moms and cubs

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

© @BJ Kirschhoffer/Polar Bears International

7/13/2020 4:47:47 PM

Bear Tracker Update Summer 2020

By Emily Ringer, Communications and Marketing Manager

It’s summer in the Canadian Arctic—temperatures are rising, the sea ice of Hudson Bay is starting to break up, and the polar bears that call this platform home are riding the ice for as long as they possibly can. Polar bears have adapted to eat high-fat marine mammals, mainly seals, and the sea ice grants them access to this prey.

Satellite imagery of sea ice concentration across the Arctic, courtesy of Universität Bremen.

Seasonal Sea Ice

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 polar bears of Hudson Bay bears are forced back to shore for 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 coming off the ice fat 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. And females who mated on the sea ice this spring have some extra meal motivation! They’ll hopefully enter a maternity den later this year and give birth next winter, not emerging to hunt again until next spring. To prepare for this roughly eight-month fast and set themselves up for a successful pregnancy, they’ll gorge on seal fat, gaining potentially hundreds of pounds in just a couple months.

Sea Ice Pulse

This June’s Arctic sea ice extent was the third lowest in the 40-year satellite record. Ice loss during June was most pronounced in the Kara and Laptev Seas, off the coast of Russia, where temperatures soared, and the sea ice extent was well below average.

In Hudson Bay, polar bears are still out on the sea ice. The ice is retreating quickly now and packing up in the southwest corner—along with all the bears eagerly trying to catch their final meals before the summer fast. Historically, Hudson Bay sea ice would break up around mid-July, but in the 1980s some bears stayed on the ice until August. Sea ice season in this region has dramatically shortened since then. Once the ice cover drops to 50% or less, most bears will move onto land to wait for cooler temperatures.

Polar Bear Pins 

By now most of the bears on the Bear Tracker have made their way back to the west coast near Wapusk National Park—the region in which many were born and where most 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 ice floes down 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.

As these bears swim to land in the coming weeks, we wish them a cool and short summer and cross our fingers that the ice comes back soon!

Collared Bear Updates

X33931 (Toledo Zoo, purple)

Toledo Zoo’s bear has travelled 4300 kilometers (2672 miles) since the fall—the second longest distance on the Tracker. Since we last checked in, she’s maintained her preference for the sea ice in the southwestern corner of the bay, which we hope means she found productive waters with lots of seals during her spring hunting season! This female is accompanied by a single yearling cub who we hope is offering some hunting support in these final days on the sea ice. She has less than a year left with this cub, which should be enough time to help refine its sea bear skills before setting off on its own next spring. Currently, this mother-cub pair are off the coast of Nunavut. It will be interesting to see if they start to track south back towards Wapusk National Park soon...or maybe they’ll come ashore in Nunavut and walk the coastline towards Wapusk in anticipation of the bay freezing again in the fall.

X32444 (Erlebnis Zoo Hannover, Hope, tan/gold)

Hope has journeyed 3694 kilometers (2295 miles) so far, and she is currently deeper in the bay than most of the other bears. Since we last checked in, her movements have been pretty concentrated on a stretch of sea ice in line with the Manitoba/Nunavut border. Hope has two yearling cubs in tow, and they are likely experienced enough to help her hunt and fatten the whole family up for the summer fast. The sea ice in Hudson Bay is starting to retreat and packing up in the southwest corner, and this family is still fairly far from land. Maybe the bounty of seals they’ve found in this region make the risk of sea ice break-up and a long swim back to land seem worth it? At seventeen years old, Hope is a well-seasoned polar bear and likely an experienced mother so she knows what she’s doing—these are some of the questions we just can't fully answer from where we sit. We will certainly watch this family’s movements with great curiosity over the next few weeks!

X33928 (Munich Zoo, Tenya, dark blue)

Since September, Tenya has walked, swam, and drifted 3361 kilometers (2088 miles), and she is currently closer to land than any other bear on the Tracker right now. For much of the spring, Tenya circled one region of southwest Hudson Bay, but come mid-June, she broke course and started towards the coast of Wapusk National Park. Most likely, she is preparing to get back on land as soon as the sea ice concentration is too low, and she wants to shorten the distance that she and her single yearling cub need to swim to get there. Long distance swims are very energetically expensive, so reducing these distances can help the bears conserve energy. And holding onto precious body fat (energy) is especially important right now because once this family comes off the ice, they won’t have a substantial meal again until the sea ice freezes in the fall. With any luck, Tenya’s cub is helping her hunt and the two are busily fattening up. Tenya has less than a year left to impart all of her polar bear lessons on her cub—we hope they make the best of it!

