Grizzly and Polar Bears Interbreeding is another threat to Polar Bears

It was one of the most awe-inspiring experiences of my wildlife career: in the autumn of 1975 a colleague and I watched a polar bear swim up an inlet toward us on Bathurst Island, then Northwest Territories (now Nunavut). We were near the head of an inlet on a high promontory, and were excited to watch the white bear swim for a mile or so until it reached the shore just below us. There it walked on the the shore and sniffed in the mud where we had walked moments before. We could see him sniffing in our individual footprints. He looked up and around, nose high, testing the wind. Then started following our tracks towards us.

My colleague ran, but since there was nowhere to hide and nothing to climb on the featureless tundra, I stayed put. In a few moments, the bear abandoned our scent trail and went on up the draw, passing out of sight among the rocks.

There are still polar bears throughout the Arctic and some populations are healthy, but some are declining, with low production of cubs and low survival of all age classes. Climate change is the main culprit, but now another threat has appeared.

The confirmation of a grizzly-polar bear hybrid (DNA confirms suspected rare grizzly-polar cross shot in High Arctic, Vancouver Sun, May 1, 2010) at Ulukhaktok, N.W.T, (formerly Holman, on Victoria Island) is part of a trend that began at least 20 years ago.

In the winter of 1951-1952, Frank Banfield, a government wildlife biologist, recorded a grizzly bear taken on Banks Island (Banfield 1974). This was so unusual that he reported it as an “extra-limital record,” that is, outside of the known range.

In the last 19 years, sighting of grizzly bears unusually far north have become common: Melville Sound (1000 km north of mainland) in 1991, Banks and Victoria Islands (160 km north of the mainland), Hudson Bay, and Melville Island in 2003 and again in 2007 (Kaufmann 2007; Struzik 2006). They have become so well established on Victoria Island as to be a significant predator of muskoxen (Gunn and Lee 2000) .
The one shot in May was a second-generation hybrid, the offspring female grizzly-polar hybrid mating with a male grizzly bear. It was the second known grizzly-polar bear hybrid. In April 2006 the first known hybrid polar-grizzly bear in the wild was shot on Banks Island (Roach 2006). DNA tests showed it had a polar bear mother and a grizzly bear father.

After I gave a talk on my grizzly bear research at an international bear conference in 1977, several Norwegian bear researchers rushed up to me. They had read my earlier paper in the Canadian Journal of Zoology on grizzly bear denning on the Arctic coast, in which I mentioned that polar bears also occurred in my study area (Harding 1976). It turned out that this was the first report of grizzly bear and polar bear ranges overlapping, and the Norwegians wanted to know how the two species interacted. Their interest was stimulated because a polar bear and grizzly bear had mated in a zoo and produced fertile offspring (c.f. Stirling 1999), and they wanted to know if this could happen in the wild. I had to disappoint them by explaining that, since polar bears only came ashore in winter when grizzly bears were asleep in their dens, they never had an opportunity to interact, even though they shared the same habitat temporarily.

How times have changed! The recent shrinking of the polar ice cap and withdrawal of seasonal ice from shore has driven many polar bears ashore in the summer, bringing them into contact with coastal grizzly bears. At the same time, more and more grizzly bears are taking up residence on the Arctic Islands. Such hybrids may become more common. Over many generations, this could, hypothetically, destroy the polar bear as a species by genetic contamination. That is, if they aren’t first destroyed by shrinking sea ice seal-hunting habitat.

References

Banfield, A.W.F. 1974. The mammals of Canada. National Museum of Natural Sciences, Univ. of Toronto Press, Ottawa.
Gunn, A., and Lee, J. 2000. distribution and abundance of muskoxen on northeast victoria island, n.w.t., august 1990. Government of the Northwest Territories, Department of Rresources, Wildlife and Economic Development Manuscript Report No. 119.
Harding, L.E. 1976. Den site characteristics of Arctic coastal grizzly bears (Ursus arctos L.) on Richards Islands, Northwest Territories, Canada. Canadian Journal of Zoology 54(8): 1357-1363.
Kaufmann, B. 2007. Grizzly sightings on northern Arctic island.
Roach, J. 2006. Grizzly-polar bear hybrid found -- but what does it mean?
Stirling, I. 1999. Polar Bears. University of Michigan Press.
Struzik, E. 2006. Grizzly bears on ice.