Think Out Loud

How studying polar bears in zoos can help protect them in the wild

By Sheraz Sadiq (OPB)
Feb. 8, 2022 1 p.m. Updated: Feb. 15, 2022 9:30 p.m.

Broadcast: Tuesday, Feb. 8

Tasul, a polar bear who lived at the Oregon Zoo, is seen in this 2013 photo wearing a collar that collects data about her activity to help scientists who study the behavior of polar bears in the wild.

Tasul, a polar bear who lived at the Oregon Zoo, is seen in this 2013 photo wearing a collar that collects data about her activity to help scientists who study the behavior of polar bears in the wild.

Oregon Zoo


Perhaps no animal evokes as potently the existential threat of climate change as the polar bear. Global warming is causing sea ice to rapidly melt, leading to loss of habitat for the world’s largest land carnivore, which uses the Arctic ice as a platform to hunt ringed seals and other prey. Scientists face daunting challenges when studying wild polar bears in part because they live in remote places like Alaska’s north coast. But polar bears in captivity, including at the Oregon Zoo, are providing a trove of data that is helping scientists unlock clues to the health and survival of their wild counterparts. Joining us are Amy Cutting, interim director of animal care and conservation at the Oregon Zoo, and Karyn Rode, a research wildlife biologist based in Portland with the U.S.G.S Alaska Science Center.

This transcript was created by a computer and edited by a volunteer.

Dave Miller: This is Think Out Loud. I’m Dave miller. We turn now to polar bears, the animals most closely associated with the existential threat of climate change. Polar bears are in trouble because the sea ice they rely on is melting in our warming world. It can be difficult to study these animals in the wild though it turns out that polar bears in captivity in places like the Oregon Zoo have helped researchers better understand the challenges facing their wild counterparts. Amy Cutting is the interim director of animal care and conservation at the Oregon Zoo. Karyn Rode is a research wildlife biologist based in Portland with the U. S. Geological Survey’s Alaska Science Center. They both join me now. It’s good to have both of you on the show. Karyn Rode first.I gave the short version of the challenges that polar bears in the wild are facing because of climate change. Can you help us better understand their general plight right now in a warming world?

Karyn Rode:  Polar bears live in the Circumpolar Arctic and they live out the majority of their life history on sea ice that occurs over the arctic oceans and that sea ice, as the earth is warming, the Arctic is seeing some of the fastest changes in global temperatures of anywhere in the world and that’s leading to loss of sea ice.  Polar bears use that sea ice to access marine mammals primarily ice associated seals that are their primary prey. As that sea ice loss occurs, it’s increasing challenges for accessing food and moving across their habitat.

Miller:  What are some of the most pressing questions that you and other scientists want to answer about polar bears right now?

Rode:  One of the most important questions is trying to understand what affects whether polar bear populations increase, decrease or stay stable. So what are the drivers of the population? And then another important question is understanding changes in land use. Polar bears in different populations use land differently. So in some areas, whole populations come on land during the summertime when there’s no sea ice and then in other parts, there’s reduced ice and bears will come on land in some of those areas as well. And there’s a general response that in most places where there’s a lot of sea ice that more bears are coming on land. There’s two questions associated with that. One is, we’re trying to understand how many more bears are going to show up on land and for how long. Also, what are the implications of when they come on land?  If they’re spending more time there, how are they going to cope with that?

Miller:  I was curious what the challenges are in terms of studying wild polar bears.

Rode: The challenge is that they spend the majority of their life out on Arctic Sea ice and they have huge home ranges. So their home ranges are larger than any carnivore of their size. So for example, one of the population’s I study occurs off the northwest coast of Alaska and ranges all the way to the eastern coast of Russia and back. So there are in these huge areas where we just can’t directly observe them.

Miller: This gets us to the work that you and others have been doing at zoos like the Oregon Zoo. Amy Cutting, there are currently two polar bears at the Oregon Zoo, Nora and Amelia Gray. What are they like when you get to know them?

