like this: in the spring or summer, mother black, brown, and polar bears manage to approach close enough to a potential father to have bear sex, which is different from fighting only in that insemination somehow occurs. Their fertilized eggs grow into blastocysts. But then they stop growing for months while the mother tries to get fat enough to live through the winter.
Then, in late fall, the mother bear curls up in some cozy snow cave and goes to sleep. (Memo to scientific nitpickers: bears hibernate, regardless of what your narrow definition says. They spend months with a heart rate of 9 beats per minute, their metabolism reduced by more than half, and that's good enough for me and most bear experts.)