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The Bear Facts - General bear information
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Family Life

Bears are not social creatures. But, it takes more than one bear to start a family; and growing up still takes a lot of help.
Sex and the Single Sow
Female bears are called sows, males are called boars and when the two come together to produce baby bears, called cubs, sparks can fly! Being solitary animals, the two sexes usually stay well away from each other most of the time, coming together only to mate, staying together for periods varying from a few days to a few weeks. The courtship and mating activities vary between species but all are often quite noisy and boisterous. A receptive female will play-wrestle with the male, often barking, biting, chasing, hugging, and roaring her acceptance of the suitable mate. Like many carnivores, the male will often hold the willing female in a "love-bite" grip to the back of the neck as he mates with her. The male of most bear species must mate with the female several times in order to stimulate her to ovulate. This "induced ovulation" makes sense for a solitary female, for it would be of little use to ovulate when no male might be within a 100 miles radius. It is not known if this is true in all bear species. After mating, the males of all bear species wander off and have nothing to do with rearing the cubs.
Like most large mammals, the bears' breeding cycle is a slow one. Most females will only give birth to 8 to 10 cubs during their lifetime and they do not normally mate for the first time until they are around four years old. First sexual encounters for males usually come a few years later when they are able to compete successfully with other males for an available female.

Sloth bear cub (Melursus ursinus), eight weeks of age
Mother Knows Best
Once the successful male bear swaggers off into the sunset, the female is left on her own to raise the resulting cubs, which will often not be born for several months. Embryonic growth in all bears takes about two months but, due to a process called delayed implantation, the overall gestation period is much longer. Mating may take place in summer but the implantation of the fertilized egg into the uterus is delayed until a more suitable time for the female, usually at the end of an abundant feeding season. When implantation does finally take place, then the true gestation period begins. Bears are able to breed and give birth only when they are in their best condition. If there is a shortage of food and the female is thin and in poor condition, she aborts and the fertilized ovum is absorbed by her body. The female bear in good condition and healthy weight gives birth and begins nursing her cubs in a den, without food. All of her nutritional requirements must come from stored body reserves: the fat she was able to put on during the preceding season.
In spring, the mother and her young leave the den. She will teach them how to hunt or forage for their food, she will teach them to seek safety in trees if threatened, she will show them how to fish, how to navigate their territory and how to find suitable denning space. Mother bears are legendary for protecting their cubs from all perceived threats, whether it's a male bear that surely would harm an unprotected cub, a mountain lion or other big cat hungry for an easy meal, or an unsuspecting hiker that startled the bear family in the woods. The cubs learn by following and imitating their mothers during the long period they are with her. Orphaned cubs stand little chance of surviving even long past weaning. They need their mothers as tutors for the many skills they'll need in adulthood. It is only after two to three years of age that the young bears are able to fend for themselves.

Sloth bear cub (Melursus ursinus)
My, How You've Grown
Bears are the largest of all land carnivores but, pound for pound, produce the smallest young of any mammal. Newborn cubs weigh about 1/420th as much as their mother compared to a newborn human which weighs about 1/20th as much as its mother. For example, a 440 pound polar bear will give birth to one or two cubs weighing a little over one pound each. This extremely small birth weight makes sense when the denning mother's own nutritional needs are taken into account. A pregnant mammal devotes extraordinary caloric energy to the developing fetus and for a denning bear that would be life-threatening coming at a time when no additional food is being eaten. Giving birth to tiny young conserves the mother bear's fat stores, both for her continued existence and to begin producing milk for the new cubs.
Bear milk is one of the richest known, having as high a fat content as 46 percent, compared to human milk at 4 percent. This rich milk allows the tiny, blind, and almost naked cubs to grow at a considerable rate. When old enough to leave the den, their eyes will be open, their fur will be thick and warm and they'll be large enough to meet the challenging world outside.
Tiny young make sense in bear species that den up during cold weather but does not easily explain the small birth weight of tropical bears. Perhaps denning ancestral bears, giving birth to tiny cubs, set the stage for all bear species that would come later.
                                                             
                                                                                                                                                                Polar bears (Ursus maritimus)