What is Delayed Implantation?
Only the coolest part about being a momma bear! Did you know they are only REALLY pregnant for about 2 months?!
Let me explain…North American Black bears usually mate in May and June, however, the cubs are not born until mid January. So, how are they pregnant for only 2 months you ask? Delayed Implantation is how. After mating, the fertilized egg develops into a tiny ball of cells or “blastocyst”, at which time development stops and the blastocyst remains unattached in the uterus. If the female gains enough weight in the fall, around 150lbs, the blastocyst IMPLANTS in the uterine wall in late November. Roughly 2 months later… we get the cute and cuddly little cubs (usually 1-3). If the female fails to gain enough weight, the blastocyst will not implant and pregnancy is terminated.
Black bear cubs are born between early January and early February. Newborn cubs are blind, hairless, and weigh about half a pound and are about the size of a stick of butter!. They locate their mother’s nipples and suckle immediately after birth. Momma bears, or sows, usually have 6 functional mammaries. The shortened gestation period and later birth of very small young allows bears to shift from transplacental to mammary nourishment of the young and is an adaptation to hardship associated with supporting the cub while hibernating and avoiding food intake.
They get to eat as much as they want AND are only pregnant for 2 months AND have tiny little babies! Oh the life of a momma bear.