Climate Change Plays Role in Annual Polar Bear Migration

Population has dropped as sea ice melts.

polar bear cub and mother

B.J. Kirschhoffer / Polar Bears International

Hundreds of polar bears are gathering on the shores of Hudson Bay near Churchill, Canada, waiting for the sea ice to freeze so they can return to hunting for seals. The bears typically fast for about six months or more.

Female polar bears stop eating before they make their dens and don’t eat again until the ice freezes. This makes them very vulnerable to the warming temperatures of climate change because they depend so much on sea ice.

Polar Bears International, a nonprofit dedicated to wild polar bears and sea ice, holds Polar Bear Week (this year through Nov. 5) to coincide with the Hudson Bay bear migration. The goal is to educate people about the bears and their melting sea ice habitats and encourage them to get involved to protect them.

Treehugger spoke to John Whiteman, chief research scientist for Polar Bears International and assistant professor of biology at Old Dominion University in Norfolk, Virginia. He addressed the annual migration, the interesting things researchers observe, and how people can get involved to help the animals.

Treehugger: What is the annual polar bear migration? Where do the bears travel and how many do you expect?

John Whiteman: The global population of polar bears includes 19 distinct subpopulations, one of which lives on the western side of Hudson Bay (the name is a bit deceiving; the bay covers over a million square kilometers). This subpopulation is estimated to include about 850 bears, which spend their lives out on the sea ice, hunting seals. But every summer this sea ice melts, forcing the bears to migrate to shore. They spend the next few months living off their fat reserves, losing about 1.5 kilograms (3.3 pounds) of weight each day. 

By late October or early November, the bears begin clustering along the coast in anticipation of colder weather, ice freeze-up, and a migration back to their seal-hunting grounds in the bay. Many of the bears gather near the mouth of the Churchill River, as the freshwater input causes some of the first ice of the season to form here. The town of Churchill is also near the river, making it one of the best places in the Arctic from which to see polar bears. As the sea ice forms, bears leave the shore and eventually roam far into the bay, in search of seals.

How have these migrations changed over the years? How has climate change played a part?

Although the annual gathering of polar bears near Churchill is part of an age-old pattern, climate change has caused Hudson Bay to melt earlier in summer and freeze later in the fall. Over the last 30 years, polar bears have shown a gradual northward shift in where they gather on the coast for their return migration, shifting by an average of 7 kilometers (4.3 miles) per year, possibly in search of earlier-forming sea ice.

Overall, the on-ice hunting season for the Western Hudson Bay bears is three to four weeks shorter than it was just 40 years ago. As a result, their numbers have dropped by approximately 30% over the past 40 years—this subpopulation was previously estimated at about 1,200 bears—and current projections show the population may vanish completely. Similar declines in both sea ice and the number of polar bears are expected to eventually occur in other areas in the foreseeable future unless we take meaningful action on climate change.

polar bear with cubs on sea ice

B.J. Kirschhoffer / Polar Bears International

What are some of the more interesting observations your scientists have made in the field?

We are definitely seeing fewer polar bears and fewer moms with cubs—especially triplet cubs, which are now a rarity—than when scientists first began studying this population in the late 1970s. We have also witnessed a drop in body condition. They are a harbinger of what is to come for other populations without bold action on climate change.

How do they track polar bear activity?

Researchers with the University of Alberta, Environment and Climate Change Canada, and the Ontario Ministry of Natural Resources attach satellite collars to a select number of polar bears on Hudson Bay every year—and you can follow these bears on our Polar Bear Tracker. Right now, the tracker shows that the bears are clustered on the shores of Hudson Bay, waiting for the sea ice to return. When the bay finally freezes, you’ll see them scatter across the ice, making different choices on where to hunt. The long-term monitoring of the Western Hudson Bay population has provided us with invaluable data on polar bears and helped us understand their dependence on sea ice.

Polar Bears International’s research team also observes the bears from Tundra Buggies and we’re endlessly fascinated by their behavior–from play-wrestling adult males to bears testing the ice along the shore to moms snuggling with cubs. Anyone in the world can watch this behavior, too, through our live Polar Bear Cams in partnership with and Frontiers North Adventures.

How is Polar Bears International working to protect this species?

We take a two-pronged approach to conservation. First, we raise awareness about the overarching threat of climate change, the loss of sea ice, and the urgent need to act. Second, we support research to better understand the unique characteristics of subpopulations around the Arctic, and where possible, we work to maintain healthy populations in the short term until climate change is addressed. This includes efforts to protect polar bear moms and cubs while they’re denning—the most vulnerable period in their life—and helping polar bears and people coexist. 

Our coexistence efforts have loomed in importance in recent years as more polar bears are spending more time ashore in more places, leading to an uptick in encounters with people. We’re working with Arctic communities as they adjust to this new reality so bears and people can live safely together. 

How can people get involved, both in watching the migration and in helping to conserve polar bears?

The Polar Bear Cams mentioned above provided a window into the migration. Also Polar Bears International has developed a unique outreach program that allows for high-quality, live broadcasts from a Tundra Buggy as polar bears roam outside. We use this roving studio for a free educational webcast series, called Tundra Connections, which links polar bear scientists and other experts with viewers around the world. All webcasts are supported by our free learning materials. Viewers can ask questions and receive answers in real-time—and it’s a great way to get involved.

We founded Polar Bear Week to coincide with the polar bear migration and draw attention to the threats bears face. In addition to watching the Polar Bear Cams and tuning in for a live broadcast, people can get involved by sharing information on social media (we’ve created a toolkit to make this easy) or supporting our efforts to develop “Detect and Protect” radar technology that will alert communities to approaching polar bears before they reach town—part of our coexistence efforts to keep bears and people safe. They can either donate or start their own fundraisers.

And, finally, with midterm elections coming up in the U.S., it’s important to vote with polar bears and the need for action to address climate change in mind, at every level of government. We can’t overstress the importance of this. Every single vote is important to keep the momentum going, for polar bears and for all of us.

View Article Sources
  1. Polar Bears International

  2. "Polar Bear." National Wildlife Federation.

  3. "Polar Bear Week 2022." Polar Bear International.