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Scientists monitoring free-roaming polar bears in northern Canada witnessed something exceedingly rare this fall: a mother bear taking in a cub that was not genetically her own.

The half-decade-old mother and her 10- to 11-month-old cubs were observed and captured on camera during the annual polar bear journey along the Hudson Bay's western shore near the Manitoba town of Churchill, an locale known for its polar bear population.

"It's unusual," remarked a researcher with a polar bear conservation group. "We don't really know why it occurs...but we know it doesn't happen often at all."

This represents only the thirteenth documented instance of fostering out of nearly five thousand bears studied for almost fifty years in that region.

The mother bear was first captured as she emerged from her maternity den this spring. At the time, she had a single offspring, which researchers marked for study.

In the autumn, she was seen again, but this time with a pair of cubs - the original cub and another that was untagged. Scientists aren't sure what became of the second cub's biological mother, but they are attempting to locate her using genetic samples.

"The bears need all the help they can get in the current era with a warming climate," commented a polar bear scientist. "When mother bears have the chance to take in another cub and raise it and successfully wean it, it's a positive development for the population."

Polar bears in the natural world only have a fifty-fifty survival rate of living into adulthood, but having a maternal figure caring for them boosts their chances.

The young bears are reported as healthy, researchers said, and they will probably remain with their adoptive mother until they are about two-and-a-half years old.

Next, the family is expected to head out to sea ice, where the youngsters will be taught from their mother bear how to catch prey and live on their own.

"It is heartening to know that the bears are caring for each other," concluded the scientist.