Grizzlies Move Into Polar Bear Turf On Hudson Bay Reporting in The Canadian Field-Naturalist, researchers write of spotting grizzly bears in Canada's Wapusk National Park, on the shores of the Hudson Bay — land previously inhabited only by polar bears. Author Robert Rockwell discusses potential competition between the species.
NPR logo

Grizzlies Move Into Polar Bear Turf On Hudson Bay

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript
Grizzlies Move Into Polar Bear Turf On Hudson Bay

Grizzlies Move Into Polar Bear Turf On Hudson Bay

  • Download
  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript

JOE PALCA, host:

This is SCIENCE FRIDAY from NPR. I'm Joe Palca. Ira Flatow is away.

Polar bears are the poster children for climate change, floating out there on their melting blocks of sea ice, but for polar bears that live below the Arctic Circle, down around Hudson Bay, for example, melting sea ice is normal.

It happens every summer, and when the ice melts, the bears swim ashore to snack on stuff like birds' eggs and fish and berries. What's not normal is for the polar bears to find grizzly bears hanging out on shore, fishing in their streams and taking up residence in their dens.

But lately, wildlife biologists have been spotting some grizzlies along the shore of Hudson Bay, a place that used to be just polar bear habitat. A research paper describing the changing range of grizzly bears appears in the journal The Canadian Field-Naturalist. My first guest this hour is an author on that paper.

Robert Rockwell is a research associate at the American Museum of Natural History. He's also a biology professor at the City College of New York, here in New York City. He joins us by phone. Welcome to SCIENCE FRIDAY, Dr. Rockwell.

Dr. ROBERT ROCKWELL (Research Associate, American Museum of Natural History): Hi, good to be there.

PALCA: Great, and if you want to talk grizzlies, give us a call. Our number if 800-989-8255. That's 800-989-TALK. If you're on Twitter, you can tweet us your questions by writing the @ sign, followed by scifri. If you want more information about what we're talking about this hour, go to our Web site,, where you'll find links to the topic.

So again, the telephone number is 800-989-8255. Robert Rockwell, maybe you can first describe. I mean, the Hudson Bay isn't the kind of place that you would be totally surprised to find grizzly bears. It's the kind of habitat that they're found in, right?

Dr. ROCKWELL: That's correct, and if you go back far enough in time, back into the 1700s and early 1800s, there were grizzly bears in northern Manitoba and central Manitoba, but they were pretty well hunted out. The province lists them as extirpated.

That was a population called the prairie population of grizzly bears, and since that time, I have been up there for 41 years, and I've just sort of always been wanting to see a grizzly bear in polar bear habitat - that just seemed to be the right thing to find, and it wasn't until 2008 that that finally happened.

PALCA: And you saw it, or you heard of sightings, or which was it?

Dr. ROCKWELL: No, I saw it. We have been flying transects along the coast of Hudson Bay, counting geese and sandhill cranes and caribou and polar bears for 41 years now. We fly very regular flights along the coastline and count the normal things that we do. And in 2008, Linda Gormezano, who's one of the co-authors of the paper, and I were flying a transect counting, in this case, fox dens, when all of a sudden, she spotted a grizzly bear and yelled, and the helicopter pilot, after he recovered from someone yelling...

(Soundbite of laughter)

PALCA: Never a good idea in a helicopter to yell.

Dr. ROCKWELL: Well, you know, but it was excited, and he was at least as excited as both of us were about seeing a grizzly bear, and he flew over, and Linda got a great picture of it. And one of the problems is that there had been reports that I'd heard about since, oh, the early '90s, the mid-'90s, and oftentimes you go and talk to these people and say, well, you saw a grizzly bear, describe it to me.

Well, I came out, and I saw this brown thing running away from me. Well, you don't know whether the brown thing running away was a grizzly bear or a brown black bear or even a moose.

