A Fitbit for Polar Bears Reveals Their Struggle to Survive
It takes a lot of energy to survive in the Arctic, especially when your dinner is disappearing with melting sea ice.
Scientists who outfitted polar bears with Fitbit-like devices along Alaska’s Beaufort Sea have found that the animals need to eat the equivalent of one ringed seal every 10 days to survive. When they’re not eating, the bears spend upwards of 70 percent of their daylight hours resting in an effort to burn as few calories as possible.
The findings come from two years of research by scientists at the United States Geological Survey.
Seven female polar bears were fitted with collars (males can’t wear them because their necks are wider than their heads) that monitored the animals’ activities. The collars also included video cameras, which were used to match the bears’ distinct movements with a motion-sensing accelerometer. Once a specific polar bear’s movements could be identified, scientists determined how much time it spent swimming, grooming, eating, resting, or interacting with males.
The seven bears were monitored for eight to 11 days in the spring of 2014 and over a similar period in 2015. During that time, three of the bears caught and ate ringed seals while the other four either scavenged meat from carcasses or did not eat.
Anthony Pagano, the USGS research biologist leading the study, said he hopes the data will give a clearer picture of how sea ice–reliant species like the polar bear will fare as the Arctic melts thanks to climate change.
“We are seeing that polar bears spend much of their time conserving their energy and resting, but they still do require a considerable amount of energy to meet their demands,” Pagano said.
He also found that the animals only spend about 15 percent of their time walking, but that could soon change.
According to USGS wildlife biologist David Douglas, stronger winds and thinner ice are starting to force polar bears on Alaska’s coast to walk farther distances.
He compared the movements of female bears satellite-collared between 1987 and 1998 with those of female bears monitored from 1999 to 2013.
There was more sea ice and lighter wind around the Beaufort–Chukchi Sea region in the 1980s and ’90s. Today, the ice sheets bears rely on to hunt seals are thinning and being pushed farther from shore by increasing winds. That means the bears have to walk longer expanses to stay in the same place today than they did 20 years ago.
To make up for the energy lost, polar bears need to eat about four more seals a year, Douglas said.
“That may not seem like a lot, but keep in mind that’s at a time when their habitat to hunt seals is shrinking,” Douglas said in a statement.
The new data backs earlier research published in the journal Science that examined changing polar bear eating habits. The 2015 study found the species won’t be able to adjust its metabolism from a blubber-based marine diet to feather-filled, land-based prey.
“Many people would have you believe that polar bears will somehow escape the negative impacts of sea ice disappearance,” study coauthor Steven Amstrup, chief scientist at Polar Bears International, said in a statement. “This evidence that they have no special ‘metabolic escape’ further confirms that retreating sea ice can only negatively affect polar bears.”
The nutrient-rich bounty of one ringed seal takes little energy to hunt when sea ice is plentiful, as polar bears often lie in wait at a breathing hole until a seal pops up. But hunting land-based prey and scavenging bird eggs means expending more energy on a relatively low-nutrition meal.
Pagano will continue studying the bear's energy levels this upcoming April, and plans to publish his findings next year. His work could give scientists a better understanding of how much energy it would take for bears to switch from their current marine-based diet to a land-based one.
“You are talking about changing from low-energy hunts of high-calorie meals like ringed seals, and transferring to actively searching for prey that is not nearly as profitable,” Pagano said. “The increase in energy it takes to hunt other food sources could offset any meals they actually acquire on land.”