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Black Bear Cubs

Black Bear Cubs Sampling Solid Food But Continue to Nurse For The Next Year

Black Bears only mate every two years, due to the fact that their cubs are not weaned until they are a year and a half old.  When born in January, a cub weighs less than a pound and is roughly 9” long.  For the next three months it nurses steadily on its mother’s very rich milk (20-25% fat compared to a human’s 3-5%).  Depending on the number of siblings a cub has as well as the amount of milk its mother produces, it weighs between four and six pounds when it emerges from its den in April. 

Soon thereafter the cub starts sampling the food that its mother eats, but swallows very little. Slowly it begins to eat and digest solid food (cubs are partial to ant brood when very young), but it will still be nursing for the next year, right up until next April or May, when it is weaned by its mother who will then turn her attention to finding a mate. 

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Black Bears Giving Birth

It’s hard to imagine at this time of year, but sometime between the last half of January (the full moon in January is often called the ‘bear moon’) and the first part of February Black Bears give birth to between one and five (usually two) tiny, blind, almost hairless, 9-inch long, one-half pound cubs, each about the size of a chipmunk. The cubs are totally dependent on their mother for food and warmth.

Most dens are exposed to the cold air, as they are located under fallen logs and brush, or are dug into a bank. Occasionally they are on the ground with little or no cover; in all of these locations, the mother acts like a furnace, enveloping her young and breathing on them to keep them warm. The cubs do not hibernate, but nap frequently. Like human mothers, Black Bear mothers sleep when their young sleep, and are alert when their cubs cry and let them know that they are in need of attention. (Photo: taken in March of two-month old Black Bear cubs)

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This Year’s Black Bear Cubs Growing Up Fast

5-8-17 black bear cub 054

It’s hard to believe that four months ago when it was born this Black Bear cub weighed less than a pound and measured about eight inches in length! Most Black Bears mate in June, but because of delayed implantation their fertilized eggs don’t implant in the uterine wall and the embryos don’t begin developing until the fall (if the mother has had a sufficiently nutritional diet), just as the mother is entering hibernation.

The cubs are born in January, after only a few months inside their mother. They are just a fraction of one percent of the mother bear’s weight, compared to an average human baby that is about seven percent of its mother’s weight. The cubs nurse constantly for the next four months (during which time their mother is not eating or drinking).  The fat content of Black Bear milk can be as high as 20-25 percent. Human milk is comparable to cows’ milk, generally ranging between three and five percent fat. (A biologist who had the opportunity to sample Black Bear milk reported that it was similar in taste to sweetened condensed milk.)

In April, when the cubs emerge from their den, they weigh about six pounds.  Milk production and intake now increases four-fold. Peak lactation (45 ounces of milk per day per cub) occurs in June and July. As a result, the cubs have a huge growth spurt their first summer and will weigh between 40 and 60 pounds by the end of it.

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