Polar Bear Moms Stick to Their Dens Even Faced With Life-Threatening Dangers Like Oil Exploration

As a warming climate melts sea ice in the Arctic, female polar bears have increasingly been forced to make their dens on land. But a new study has found that mother bears are unlikely to abandon their dens when they are disturbed—for example, by fossil fuel companies’ exploration for new sources of oil—even if the disturbance is life-threatening.

As the Trump administration works toward allowing oil drilling in the Coastal Plain of the Arctic National Wildlife Refuge (ANWR), which counts polar bears among the many species that live there, that reluctance to flee could pose a danger to the bears. 

Scientists have found signs that polar bears are at risk from climate change, including changes in reproductive rates, physical condition and size, some of which have been linked to sea ice loss.

Published Tuesday in the journal Arctic, the study found that a one-mile buffer to protect polar bear dens from industrial activity is adequate to keep pregnant bears and new mothers safe—but, according to the study’s authors, that’s only if those dens can be located.

While the oil and gas industry’s attempts to identify polar bear dens before exploring for fossil fuel resources, the technology it uses to detect the dens—a type of thermal imaging camera called forward looking infrared—misses about 55 percent of the enclosures.

“It presents this problem where if [the oil and gas industry] can’t locate all these dens and they’re just doing business as usual up there, there’s a decent chance that at some point they’re going to kill bears with their cubs or make the mom run off and leave her cubs,” said lead author Wesley Larson, who was a graduate student at Brigham Young University during the study.

In ordinary times, most polar bears would build their dens on the Arctic sea ice, but as climate change leads to the loss of sea ice, more and more bears are forced to den on land. 

In the late fall, pregnant polar bears build dens by digging a cave into snow drifts, just big enough for them to fit inside. During the winter, they give birth while snowfall seals them inside, making the den invisible from above ground. In the spring, when the cubs are old enough, the female bears emerge from the dens. 

“That puts them in direct conflict with people who are using the land, whether it’s the oil industry or other people on land,” Larson said. “So we’re seeing a higher level of conflict.”

A Place of Safety?

The study, based on 42 years of data and conducted by researchers from Brigham Young University and the advocacy group Polar Bears International, monitored the Southern Beaufort Sea population of polar bears in northern Alaska. It focused on the area around Prudhoe Bay—the historical home of drilling on the North Slope—and included the Arctic refuge. 

In the study, researchers recorded responses to disturbances near polar bear dens. Disturbances ranged from humans walking nearby to aircraft flying overhead, while responses varied from no response to abandoning the den.

The study found that den abandonment occurred in about 8 percent of disturbances, mostly from aircraft flying over the den and almost exclusively when the female did not have cubs yet. 

“Most bears were remarkably comfortable at their den sites,” said co-author Geoff York, senior director of conservation for Polar Bears International. “They seemed to see their den sites as a place of safety.”

The Arctic refuge is one of the remaining untouched wilderness areas in the United States where polar bears can den with little risk of disturbance. Since the Trump administration’s early days, when the plan to open the refuge to drilling became clear, critics have worried that any industrial activity there could have an impact on the native Gwich’in, who rely on caribou there for survival, and on species that call the area home.  

The Trump Administration has been planning to hold a lease sale in the refuge, though the last step before that can happen—the publication of the final environmental impact statement—has not yet taken place, and it’s unclear whether the lease sale will go through this year.

In a statement, the Alaska Wilderness League said that a recent U.S. Fish and Wildlife Service analysis of the risks of drilling in the Arctic refuge did not sufficiently address polar bears, but rather came to an “unsupportable conclusion” that this population of polar bears would not be jeopardized by industrialization of the region.

“There’s many reasons why this landscape should be protected,” said Adam Kolton, executive director of Alaska Wilderness League. “There’s no way to ensure that we’re not going to end up killing polar bears during an industrial intrusion into the heart of the wildest place in America.”

‘A Bit of a Catch-22’

The Southern Beaufort Sea population of polar bears declined 40 percent from 2000 to 2010, when the population was approximately 900, according to a 2014 study. Cub survival, which is vital to supporting polar bear populations, was dismal during this period. Out of 80 cubs observed from 2004 to 2007, only two survived, the 2014 study said. 

“From a polar bear population standpoint, what we need is four or five good years in a row to bring cubs into the adult population and either stabilize or grow a population,” York said. “What we’ve been seeing in places like the South Beaufort Sea is we’re getting more bad years and we’re seeing lower cub survival and we’re seeing population decline.”

The denning period is just the beginning of a cub’s struggle to survive. For the first two months of their lives, cubs and their fasting mothers are too vulnerable to withstand the harsh conditions of Alaska winters. 

The proportion of the Southern Beaufort population denning on sea ice decreased from an average of 62 percent between 1984 and 1994 to 37 percent between 1998 and 2004. Much of this denning is in the Arctic Refuge.

“Climate change is having an enormous impact on places like Arctic National Wildlife Refuge, which is protected and pristine,” Kolton said. “There’s no reason to put polar bears at risk there, but we ought to do everything we can to reduce risk.”

A 2019 study by the Fish and Wildlife Service found that disruptions to polar bear dens by seismic surveying—an intensive method of oil exploration—can be reduced by 90 percent if industrial operators maintain a buffer around dens and conduct operations after polar bears have emerged from their dens, which happens around late March. 

This is good guidance in theory, York said, but den locations are often unknown and spring warming can complicate drilling operations. 

“Today, the ice road window for the north slope of Alaska has been shrinking due to climate change and has become less reliable,” he said, “and that time period where [fossil fuel industry operators] know they can get on to solid frozen tundra with adequate snow coverage and do minimal damage is shrinking.” 

“It’s a bit of a Catch-22 for them and, ironically, it’s an issue partly of their own making,” York said. “[Climate change] is a side effect of the industry itself that’s warming the environment.”

The best solution for minimizing disturbances to polar bear dens is to stay out of the Arctic refuge, a “hotspot” for polar bear denning, York said. 

“Give bears that one place where they can den in peace and safety,” he said, “especially at a time when their habitat is changing dramatically.”