SEARCHING FOR PREY: Polar bears rely on sea ice to find seals—their primary food source.

MIKE HILL/GETTY IMAGES

STANDARDS

NGSS: Core Idea: LS4.C    

CCSS: Writing: 1    

TEKS: 6.3A, 7.3A, 8.3A, B.12B


Walking on Thin Ice

Will polar bears be able to survive a melting Arctic?

ESSENTIAL QUESTION: How might changes in the environment affect the animals that live in an ecosystem?

The helicopter’s blades whirred in the frigid Arctic air as Anthony Pagano scanned the sea ice below. Finally, he spotted what he’d been looking for. A white bear was moving across the frozen landscape, more than 100 kilometers (62 miles) off the northern coast of Alaska. The helicopter swooped closer, and Pagano aimed a tranquilizer dart at the bear. The shot hit its mark.

The helicopter’s blades beat the cold Arctic air. Anthony Pagano scanned the sea ice below. Finally, he spotted what he was looking for. A white bear was moving across the frozen ground, more than 100 kilometers (62 miles) off the northern coast of Alaska. The helicopter moved closer, and Pagano aimed a tranquilizer dart at the bear. The shot hit its mark.

Ten minutes later, the helicopter touched down on some ice near the bear. Pagano, a wildlife biologist with the U.S. Geological Survey, cautiously approached the furry mound lying in the snow. He got to work fitting a tracking collar around the sedated animal’s massive neck. The collar contained an accelerometer. The device detects changes in velocity, allowing Pagano to collect information about the bear’s movements.

Polar bears roam the floating sheets of ice that cover the Arctic Ocean searching for holes where seals might surface to take a breath. Once a bear finds a good spot, it lies in wait on the ice floe, sometimes for hours, to ambush its next meal. But in recent years, warming temperatures linked to climate change have caused a major meltdown in the Arctic. Sea ice has been steadily shrinking—and so has the number of polar bears (see Shrinking Sea Ice). “We’re trying to get a better understanding of how these changes in sea ice are actually impacting them,” says Pagano.

Ten minutes later, the helicopter landed on some ice. The bear lay in the snow nearby. Pagano, a wildlife biologist with the U.S. Geological Survey, carefully approached. He fit a tracking collar around the sleeping animal’s huge neck. The collar contained an accelerometer. The device detects changes in velocity. It would allow Pagano to collect information about the bear’s movements.

Floating ice sheets cover the Arctic Ocean. Polar bears travel here, looking for holes in the ice. That’s where seals might come up to breathe. When a bear finds a good spot, it waits on the ice floe to grab its next meal. Sometimes it waits for hours. But in recent years, temperatures have warmed due to climate change. This has caused major melting in the Arctic. Sea ice has been shrinking more and more. So has the number of polar bears (see Shrinking Sea Ice). “We’re trying to get a better understanding of how these changes in sea ice are actually impacting them,” says Pagano.

MEASURING ENERGY

Scientists fear that as sea ice disappears, polar bears will have to work harder to find food. If hunting becomes too exhausting or the bears fail to find enough to eat, they could starve. Pagano wants to determine how much energy the animals use while searching for prey. The data could help him predict how polar bears might fare as their habitat continues to warm.

Researchers study people’s energy use while walking by having subjects stroll along on a treadmill. But that wasn’t an option for polar bears . . . at least not in the wild. If someone could teach polar bears in zoos to walk on a treadmill, thought Pagano, he could take the measurements he needed. Paired with his accelerometer data, he could determine the amount of energy wild polar bears typically expend while hunting. He’d just need to convince captive bears to go along with the plan.

Scientists are worried. As sea ice disappears, polar bears may have to work harder to find food. Maybe hunting will take too much energy, or the animals won’t find enough to eat. Then they could starve. How much energy do polar bears use when looking for prey? Pagano wants to find out. The data could help him answer another question: What might happen to polar bears as their habitat warms?

Researchers can easily study people’s energy use. They have subjects walk on a treadmill. That wouldn’t work for polar bears, at least not in the wild. But Pagano had an idea. Maybe someone could teach polar bears in zoos to walk on a treadmill, and he could measure their energy use. He could add that to his accelerometer data. Then he could figure out how much energy polar bears use while hunting. He just needed to get zoo bears to follow the plan.

Pagano contacted the San Diego Zoo in California, where senior keeper Nate Wagner didn’t think the idea of a polar bear walking on a treadmill sounded strange at all. These intelligent, curious bears were always up for a new experience. Wagner chose Tatqiq (taht-KEEK), a 17-year-old female, for the job. “She’s incredibly inquisitive, and she’s very happy to participate in just about any kind of activity that she’s presented with,” says Wagner.

Tatqiq and her twin brother were born in the Alaskan wilderness, but their mother died two months later. The cubs would have starved to death, except that their mother was wearing a tracking collar. Its unchanging signal clued researchers in that something was wrong. They found the orphaned cubs and relocated them to the San Diego Zoo. Now Tatqiq, along with another polar bear at the Oregon Zoo that was recruited for Pagano’s study, would have a chance to help bears in the wild.

Pagano called the San Diego Zoo in California. Senior keeper Nate Wagner heard the plan to put a polar bear on a treadmill. Wagner didn’t think that sounded strange at all. He knew that polar bears are smart and curious. They’re always ready to try something new. Wagner chose Tatqiq (taht-KEEK), a 17-year-old female, for the job. “She’s incredibly inquisitive, and she’s very happy to participate in just about any kind of activity that she’s presented with,” says Wagner.

