Black bear cubs are born completely dependent on their mothers. They are born with very little fur, they don't even weigh a pound each, and they can barely crawl. Cubs are most frequently born in litters ranging from two to four.
Cubs are usually born in late January, in the midst of the hibernating season.
Since the majority of dens are not any warmer than the outside temperature, the mother bear goes into a lighter sleep than the other bears. She maintains her mental functioning and a body temperature capable of keeping her cubs warm. The mother bear will sleep lightly when the cubs sleep, and be able to respond to their needs when they are awake.
The mother bear keeps the cubs beneath her to help them maintain body temperature. She keeps her head tucked under her chest, so her warm breath blows on the tiny black bear cubs. Her legs keep the cubs safely enclosed.
When the cubs creep away from the nipples, she nudges them back in place when they complain of hunger. She also helps them relieve themselves. Like dogs and cats, bears stimulate their young to defecate by licking them. They then ingest the feces to keep the den clean and to absorb any available nutrients.
The mouths of the newborns are shaped for nursing, since milk is the only food they eat. In order for the cubs to grow quickly, they do not go into hibernation. They spend most of their time nursing.
Interestingly enough, the cubs make a humming sound when they nurse. It is thought that this hum lets the mother bear know not to move around.
By the end of February, the weather is beginning to warm up a little bit. The black bear cubs will be 4 to 6 weeks of age, and they will have grown to 2 to 3 pounds. They have grown a dense coat of fur that almost reaches an inch in length. They are starting to open their eyes.
On days when the temperature gets up to the balmy 20's, the cubs may actually sleep while partially exposed to the air.
To make enough milk to sustain her babies, the mother bear can lose from .36 to .61 pounds every day as her body stores are converted to feed the cubs.
By March, the black bear cubs' fur coats have grown longer than an inch long. The cubs begin to explore the den.
By April, the cubs can weigh up to 10 pounds each.
One of the biggest dangers that face young cubs is flooding during the winter. If the den floods when the cubs are too young, they can drown or get chilled.
Sometimes the mothers can remove the cubs to safety, one at a time. They may return to the den once it is dry, or some mother bears will build up the floor of the den to keep the cubs dry.