their den. In addition, male bears in southern states like Florida may have a reduced denning period or none at all.
What Makes a Den?
In Florida, males and females that are not pregnant may den in dense vegetation for only a few weeks or a month.
Pregnant females will den for the entire winter. Because their cubs will be born in the den, they often select more protected sites than other bears. Dens are commonly made on the ground in 'nests' in dense thickets, but have also been found in tree cavities and under blow-downs or fallen logs.
Breeding and Reproduction
Bears are considered sexually mature between 3 and 4 years of age. The breeding season for black bears runs from June to early August. Bears have a unique breeding adaptation that is called "delayed implantation." The egg is fertilized in the summer but does not implant in the uterine wall until late November or early December. If the mother is in poor condition, the fertilized egg may be reabsorbed, the fetus will not continue to develop, or the female will miscarry and eat the fetuses. A female in better body condition will have a larger litter of cubs. This adaptation to periodic food shortages prevents the female from producing more offspring than she can handle.
The Bear Cub
The fertilized egg grows in the mother for about 8-12 weeks. Bear cubs are very small at birth, only 8 - 15 ounces (225 - 450 grams), about the size of a small squirrel.
At birth, bear cubs have a very fine coat of hair and their eyes are closed. The average litter size in Florida is 2 to 3 cubs, but litters can range from 1 to 5.
The cubs nurse in the den until spring and emerge to spend their first summer and fall learning to forage and be a wild bear. They will usually/almost always den with her the following winter.
Bear cubs stay with their mother until the summer of their second year, so young bears may be called either "cubs of the year" or "yearlings" when they are still with their mother, depending on their age and size.
During their second summer, the family group divides. The juveniles wander off and the adult female is ready to breed again. Female yearlings will likely establish a home range that is near or overlapping their mothers, while male yearlings are forced to find new areas well away from their mother's home range. Taking care of the cubs for this period of time means that adult females will typically breed every other year.