Polar bears and load cells [Updated February 2023]
Published On: February 22 2023
International Polar Bear Day 2023 is February 27, and so we’re revisiting one of our all-time most popular blogs.
It all started with a simple question: had load cells been used in any form of polar bear research, given the extremes of temperature in the bear’s native Arctic, and the challenges of performance and data storage extreme cold presents. Not to mention the dangers of tracking the world’s largest land carnivore, when an adult male can weight up to 700kg.
Since last we wrote in 2020, things have got considerably tougher for polar bears. High summer temperatures and retreating Arctic ice has forced them on shore to forage for food. Deprived on their normal diet of seals, polar bears can lose up to a kilogram in weight a day when onshore. What’s more, hunting for food onshore brings them close to human populations.
In January 2023, this contact had tragic consequences when a young mother and her baby were killed by a polar bear in the city of Wales, Alaska. Wales is the westernmost city on the North American mainland and sits on the Baring Strait. The fatal attack, the first in Alaska in 30 years, happened outside the local school gates. Staff rushed out to try and scare the large polar bear off with snow shovels. When the bear turned on them, the school’s principal slammed the school doors closed.
“The polar bear was chasing them and tried to get in as well. Just horrific. Something you never think you would ever experience.”
Airlifting polar bears
The town of Churchill in Manitoba sits on the shores of Hudson Bay in Canada. Churchill is known as the polar bear capital due to the ease of access to the Bay to spot wildlife – but it works both ways. Polar bears are now such a problem that the town dump has been fenced off and is patrolled. Bear attacks are rare but the town’s bear patrol, run by the provincial conservation officer, regularly has to scare them aware from people’s homes.
“Sometimes the animals have to be sedated, then winched up by a helicopter to be transported to the north, or kept in a cage until winter, when they can again feed on the bay.
Churchill’s only “prison” is inhabited entirely by bears, a hangar whose 28 cells can fill up in the autumn as the creatures maraud in mass around town while waiting for the ice to re-form in November.”
As per our original blog, load cells will play their part in assessing the weight of any sedated polar bear and the capacity of the helicopter winch, before any bear can take to the air.
How to weigh a polar bear
Back in 1999, Douglas Page wrote about research into the polar bear’s ability to cope with the extreme fasting between seasonal gluts. Page describes how the researchers tracked and tranquilized polar bears to determine their body mass “By weighing the bears with an electronic load cell.”
A male polar bear can weigh over 650kgs, and measure up to 3metres in length, so we assumed they were weighed in a net or similar. Certainly, getting a single load cell to measure a bear when it’s fast asleep (hopefully) on the ice would not be possible.
Pick up the bear – the hand lift method
Another search(on page 19)revealed how some researchers did it – by hand. They put the bear in a sling and suspended it above the ice on the shoulders of two (strong) researchers. They then simply read off the results, and popped the bear down again.
Pick up the bear – with a helicopter
Other researchers were more pragmatic. Having found the polar bears by helicopter, they weighed them by helicopter too. However, as one research study revealed, this method did have its problems:
“Body mass(kg) of some polar bears >1-year-old was determined using an electronic load cell mounted below the helicopter. Bears were placed into a large web net and lifted by the helicopter until clear of the ground. The scale could provide estimates of mass accurate to ±1 kg, but because the helicopter could not be held absolutely steady in the hovering position, mass estimates were accurate to ±5 kg in most instances.”
Spring scales and polar bear cubs
Weighing polar bear cups is much easier. In two studies cited in, the researchers sampled a population of bears twice within an 88 day period. Again,
“Total body masses were determined by spring scale for cubs-of-the-year in spring (±0.25 kg) and with a spring-loaded scale or an electronic load cell otherwise (±0.5 kg).”
The polar bear hammock technique!
And finally, a solution that took away the grunt of manual lifting and eliminated the movement of the helicopter – its own hammock, as devised by the Southern Hudson Bay Polar Bear Project.
“Total body mass was measured to the nearest 500 g by suspending the bear from a spring-loaded weigh scale (1984-86), or from an electronic load cell scale (2000-05). During weighing, bears were placed in a semi-supportive sling and lifted by chain pulley until clear of the ground.”
The most popular method still seems to be this ‘sling on a tripod’ technique. Polar bears who live in and around the Chukchi Sea are monitored by both US and Russian scientists, who track their movements and weigh them. The weighing rig is simply a tripod, with a hook, lifting chain and a crane scale with load cells and digital readout. Click to see a great (sunny) pic of the team weighing a mother polar bear and a sleepy adult polar bear.
