Happy birthday to our black bears Kuma, Uli, and Kobuk, as well as our brown/grizzly bears JB, Patron, and Hugo! Brown and black bears give birth in their dens as early as December, and as late as February or March. January 20th marks the the average date that mother bears give birth to their cubs in their dens and is known as “All Bears’ Birthday”.
For black bears, females give birth to one to four cub with two being the most common. For brown and grizzly bears, a female will typically have a litter of one to three cubs, although litters of four can occur. Bear cubs are born tiny and hairless, sometimes weighing less than half a pound. They spend the winter sleeping and nursing, warm in their dens with their mother. In the wild, bear cubs stay with mom for about two years. During this time, they’ll learn the vital skills to survive on their own. Hugo the rescued grizzly bear, for example, came to us at such a young age that she had not yet learned the skills to survive on her own in the wild.
A little known fact is that after mating season in June/July, bears exhibit delayed implantation. This means the fertilized embryo does not implant in the female’s uterine wall until she enters her den. If the female has not gained adequate weight to support reproduction, implantation will not occur. After 60 days gestation, cubs are born in the den.