Rare video footage of polar bear cubs emerging from their dens for the first time has been captured in the Arctic mountains.
Researchers from Polar Bears International, San Diego Zoo Wildlife Alliance, the Norwegian Polar Institute, and the University of Toronto Scarborough worked on the project for nearly a decade in Svalbard, Norway.
Their research, published on International Polar Bear Day (Feb 27) in the Journal of Wildlife Management, marked the first time satellite-tracking collars have been combined with remote camera traps to answer questions about polar bear denning, which is notoriously difficult to study, as polar bear mothers build their dens under the snow in remote areas.
"Like an extension of the womb"
The denning period is vital for the survival of polar bears cubs. "Without maternal dens, we wouldn’t see a single polar cub survive that Arctic winter,” says Dr. Louise Archer, lead author and Polar Bears International Postdoctoral Fellow at the University of Toronto Scarborough.
"Weighing just 600 grams at birth and covered only in a light downy fuzz, newborns are too small and too feeble to cope with the freezing world outside.
"The snow-covered den is almost like an extension of the womb – it provides a warm and stable environment, allowing cubs to continue to grow and develop for a further three months. Populations require healthy cubs to ensure the survival of the next generation - this really starts with giving bears the best chance during these first few months in the den.”
Early risers
The new research provides valuable insights into the timing of polar bears emerging from dens and their post-emergence behaviours.
"We saw polar bear families tended to depart more than a week earlier, on average, than previously recorded in Svalbard,” says Archer.
"This could be a cause for concern because previous studies have indicated that a longer time spent at the den has a positive impact on the subsequent survival of cubs, as cubs have less time to develop before venturing further afield to the sea ice.”
Some mothers also left their original dens to move their family to a new one.
The camera footage also indicated that emerging polar bears remain near their dens for an average stay of 12 days. Cubs rely heavily on their mothers, rarely venturing outside the den alone. Cubs were seen without their mothers only 5% of the time.
In Svalbard, cubs depend on their mother for up to 2.5 years.
Den adaptations
Climate change is understood to be altering polar bear denning behaviour.
"As the Arctic has warmed and sea ice has been lost, what we’re seeing in some regions is polar bears changing where they’re going to build their dens and have their cubs,” explains Archer.
"For example, in Alaska, many polar bears used to den out on the sea ice, but as ice conditions in the summer and autumn have deteriorated, the majority of bears now den on land, bringing them into closer overlap with industrial activities, including drilling for oil and gas.
"In Svalbard, certain areas have in the past acted like ‘polar bear maternity wards’ where a high density of females would return year-on-year to den in these prime locations. With rapid climate warming, autumn sea ice in the southeast of Svalbard has resulted in female polar bears no longer accessing these important denning habitats because there’s too much open water for the bears to reach these areas. Shrinking denning habitats doesn’t spell good news for polar bears into the future.”
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Monitor and protect
With polar bear dens often so well hidden that the oil industry’s den-detection tools miss half of the known dens, Polar Bears International is developing new technology to locate dens more effectively.
As industrial activity expands across the Arctic, the new study highlights the importance of undisturbed denning areas to protect polar bear populations, and the need for monitoring and protection of denning areas to ensure the survival of future generations, as cubs rely on the den emergence period to acclimatize to the environment and prepare for life outside the den.
"To prevent humans from disturbing denning polar bears, we really do need to know what exactly the bears are up to,” says Archer.
"Can we accurately say when a bear is still in her den, when she emerges and is out on the surface, or when the family has finally left the area? Getting a stronger handle on the kinds of behaviours we expect to see, and improving our ability to detect these behaviours remotely, leaves us in good position to minimize negative interactions between people and polar bear families. I really hope we see some creative solutions put in place.”
Intriguing behaviour
Outside of the more concerning changes, the cameras also captured some entertaining and intriguing behaviours.
“What really stuck out was just how different behaviours could be between bears,” says Archer.
“Where one mother beelined to the sea ice with her cubs only a couple of days after first popping out of the den, another family remained in place for a full month, taking regular jaunts outside the den to explore.
"We also witnessed two mothers that moved the cubs to new dens after emerging – one of which included a tumble down a steep slope by the cub, followed by a swift retrieval by mum. Where bears chose to build their dens was also impressive. Some of the steep slopes where females dug in seemed a pretty precarious setting for their newly-emerged cubs to take their first wobbly steps.”
Main image: polar bear mother and cubs/Steven C Amstrup, Polar Bears International
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