What sounds can polar bears hear? What noises disturb them? It's almost impossible to answer questions like these by studying wild polar bears so we turned to researchers and trainers at the San Diego Zoo and SeaWorld San Diego for help.
Our Hearing Study team chose five healthy, adult female bears of breeding age as test subjects. They focused on adult females, because denning mothers with cubs:
- Are the most likely to react to noise disturbances
- Probably rely on vocal communications more than other age/sex classes of bears
How Do You Test a Polar Bear?
First the zoo scientists made the polar bears' bedrooms soundproof. Then they trained the bears to respond to tones by touching their nose to a target. All five bears quickly figured out the new game—they're intelligent and actively take part in training sessions.
- Presented over 4,000 tones ranging from 125 to 31,5000 hertz (Hz)
- Created an audiogram based on the data that shows the frequency range and best sensitivities of polar-bear hearing
So now that we know how sensitive polar bear hearing is, our team is testing how noise from vehicles and machinery travels through the snow where mother bears dig their maternity dens. This information will help protect polar bears from industrial disturbances, especially during the sensitive time when mother bears are in the den with cubs.
Although polar bears are generally solitary mammals, they come together at key times throughout the year. Vocal communication may play an important role in their social behavior at these times. In fact, the period when new polar-bear mothers are in snow dens with young cubs is potentially the most important social period of a polar bear's life.
Cubs vocalize a lot in the den! But we don't really know what these vocalizations mean or how important they are for cub survival. This aspect of our hearing study will help answer whether disruptions to cub vocalizations from industrial noises may impact their survival.
How do polar bears find mates in the vast expanses of the Arctic? A PBI study is helping to unravel that mystery and provide a better understanding of the polar bear's breeding process.
Scientist Megan Owen of the San Diego Zoo's Institute for Conservation Research is the project leader. Her hypothesis is that polar bears—like many solitary, wide-ranging animals—use scents to send signals to each other over long distances.
Love is afoot—er, maybe apaw. Most bear species mark their environment, usually trees, with cues that let other bears know who and where they are. But in the Arctic there aren't any trees to mark, so what do polar bears do?
- Observations of bears in the wild suggest that polar bears passively deposit a scent "signature" on the sea ice as they walk.
- These scented trails may tell other bears exactly who they are following—and help male polar bears know when a female is ready to breed.
If this proves true, as the Arctic continues to warm and the sea ice melts, scent trails could be broken up by large stretches of open water. This would make it harder for polar bears to find mates.
PBI Advisory Council scientists who work with wild polar bears are helping with the study. They collect scent samples from the paws of tranquilized bears that they handle in capture-release efforts. The project is a good example of how our zoo and wild-bear Advisory Council members work together to answer key questions.
Don't scratch—just sniff. Within a zoo setting, Owen's team members mount scent boxes to:
- Test whether male polar bears can smell the difference between sex and reproductive condition
- Study responses from female bears as well
The basic measurement tool? How much time the bears spend checking out a scent.
Because the scent boxes are so easy to transport, the team has already tested both male and female polar bears at the San Diego Zoo, Oregon Zoo, Reid Park Zoo in Tucson, Maryland Zoo in Baltimore, Toledo Zoo, Buffalo Zoo and SeaWorld San Diego.
Early results support Owen's theory. Conrad, a male polar bear at the Oregon Zoo, displayed a strong response to the female scent and some aggression to the male scent.
His female sibling, Tasul, was so intrigued with the male scent that researchers had to pause the trial before she completely destroyed the hanging support of the scent box.
Special thanks to Hearing Study Project Leader, Advisory Council member Megan Owen of the San Diego Zoo's Institute for Conservation Research (SDZICR), and Anne E. Bowles, senior research scientist with the Hubbs-SeaWorld Research Institute. And, thanks to Trainer JoAnne Simerson and her crew, and to B.J. Kirschhoffer and Rusty Robinson for field support.
Thanks also to our Olfactory Study team: Megan Owen, San Diego Zoo's Institute for Conservation Research (SDZICR), project leader; Dr. Ron Swaisgood, SDZICR, consultant and coauthor; Christine Slocomb, research technician; Dr. Steven C. Amstrup, our chief scientist; and Karyn Rode, U.S. Fish & Wildife Service.