It’s not easy to swim 175 km (109 mi.) when you’re starving to death. It’s not easy either to try to survive when you’re shedding body weight at a rate of 1 kg (2.2 lbs.) a day. And it might be hardest—or at least most tragic—of all if you’re a nursing mom and your calorie intake has dropped so low that you can no longer produce the milk you need to care for your young. As a new paper in Nature Communications reveals, all of those challenges and more are facing the world’s polar bears, thanks to vanishing sea ice in our warming world, denying the animals a platform that they need to hunt for seals. If the trend isn’t reversed soon, the estimated 26,000 polar bears in the wild could start to lose their hold on survival before the middle of this century.
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00:00 Foods, particularly that they were getting when they were on land, have pretty low caloric
00:06 content, and the bears have to expend energy to obtain them.
00:10 So out on the sea ice, they're primarily a sit and wait predator, and they're eating
00:15 primarily the fat of seals, which has twice the calories of protein and carbohydrates,
00:21 which is what they are primarily getting when they're on land.
00:25 Similarly, when they were swimming out into the bay and encountering carcasses, we found
00:29 that it was difficult for them to eat those carcasses while they were swimming, and they're
00:34 getting a single carcass over a three-week period versus catching seals every few days
00:41 out on the sea ice.
00:42 So it's just a big difference in the availability and quality of the food resources they can
00:47 get when they're on land.
00:49 All of the bears we studied, that we tracked in this study, were in relatively good condition.
00:55 There are no bears that we consider to be in poor condition.
00:59 With the caveat being that the time period that we conducted this study was basically
01:04 right in the middle of the time that they're on land.
01:07 So as I mentioned, they typically come on land around late July, early August.
01:14 We did this work in late August to early September.
01:18 And so they still have another 70-so days on land where they will be continuing to lose
01:24 mass.
01:25 I think our study confirms previous evidence that they're not very adaptable to spending
01:32 time on land.
01:33 That there's going to have to be other changes that would have to occur that are going to
01:37 help them withstand spending longer times on land.
01:42 One of the things that was really appealing to me was the fact that it's a very elegant
01:47 study in that they combine many different techniques to study a question about what
01:53 is happening in this population relative to the increasing length of the ice-free period.
02:02 So for me, I think it's a combination of physiology, behavior, and looking at the movements of
02:09 the animals.
02:10 And of course, the video colouring is a very nice addition.
02:14 So it gives you a better complete picture of what the animals are doing in that environment.
02:20 So one thing that would have been very nice to see would have been mothers with cubs included
02:25 in the study.
02:27 Partly because some of the research in my group is indicating that that is a very vulnerable
02:32 link in the population.
02:35 And so our concern is that once mothers with cubs lose their body condition to a certain
02:41 point, they stop producing milk.
02:44 And all of a sudden at that point, the cubs now have to rely on their own fat reserves.
02:49 And cubs in their first year in particular are growing rapidly, have very little stored
02:54 fat of their own.
02:56 And we think that this is probably one of the major weaknesses in the population ecology
03:01 of the bears.
03:03 And so if the mother doesn't get them back out on the ice and feeding on seals shortly
03:07 after she stops nursing, we've seen this in Western Hudson Bay, where the cubs actually
03:13 starve to death on land.
03:15 And so that point might have been nice to have included, but it also adds another level
03:21 of complexity.
03:22 And then you get into ethical issues of handling mothers with small cubs.
03:26 And because you have to handle them more than once, it does present some animal care challenges
03:32 for sure.
03:33 [BLANK_AUDIO]