In an unusual, but apparently not unprecedented, move in wildlife behavior, two grizzly sows in Grand Teton National Park have swapped a cub. Making the swap even more curious is that the sows involved are themselves mother and daughter.

The cub swapping was detected last week when those monitoring the park's grizzlies compared notes. According to park officials, the swapping was between 15-year-old grizzly No. 399, a prodigous sow when it comes to bearing triplets, and one of her daughters, 5-year No. 610.

No. 399 had given birth to three cubs this past winter. During the spring and into the summer she traveled with her young trio through much the same home range that she has maintained in recent years.

No. 610, who has a home range that overlaps with No. 399, meanwhile, had twins during the winter.

"The apparent adoption of a single cub occurred on or about July 21; the noteworthy event was confirmed by observations of  No. 610 traveling with three cubs in the Willow Flats area of Grand Teton National Park, and later observations of  No. 399 with just two cubs in an area further north of Willow Flats," a park release said. "Biologists are not sure what caused the exchange of offspring, or whether this will be a temporary or permanent situation. However, these observations offer a fascinating glimpse into bear behavior.

"Scientists speculate that cub adoption in bears is an adaptive behavior that increases cub survival when they become separated from their mothers as a result of conflicts with other bears, the death of a mother, or other disruptive events."