Amy Cutting:   I’m glad you started with the fact that polar bears as individuals are really amazing animals. We have the unique opportunity to get to know them as individuals rather than just on a population level. Nora and Amelia are actually half sisters. They’re from the same mom. They were both born at the Columbus Zoo, but a year apart. So they had never met until they arrived here. And surprising how different they are. Nora is a little more laid back, a little more playful, very people oriented in part due to her history with being hand raised. Amelia is just a little more high strung and it’s interesting to see how they interact. They have their moments where they play and have a good time and then Amelia definitely is ready to move on. They have distinct personalities. But it is nice that we have two adult females, which is really the demographic of interest for biologists and a lot of these research questions.

Miller:  Why is that? Two adult females?

Cutting:  The population is really going to be driven by reproductive rates.  So Karyn talked about the concern about what kinds of things are affecting animal survival and reproduction is going to be one of the precursors, changes in reproduction is going to signal changes in your population. So, understanding what adult females need to thrive and survive and reproduce is really an important question for us to understand as we look at these different populations.

Karyn mentioned this, but I think it’s important for listeners to know that there’s actually 19 different populations of polar bears spread throughout the Arctic and the vast majority of those are considered data deficient. So in terms of just the numbers, let alone how they spend their days, and compared to many well-studied carnivores, there’s very little known about this species in different parts of the Arctic and how they’re getting on. So it’s really critical to get as much information as we can.

Miller: About a decade ago zookeepers there were able to draw blood from polar bears without sedation and from what I’ve read, it’s thought to be the first time that anybody was able to do that. Why was that important?

Cutting:  Well, it’s an interesting question. It was important to us because we are committed to the welfare of every individual animal at the zoo. And when an animal gives a blood sample voluntarily, that allows us to learn all kinds of interesting things about their health status, it may mean we do not have to do an anesthetized exam just to do a checkup. So it’s a great value to us and we are able to do that with a number of species. But it was really exciting for polar bears because it was sort of seen as not possible.

Typically with large carnivores, you’re drawing blood from a large vein like a tiger has a very large vein in its tail and hardly notices once you train them how to draw a blood sample. But polar bears have very short little tails. So it was only once we had a polar bear who had been trained to extend her hind foot for some radiographs that we realized we had access to a vein and we’re able to draw a blood sample from her.  I immediately started telling the people that I know through a professional context, because I know that researchers are really interested in getting access to do bears, but have always been a little bit stymied because we have limits on what we will and will not do. We always want to do everything through these voluntary, cooperative processes. So, being able to get a blood sample through that process was really a game changer.

Miller:  Karyn Rode, what went through your mind when you heard that folks at the Oregon Zoo were able to get blood that easily?

Rode:  Well, I was excited at the opportunity that posed in terms of the variety of research that we could start to do in a zoo setting that would help us answer some key questions that we had been wanting to address.

Miller:  What are examples, what have you been able to learn from zoo bear blood?

Rode:  One of the primary things we were wanting to be able to understand was to better understand their diets and their nutrition. We needed new tools to understand what polar bears are eating if, for example, they don’t have as much access to their primary prey, which is typically ring seals. There’s one species of seal that’s particularly abundant throughout the Arctic that’s the primary prey of polar bears. So we wanted to better understand what they are eating, so if there is less access to ring seals, can they eat something else?  And what is the optimal diet nutritionally for a polar bear?

We’ve long known that they primarily eat the blubber of marine mammals, but they are carnivores so we’re also trying to better understand the nutrition of bears and what they need relative to the fat and protein in their diet. Being able to get examples from zoo polar bears opened up an opportunity to improve methods for being able to study bears in the wild and then also being able to understand and interpret any changes that we might see in their diets and nutrition.


Miller: I’ve read that when polar bears have access to all the seals they could want and are healthy, they often just eat a seal’s blubber and skin. Who are the polar scavengers who would eat the rest?

