Posted onFebruary 8, 2023|Comments Off on Polar bear evolution book is progressing well
Just a short update regarding progress on the book. I am deciding on a cover design while addressing suggested changes as they come back from the editor, and preparing marketing material. If all goes to plan, I am on track for a March publication date–thanks to your support.
In the early 1960s paleontologist Bjorn Kurtén thought that polar bears likely arose from a brown bear ancestor based on fossil evidence alone, and his estimate of when this happened was determined by the age of fossil remains of both species. As I will show in the chapters that follow, despite more fossil evidence being available and additional evidence from molecular genetic studies, his estimate is still the most likely time frame for when the polar bear came to be.
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I’ve decided to use this occasion to kick-start a donation drive to help cover production costs of my new polar bear evolution book. In many ways, your enthusiastic support over the years has led me to write this book: the complete story of polar bear evolution, including the role of hybridization, but without the baffling scientific jargon. It will put everything we know about polar bears into evolutionary context–not just the when and where but the why and how.
Nothing like this exists and I don’t think you’ll be disappointed. I’m on track for publication in early 2023.
I’m asking those of you with the means to help, to assist me in getting this important book across the finish line. Details below.
UPDATE 1 December 2022: GOAL REACHED! What an amazing community this is–$5210 raised in two days. I am truly grateful for your generosity and moral support. Your donations will ensure that this polar bear evolution book gets published quickly and looks professional. Heartfelt thanks to all who participated. I will announce the winners of the special incentive (see below) next Tuesday, 6 December.
Posted onJuly 4, 2022|Comments Off on Polar bear evolution and recent genetic papers
Two scientific papers in June on polar bear evolution got a bit of media attention but not what the topic deserves. I’ve not written about them because I am currently working on a larger piece putting this conflicting genetic information into full context. Have patience, it’s coming.
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Posted onJune 2, 2022|Comments Off on 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).
Posted onMay 6, 2022|Comments Off on Ancient polar bear remains explained by sea ice and polynyas: my peer-reviewed paper
My open-access, peer-reviewed paper on the ecology of ancient polar bears in relation to sea ice has just been published in Open Quaternary. It’s called ‘Polar Bear Fossil and Archaeological Records from the Pleistocene and Holocene in Relation to Sea Ice Extent and Open Water Polynyas’.
A unique compilation of more than 104 polar bear skeletal records from the Holocene and late Pleistocene shows that most ancient remainsare associated with existing or ancient open water polynyas or the expansion of sea ice during past cold periods. This big-picture analysis indicates that as they do today, polar bears were most commonly found near polynyas throughout their known historical past because of their need for ice-edge habitats.
Read my longer summary below and download the paper here. This is a much-updated and expanded analysis based on an informal study I did in 2012.
Posted onDecember 1, 2021|Comments Off on Higher than average Svalbard sea ice extent in November 2021 has implications for birth of cubs
Early last November, sea ice around Svalbard was the lowest it had been since 1967 and pregnant females were simply unable to den on the eastern islands of the archipelago and instead had to make their dens and give birth in the pack ice or the Franz Josef Land archipelago further east, as they have done before. However, the ice is back this fall with a vengeance: even Hopen Island in the south of region was surrounded by ice well before the end of the month but whether it will attract a few pregnant females remains to be seen.
Posted onSeptember 8, 2021|Comments Off on Svalbard polar bear paper falsely assumes that loss of genetic diversity has negative consequences
A new paper published today deals with an animal conservation issue I’ve addressed twice before: the theoretical assumption that loss of genetic diversity must be detrimental to species survival despite there being little evidence that this has been the case in real life. For this new study, the authors carried out some complicated measuring of genetic diversity loss and inbreeding amongst and between Svalbard region polar bear populations between 1995 and 2016 (see map below), and then modelled what this could lead to in 100 generations (1210 years), with the over-anxious hand-wringing we’ve all come to expect from such prophesies. As far as I can see, it’s all meaningless number-crunching without relevance to the real world of polar bears.
To support their claim of harm from loss of genetic diversity, the authors of this paper (Maduna et al. 2021) cite four theoretical papers that assume as fact that loss of genetic diversity is harmful but not the evidence to back up the claim. They apparently never bothered to look at species that have actually suffered dramatic loss of genetic diversity. Northern elephant seals, for example, reduced to 20-30 animals more than 100 years ago, have rebounded to a population of about 170,000 with extremely low genetic diversity but no apparent health or survival repercussions. Similar genetic bottlenecks and recoveries have been documented in Guadalupe fur seals, San Nicolas Island foxes, mouflon sheep, and North Atlantic right whales (among others), which I discussed in detail here (with references). I discussed the issue again in regards to a similar polar bear ‘genetic diversity’ paper in 2016.
