Americans will often joke and modify the four food groups (as approved by the USDA) to something more palatable to our junk-food loving appetites, e.g., alcohol, chocolate, fried food and ice cream, anyone? The prolonged winter we're having here in the midwest, a backlog of sedentary work, and recent conversations with a convalescing family member all have had me thinking about energy balance - for humans and, of course, for polar bears.
When we were in Churchill, we were told that bears are in "walking hibernation" during the summer when they can't be out catching seals from the Arctic ice. It came as a bit of a surprise to us then (and to my audiences when I give talks) that polar bears aren't out chasing down dinner during the summer when they can't get to their preferred meal of seal blubber.
But then, as you start to explore the science, it makes complete sense that an animal as large as the polar bear isn't going to be lumbering after a lemming, expending hundreds of calories, for only a few tens of calories in return. And it explains that though bears will swim to get to better ice shelf for sealing, they aren't in the water "chasing down" a seal for dinner. Too many calories out for too few calories in - a bad energy balance.
That said, the Arctic landscape isn't completely barren during the summer. The Inuit in Gjoa Haven record their observations that polar bears will eat vegetation and bird eggs when they come upon them. And there is the video showing hordes of bears that descended on a whale carcass that washed up on Wrangel Island. Even on our trip to Churchill we witnessed bears eating seaweed and shellfish on the shore.
So thinking forward to spring (it will come some day, right?) I offer you this video from the collar of a young female bear - managing to find food and drink on Akimiski Island.
Energy balance is a complex topic. And all of the studies only whetted my appetite (I couldn't resist) to figure out who thinks of these studies and then how they are conducted. Even a recent PBI article had me wondering - were the bears they studied good samples? does the stress of being tracked and re-tracked affect the biochemistry of the tracked bear? how do you track a polar bear, closely enough, to **really** understand their baseline now to better understand the affect global warming will have on them soon (if not already?). And who on earth thinks about a polar bear treadmill!
Which led me back to WWF's polar bear tracker and the three female bears (with cubs) that are tagged and moving about in Hudson Bay.
Remember each of these bears has a cub (or cubs) who were born in the spring of 2017. It will be fascinating, later this year, to see if researchers are able to identify the bears when they are on land and record the development of the un-tagged cubs. I'm honestly surprised they haven't wandered further within the Bay. But I'm also hopeful that they've been successfully hunting and eating seal blubber all winter. Polar bear milk is 30-35% fat (cow milk is 4%) and critical to the development of the cubs who may stop nursing at 18 mos but who continue to be with their mother until they are ~30 mos old (and may nurse until then!)
In the most recent PBI article, Polar Bears Burn More Energy Than Previously Thought, the importance of energy balance is really brought home. The bears in the study used 1.6 times the energy previously thought. And, even more concerning for the future of polar bears, the researchers found the bears do not reduce their metabolism when food is scarce. There is an inherent imbalance in that scenario. If you've developed a metabolism requiring blubber, berries will be a very light diet indeed.