Polar bears are relocating from ice-sparse parts of the Arctic to the Canadian Archipelago, an area with more dependable summer and fall sea ice, says a new study that tracked the animals' gene flow.
The study, published Tuesday in the journal PLOS ONE, examined DNA from about 2,800 polar bears. Samples were in the form of tissue or hair taken from polar bears in all of the countries where the animals live.
The population shift has been recent -- happening in just the past one to three generations, or 15 to 45 years, said lead author Lily Peacock, a U.S. Geological Survey wildlife biologist.
The migration was tracked through the flow of genes and genetic similarity between polar bears in four population clusters around the Arctic -- grouped as the Southern Canada, Eastern Polar Basin, Western Polar Basin and Canadian Archipelago clusters.
The flow to the Canadian Archipelago, the area in the farthest-north part of Canada, came from the Southern Canada and Eastern Polar Basin population groups, Peacock said in an email. There is no evidence of any such specific directional movement in the past, she said. "So we think this directional gene flow is new," she said.
The Southern Canada group is in Canada's eastern Arctic region, and the Eastern Polar Basin stretches from the marine areas off eastern Greenland to central Siberia.
The samples used for extraction of DNA came from decades' worth of studies dating back as far as 1973, with the bulk of them coming from live-capture studies operating under permit in the various countries. Some samples came from polar bears killed in legal hunts in Nunavut, and some of the hair that was studied was collected from the ground in Russia, the study said.
The study was led by the USGS and the government of the Canadian territory of Nunavut and was co-authored by scientists from several agencies across all the nations that have polar bears.
A few other findings: Female polar bears are more loyal to their place of birth than males, and polar-brown bear hybrids are extremely rare and probably restricted to specific areas.
Tracking the movement of adult males is difficult because their necks are larger than their heads, making radio collars impossible, the study noted. But analysis of genes passed on by maternal bears only, contrasted with genes passed on by both male and female bears, indicated that even though females with cubs are known to travel great distances, males are more likely to relocate away from birth sites, the study said.
As for the hybrids, the tissue and hair samples analyzed produced "no evidence of contemporary admixture (crossbreeding) between polar bears and brown bears," the study said.
Polar-brown hybrids have been found only in the Northern Beaufort Sea and Viscount Melville populations, adjacent populations in Arctic Canada, the study said. It is likely that such hybrids are few and limited to those specific local areas, the study said.
Peacock said the authors are hypothesizing that polar bears are migrating from ice-poor areas in the more southern part of their range to more favorable territory where ice is more likely to persist year-round. The Canadian Archipelago features a more northern latitude, with waters that are somewhat sheltered from ocean currents, thanks to the numerous islands divided by narrow watery straits.
The Canadian Archipelago, however, may not be a polar bear refuge for long, concludes another study published recently in PLOS ONE.
The region, which straddles northeastern Arctic Canada and Greenland, supports seven polar bear subpopulations. Past climate models have identified it as a place that will sustain polar bears even as other parts of the animals' global habitat thaw.
But even in the Canadian Archipelago, multiyear ice is being replaced by annual ice that melts out in summer and fall, said that study, led by Stephen Hamilton of the University of Alberta. If current trends continue, each of the seven polar bear populations in the region will experience two to five months of ice-free conditions in areas where they do not exist now, said the study, published Nov. 26.
"Under business-as-usual climate projections, polar bears may face starvation and reproductive failure across the entire Archipelago by the year 2100," said the study, which makes projections based on models.
Up to a fifth of adult males will starve to death if the ice-free period in the Canadian Archipelago extends to six months of the year, and between 55 percent and 100 percent of pregnant females will lose their cubs, the study said.
Peacock said that despite the pessimistic predictions about long-term conditions in the Canadian Archipelago, the region still looks like a good place for polar bears in the near future, Peacock said.
"So if there will be a refugium for polar bears -- they will likely have the best chance there," she said in her email.
Polar bears haven't suffered physical harm from being temporarily sedated for research, according to another recently published polar bear study.
The study examined Southern Beaufort Sea polar bears that were tracked, monitored or examined on the U.S. side of the border over the past four decades.
Captured polar bears, which are immobilized with drugs to allow biologists to examine the animals and take samples from them, return to near-normal activity levels within two to three days, and are fully back to normal within five days, said the study, by scientists from the USGS Alaska Science Center and the nonprofit group Polar Bears International. Even repeat captures of particular bears did not have adverse impacts, the study found.
That study was published in the Dec. 16 issue of the journal Wildlife Research.