How long is a black bears gestation period?
Black bears, like brown and Asiatic black bears and many other carnivores, have a prolonged gestation period resulting from an arrest in embryonic development or “delayed implantation”. After mating, the fertilized egg develops into a minute ball of cells or “blastocyst”, at which time development stops and the blastocyst remains unattached in the uterus. If the female attains a minimum weight in the fall, usually about 150 lbs. (but perhaps less in the southern states), the blastocyst implants in the uterine wall in late November and embryonic growth proceeds until birth of the small, feeble cubs about 45 to 55 days later. If the female fails to accumulate sufficient fat reserves, the blastocyst fails to implant and pregnancy is terminated. Delayed implantation has been assumed to convey a selective advantage by allowing the young to be born as early as possible in spring, to avoid mating at an unfavorable time of year, or to ensure synchrony of one or more reproductive processes. The
Good question. The fertilized egg matures to the blastocyst stage and goes dormant. Blastocyst will not implant in the uterus until late November. In early December, embryo development proceeds normally (delayed implantation: a process shared with badgers, mink, weasels, otters, and wolverines). Birth occurs in late January. Gestation is approximately 7 months. The delay in gestation is approximately 5 months and true gestation is approximately 8 weeks. A black bear usually has between 1 to 5 cubs.
