Hybridization with grizzlies comes up repeatedly in genetic studies that aim to zero in on polar bear origins and is one of the issues I explore in detail in my upcoming new book, Polar Bear Evolution: A Model for How New Species Arise. Here is a photo essay to get you thinking about grizzly X polar bear hybrids, because understanding the topic is critical to unravelling the genetic evidence on how polar bears came to be.
For example, who can forget the hoopla over the bear shot near Arviat on the shore of Western Hudson Bay in 2016 (shown above) that everyone, including polar bear expert Ian Stirling, decided must be a hybrid–but it turned out to be a blonde grizzly.
Explaining all the ins and outs of why hybrids are important to polar bear evolution is an important part of my book.
As you’ll see, it’s not easy to tell a polar bear hybrid from a brown bear or grizzly (same animal) by its coat colour alone.
Blonde brown bears and grizzlies
The bear below was photographed on the shore of the Chukchi Sea in 2014, feeding on the carcass of a grey whale by NOAA employees surveying the coast. The location suggests it could be a hybrid but if researchers followed up with a DNA test that proved it was, I’m sure we would have heard about it by now. I’m assuming it’s just an oddly-marked, blonde grizzly.
The bear in the photo below, taken on the North Slope of Alaska in 1995 by Richard Shideler at the Division of Wildlife Conservation, Alaska Department of Fish and Game (ADF&G), had biologists wondering if it was a grizzly X polar bear hybrid. But DNA testing revealed it was a blonde grizzly with typical grizzly mtDNA (see Lan et al. 2016 supplement), as were all other suspected hybrids that were tested. Photo from the Lan et al. 2022 press release.
The grizzly below was photographed on the Sagavanirktok River, Alaska (aka, “Sag River,” south of Prudhoe Bay, North Slope of Alaska on the edge of the Beaufort Sea), ADF&G photo, on 21 September 2003 (Puryear 2022). Although I thought it might have been one of four light-colored bears tested by geneticists Lan and colleagues for their 2016 paper (Lan et al. 2016), Riley Woodford at ADF&G told me via email that this bear was not part of a research project and wasn’t sampled.
Apparently, the photo was taken by the staffer who saw the grizzly digging for roots and thought it was a beautiful bear!
Compare the coloring on this blonde bear to the image below from the known 2nd generation polar bear hybrid shot in Ulukhaktok in the second part of this post on wild hybrids.
From the Alaska Peninsula (well outside polar bear territory), the grizzly cub shown below, next to its typically-coloured sibling, has ‘dirty feet and face’ markings but is otherwise very light all over. Photo courtesy Tom Walker, with permission:
A slightly different pattern seen in a blonde grizzly is shown in the photo below, from an article by ADF&G researcher Riley Woodford (2020), of a bear spotted in Berners Bay, Alaska (on the SE Alaska mainland, about 50 miles north of Juneau). It has a pronounced dark line running along the midline of its back that runs up onto its forehead.
The photo was taken by Anthony Crupi of ADF&G.
Similar to the animal above is a very pale female grizzly spotted near Lake Louise in Banff National Park in the Canadian Rockies shown below, from Parks Canada. There is video of this bear here, taken in 2022. Note the similar dark, mid-line stripe.
At the other extreme, the grizzly shown below was taken on sea ice north of Banks Island, in the western Canadian Arctic by Andrew Derocher in 2014 during field work for a paper authored by two of his students, Jodie Pongracz and Evan Richardson (Pongracz et al. 2017). Even this grizzly has some light shading.
Grizzlies have been regularly seen in polar bear habitat in the western Canadian Arctic since about 1991 (Doupe et al. 2007), but this seems to be due to increasing grizzly numbers, not climate change or sea ice declines.
Male grizzlies expanding into this area of polar bear territory are responsible for a rare series of hybridization events, described below.
Confirmed wild hybrids
The one that started all the “Love in the Time of Climate Change” nonsense (Popescu 2016) was a first generation hybrid mistaken for a polar bear (below) that made international news in 2006. More reports of other wild hybrids followed.
All of these wild examples are crosses between a female polar bear and male grizzly, or between one of those hybrid females and a male grizzly.