So you have to get a really good look at it. You have to see the hump, and you have to see the face, which on a grizzly bear is sort of flat. Their eyes and stuff are sort of flatish, and it sort of looks like they almost have a party hat for a nose. So, two very distinctive features, and if you can see that, then it's a grizzly for sure.

PALCA: So okay, so here you are doing transects along the Hudson Bay in an area where you've always wanted to see grizzly bears, you thought you might see a grizzly bear. Now you've seen one. I mean, is the right question what took so long, or is it just why did this happen? I mean, what's going on here?

Dr. ROCKWELL: I think the right question is: What's going on? And as I said, I think a key part to it is we were very careful. We went back and interviewed other people and records to see exactly what had been seen, to make sure that the sightings were grizzly bears when they were seen. And the important, other important part is that we have done these surveys rather systematically.

So it's not like you see an upsurge in grizzly bears because suddenly people are looking for them. We've been flying these for years, and all of a sudden, they started occurring, which is very consistent with the grizzly bears starting to move into the area. And that trend seems to have increased. Two thousand nine, we actually saw I saw three myself, and there was a fourth one reported in the area.

PALCA: Wow. So I mean, but again why? Is it just because they heard there was good real estate prices, or what's going on?

Dr. ROCKWELL: Well, I think it is partly that. The grizzly bear that we have, the barren ground grizzly, is originally from the Rocky Mountains of both the United States and Canada. Their populations were doing quite well. Grizzly bears don't like a lot of neighbors, so when it gets too crowded, they sort of wander around.

They have pretty good-sized territories, and they gradually expand into more habitat that has food that grizzly bears like, which includes all sorts of microtines. They like eating lemmings and mice. They like eating ducks and geese. They like eating berries. They like fish. They catch caribou and moose.

So they moved north into the Yukon, and then they sort of moved east across the Northwest Territories in what is now Nunavut and reached the Hudson Bay coastline. And when you reach the Hudson Bay coastline, you can either make a left turn and go into the high Arctic, where if you're not equipped to go out on the ice and hunt seals, you're sort of going to be hungry. Or, you can make a right turn and head down towards Churchill, Manitoba. And once you cross the Churchill River, going east, you run into Wapusk National Park, which is a place that's got an awful lot of food in it.

PALCA: Cool. All right, well, we have a lot of people who do want to talk grizzlies, and so let's go to the phones and talk first to John(ph) in Kansas City. John, welcome to SCIENCE FRIDAY.

JOHN (Caller): Hi, guys, thanks for taking my call. I just had a couple questions that popped into my head. I wondered: When do they ever crossbreed or hybridized between the two species, and also, I wondered, when they bump into each other, who wins the fight usually?

PALCA: Good question, John, thanks for the call.

Dr. ROCKWELL: Okay, let's take them one at a time. On the hybridization, there are a couple of cases in the wild where there are hybrids. It's a pretty rare event, and that has a lot to do with the timing of when female polar bears versus female grizzly bears come into estrous.

So it's a pretty rare event, but it can happen. They've only been separated for probably 150,000 years in evolutionary time. So it's quite possible. It's just a rare thing.

In terms of who's going to win, all really top-end carnivores have behavioral mechanisms that they use to really avoid confrontation. All these guys are really big. They could really do some damage, and if you think about it, if they didn't have some behaviors that would allow them to not be aggressive, to sort of back off in a schoolyard-bully-confrontation kind of thing, the species would quickly wipe themselves out.

And I think both grizzly bears and polar bears certainly have that, and my guess is that when the two get together, they're going to operate in the same way.

The other part of that is most of the confrontations or potential confrontations are going to be around food, and at that point, my experience with the bears is that it's, well, let's see, we could eat, or we could fight, and I think we're going to eat.

PALCA: Well, you know, at least eat first and then fight.

(Soundbite of laughter)

Dr. ROCKWELL: Right.

PALCA: Well, let's go to the let's take another call and now go to Bill(ph) in Reno. I suppose that's Reno, Nevada. You're on the air, Bill.

BILL (Caller): Hi, thanks for taking my call.