Conspicuous by its absence in this new publication is a citation of the recent paper that revealed the body condition of female Svalbard polar bears had increasedsignificantlybetween 2004 and 2017 despite a pronounced decline in summer and winter sea ice extent (Lippold et al. 2019: 988). Nor did the paper cite data collected by the Norwegian Polar Institute that show the body condition of adult males in Svalbard has not changed since 1993 or that population numbers have not declined. Instead, the authors mention only that reduced numbers of pregnant females have reached traditional denning areas due to lack of ice and that bears have spent less time feeding at glacier fronts than they used to do (Maduna et al. 2021: 2), as if the only polar bear data available in relation to sea ice decline was negative.
Population bottlenecks during the Last Glacial Maximum when suitable habitat was scarce and another in the late 1800s/early 1900s due to wanton overhunting left polar bears with remarkably low genetic diversity but no apparent ill-effects to their overall heath. Oddly, this recent work by Maduna and colleagues assumes without evidence that a bit less genetic diversity could be devastating to Svalbard bears more than 1000 years from now. While the media expectedly promote this as scary new evidence of what climate change has wrought (here and here), I am not impressed.
This is conservation biology done WWF-style: loss of genetic diversity sounds bad to people who don’t know better, but real-world evidence shows it isn’t.
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. https://pubs.acs.org/doi/10.1021/acs.est.8b05416
Maduna, S. N., Aars, J., Fløystad, I., Klütsch, C. F. C., Zeyl Fiskebeck, E. M. L., Wiig, Ø. et al. 2021. Sea ice reduction drives genetic differentiation among Barents Sea polar bears. Proceedings of the Royals Society B 288 (1958): 20211741. https://doi.org/10.1098/rspb.2021.1741 OPEN ACCESS
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Posted onNovember 11, 2020|Comments Off on Shorefast ice formation and the fall feeding season for polar bears
What may seem like a silly question is actually fundamental to polar bear survival: in the fall, why do Western Hudson Bay bears correctly expect to find seals in the new ice that forms offshore? Why are seals attracted to that new ice – called ‘shorefast ice’ or ‘fast ice’ – when they would clearly be safer out in the open water where there is no ice and no bears?
As the picture below attests, polar bears can and do kill ringed seals in the new ice that forms off the coast of Western Hudson Bay even when it is but a narrow strip of thin ice – and so close to shore their successes can be caught on camera.
Three adult male polar bears share a seal kill on the newly-formed ice off Wapusk National Park, Western Hudson Bay. 5 November 2020. Buggy cam, Explore.org
A different bear was also filmed killing another seal on 31 October. And these are only the kills we know about along a very short stretch of coast – the killing is almost certainly going on up and down the entire coast, into James Bay (see below), where there is just as much ice but no cameras.
As far as I am aware, this seal killing by polar bears goes on in newly-formed shorefast ice everywhere across the Arctic in early fall, not just in Hudson Bay. Although the timing varies, virtually everywhere in the peripheral seas of the Arctic Ocean (Barents, Kara, Laptev, Chukchi, Beaufort, as well as Baffin Bay and Davis Strait), shorefast ice forms before the mobile ice pack expands to meet the ice developing from shore.
This shorefast ice formation in fall provides a predictable but short-lived source of prey for polar bears as they strive to regain some of the weight lost over the summer.
Posted onJanuary 24, 2018|Comments Off on Early Holocene polar bear skeleton from Norway vs. other ancient remains
A press release issued yesterday (23 January 2018) by the University of Stavanger tells the story of decades of work on the most complete ancient polar bear skeleton in the world, found in 1976 in southern Norway, that culminated in an articulated museum display. This specimen was described in my research paper, Annotated Map of Ancient Polar Bear Remains of the World (Crockford 2012), which shows how many very early Holocene remains have been found outside current polar bear range.
A polar bear X grizzly hybrid, see Kumar et al. 2017. Photo by A. Derocher.
In my opinion, the most important conclusion of this paper is that occasional but widespread hybridization among bears is why it has been so hard to say with confidence when polar bears arose (which I addressed years ago, in my Polar bear evolution series: Part 1, Part 2, and Part 3). You cannot use traditional methods of pinpointing the timing of speciation events from genetic data if one or more of the species have hybridized (traded genes). See the long, fuzzy “divergence times” for bears in the image below from the Kumar paper.
From Kumar et al. 2017, Fig. 5: “The scale bar shows divergence times in million years and 95% confidence intervals for divergence times [speciation events] are shown as shadings.”