Black bear cubs are born in January while the mother is in hibernation. The cubs are born blind, without fur and weigh less then a pound. Even though the mother is in hibernation she is awake enough to take care of the helpless cubs. Here in Minnesota the temps in January can fall well below zero and since most dens provide little protection from the cold it is up to the mother bear to keep the cubs warm, dry and fed. While in the den with her cubs the mothers body temp runs around 95 to 98 degrees, only a few degrees less then during the summer. She uses her body heat to keep the cubs warm. She will stand over them like a big furry blanket and even breath her warm breath on them if necessary. If water leaks into the den she will lick the cubs dry.
For the first month of their lives the cubs can not even crawl. They spend all of their time sleeping and suckling the extremely fat rich milk from their mother. By 4 to 6 weeks they have grown to about 3 to 4 pounds. They have also begun to crawl and have about an inch think layer of fur. They still rely on their mother for food and warmth but are now able to thermo-regulate to some extent. This is helpful to the mother who has been burning a third to over a half pound of stored fat each day in order to keep her family warm and fed. By April or May, depending on the weather, the bears will emerge from the den.
The cubs now weigh around 4 to 10 pounds. Their legs have grown long enough for them to walk and they follow mom, who by this time needs to get some food for herself. At the beginning of summer the young cubs teeth grow in and they begin to eat solid foods, such as ant larvae, vegetation and berries. The mother bear will continue to feed the cubs through out the summer however as the cubs eat more solid food their dependency on mom's milk lessens.
In the fall the cubs will hibernate with their mother. They will snuggle together to help keep themselves warm, and sleep until spring. They leave the den in April or May again. The cubs will stay with their mother for a month or two after leaving the den. At that point the mother will chase the yearling cubs away. It is time for them to go out on their own and time for mom to look to mate. All of these pictures are of yearlings. We spotted 4 or 5 yearlings at the Vince Shute Wildlife Sanctuary. Since it was the beginning of July these bears had probably recently been sent off on their own and you could tell that they were a bit nervous, especially with the larger bears around.
These are the end of my bear pics from our trip to Vince Shute.