Polar bear survival on land food as sea ice melts

HostI was looking at some photos recently of polar bears in the summer, and it was a bit of a shock. Instead of seeing them on a big white sheet of ice, they were standing in these bright green meadows, munching on tall grass and picking berries. It looks almost like they're on a nice vacation, but I know the ice is melting faster than ever. Are these bears actually finding a way to make it work on land without their usual diet?

GuestIt's a sight that really messes with your head because we're so used to seeing them as the kings of the frost. But what you're seeing is a bear trying to make do with what's left. For a long time, we hoped that maybe these bears would just act like their cousins, the brown bears, and eat whatever they could find on the ground. They're smart, and they have been seen eating all kinds of things lately, from blueberries and crowberries to bird eggs and even some types of kelp. But here is the problem. A polar bear isn't just a white grizzly bear. Their bodies are built for a very specific kind of fuel, and that fuel is seal fat. When they're on the ice, they catch seals and eat the thick layer of blubber, which is just packed with energy. When they move to land, they're switching from a high-fat diet to a diet that's mostly sugar from berries or protein from grass and birds. It sounds like they're eating healthy, but for a bear that size, it's like a human trying to live off of celery and rice cakes.

HostBut if they're eating enough of it, shouldn't that keep them going? I mean, if they find a huge field of berries, that has to count for something.

GuestYou would think so, but the math just doesn't work out in their favor. To understand why, you have to look at how much energy it takes for a bear that big to even move. A polar bear can weigh over a thousand pounds. Just walking across the tundra to find those berries burns a lot of fuel. Scientists recently put cameras and trackers on bears in Canada to see exactly what happened when they spent time on land. They found that even when the bears were busy eating all day, almost every single one of them was losing weight fast. Some were losing as much as two pounds of body weight every single day. The berries and the grass just don't have the punch they need. To get the same energy they get from one single seal, a bear would've to eat tens of thousands of berries. Imagine how much walking and picking that takes. They're basically spending more energy to find the food than the food actually gives back to them.

HostWait, so even if the food is right there in front of them, they're still essentially starving because they're working too hard to get it?

GuestThat's exactly it. It's like being on a treadmill where the faster you run to reach a snack, the more weight you lose. And it gets even tougher when you look at things like bird eggs. A bear can find a colony of seabirds and eat every egg in the nests. That's a great boost of protein, sure. But these birds only lay eggs once a year. Once the bear eats them, the food is gone, and the birds might not come back the next year if they keep losing their chicks. So it's a very short-term fix. Plus, the bear has to compete with other land animals that are much better at this. This is where the friction with brown bears comes in. Brown bears are smaller and their bodies are much better at getting through the winter on plants and roots. A polar bear is like a giant truck that needs high-grade fuel, and right now, it's trying to run on fumes.

HostI have heard people say that maybe they'll just change over time. If the ice keeps shrinking, couldn't they just grow smaller or change how their bodies work to match the brown bears?

GuestChange like that usually takes thousands of years, and the ice is vanishing in decades. There's a huge gap in how their bodies handle food. Polar bears have these special ways of processing fat that keep their hearts healthy even though they eat so much of it. Brown bears don't have that. Also, polar bears have much longer necks and different teeth made for grabbing and tearing meat, not for grinding up tough roots and plants. We're seeing some bears stay on land longer and longer, but they're not really thriving. Some of them are just trying to stay as still as possible to save energy, almost like they're sleeping while awake, waiting for the cold to return so they can get back to the ice where the real food is.

HostSo the grass and the berries aren't a new way of life, they're more like a last resort that's not quite enough.

GuestThe bears on land are basically running a race they can't win, burning more fuel to find snacks than those snacks can ever provide to keep a thousand-pound frame going.

HostThat white bear in the green meadow looks like he's finding a new home until you see the weight he's losing while he waits for the ice to come back.