08/05/2026
In the summer of 2007, biologists near Dunraven Pass in Yellowstone spotted a young female grizzly with four cubs. She had produced two of her own that spring. Two is normal. Four is not. The extra cubs were smaller and clearly not hers. DNA testing told the rest. The two additional cubs belonged to her mother, Grizzly #125. The young female was raising her own baby brother and sister alongside her own children. All four cubs shared the same father: Grizzly #211, the massive scarred male the park called Scarface.
Grizzly #125 had produced cubs that spring and lost them. Nobody witnessed the separation. Researchers believed wolves or another disturbance may have driven the cubs away from #125 before they could follow her. The cubs were small enough to be vulnerable and old enough to walk. Somewhere in the timber between Dunraven Pass and the Yellowstone River, they found their older sister.
She took them.
Grizzly mothers do not always accept unfamiliar cubs. A female defending her own young will sometimes kill a strange cub that approaches because a cub she does not recognize represents a potential competitor for the milk and attention her own offspring need. The P-65 cougar post we published a while ago told the same story from the other side: a mother that was given orphaned kittens sorted her own from the strangers, took hers, and left the rest. The Yellowstone daughter did the opposite. She absorbed two additional cubs into her family group and continued traveling with all four through the summer.
Steve Cain, a National Park Service biologist, explained why bears may be more willing to accept strange cubs than other large mammals. Bears do not live in herds. They do not need to pick their offspring out of a crowd of identical animals the way an elk cow identifies her calf among hundreds. A bear's social world is small: herself and her cubs, moving through the forest as a tight unit. If a cub is present and behaving like a cub, the female's maternal response may not require a precise identity check. Cain also noted that adopting related cubs could be adaptive. A female that raises her own siblings is preserving copies of her own genes even if the cubs are not her direct offspring. The genetics reward the behavior even if the bear does not understand why she is doing it.
The young mother was still traveling with all four cubs in August when researchers last confirmed the group. Four cubs is an enormous burden for a grizzly. A typical litter is two. Nursing four cubs through the summer and into the fall hyperphagia, the period when a bear must eat 15,000 to 20,000 calories a day to build the fat reserves needed for hibernation, drains the mother's body at a rate that can approach the limits documented in sea otter end-lactation syndrome. Whether the Yellowstone daughter survived the winter with all four is not recorded in the published accounts.
Image is for illustration purposes only
Source: Interagency Grizzly Bear Study Team / Jackson Hole News & Guide / National Park Service / Greater Yellowstone Grizzly Project.