An identical method of weighing bears was used by a team investigating how much energy free-ranging polar bears were expending. The team used pre-existing data on female polar bears on the sea ice of the Beaufort Sea. In that original study:
“Data were collected in 1989–1996 in western Hudson Bay and in 1984–1986 and 2000–2005 in southern Hudson Bay. Total body masses were determined by spring scale for cubs-of-the-year in spring (±0.25 kg) and with a spring-loaded scale or an electronic load cell otherwise (±0.5 kg).”
Pagano’s team used data gathered from polar bears tracked via from their pre-existing collars:
“Polar bears were located from a helicopter and immobilized with standard methods. Following immobilization, we weighed bears using an electronic load cell suspended from an aluminum tripod.”
Polar bear tracking for everyone
Thanks to an interactive map at Polar Bears International website, you can track polar bears from the comfort of the sofa! Eleven individual bears are being tracked across the ice of Hudson Bay, including 20 year old Yuka and 14 year old Vilma, who are heading out towards Coats Island from their previous base at Wapusk National Park in Manitoba, Canada. By contrast, mother bear Polaris has kept within striking distance of Akimiski and Sanikiluag islands at the south of the bay, in Quebec.
Polar bears fishing for beluga whales
The BBC TV series “Seven Worlds One Planet” gave us new insights into animal behaviour, including Hudson Bay polar bears fishing for young beluga whales from rocks. Previously, the bears had hunted the whales on the ice flows, or by swimming in the water with them. This time, the bears swam out from the shore and perched on rocks above the water line, gazing down into the water. The white beluga whales swam around in the shallow bay, seemingly oblivious to the bears, until the bear sprang into action. Sometimes the whales got away, other times the polar bears got to eat.
Weighing wild animals
This, of course, led us to wondering how you weigh other creatures. So, what have elephants, hippos, rhinos, lions, gorillas, walruses, giraffes, and dolphins all got in common? They’ve all been weighed on scales made by US company Emery Winslow. A post explains the unique challenges:
“The reliable weight data provided by these scales is critical for monitoring overall animal health, to measure the effectiveness of various diets, and for proper application of medications and supplements. These scales meet the challenges of harsh environments, which may include physical abuse from the animal, corrosive conditions from animal urine and waste, the effects of water washdown, and even submersion in salt water.”
Killer whales on the scales
Orca (killer whale) shows at SeaWorld were discontinued by 2019, but the keepers had a novel approach to ensuring the wellbeing of the whales still in their care. As the Seaworld site said in 2017:
The platform was sunk into a low pit at the side of the pool, so it was a seamless glide from water to scale.
Bring us your weighing and load cell challenges
Whatever your project, whatever the conditions, we can help with accurate, reliable, robust load cells to help you get the job done. Call us at Richmond Industries. We’ve helped create bespoke solutions for a wide variety of clients, and we can do the same for you. All our load cells solutions are designed in-house here in the UK, and most of our load cells are manufactured here too.
We’ll be honest; if you’re looking for cheap as chips load cells for simple light load weighing applications, we’re probably not the company you need. But if you want to weigh a whale, or measure the force exerted by a polar bear smashing through the polar ice, we could be just the company you need! Give us a call.
Postnatal growth in body length and mass of polar bears (Ursus maritimus) at Barents Sea. Journal of Zoology 256(3):343 – 349 · February 2006
A body composition model to estimate mammalian energy stores and metabolic rates from body mass and body length, with application to polar bears. Péter K. Molnár, Tin Klanjscek, Andrew E. Derocher, Martyn E. Obbard, Mark A. Lewis.
Journal of Experimental Biology 2009 212: 2313-2323; doi: 10.1242/jeb.026146
Southern Hudson Bay Polar Bear Project 2003-05 – Final Report December 2008. Martyn E. Obbard
Pagano, A. M., & Williams, T. M. (2019). Estimating the energy expenditure of free-ranging polar bears using tri-axial accelerometers: A validation with doubly labeled water. Ecology and evolution, 9(7), 4210–4219. https://doi.org/10.1002/ece3.5053
A body composition model to estimate mammalian energy stores and metabolic rates from body mass and body length, with application to polar bears Péter K. Molnár, Tin Klanjscek, Andrew E. Derocher, Martyn E. Obbard, Mark A. Lewis Journal of Experimental Biology 2009 212: 2313-2323; doi: 10.1242/jeb.026146