At least a month earlier than in more northerly areas of the Arctic, the first known female with new cubs-of-the-year has been reported on the sea ice hunting for seals in Western Hudson Bay. Remember this when the cries of “early” breakup of sea ice on Hudson Bay come in the summer: these WH bears routinely get a head start on spring feeding that other bears don’t get.
Courtesy a tweet from Andrew Derocher (5 March 2023):
Bear O4 just left her den & made it to the sea ice (bear closest to coast): likely with her cubs out to hunt. She needs to rebuild depleted fat depots for next summer.
Here is the map he included, on which I’ve circled “Bear 04”:
As I’ve stated previously, in most areas of the Arctic, December is when polar bear cubs are born, although in southern regions (like Western and Southern Hudson Bay), some may be born in late November and in the far, far north, a few may be born as late as early February.
The actual date of birth for polar bear cubs is often back-calculated from when they emerge with their mothers in the spring at about 3 months of age, because they are born well away from our prying eyes in the dark of the Arctic winter, deep within a snow or soil den dug for that purpose. So our knowledge of the true dates of birth in various regions is limited.
We have some evidence from native Canadian hunters prior to 1968, when it was both legal and common practice in Canada for Inuit to hunt bears in their dens (Van de Velde et al. 2003), and from a few scientific research expeditions (Amstrup and Gardner 1994; Harington 1968; Ramsay and Stirling 1988).
It appears that the female shown on Derocher’s map (“04”) indeed must have given birth in late November in order to have cubs old enough to be well offshore by 4 March. In other words, the family were likely out of their den, getting ready to move out, close to the middle of February (presuming this female indeed has cubs with her, which has not been confirmed).
This female’s location in early February:
For comparison, the video below offers a discussion of polar bear den studies in Svalbard, produced by Polar Bears International in 2021. They map they show indicates how much further north Svalbard is than Western Hudson Bay.
Keep in mind that since sea ice conditions have changed around Svalbard (about 2003), most pregnant females make their dens on the sea ice or in Franz Josef Land. And despite pessimistic prognostications for the future, Svalbard bears (including adult females) have been doing very well despite much less sea ice (Lippold et al. 2019:988), as Jon Aars honestly admits in the video.
Amstrup, S.C. and Gardner, C. 1994. Polar bear maternity denning in the Beaufort Sea. Journal of Wildlife Management 58:1-10. http://www.jstor.org/discover/10.2307/3809542
Harington, R. C. 1968. Denning habits of the polar bear (Ursus maritimus Phipps). Canadian Wildlife Service Report Series No. 5., Ottawa
Lippold, A., Bourgeon, S., Aars, J., Andersen, M., Polder, A., Lyche, J.L., Bytingsvik, J., Jenssen, B.M., Derocher, A.E., Welker, J.M. and Routti, H. 2019. Temporal trends of persistent organic pollutants in Barents Sea polar bears (Ursus maritimus) in relation to changes in feeding habits and body condition. Environmental Science and Technology 53(2):984-995.
Ramsay, M. A. and Stirling, I. 1988. Reproductive biology and ecology of female polar bears (Ursus maritimus). Journal of Zoology London 214:601-634. http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1988.tb03762.x/abstract
Van de Velde (OMI), F., Stirling, I. and Richardson, E. 2003. Polar bear (Ursus maritimus) denning in the area of the Simpson Peninsula, Nunavut. Arctic 56:191-197. http://arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/615