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Scientists tracking free-roaming polar bears in Canada's northern regions observed something remarkably uncommon this autumn: a female bear taking in a cub that was not genetically her own.

The five-year-old maternal bear and her 10- to 11-month-old cubs were spotted and captured on camera during the annual polar bear journey along the Western Hudson Bay near Churchill, Manitoba, an area known for its polar bear population.

"This is uncommon," remarked a researcher with an international bear organization. "We don't really know why it occurs...but we know it doesn't happen often at all."

This represents only the 13th known case of fostering out of nearly five thousand bears studied for nearly five decades in the area.

The mother bear was initially tagged as she came out from her birthing den this springtime. At the time, she had a single offspring, which scientists marked for study.

In the autumn, she was seen again, but this time with two cubs - the initially tagged cub and another that was untagged. Scientists aren't sure what happened to the new cub's birth mother, but they are attempting to identify her using DNA analysis.

"The bears need every advantage they can get these days with climate change," commented a wildlife biologist. "If females have the opportunity to take in an additional youngster and care for it and successfully wean it, it's a positive development for the population."

Polar bears in the wild only have a 50% chance of surviving into maturity, but having a maternal figure caring for them improves their odds.

The cubs are reported as healthy, according to experts, and they will probably remain with their mother until they are about two-and-a-half years old.

Next, the bear family is expected to venture out to sea ice, where the cubs will learn from their mother bear how to hunt seals and live on their own.

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