National Park News

Grizzly Sows in Grand Teton Exchange Cub

By New West Editor, 7-27-11

	Grizzly bear No. 610 watches as one of her cubs climbs a tree. Photo by Gary Pollock.

In a rare occurrence among grizzly bears, Grand Teton National Park biologists have reported that two sows—a mother and her five-year-old daughter—have exchanged a cub.

The two female grizzlies have occupied overlapping home ranges since both emerged from hibernation with newborn cubs this past spring. The adoption or fostering of cubs between two female bears is rare, but not unprecedented, according to a blogpost filed by public affairs officer Jackie Skaggs. This behavior was documented in an article written by Mark A. Haroldson, Kerry A. Gunther and Travis Wyman in a Yellowstone Science 2008 publication.

Fifteen-year-old grizzly bear No. 399 (a research number assigned to her in 2001) gave birth to three cubs during hibernation this winter. Over the spring and summer months, she has traveled with her trio of cubs throughout a home range that she has occupied for several years. Five-year-old grizzly bear No. 610, born to No. 399 in 2006, also gave birth to two cubs of her own this year. These were previously radio-collared as part of a decades-long research study conducted by the Interagency Grizzly Bear Study Team. Bear No. 399 last wore a collar in 2006 and No. 610 shed her collar in 2010. Colored ear-tags remain on the bears, providing continued identification in the field.

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 the park, and later observations of No. 399 with just two cubs in an area further north of Willow Flats.

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.

The two female grizzly bears and their respective cubs have lingered near park roads over several months time, allowing visitors and local residents an exceptional opportunity to view wild bears in their natural environment.

Park managers remind wildlife watchers that all park bears are wild and unpredictable. For the protection of bears and for the safety of visitors, federal regulations require people to remain at least 100 yards (the length of a football field) from bears at all times. 

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