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. 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 2 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, that is 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.