PALCA: Sure.

BILL: Yes, I'm real interested in finding out, there's a number of mammals, including the polar bear and the grizzlies, that have to endure the real harsh, wintery conditions I'm talking 30, 40, 50 degrees below zero. How do these animals do it?

PALCA: Oh, interesting question. Robert Rockwell.

Dr. ROCKWELL: Okay, let's take the species one at a time. There's a slight difference in their behavior. The grizzly bears do it by tanking up on a lot of food, getting really fat and then going into a nice den and pretty much hibernating. It's not a true hibernation, but it's a really deep sleep. They stir every once in a while, and they're in a nice, warm place, metabolizing body fat, and they pretty well stay out of the elements. Those dens cut the wind, and they're actually just right around freezing at times.

The polar bears have a slightly different lifestyle. The pregnant females go into maternity dens, and they, like the grizzly bears, survive there. The adult male polar bears and the females that have cubs from the previous year or females that are not pregnant, actually spend their winter on the sea ice.

And their way of coping with it is some amazing layers of fat, very thick skin and fur and insulation, to the point that their thermal neutral zone, where they can actually sit outside in very cold temperatures and not shiver, is close to 40 below zero.

PALCA: Wow, that's amazing. Before we go on you said that the bears don't the grizzly bears dont truly hibernate. Maybe you could tell me what the difference is between truly hibernating, and if grizzly bears don't hibernate, who does?

Dr. ROCKWELL: Well, there are a number of ground squirrels, for example, that go into a true hibernation, where the metabolic rates actually change and shut down completely or to a very, very minimal level so they're using very few nutrients. It's really a question of exactly how physiologically calm the critter gets.

PALCA: I got it. So these guys are not as in deep a stage of quietude as they're closer to sleep and a little further from hibernation.

Dr. ROCKWELL: Correct.

PALCA: Okay, interesting. They other question that we sort of, we haven't really addressed is, is any of this movement related to climate change, do we think? I mean, certainly the disappearing sea ice, people have blamed climate change for, but is this change in direction for the grizzlies anything related to climate?

Dr. ROCKWELL: Well, I think at this stage, it's a little premature to say. I think the one thing we know for sure is that the grizzly populations across the Yukon and Nunavut are very healthy.

There's lots of the population there. There's lot of food for them, and the populations are simply growing. And as I said earlier, grizzly bears don't like a real high density. So when it gets too crowded for them, they sort of move out.

Now, whether or not those growing populations are because of climate change, or whether it's because there are more humans living in Nunavut and the Yukon now, and the grizzly bears are taking advantage of some of that, much like the coyotes we have in the Northeast are doing, I don't think anybody knows yet. I think it's a little too early to say.

PALCA: So do I understand you're saying that human population are a good thing for grizzlies because they find easy pickings for food? Is that's what's happening, or would've thought they might be an easy target for hunters, too.

Dr. ROCKWELL: Well, it's a little bit of both. I think the grizzly bears are a very opportunistic species, and they're going to take advantage of a free meal anyplace they get it.

FLATOW: I got it. So you're going back, or is the season over for you?

Dr. ROCKWELL: I will going back, the end of May, for the 42nd year.

FLATOW: Forty-second, wow. Well, that's a pretty good, long stretch of grizzly hunting, I would think.

Dr. ROCKWELL: Well, we do most of our work on migratory birds and on the habitat that's involved with the migratory birds, but most of us that work in the Arctic have realized a long time ago that it's very expensive to get up there, and while we're there, we try to look at as many things as we can.

FLATOW: Okay. Well, I'm afraid that's all the time we have. Robert Rockwell, thanks very much.

Dr. ROCKWELL: Okay, thanks very much.

FLATOW: Robert Rockwell is a research associate at the American Museum of Natural History. He's also a biology professor at the City College of New York here in New York City. After the break, mathematician and writer Steven Strogatz joins us to talk about math and relationships. Stay with us.

(Soundbite of music)


Copyright © 2010 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.