Is it bear fat or just chunky? Lasers can help scientists figure this out

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Cusick took a break from work and stood on a platform along the Brooks River in Alaska’s Katmai National Park and Preserve – a world famous bear-watching spot, as the giant mammals love to wade in the water to hang out and catch fish. Otis was a few hundred yards away and was relatively still.

Cusick, who works for the National Park Service’s regional office in Alaska, creates maps and trains people in using GPS and using scanners on site. He usually uses a laser scanner – specifically a terrestrial lidar scanner – to measure the volume of stationary objects in the park such as buildings and piles of gravel. It’s an industrial-grade tool for $ 70,000 that sits on a sturdy tripod. That evening, Cusick pointed it at Otis and did a scan.

Lidar is short for “Light Detection and Ranging” and is probably best known for its use in autonomous vehicles. A lidar scanner sends out millions of pulses of infrared light and measures how long it takes for them to return after hitting an object like Otis. These measurements form a point cloud from which a three-dimensional map of the object can then be created.

In a matter of seconds, on a tablet connected to the scanner, Cusick could see what looked like dots from Otis’ rear end. Computer software later processed the scan and created a 3D model that could be used to determine the width of the bear’s buttocks.

Cusick was excited; he didn’t think his experiment would work.

“I was like, ‘Wow, I’ve got a return on investment – I can measure Otis’ bum here!'” He recalled with a laugh to CNN Business this week.

That lightbulb moment resulted in a multi-year effort for Cusick to use a lidar scanner to inconspicuously estimate the volume (and thereby weight) of some bears in Katmai during winter fattening, which could help biologists understand more about their health of the animals (around 2,200 brown bears live in the park). In 2019 and 2020, bears were scanned in the park during Fat Bear Week – an annual online competition that currently runs through Tuesday, where people can vote for the stockiest (or stockiest) brown bears while they are on hibernation prepare winter. Although the lidar-assisted attempt to estimate the bears’ weight was halted this year due to the pandemic, which left fewer staff available for the process, Cusick hopes it will continue in the future.

It may sound easier to use a scale to weigh bears, but it’s inconvenient in the wild where it might be chewed up. (Also, you’d need to lure the bears onto the scales and let them stand still for about 11 seconds.) In the spring, bears in the wild can be weighed by biologists who fly in by helicopter, calm the bear, slide it into a net, and lift Connect it with a pulley system. But in addition to being intrusive, the fall method may not be possible when the bears have fattened up for the winter.

“A huge advantage of this method is that it is non-invasive; we don’t have to catch any animals,” said Lindsey Mangipane, an Anchorage-based polar bear biologist for the US Fish and Wildlife Service. “For us, it is also much less logistically demanding.”

Estimating a bear’s weight with lidar is much less troublesome, although it is still a very complicated guessing game. For example, those who do the scans can only capture part of the bear because there is no way to place a scanner across the river, Cusick said. To compensate for this, they can cut a bear scan in half and double the volume of the fuller side of the body to estimate the total volume of the bear. And while a 3D scan can be used to determine the bear’s volume (how much space it takes up in three dimensions), it says nothing about its density, which is needed to figure out how heavy it is.

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To get a good estimate of the density, which can vary from bear to bear depending on gender, bone structure, season and many other factors, Cusick spoke to biologists who study the animals. They thought it would be reasonable to estimate that a bear is 60% water and 40% fat, he said for a number of bears at Katmai.

The overall process requires multiple people, Cusick said: one person performs the scan while another verifies the bear’s identity, for example. The weight estimates that can be made for an individual bear with numerous scans are also made and compared independently of individual persons.

A 3D model of the 747 is shown next to a picture of the bear;  747 was the 2020 Fat Bear Week winner at Katmai National Park and Preserve and had the highest estimated weight.

It is currently impossible to know how accurate this method is, but Mangipane hopes to validate the scanning technology by working with zoos to scan captive polar bears whose weight is known since they can be trained to be on scales step. These known weights could be compared to weights derived from 3D scans of the bears.

Aside from accuracy, Cusick said the results were consistent: for example, last year he and his colleagues used about 10 scans taken over several days by a bear named 747. Two people independently estimated the weight of 747 from each scan, giving 20 estimates an average of 1,416 pounds. Each of the individual estimates were within about 100 pounds, Cusick said, and the average was an eight pound difference from the bear’s weight in 2019.
747 was valued as the most voluminous and also the heaviest bear last year. He was also voted top of the rankings by Fat Bear Week voters.

While it will be impossible to say for sure which bear really is the fattest this year, Cusick thinks that the 747 is once again the biggest.

“We all have our favorites,” he said. “The anthropomorphism here is pretty strong.”

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