X33110 (Rostock Zoo, Vilma, grey)

My oh my, Vilma is quite the athlete! Since being collared in the fall, she has travelled 6164 kilometers (3830 miles)—and her path on the Tracker looks like a mass of scribbles to prove it. This is, by far, the longest distance traveled by any of the bears that we’re following this year. Vilma is also farther north than all other bears which is consistent with what appears to be her general preference for the upper bay’s waters. Since the last report, she zig-zagged up the bay and closer to the shores of Nunavut—likely in anticipation of the sea ice break-up. The closer she is to shore, the shorter distance she’ll have to swim when the ice is too fragmented for hunting. And this is extra important because she has two yearling cubs hot on her heels! Long distance swims cost a lot of energy and they need to conserve as much energy as possible for the ice-free summer fast ahead. Vilma’s cubs are no doubt watching her every move, modeling her behavior, and actively helping her hunt in these final days on the sea ice. We’ll be watching this family’s movements with great interest in the coming weeks. Vilma certainly continues to keep us on our toes!

X32491 (Tiergarten Schönbrunn, Hope Vienna, dark green)

Hope Vienna has travelled 3789 kilometers (2354 miles) so far, and she looks to be strategically positioning herself for a short journey to land when the sea-ice breaks up. Since the last update, she’s stayed in the southwestern corner of the bay and has gradually moved closer and closer to shore over the last few weeks. She is currently off the tip of Wapusk National Park and is likely preparing to come ashore there when the sea ice concentration is too low for productive hunting. Hope Vienna has two yearling cubs following in her footsteps, and we expect they are absorbing important polar bear lessons from their mom and helping her bring home the seals! At sixteen years old, she’s likely an experienced mother and a pretty good polar bear teacher. While on land this summer, these bears will lose about one kilogram per day of body mass, so every single seal counts right now. Once they are on shore, they will conserve as much energy as possible, resting often and trying to keep the pounds on until their hunting grounds return in the fall.

X33401 (Canada Goose, Aurora, red)

Aurora’s tracker is logging 2468 kilometers (1534 miles), and it seems that her collar may be offline at the moment. It’s fairly normal for these GPS collars to encounter issues transmitting locations. Polar bears do their fair share of swimming and collars can get water-logged. The cold, salty Arctic Ocean is tough on electronics! Aurora has likely had a pretty exciting few months out on the sea ice. She weaned her cub this spring and may have mated soon after, so by now she will simply be focused on being as fat as possible. If she did mate, 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! When Aurora’s collar gets a chance to dry out, we anticipate her path will update and we look forward to getting some information about what she’s been up to!

X19271 (Adventure Canada, Yuka, orange)

Yuka has travelled 3453 kilometers (2145 miles) in the last ten months. Early on in her sea ice traverse, she ventured further north than any other bear on the tracker this year. Alas, the last few months have brought her south and she’s been weaving her way along the coastlines of Manitoba and Nunavut. Yuka is accompanied by a single yearling cub. These final weeks on the sea ice—in which the bears will be focused on getting as fat as possible—is an important period of learning for Yuka’s young. This pair has less than a year left together before her cub sets out on its own. Fortunately, at 20 years old, we expect this experienced mama is a 5-star teacher. Over the coming weeks, we’ll be curiously watching this family’s movements. Yuka and her cub began their journey in Wapusk National Park—will they head in this direction while the sea ice is still intact? Or will they come off the ice in Nunavut and walk the coastline back towards the park? Only time and some more location data points will tell!

X37054 (Shared Planet, Luna, pink)

Luna has clocked 3114 kilometers (1935 miles) on the Tracker thus far. She is both our southernmost and easternmost bear, and she belongs to what scientists recognize as the Southern Hudson Bay polar bear population—and she has the path and position in the bath to prove it! Luna is currently north of Ontario, and this may be a strategic choice because sea ice lasts longest off the coast of Ontario. By choosing to ride this ice out, she may get an extra week or two of hunting—and every seal counts right now! Luna is out on the sea ice with two yearling cubs, and with any luck all three of them are bringing in seals. Though yearling cubs are still learning and will not set out on their own for another eight-ish months, they tend to be fairly helpful hunters. Though hunting will only get harder over the next few weeks. As sea ice breaks up, seals are no longer restricted to small cracks and breathing holes which make them harder to track and catch. At this point, Luna and her two cubs will swim to shore and find a place to hunker down and rest until the bay refreezes again in the fall. We wish them a bounty of seals and a cool, comfortable place to conserve energy this summer!

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