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 ...