Grizzly spotted on Western Hudson Bay shore but there are no polar bears on land for it to mate with

On 28 May last week a big grizzly (probably a male) was spotted on the shore of Wapusk National Park just south of Churchill, Manitoba but unless he heads out onto the sea ice, he has no chance of finding a polar bear female to mate with. Even if he does, he is unlikely to find a polar bear female willing to mate: most polar bears mate late March to early May (Smith and Aars 2015). Brown bears (called grizzlies across most of North America) mate later in the year, from late May to July, which means finding hybrids here is highly unlikely.

A few tundra grizzlies from the Northwest Territories have been spotted moving southeast into the Hudson Bay area since 2008. There was some media-and-expert-generated excitement back in 2016 when a hunter shot what he thought might have been a grizzly/polar bear hybrid near Arviat but it turned out to be a blonde grizzly, which are not uncommon in the tundra population from which it came. A similar result came from recent genetic study: samples from two pale blonde grizzlies from the North Slope of Alaska that looked remarkably like polar bear hybrids were not only unrelated to each other but showed no evidence of being hybrids (Lan et al. 2016 Supplementary data, pg. 3).

Contrary to some predictions, grizzly/polar bear hybrids are still quite rare (Crockford 2018:23).

Historical range of grizzlies (brown bears) in Canada:

Population sizes of northern grizzlies are almost certainly growing after decades of protection (SARA 2022) and with growth often comes range expansion, especially if there is former territory to reclaim (Manitoba’s grizzlies were wiped out decades ago). A few of these brown bears, primarily males, have been spotted in southern Nunavut and northern Manitoba within the last two decades (Clark 2000; Clark et al. 2018): multiple sightings some years may be of the same individual.

A better quality live cam photo of a grizzly from Wapusk National Park, 26 June 2016 (courtesy D. Clark), from the press release announcing his 2018 paper:

Hudson Bay Sea Ice

For the week of 30 May 2022, showing why polar bears are still on the ice.

References

Clark, D. 2000. Recent reports of grizzly bears, Ursus arctos, in northern Manitoba. Canadian Field Naturalist 114(4):692-696.

Clark, D.A., Brook, R., Oliphant-Reskanski, C., Laforge, M.P., Olson, K. and Rivet, D., 2018. Novel range overlap of three ursids in the Canadian subarctic. Arctic Science 5(1):62-70. https://doi.org/10.1139/as-2018-0013

Crockford, S.J. 2018. State of the Polar Bear 2017. London, Global Warming Policy Foundation Report 29. pdf State of the Polar Bear Report 2017

Lan, T., Cheng, J., Ratan, A., et al. 2016. Genome-wide evidence for a hybrid origin of modern polar bears. bioRxiv Preprint. https://doi.org/10.1101/047498

SARA Canada 2022.  Ursus arctos: Species at Risk Public Registry, by province, for Canada. https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry.html

Smith, T. G., and J. Aars. 2015. Polar bears (Ursus maritimus) mating during late June on the pack ice of northern Svalbard, Norway. Polar Research 34:25786. https://doi.org/10.3402/polar.v34.25786