A polar bear mom and cub.

With the sea ice melting on Hudson Bay, the polar bears on our Bear Tracker map are making different choices about where to come ashore.

© Kt Miller/Polar Bears International

7/3/2019 7:17:08 PM

Bear Tracker Update

By Alysa McCall, Staff Scientist and Director of Conservation Outreach

The Western Hudson Bay polar bears are currently working on their ideal summer bodies: as fat as possible. Though some polar bears spend their whole lives on sea ice, Hudson Bay lies in the Seasonal Sea Ice Ecoregion, where sea ice melts completely in the summer before refreezing again in the fall.

When the sea ice melts, the Western Hudson Bay bears will be forced back to shore for the next four to five months, during which time they will mostly subsist on their own body fat. Polar bears eat what they can while on land (e.g., eggs, berries, carrion), but terrestrial foods don’t offer much energy compared to the bears’ normal blubber-filled diet. While on land, the bears lose about one kilogram per day of body mass, so every seal counts right now.

Bears who are fat now should be in better shape by the fall as they wait for the sea ice to refreeze and seals to come back on the menu. Being fat now is especially important for pregnant females who hope to den later this year and give birth next winter, not emerging to hunt again until next spring. This roughly eight-month fast is brutal, so it is critical for females to hunt and eat as much as they can while they can in order to sustain a successful pregnancy.

However, it is getting harder to predict how much time they have to keep hunting. Historically sea ice would break-up around mid-July in the western part of Hudson Bay; now it tends to break up around late June. These couple weeks can have a huge impact and make this an especially interesting time to watch the Polar Bears International Bear Tracker. Each bear chooses to do something different as the ice starts to break up, all in the name of fat.

Many of the tracked females on our Bear Tracker map have already moved toward Wapusk National Park, the region in which they were born and where most (if not all) will choose to spend the summer. This is a good move because when the sea ice breaks up, the bears will swim shorter distances back to shore and can find a good spot on land to rest. Longer swims can be energetically costly and waste precious body fat.

However, some bears may choose to ride the floes down closer to Ontario where ice persists longer, adding a couple of extra weeks of hunting seals. Those bears will likely walk a longer distance home over the summer, but the energy balance may work out in their favor. We don’t yet know what spurs polar bears to make different choices but it’s something researchers are interested in, especially as Arctic sea ice continues to decline.  

This year set a record for the lowest Arctic sea ice extent for June in the 40-year satellite record. The Arctic experienced record-breaking temperatures this spring, especially around Alaska where ice cover had almost disappeared in the Bering Sea by March. Impacts on the local polar bear, seal, walrus, and whale populations will become clearer in the coming months but are expected to be substantial. It remains to be seen what happens in Hudson Bay, but we will continue to observe, research, and educate.

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Updates on Individual Bear Tracker Bears

Map showing tracked locations of polar bears on Hudson Bay.

X33714 (Rostock Zoo, Vilma, gray)

Eight-year-old Vilma has now travelled 2608 km (1621 mi) since being collared last fall and is no longer the most northern bear on the tracker. Since the last update she swung back down south and is currently fairly close off the coast of Wapusk National Park. She may know the ice will be breaking up soon for the summer and, if so, wants to minimize swimming home with her yearling cub. Vilma has stayed firmly in the western part of Hudson Bay all year, in areas known to have lots of seals. As a fairly young mom (this is likely only her second time with a cub), she seems to know what she is doing! Hopefully her yearling is a helpful hunting partner and this family can get nice and fat over the next few weeks before returning to land and fasting for the summer.   

X33732 (Canada Goose, Aurora, red)

Ten-year-old Aurora has now moved 1730 km (1075 mi) compared to the 1493 km (928 mi) at our last update. She weaned her cub this spring and would have mated soon after, so by now she will simply be focused on being as fat as possible. Her fertilized zygote(s) won’t implant until the fall, and only if Aurora is still fat enough. If she doesn’t gain enough weight now, she will not sustain a pregnancy and will return to the sea ice this fall. Hopefully she is fat enough, though, which would mean entering a den this fall, giving birth this winter, and emerging next spring with new cubs- a whopping eight months without food! Aurora is currently just off the east coast of Wapusk National Park; knowing that the sea ice will break up soon, this is a good bet as it means less swimming on her way back to land. Once on shore she will conserve as much energy as possible, resting often and trying to keep the pounds on. Her collar has not been updating regularly, probably because it’s waterlogged. Hopefully once back on land and dried out, her collar will come back online this summer with her latest movements.

