Do bears actually hibernate?

Yes and no.

Bears here in WY (black and grizzly) do take a nap, which is generally termed hibernation.  However, they actually go into a much more lethargic physical state of “hyperphagia”, during which time their heart and breathing rates decrease, while their blood-nitrogen level increases.

Over the previous summer, bears have been told by Mother Nature to eat everything they can to build up fat reserves to live on during the winter.  While in their den, they sleep but do not eat, drink, defecate or urinate.  Their bodies simply slow down.  Yet, sows still nurse their young cubs through this time.

Depending on their physical health, sow bears will have 1-3 cubs in winter, months after mating the previous spring.  Unbelievably, their bodies tell them well before giving birth how many cubs they are fit to support !!

This is a  biological happening  known as “delayed implantation”. The sow’s body lets her know how many “fertilized eggs” to implant, based upon her physical fitness.  Sows mate in spring, thus the term delayed implantation.  Once her body and mind agree, the sow will give birth from January to February.

Each year sows with no cubs emerge from the den in March, then those with one-year olds, then those with recently-born cubs.  All are out of the den by late April.

Beware sows!!  Boars will make your cubs disappear  to drive you back into estrus!!

At the time of their emergence from the den, bears are very hungry. They feed on pretty much anything….grass, carcasses, winter-kill fish, rodents and newly birthed ungulates (deer, elk, moose). Later in the year, their diet will change to live fish, cutworm moths, berries.

Bears are not herd/pack animals, but individuals will take over a wolf kill and bison/elk carcasses left behind by hunters.

Mark  Bolen
Teton Wild