January/February is Birthday Time for Bears

The fact that bears mate in summer and give birth seven or eight months later might make you think that bear pregnancies aren’t all that different from human ones. But even though bears mate in summer, they’re not officially pregnant until late fall. Nevertheless, they give birth a few short months later, in January or February.

Why Bears Have A Two-Step Pregnancy

Mother Nature has engineered a unique two-step pregnancy process for bears. During step one (mating), eggs are fertilized, but don’t implant or begin to further develop. Several months later, development (step two) begins when the fertilized eggs finally implant. This process is called delayed implantation.

Implantation is delayed because if the bear is underweight, sick or injured, the fertilized eggs may not implant or develop any further. Instead, the eggs can be reabsorbed in order to give the bear the best chance to survive and breed again.

During late summer and fall, an almost-pregnant bear works very hard at gaining as much weight as she possibly can so she has enough fat reserves to sustain herself and produce an abundant supply of the rich milk her cubs will need to fully develop. Then it’s on to step two. Implantation generally occurs and development begins in earnest once the bear is safely tucked into her den.

Read more from BearWise, the author of this information.

Photo Credit: North American Bear Center