North American River Otters Mating and Giving Birth
North American River Otters are induced ovulators – copulation releases the female’s egg from the ovary. Once the egg is released and fertilized, however, there is a nine to eleven month delay before the embryo begins actively developing (delayed implantation). Actual gestation takes about two months. Thus, otters sometimes give birth up to a year after mating, just before their next breeding cycle. April and May are busy months for this semiaquatic mammal.
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This Year’s Black Bear Cubs Growing Up Fast
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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