SATAN thunders along, head lowered and black eyes transfixed by her reflection in the mirror 3 metres away. She runs at nearly 30 kilometres an hour, hardly distracted by the burning heat, pungent stench of faeces or deafening roar from the four-tonne treadmill beneath her. Black wings fanned, feathers quivering with excitement, her long, white legs blur with speed.
Good thing the infrared cameras can track the flickering reflective markers stuck at five joints on her body. Good thing she doesn’t try to eat them. Good thing that she, unlike Eric preening over there in the corner, won’t stop dead on the track and flatten Nicola Smith, who is standing braced behind her.
But then, Satan is a very good ostrich. “When she was tiny, she was really horrible to the other ostriches,” says Smith, a doctoral student in biomechanics at the Royal Veterinary College in Hatfield, UK. “But it turned out that she’s probably our best experimental bird. She runs on the treadmill brilliantly. We feel a bit guilty for calling her Satan.”
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Some people might wonder why Smith, with her flock of 15 hand-reared birds, opts to risk life and limb to study ostrich locomotion. Sure, they make a good burger, but what do we really need to know about them?
While fascinating on their own, boasting the record for bipedal speed, they are also among the best species for teaching us about locomotion in two very different creatures: people and dinosaurs. Ostriches are the largest two-legged relative of infamous beasts like Tyrannosaurus. A peek at the finer details of their anatomy helps computer modellers flesh out fossilised skeletons and sort out how T. rex really lumbered around Cretaceous forests.
Measuring around 2 metres tall and weighing 100 kilograms, they also have human-like proportions. Comparative studies can test the pros and cons of our different takes on bipedalism, even learn how to treat human injuries better. “We know an awful lot about how humans move – normal and abnormal gait, kids and adults, but what we lack is some sort of perspective,” says Stephen Gatesy, an expert in animal locomotion at Brown University in Providence, Rhode Island, US.
True, an ostrich’s crouched legs don’t look very much like ours. Their squat thigh bone lies horizontal and hidden under a shaggy umbrella of feathers, while the rest of the leg bones are elongated and fused to generate great, swift strides (see Graphic). The whole limb balances on two sturdy toes.
Jonas Rubenson of the University of Western Australia in Crawley hopes that by figuring out how ostriches handle the punishing forces on their joints, he will learn why knee injuries are so common in people – and possibly how to surgically reconstruct torn tissues for better stability.
But he also wanted to know how much energy ostriches and humans expend to run. Rubenson, too, trained a flock of ostriches to run on treadmills. He was not as lucky as Smith, whose massive machine was engineered for studying racehorses; Rubenson had to use a treadmill designed for humans. And while he spent hours designing ostrich diapers to prevent the pitter plop of giant bird poo, he confesses that “there are probably some marks on the treadmill belt that won’t be coming out”.
“A peek at the details of ostrich anatomy could help sort out how T. rex really lumbered around”
Rubenson found that ostriches move much more economically than people do. The key is the spring-like action of their legs. When their feet strike the earth, the toe joint flexes, which stretches an 80-centimetre long bundle of tendons that run down the back of the leg. And then, like a coil releasing, all that stored elastic energy discharges as the foot takes off. This means they get some serious lift for minimal cost. We also store elastic energy in our Achilles tendon while running, but not nearly so efficiently.
Energy conservation is important for big animals because as body weight increases, it gets harder to pack in enough muscle mass to move quickly. And it’s especially important for ostriches, who have to outrun hungry cheetahs on the African plains.
But ostriches are not just champion runners, they are frighteningly fast growers, too. In one month they grow more than 30 centimetres, piling on at least 70 kilograms in the half-year it takes them to reach full size. Few biomechanical studies opt to track the effects of body size in a single animal, an important aspect for scaling up results to fit the giant bones of dinosaurs.
So every week Smith swings open the paddock gate and leads her lanky flock through the English countryside towards a covered tunnel. There they run over a force platform, which measures the contact time and impact of a step. Then the good ones, like Satan, get a jog on the treadmill.
Although treadmills and force platforms are the bread and butter of locomotion research, they are not perfect tools. Animals get stressed on treadmills and may use abnormal gaits. And it can take tens of runs to get a good reading from the force platform, because however willing to please, their long strides mean ostriches often miss the mark.
That’s why Smith and her supervisor Alan Wilson have big hopes for the fist-sized GPS units they’ve been strapping on the flock’s feathered backs in tandem with ankle-hitched accelerometers. Together these black boxes can measure the speed and ground forces of natural running. If all goes as planned, Smith will end up with a complete profile of the way joint, muscle and tendon performance varies with speed and body weight. And it’s that kind of data that makes John Hutchinson, a modeller of dinosaur locomotion at the Royal Veterinary College, drool.
“You can build a computer model for an extinct animal that shows anything. You could show that T. rex could jump over skyscrapers. But unless that model is validated by living animals, it is useless,” says Hutchinson. In 2002, he constructed a model that suggested T. rex probably couldn’t muster anything beyond a quick walk – its body just could not have supported the necessary muscle mass (Â鶹´«Ă˝, 2 March 2002, p 6). But the model also implied that younger, lighter T. rexes may have been much sprightlier than their 6-tonne parents, a puzzle that Smith’s growth data may help to solve.
The 3D models that Hutchinson works with today will give Smith an inside view on the limbs of her birds and allow her to zero in on the activity of single muscle groups. From scans he can build up a computer replica of Satan, for example. Running on screen, Smith can see which muscle groups and tendons are important at different speeds or angles of movement. And she can tell which anatomy yields the best performance.
While the potential applications are broad, from creating more realistic creature animations to improving rehabilitation therapies for lame horses, Hutchinson has his eye firmly on the basics. “We’re not doing this so we can build a robot ostrich that can go to Mars, we just want to understand how animals move…but you never know.”
