By Emily Shenk
Imagine you’ve drawn a line across a jigsaw puzzle, and you’re following that line from beginning to end. Suddenly the puzzle breaks apart and the pieces move in different directions. How do you follow the line to your destination?
In the case of polar bears, the destination is a potential mate walking across the sea ice. A new article published this month in the Journal of Zoology confirms what many researchers have observed in the wild—that polar bears leave scents behind in their tracks, which they use to find each other in their vast habitat.
The first-of-its-kind study was a decade in the making. In 2004, scientists began collecting samples from polar bears in the wild by swabbing their paws. Researchers then conducted a series of experiments with captive polar bears in zoos, where they presented the scents to them and observed how the polar bears responded.
“We had hypothesized and certainly scientists had long assumed that polar bears would have to rely on scent to navigate their social landscape,” said lead author Megan Owen, associate director at the San Diego Zoo’s Institute for Conservation Research. “But the details are always interesting and they tell us a lot about how vulnerable or resilient animals may be to changes in their environment.”
Owen and her team found that polar bears—particularly females—were more interested in scents during the spring. The polar bears studied spent more time investigating scent samples from the opposite sex, particularly males, who could also discriminate the scents of estrus and non-estrus females.
Deciphering this information using scent trails helps solitary polar bears find each other in their icy environment. While other bear species, such as black bears, are known to communicate with each other by rubbing scents on trees and other objects, polar bears do not have those kinds of markers available.
“The idea that [polar bears are] leaving a low-amplitude signal with every step that they take, and that they are relying on these cues to coordinate social behavior, may be unique among bears,” Owen said.
With a shifting polar climate, these findings are particularly important, the scientists said. As sea ice becomes more fragmented, as has been seen in the Beaufort Sea in recent decades, it is likely that the chemical communication between polar bears trying to find mates may also break down.
“With the ice becoming increasingly fragmented, the only thing likely to happen is that the ability to communicate will become increasingly compromised,” said study co-author Steven Amstrup, chief scientist at Polar Bears International.
Since polar bears are solitary animals that roam large territories, conducting studies like this in the wild presents inherent logistical challenges. By bringing together researchers from the field and researchers from zoos, the team was able to overcome some of those challenges.
The findings could have vital implications for captive breeding programs as well, since they help scientists understand how polar bears communicate with potential mates in the wild.
“Looking at such a critical conservation issue, you really have to take an all-of-the-above approach to research,” Owen said. “Understanding as much as we can about the behavioral or physiological mechanisms that support reproductive success may enhance our ability to predict, and hopefully ameliorate, what’s going to happen.”
Amstrup said the study gives more context to the challenges polar bears face throughout their reproductive process. Some polar bears have been documented to have trouble reaching appropriate birthing areas due to reduced sea ice.
“So that’s a whack that could be hitting them at the end of their reproductive cycle, when they’ve actually bred and are ready to give birth,” Amstrup said. “This study adds information to the beginning of that process. Can these bears even find each other to breed in the first place?”