Rode:  There’s not many. There’s the Arctic fox. Those tend to be closer to shore though, so not necessarily out in the center of this Arctic Sea ice. There’s probably some differences between sex and age classes.  Polar bears that the older, more adult bears can be more selective. A young cub that has recently left its mom would be more of a scavenger and feeding on whatever they can find. And a smaller bear can eat more of the muscle and still get by. Whereas a large bear needs lots of blubber because fat has twice as many calories as protein. Polar bears are the biggest bear species in the whole world and they live in this really cold, harsh environment. So they need a lot of energy. So scavenging is mainly going to be from younger, smaller bears.

Miller:  What are the implications if there’s nothing quite like the fat from seals in terms of the evolutionary needs of these bears? This is how they have developed over probably millions of years. If because of melting sea ice they’re less likely to have access to those good fatty seals, what does that mean?

Rode: Our ability to answer that is tied to multiple studies that have been done with bears and zoos, and we wouldn’t wouldn’t even be able to answer that question at all without the zoo-based research that we’ve been able to do in recent years. Polar bears evolved from brown bears and brown bears are omnivorous and they have low protein environments. But polar bears on the sea ice are purely carnivorous but what we’ve learned from some of the research we’ve done is that polar bears have low protein requirements. In addition to the energetic differences between blubber and muscle. And so as polar bears get less access to seals, then they can eat more of the muscle and eat more of the protein. And we know that that doesn’t provide them the energy that they need. If they eat too much protein, they actually have to excrete the nitrogen that their body doesn’t need.

A lot of people may be familiar with the Atkins diet. That was a fad for a while and that people consumed a lot of protein and that helped them lose weight. It’s actually the same mechanism for a polar bear. If they have too much protein, they happen in your body. Their bodies have to excrete that extra nitrogen. It costs them energy. So it actually costs them more energy to process the diet. And at the same time they’re consuming fewer calories because muscle has fewer calories than blubber.

Miller: But they need those calories for energy and for fat storage because they’re living in freezing places and covering tons of miles. So, this is not just a question of body image, this is survival.

Rode:  Absolutely. And you know, as Amy mentioned, reproduction is critical to the population obviously.  The environmental changes that are occurring, we’re seeing those effects primarily lower cub survival. So polar bears will still have cubsA pregnant female polar bear  will enter a den. She won’t eat that whole time. So she has to get fat. And then when she’s in the den, she has to live off that fat and how fat she is determines how big her cub is when it comes out of the den and that affects their survival. So the condition of the bear and how much food they’re getting is just absolutely critical to reproduction and survival in the population. And so one of the links that we’re now able to make with some of the zoo-based method development and understanding of diet is to look at how the proportional blubber in the diet is related to survival and reproduction.

Miller:  Amy Cutting, another field where you have really worked hard at the Oregon Zoo is in getting polar bears to do different kinds of exercise just to see what’s happening in their bodies. That includes training a bear to walk on a treadmill and training other bears to go into swim chambers. Let’s start with the Treadmill first. How do you train a bear to get on a treadmill and walk on it?

Cutting:  Everything that we do is through this positive reinforcement or voluntary training and the animal has a chance to walk away and still receive their daily portion. But as it turns out, polar bears are super curious and very intrigued by what’s going on and if you take this step slowly enough, they feel comfortable doing just about anything. One of our trainers says “Sometimes all you’re limited by is the animal’s physical abilities and your own imagination.” So we actually collaborated with a number of different folks in developing that treadmill. Let me back up a little bit. Karyn talked quite a bit about calories in and when we talk about these energetic and exercise projects we’re really looking at calories out.  Because at the end of the day that animal’s body condition is based on both.

We’re working with Dr Anthony Pagano, also a USGS colleague of Karyn’s, and he had a lot of questions about what it really costs an animal, a polar bear, to walk. These studies are done fairly routinely with other species in research settings, [typically] smaller animals. But of course we’re working with zoo bears. They need to be out on exhibit, they need to be you know participating and have their own health care with their keepers. But a little bit of time every day and we can get them to do all kinds of funky things.

