How Climate Change Might Affect Polar Bears' Bodies

Zoo polar bears help scientists understand effects of Arctic bears’ shifting diets

PORTLAND, Ore. — You really are what you eat. That’s the taking-off point for a new polar bear study, conducted by U.S. Geological Survey researchers with an assist from the Oregon Zoo — and published this week in the journal Physiological and Biochemical Zoology.

As sea ice shifts in the Arctic, scientists have noted a corresponding shift in polar bears’ diets. In Western Hudson Bay, for example, sea-ice loss has been associated with declines in the consumption of benthic-feeding prey, such as bearded seals. In East Greenland, polar bears have increased consumption of hooded seals and decreased consumption of their more typical prey, ringed seals.

The degree to which these types of changes are common throughout polar bear populations, and their implications on bear health, are not well understood. To determine whether bears are changing their diet in these remote Arctic regions, scientists are gathering baseline data from a couple of animals closer to home — Tasul and Conrad, two resident polar bears at the Oregon Zoo.

“Science can sometimes be a slow process,” said Amy Cutting, who oversees the zoo’s North America and marine life areas. “And climate change is happening rapidly. Anything we can do to quickly gain information about how polar bears respond will help managers make critical decisions for protecting them in the wild.”

Using a handy chemical tool called “stable isotopes” — which include the carbon and nitrogen atoms that exist in every living thing — researchers from the U.S. Geological Survey are revealing how polar bears, which currently boast the highest-fat diets of all the animal kingdom, process different types of meals.

“This new tool is allowing us to use hair and blood samples to discover whether polar bear diets have changed since the ’80s, when we began keeping records,” said Dr. Karyn Rode, the USGS wildlife biologist who led the study.

This is possible, Rode says, because when a polar bear eats a meal of seal, whale or walrus, it takes on that organism’s isotope load as well.

These chemical markers can then be detected in the bears’ own tissue samples, such as their blood or hair, which grows at a predictable rate and reveals the bear’s past “dietary signature” — or what and where their meals were eaten, she says.

But it’s not quite that simple.

“It’s not just that a 50 percent salmon diet shows up as 50 percent salmon in the body,” Rode said. “Some gets routed toward body fat, some gets stored and some is transformed directly to energy. I need to understand how the bear body processes food before I can understand how different diets may affect them.”

During data collection, the zoo bears participated in what zoo staff dubbed a “surf and turf” experiment — switching between marine and terrestrial foods. By comparing this new data to USGS archive samples from the Chukchi and Southern Beaufort Sea bear populations over the past 25 years, Rode and her team may reveal the effects of this new meal diversity on polar bears.

“We’re hoping to study their diets over time to explain potential changes in resource use as a result of climate-related changes in this sensitive Arctic ecosystem,” said USGS research biologist Craig Stricker.

This project, conducted by the USGS Polar Bear Team, is part of the USGS’s Changing Arctic Ecosystems research on the effects of climate change on polar bears.

The zoo is a service of Metro and is dedicated to its mission of inspiring the community to create a better future for wildlife. Committed to conservation, the zoo is currently working to save endangered California condors, Oregon silverspot and Taylor’s checkerspot butterflies, western pond turtles and Oregon spotted frogs. Other projects focused on saving animals from extinction include studies on Asian elephants, polar bears, orangutans and cheetahs.

Support from the Oregon Zoo Foundation enhances and expands the zoo’s efforts in conservation, education and animal welfare. Members, donors and corporate and foundation partners help the zoo make a difference across the region and around the world.

The zoo opens at 9 a.m. daily and is located five minutes from downtown Portland, just off Highway 26. The zoo is also accessible by MAX light rail line. Visitors who travel to the zoo via MAX receive $1.50 off zoo admission. Call TriMet Customer Service, 503-238-RIDE (7433), or visit trimet.org for fare and route information.