page_title: Grizzly bear
section_title: Reproduction
hierarchical_section_title: Grizzly bear / Biology / Reproduction
caption_attribution_description: English: en:Grizzly bear sow and two cubs in en:Kananaskis Country.
context_page_description: The grizzly bear, also known as the North American brown bear or simply grizzly, is a large population or subspecies of the brown bear inhabiting North America.
  Multiple morphological forms sometimes recognized as subspecies exist, including the mainland grizzly, Kodiak bear, peninsular grizzly, and the extinct California, Mexican, and Ungava-Labrador grizzlies. On average, bears near the coast tend to be larger while inland grizzlies tend to be smaller.
  The Ussuri brown bear, inhabiting Russia, Northern China, Japan, and Korea, is sometimes referred to as the "black grizzly", although it is a different subspecies from the bears in America.
context_section_description: Except for females with cubs, grizzlies are normally solitary, active animals, but in coastal areas, grizzlies gather around streams, lakes, rivers, and ponds during the salmon spawn. Females (sows) produce one to four young (usually two) that are small and weigh only about 450 grams (1 lb) at birth. A sow is protective of her offspring and will attack if she thinks she or her cubs are threatened. 
  Grizzly bears have one of the lowest reproductive rates of all terrestrial mammals in North America. This is due to numerous ecological factors. Grizzly bears do not reach sexual maturity until they are at least five years old. Once mated with a male in the summer, the female delays embryo implantation until hibernation, during which miscarriage can occur if the female does not receive the proper nutrients and caloric intake. On average, females produce two cubs in a litter and the mother cares for the cubs for up to two years, during which the mother will not mate.
  Once the young leave or are killed, females may not produce another litter for three or more years, depending on environmental conditions. Male grizzly bears have large territories, up to 4,000 km² (1,500 sq mi), making finding a female scent difficult in such low population densities. Population fragmentation of grizzlies may destabilize the population from inbreeding depression. The gestation period for grizzly bears is approximately 180–250 days.
  Litter size is between one and four cubs, averaging twins or triplets. Cubs are always born in the mother's winter den while she is in hibernation. Female grizzlies are fiercely protective of their cubs, being able to fend off predators as large as male bears bigger than they are in defence of the cubs. Cubs feed entirely on their mother's milk until summer comes, after which they still drink milk but begin to eat solid foods. Cubs gain weight rapidly during their time with the mother—their weight will have increased from 4.5 to 45 kg (10 to 99 lb) in the two years spent with the mother. Mothers may see their cubs in later years but both avoid each other.
caption: Sow with two cubs in Kananaskis Country
exif: {}