Grizzly bears mate during June, the males 'wooing' the females by following them, making low snorts and nibbling their backs and necks.
Gestation takes 180 to 250 days, so birth takes place during the winter when the bear is in her den. Fertilized eggs do not implant in the womb until the autumn, so that the female is able to feed freely and build up fat supplies for her and her cubs.
Cubs are born blind, toothless and almost hairless. They are about 20cm long and weigh between 450 and 700g. They remain in the den with their mother for the first few months and feed on her rich milk, protected from the cold by the warmth of her body.
The cubs leave the den with their mother in April or May. She teaches her cubs to forage and hunt and does not feed them on food which she has gathered. Many young bears die, despite the efforts of their mothers, from attacks by other mature bears. In the first winter after the cubs' birth, they den with their mother. Some young bears also do this in the second year or they may den together.Read More: Related Species