Tatqiq and her twin brother were born in the wild in Alaska. Their mother died two months later. The cubs would have starved to death, but their mother was wearing a tracking collar. Its signal didn’t change, so researchers knew something was wrong. They found the cubs and took them to the San Diego Zoo. Now Tatqiq could help bears in the wild. Another polar bear at the Oregon Zoo would also help with Pagano’s study.

MICHAEL DURHAM/OREGON ZOO

FURRY SUBJECT: It took five months of training to get Tatqiq accustomed to walking on a treadmill. With each step, researchers monitored the polar bear’s movements and breathing.

TREADMILL TRAINING

The first challenge for the researchers was finding a treadmill sturdy enough for a 263 kilogram (580 pound) polar bear. Pagano’s team bought one designed for racehorses. Next, they needed to find a way to measure the bears’ oxygen intake as they walked on the machine.

An animal’s body uses oxygen to create energy to power its muscles. Based on the amount of oxygen bears breathed in, Pagano could determine their energy use. To take this measurement, a subject would normally breathe through a mask. But, says Pagano, “you can’t put a mask on a polar bear, because it would just swipe it off instantly.” Instead, the researchers placed the treadmill inside a plastic and steel enclosure. The chamber was airtight, allowing Pagano to monitor oxygen levels inside.

First, the researchers had to find a treadmill strong enough for a 263 kilogram (580 pound) polar bear. Pagano’s team bought one made for racehorses. But walking on the treadmill wasn’t enough. The team also had to find a way to measure the bears’ oxygen use.

An animal’s body uses oxygen to make energy. That powers its muscles. Pagano wanted to measure the amount of oxygen bears breathed in. Then he could figure out their energy use. Normally, a subject would breathe through a mask to measure the oxygen they use. But, says Pagano, “you can’t put a mask on a polar bear, because it would just swipe it off instantly.” Instead, the researchers put the treadmill inside a plastic and steel chamber. The chamber was airtight, so Pagano could measure oxygen levels inside.

MICHAEL DURHAM/OREGON ZOO

SNACK CHAMBER: Keepers placed fish inside this box to reward the bears during the study.

The final step was persuading Tatqiq to walk into the unfamiliar contraption. Luckily, “true to her personality, she walked right inside with no problem,” says Wagner. With the treadmill turned off, trainers measured Tatqiq’s oxygen consumption when she wasn’t moving.

The next time Tatqiq approached the treadmill, though, she found it slowly moving. Wagner offered her fish through an opening at the far end of the chamber. Over and over, Tatqiq ambled forward to snag the snack but then slid backward. Her patient trainers kept working until she figured out she had to keep moving to stay on the device. Eventually, Tatqiq became comfortable enough on the treadmill for Pagano to measure her oxygen intake at different walking speeds.

The final step was getting Tatqiq to walk into the strange machine. Luckily, “true to her personality, she walked right inside with no problem,” says Wagner. Trainers left the treadmill turned off. They measured Tatqiq’s oxygen use when she wasn’t moving.

But when Tatqiq came to the treadmill again, it was slowly moving. Wagner stood outside the far end of the chamber. He offered her fish through a food port. Over and over, Tatqiq walked forward to get the snack but then slid backward. Her patient trainers kept working, and she learned to keep moving to stay on the device. Over time, Tatqiq got used to the treadmill. Then Pagano measured her oxygen use at different walking speeds.

UNCERTAIN FUTURE

Pagano analyzed the treadmill data and found that per pound of body weight, polar bears use about the same amount of energy as other large, meat-eating carnivores, like wolves and mountain lions, at routine walking speeds. The bears’ energy use doubled when they walked a little faster.

Pagano studied the treadmill data. He compared it with the energy use of other large, meat-eating carnivores, like wolves and mountain lions. He found that per pound of body weight, polar bears use about the same amount of energy as these animals at normal walking speeds. The bears used twice as much energy when they walked a little faster.

But because polar bears’ bodies are so massive, they need to consume a tremendous total amount of calories to survive (see Polar Bear Energy Needs). That’s why seals, which are rich in fat, make up the bulk of their diet. As sea ice declines, polar bears will have fewer opportunities to ambush seals by waiting for them to surface at their breathing holes. Melting ice may force the bears to chase prey on land, which uses a lot more energy.

With fewer ice floes, polar bears may also find themselves swimming more often in their search for food. Paddling for miles in the open ocean is even more physically taxing than walking. Pagano became curious about the energy demands of swimming on polar bears. After his treadmill study, he worked with the Oregon Zoo to set up a pool with an endless current. They’ve already begun to collect some data—after training a polar bear to swim in it!

But polar bears’ bodies are huge, so they need to eat a giant amount of calories to survive (see Polar Bear Energy Needs). That’s why seals make up most of their diet. Seals are rich in fat. As sea ice melts, polar bears will have a harder time finding seals’ breathing holes. They won’t have as many chances to lie in wait for their prey. Melting ice may force the bears to chase prey on land. And that uses a lot more energy.

With less ice, polar bears may also have to swim more to find food. Swimming for miles in the open ocean takes even more energy than walking. So Pagano also wondered about the energy use of swimming polar bears. After his treadmill study, he worked with the Oregon Zoo. They set up a pool with an endless current. They’ve already begun to collect some data—after training a polar bear to swim in it!

CORE QUESTION: Cite evidence from the text to explain why Pagano turned to captive animals to learn about their wild counterparts.

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