This first hybrid bear (above) was shot by a hunter near Ulukhaktok on Victoria Island in the western Canadian Arctic, see map below. Notice the dark rings around the bear’s eyes but overall light coat. All of the wild hybrids shown here came from the same area around Victoria Island and Banks Island.
Below is another potential hybrid example, photographed by Jodie Pongracz during her field work on the recent hybrids (Pongracz et al. 2017). Note the dark rings around the eyes, slightly muddy-looking feet and the remnant of a dark line down the centre of its back. This animal was spotted in 2012 but was not sampled and is therefore only a “suspected” hybrid. However, its markings are very similar to the hybrid shot in 2006.
Below is photo of a taxidermy mount of a confirmed second generation grizzly X polar bear hybrid (the product of a hybrid female, whose mother was a polar bear that mated with a male grizzly). It was shot in 2010, again near the community of Ulukhaktok on Victoria Island.
The original polar bear female responsible for all of the hybrids in the area, who had mated with two different grizzly males over the years, was shot in 2012 along with her two hybrid cubs. The brief spate of hybridization events ended in 2014 when the last female hybrid was shot along with her three 2nd generation, back-crossed-to-grizzly, male cubs.
No more hybrids have been documented in the area since. I discuss these natural hybridization events in detail in my book.
Hybrids in captivity
The photos below show the offspring (one male, one female) of one of the few known instances of mating between a polar bear male and a brown bear (grizzly) female, born at the Osnabruck Zoo, Germany in 2004 (Preuss et al. 2009), after being kept together for 24 years. This is the opposite cross documented in wild-born hybrids. In my book, I discuss the behavioural differences between the two species–and between the two sexes–that would prevent this pairing from happening in the wild, except under the rarest of circumstances.
The coats of these hybrids look a bit darker viewed from the side, as shown below:
Bottom line: Because blonde grizzlies often look similar to polar bear hybrids and can appear in areas where hybridization is known to occur, genetic testing is required to confirm whether a suspected wild hybrid is indeed a grizzly X polar bear cross. The critical question of whether hybridization with grizzlies has played a huge part in the evolutionary history of the polar bear, as some geneticists insist, is an issue I address in my book.
References
Doupé, J.P., England, J.H., Furze, M. and Paetkau, D. 2007. Most northerly observation of a grizzly bear (Ursus arctos) in Canada: photographic and DNA evidence from Melville Island, Northwest Territories. Arctic 60:271-276. http://arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/219
Lan, T., Cheng, J., Ratan, A., et al., including Lindqvist, C. 2016. Genome-wide evidence for a hybrid origin of modern polar bears. bioRxiv 047498. https://www.biorxiv.org/content/10.1101/047498v1
Lan, T., Leppälä, K., Tomlin, C., et al., including Lindqvist, C. 2022. Insights into bear evolution from a Pleistocene polar bear genome. Proceedings of the National Academy of Sciences USA 119(24):e2200016119. https://doi.org/10.1073/pnas.2200016119
Pongracz, J.D., Paetkau, D., Branigan, M., et al. 2017. Recent hybridization between a polar bear and grizzly bears in the Canadian Arctic. Arctic 70:151–160. https://doi.org/10.14430/arctic4643
Popescu, A. 2016. ‘Love in the time of climate change: Grizzlies and polar bears are now mating.’ Washington Post, 23 May (interview with Andrew Derocher about polar bear hybrids and climate change). https://www.washingtonpost.com/news/animalia/wp/2016/05/23/love-in-the-time-of-climate-change-grizzlies-and-polar-bears-are-now-mating/
Preuss, A., Gansloßer, U., Purschke, G., et al. 2009. Bear-hybrids: Behaviour and phenotype. Der Zoologische Garten 78(4):204–220.
Puryear, W. 2022. ‘A bear by any other name: The many monikers of Ursus arctos Part 1.’ Alaska Fish & Wildlife News, January. https://www.adfg.alaska.gov/index.cfm?adfg=wildlifenews.view_article&articles_id=1016
Woodford, R. 2020. ‘Mysterious brown bear appearance and Southeast bear research.’ Alaska Fish & Wildlife News, May. https://www.adfg.alaska.gov/index.cfm?adfg=wildlifenews.view_article&articles_id=954
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