At first glance, biologists slapping motion capture gear onto kangaroos sounds like a scientific foray into the 3-D-movie craze. But James Cameron can rest assured: The scientists are merely performing their day jobs, studying kangaroos—and using a nifty new camera to do it.
As kangaroos mosey along at low speeds, they walk, using their tail as a fifth limb. But as they speed up, they slip into their signature bounce. The mystery for scientists is why such large animals—some being over six feet tall—are so darn springy, and as Alexis Wiktorowicz-Conroy, a researcher at the Royal Veterinary College, told the BBC, “We can’t really explain … why their bones don’t break at high speeds.”So the question here isn’t only why and how roos hop, but also why they don’t fall apart when they do. To tackle these questions anew, a team of international scientists is trying out a new gadget on kangaroos at Australia’s Alma Park Zoo, in Brisbane: an outdoor motion-capture camera that uses infrared light—much like how a sonar uses sound—to study the kangaroos’ bodies movements in detail. After the scientists place several plastic-ball markers on the joints of kangaroos (a feat unto itself), they turn on the infrared light, which is strongly reflected by the markers, and let the cameras roll. They then entice the marsupials to hop onto force plates, which measure the pushing forces of the kangaroos’ feet, thereby capturing both their movements and the way their bodies distribute force.
The new camera used by the researchers provides a couple of benefits over other models. One major point is that most infrared cameras have trouble observing kangaroos outside, in their normal setting, because of the plentiful infrared coming emitted the sun. The camera used in this study, on loan from the fiber-optics firm Vicon, can sort out sunlight from artificial infrared.
Now that they have a way to study roos in a natural setting, they hope to address a couple of puzzles about their biomechanics:
“There are a number of species that, as they get larger, adopt more and more upright postures. That reduces the mechanical demands on the musculature,” Craig McGowan of the University of Idaho, told the BBC.
But kangaroos don’t do this—they don’t stand up straight or redistribute their weight despite being so large, which is doubly puzzling because they seem to jump with great efficiency. “Humans fatigue very easily when we [jump], but the kangaroos don’t; they don’t expend much energy,” McGowan adds.
You’ll have to wait for answers, though, because the team is currently sifting through all their footage. So aside from “it seems to be more efficient for them,” we still don’t know why exactly kangroos jump, or even how they stay in one piece while doing so.
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