By Kayla Heinze, Communications and Outreach Coordinator
Born blind and weighing about as much as a block of butter, the cubs that will become one of the largest and most powerful animals in North America start their lives vulnerable and dependent in the darkness of their natal dens. In the depths of winter, typically January or February, this is how the remarkable life of a wild grizzly begins. Over the next 20 to 25 years, their estimated average lifespan in the wild, they will achieve many feats of survival from astonishing foraging behaviors, the physiological wonder of hibernation and, for many individuals, navigating the challenges of sharing the landscape with a growing human population.
Before all that though, these young cubs will spend around 1.5 to 2.5 years absorbing lessons from their mother about how to be a bear. This generational transfer of practical wisdom and survival strategies is an important part of the species’ overall resilience. Sow grizzlies can pass on the time-tested insights of their experiences—favorite glacier lily meadows and how to dig their succulent bulbs, the local bear rub tree and how to interpret its many aromatic messages—and give their cubs a better chance at a long adult life.
As they grow rapidly in size and capability, the cubs will eventually leave their mothers and create their own home territories, which can be as large as 600 square miles. But for now, they nurse in the den with closed eyes. What they will find when they open them and emerge into the warming spring air is still to be determined. The landscapes they grow up on are shaped, in so many ways, by us.
A bear cub’s first year
(Photo: Lian Law for Katmai National Park and Preserve).
The remarkable biology of grizzly bears begins before they are even born. Bears have a unique reproductive strategy called delayed implantation. After mating in the early summer, a pregnant female develops a small embryo that floats around her uterus for months until winter. At that point, based on her body fat, the embryo will either be reabsorbed or, if she is healthy enough, finally implant and begin developing into a baby bear. Since sow grizzlies do not eat or drink the whole time they are in their winter dens, they must have adequate calories stored in their body fat to get them and their nursing cubs through months of hibernation.
And it does require an extraordinary amount of energy. When they leave their dens, typically in April or May, a sow’s 1 to 4 cubs will have grown some 12 to 20 times larger solely from the nutrition of her milk. She will then begin introducing them to the wide array of bear foods that exist on the landscape. They’ll often get their first tastes of wild foods in the early spring shoots, roots and grubs found in wetland habitats like Vital Ground’s recently protected Meadow Creek North project and restoration sites at Salmon Prairie and the Broadie Habitat Preserve.
Throughout a litter of cubs’ first season, their mothers will continue to teach them about a variety of foods, from bulbs and insects to berries and fish, in sync with the natural rhythms of availability. She will help them navigate threats on the landscape like aggressive male bears, road crossings and other infrastructure. But life for young bears is hard and unfortunately, many will not make it until their next winter. In Yellowstone National Park, annual cub survival is around 55 percent and in the smaller population of the Cabinet-Yaak Ecosystem it is around 65 percent, meaning nearly half will die due to a variety of causes.
This survival rate compounds with the species’ late age of sexual maturity, small average litter size and long intervals between births to make grizzly bears one of the slowest-reproducing land mammals. It can take a female grizzly 10 years or more to replace just herself in a population, and on average she will birth some 10 cubs in her entire lifetime with only half surviving their first year.
For those that do, they will return to the den after putting their newly-learned foraging skills to the test to fatten up during fall hyperphagia. Much larger than when they emerged, the cubs will once again spend winter in hibernation with their mother. The following summer (or sometimes as late as their fourth year) she will kick them, now yearling cubs, off to start them on the independent portion of their life journey. The timing depends on environmental factors and other circumstantial influences, but the sow grizzly will begin to gradually show more signs of aggression and intolerance towards her cubs until they fully separate.
Protecting habitat for bear cubs leaving mom
Dispersing and establishing their own home territory happens gradually for a grizzly. For a few years, sub-adult bears will make exploratory movements across the landscape, occasionally returning to their mother’s home range, until they eventually stick in a new spot. (Sound familiar, humans?) Male bears tend to disperse farther than females, who will sometimes stay close to or overlap with their mother’s territory even as an adult. As the carriers and guardians of future generations of grizzlies, this lack of female dispersal adds to the conservation challenges for the species.
“Female dispersal from a source population is necessary for natural augmentation or recolonization of suitable habitat. However, female dispersal appears to be rare,” said the authors of a Canadian study on bear dispersal. “Managers wishing to promote recolonization of an area by grizzly bears may need to maintain source populations with a high rate of increase by reducing all sources of human-caused mortality.”
Since female dispersal far from their home range is uncommon but important for connecting isolated populations of bears and providing genetic resilience, conservationists must make sure dispersing bears have the best shot possible at successfully moving across the landscape. Vital Ground strategically protects habitat in wildlife movement corridors so bears have open spaces to do just this, and fewer chances of running into conflicts with people.
Even after moving away from their mother, young bears still carry the lessons she taught them across the landscape. How they navigate human infrastructure, attractants and interactions will be determined by her teachings. One study found that offspring of mothers involved in conflicts were more likely to get into conflicts themselves (with 62 percent of them doing so), while there was no correlation between a father’s conflict rates and that of their offspring. This suggests it’s not genetic inheritance but rather the social transfer of behavior and knowledge from mother to cub that can make a young bear either conflict-avoidant or conflict-prone.
There are also horizontal transfers of knowledge. Non-sibling bears of varying ages and sexes will sometimes play-fight with one another, collectively learning social skills. And we humans have an influence, too. By securing our attractants, not feeding wildlife and maintaining our distance from them, we help mother bears avoid conflicts and support them passing conflict-avoidance behaviors on to their cubs.
Paths to conservation for future generations of wildlife and people
Like bears, we bestow our knowledge and behaviors on to future generations. Instilling conservation values and actively protecting the places and animals that will make our children’s world richer is exactly the kind of behavior we should be imparting. By sharing these values and Vital Ground’s message with those around you, you help create a future of abundant wildlife and coexistence between species.
We know that intact ecosystems with diverse, healthy wildlife populations are valuable both for their own sake and our benefit as people dependent on these landscapes. The choices we make now will influence whether that value is protected or eroded and whether young ones will continue our conservation legacies. Protecting habitat today doesn’t just make a tangible difference on the ground in a time when nature desperately needs your help; it also enacts your conservation ethics and influences those around you to carry that behavior forward.
Like a wise mother grizzly, you can use the experiences of your life to help those who are still learning how to navigate their own ecosystem. Your generosity in protecting habitat and helping prevent conflicts will teach them that when we take care of those around us, including wildlife, we are all better off. Together we can shape the landscapes that young bears will emerge onto, this spring and beyond, in positive, life-supporting ways. If we do so, when future generations open their eyes and take in this world for the first time they will see, like we have been so fortunate to, how beautiful it is.