American black bear
Behavior and life history
Sows usually produce their first litter at the age of three to five years, with those living in more developed areas tending to get pregnant at younger ages. The breeding period usually occurs in the June–July period, though it can extend to August in the species' northern range. The breeding period lasts for two to three months. Both sexes are promiscuous. Males try to mate with several females, but large, dominant ones may violently claim a female if another mature male comes near. Sows tend to be short-tempered with their mates after copulating. The fertilized eggs undergo delayed development and do not implant in the female's womb until November. The gestation period lasts 235 days and litters are usually born in late January to early February. Litter size is between one and six cubs, typically two or three. At birth, cubs weigh 280–450 g (0.62–0.99 lb) and measure 20.5 cm (8.1 in) in length. They are born with fine, gray, down-like hair and their hind quarters are underdeveloped. They typically open their eyes after 28–40 days and begin walking after five weeks. Cubs are dependent on their mother's milk for 30 weeks and will reach independence at 16–18 months. At the age of six weeks, they attain 900 g (2.0 lb), by the age of eight weeks they reach 2.5 kg (5.5 lb) and by the age of six months they weigh 18 to 27 kg (40 to 60 lb). They reach sexual maturity at the age of three years and attain their full growth at the age of five years.
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