Black bear cubs are born in late January or February, weighing about eight ounces. The mother has six teats, and the newborn cubs crawl to the ones closest to her pelvis. Later, as the cubs get older, they nurse from the other four, and the mother often “switches off” production in the bottom two. At birth, black bear cubs weigh one-half to three-quarters of a pound, and when they emerge from the den in April, they average about six pounds.
Most hibernating mammals are not pregnant. The fact that black bear cubs are born in late January or February, and that the mother bear nurses them for two or three months while she is not eating or drinking, is phenomenal in and of itself – just ask any ravenous, nursing human mother.
Milk production and intake increases fourfold after the cubs emerge from the den. At peak lactation in June and July, a black bear cub consumes about 30 ounces of milk per day. If a bear has two or three cubs, that means she must produce nearly two to three quarts of milk per day. The milk of black bears is very rich: human and cow milk is about three to five percent fat, while a black bear’s milk is around 20 to 25 percent fat. At roughly six to eight months of age, black bear cubs are weaned.
Thanks to researcher Ben Kilham for this photo op.