X32037 (Munich Zoo, Sira, dark blue)

Sixteen-year-old Sira is now single after weaning her cub, and likely mated sometime in the last few months. She is an experienced mom so we look forward to seeing if she is successful with a new litter next spring. Hopefully she will be able to sustain a pregnancy if she gets as fat as possible now—those fat stores need to last her for the next eight months! It seems like Sira knows what she is doing as she is currently in an area known to have seals and is not too far from the east coast of her on-land home, Wapusk National Park. This is a good strategy because, as the ice starts to break up soon, she will have a shorter distance to walk or swim back to land. Long distance swims are very energetically expensive, so reducing these distances can help her conserve energy. Sira has moved 4760 km (2957 mi) since being collared last fall, one of the biggest travelers! Most of her travels have been in one general region with a lot of zig-zagging so she clearly knows what region works for her. We wish her happy hunting for the next few weeks before we see her back on land!

X19735 (Hannover Zoo, Hope, beige)

Nineteen-year-old Hope is an experienced mom which will serve her well in the coming months. Recently she weaned her cubs and mated, and now will be preparing for a new pregnancy by packing on as many pounds as she can before returning to land soon. Then, she’ll only technically become pregnant if the zygote implants this fall and that will only happen if she has enough body fat. We’re sure Hope won’t have a problem as she has been through this many times before and is currently playing it smart. Hope is in a region known to have seals and is fairly close to the coast of Wapusk National Park. This means that when the sea ice does start to break up, this bear will have a shorter and easier time getting back to land. Long-distance swims take a lot of energy, so avoiding those is a good way to conserve energy. In total Hope has now moved 5675 km (3527 mi) since being collared and will surely add some more distance to her travels before hunkering down in a den later this year.

X17421 (Toledo Zoo, purple)

This 13-year-old female has traveled 2643 km (1642 mi) since being collared, checking out different regions in the bay but staying consistently within the western half. Recently she has done a couple zig-zags north and south and is currently on a zag south, heading in the general direction of Churchill, Manitoba. Hopefully she’ll adjust her course before coming too close to the town! This bear now has two yearlings with her who should be good help hunting, especially in the region they are currently in. Soon the sea ice will be breaking up so mom will need to decide whether to do a longer swim back with her cubs or get closer to shore earlier and minimize the cubs’ time in the water. Swimming costs a lot of energy, especially for young bears. This mother has less than a year left with her cubs to teach them about being polar bears so we hope they make the best of it.

X33720 (Vienna Zoo, Discoverer, dark green)

Discoverer is 15 years old and would have recently mated after weaning her cub. She has travelled 2265 km (1407 mi) since being collared and will now be focused on building as much body fast as possible in hopes of sustaining a pregnancy through this fall and winter. Discoverer has made some large sweeping movements while being tracked and tends to zig-zag less than the other bears. After heading east earlier this year, she has since come back toward the western part of Hudson Bay and is now off the coast near the border of Ontario and Manitoba. She will need to go up to 8 months without eating once returning to land this summer, so conserving every bit of energy counts. This may be why she has chosen this region at the moment: sea ice lasts longest off the coast of Ontario. Those bears who choose to ride that ice out may get an extra week or two of hunting, but then will likely walk back to Manitoba up the coast as they tend to den near where they were born. It remains to be seen what Discoverer will choose to do but we will follow her choices with great interest.

X33815 (Adventure Canada, Yuka, orange)

Yuka is currently hunting with her two yearling cubs who are hopefully offering some support. She has less than a year left with them which should be enough time to teach her offspring all the knowledge she has to impart. Yuka’s collar has been acting up which is normal, especially in the spring. GPS collars get drenched when the bears swim and the cold and salty water is tough on electronics. Hopefully when she returns to shore, the collar will dry out and upload the locations from where Yuka has been recently, we can only watch and wait. We don’t know exactly where she is right now but assume she is still doing fine and look forward to the next time we see her locations come online.

X33805 (North Carolina Zoo, Yura, yellow)

Yura is still our most southeast bear on the Tracker though her collar is having some issues. This is normal, especially in the spring and early summer when the bears are swimming more and the GPS collars get water-logged. Cold, salty water is tough on electronics! Hopefully when Yura returns to shore her collar will dry out and upload the locations from where she and her cubs have been recently, we can only watch and wait. She has less than a year left with her cubs and will be getting in as much hunting and teaching as possible before the ice breaks up. We don’t know exactly where Yura and her yearlings are right now, but assume they are doing fine and look forward to her collar uploading locations again soon. 

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