But this particular treadmill is actually a Horse Gym 3000 which is a device that people use to condition race horses or or get them back into shape after an injury.

And a collaboration between Washington State University, U. S. Geological Survey, San Diego Zoo, and ourselves, we fabricated a treadmill that could safely contain a polar bear.  We started very, very slowly.  In order to stay in position to receive their fish treat, they would have to eventually walk against the moving floor. And then shortly thereafter, it went down to San Diego Zoo and they were able to do it with a female polar bear there.

And what we do is they collect the respirations from the bear.  We all know that when we consume oxygen we produce CO2 [Carbon Dioxide]. There’s a methodology and some very fancy science that I can’t explain that takes the difference between O2 [Oxygen] input and CO2 output and can calculate a metabolic rate for an animal. So you can actually measure how many calories an animal is burning at different speeds. That was really the first time we think we’ve successfully quantified the cost of walking in polar bears.

Miller:  Karyn Rode, could any of the studies that the two of you are talking about provide ideas for how to help boost polar bear populations or is it simply and sadly that they’re going to give us a more granular understanding of this species decline?

Rode:  Well I think it does both.  The culmination of the different research that Amy and I have been talking about is that we have a better understanding of the limitations that polar bears have on adapting to the changes they’re experiencing. And so if you think about that in an applied way, what can that tell us something we might be able to do to help bears?  When bears come onshore, they come to places where they interact with people. That may be through tourism or it may be through human settlements or where there’s oil and gas. We have a better sense for how sensitive their energetics may be, for example, to disturbance. And so we can then use that information to say, we know that this increases this energetic cost, so we need to mitigate these types of activities where bears come on land.

So that would be an example of how we can use this information to manage the circumstances to give polar bears the best chance we can to deal with their changing environment. But at the same time I think we have a better understanding of what the situation is. I think there’s been a lot of hope about adaptation to change. And I think these studies are really showing what are the limits to that adaptation. I think they’re a pretty specialized animal and the research is showing that they have high energetic costs and a very specialized diet which creates constraints on their ability to adapt.

Miller:  Amy Cutting, you’ve been at the zoo for 20 years.  You’re going to leave in the fall to go to Polar Bears International. Why turn specifically to this one species?

Cutting: Well, I’ve always been fascinated with polar bears and as I said as individuals, their exceptional animals. But really there’s this incredible community gathering that has been gathering for the last 20 years around polar bears and Polar Bears International has been one of the conveners of that community and it’s really exciting to see how much has been possible over the last 20 years. And so as I kind of get ready to make a change in my professional life, the attraction of helping even more further this collaboration and cooperation is just too hard to pass up.  They were willing to offer me a job so I am excited about that. The Polar Bear Research Council is an ad hoc group of scientists and zoo community professionals that are trying to steer the resources that zoos are spending on this kind of research collaboration to make sure we’re laser focused on these priority projects. And I had such wonderful experiences working with people from different facilities and folks in the field like Karyn trying to kind of get them together and get them moving in the same direction that to be able to do that as my full time profession is just a really exciting opportunity.

They are an amazing species and there is hope.

Miller: Amy Cutting and Karyn Rode, thanks for joining us. I appreciate it.

Cutting: Thanks for having us, I really appreciate it.

Rode: Thank you.

Miller: Amy Cutting is interim director of animal care and conservation at the Oregon Zoo. Karyn Rode is a research wildlife biologist with the USGS Alaska Science Center. She works out of the Portland office.

Contact “Think Out Loud®”

If you’d like to comment on any of the topics in this show, or suggest a topic of your own, please get in touch with us on Facebook or Twitter, send an email to, or you can leave a voicemail for us at 503-293-1983. The call-in phone number during the noon hour is 888-665-5865.