Graphic courtesy of Oregon State University
Researchers observe the motions used by this turkey hopping over an obstacle in order to model its behavior.
When robotics experts are stumped about how to help their creations accomplish a task, many of them rely on the best and original practitioners of that task available to them: animals. A group of scientists at Oregon State University, the Royal Veterinary College, and a number of other institutions, wanted to learn more about running. They turned their attention to an obvious example: not horses, not cheetahs, not even humans. They looked to birds for help.
Running is not exactly the mode of transportation birds are best known for, but it’s something they have to be reasonably competent at in the wild to avoid unexpected close encounters with predators. In fact, researchers learned that of the two-legged land-dwelling species, birds might be the most sophisticated runners, more so even than humans.
This makes sense, scientists say—birds have had to find the delicate balance between keeping their legs intact and not wasting energy with a lot of extra strut. The result is not particularly graceful, but it works, and the research team wanted to know why.
The team of scientists examined five species of birds—ostriches, turkeys, guinea fowl, pheasants, and bobwhite quails—to see how they negotiated stepping onto and off of an obstacle. The range in species allowed the study authors to track the movement in birds weighing between .22 kg and 117 kg in weight and surprisingly, each of the five sizes had similar habits.
The researchers filmed the birds going over the obstacles, which were adjusted to be .1 to .5 times the height of the bird.
The actual running of the birds over the obstacles was itself a culmination of two years’ work on the behalf of the team. A couple of the scientists hand-raised female ostriches from hatchlings to ensure they would be good study participants.
Graphic courtesy of Oregon State University
This model outlines the forces at work as a turkey hops over an obstacle.
"Unlike the other birds in the study, the maximum weight of an adult ostrich is around or greater then 110 kg, this meant that if they didn't want to do something, they wouldn't, and there would be nothing we could do as they are so strong, so they could end up hurting themselves or us,” said Dr. Aleksandra Birn-Jeffery, research associate at the University of Cambridge.
"We would handle them everyday and spend time with them as well as do all the feeding. We also got them used to following us around, by getting them to follow the food bucket when we fed them. It was through this way that we trained them to walk into the lab, by training every day and just doing the same routine. Interestingly, the ostriches really preferred having a constant routine, if the routine changed they were obviously unsettled for the rest of the day!”
An ostrich jogs over an obstacle runway.
In Birn-Jeffery’s experience, ostriches can be surprisingly friendly.
"They are very inquisitive though, so you have to get used to lots of pecking, particularly if you wear anything shiny!” noted Birn-Jeffery.
As each bird approached and departed from the step, they alternated between "vaulting” (in which the birds launch upwards to meet the obstacle, reducing the amount of force on their legs) and "crouching” (in which the birds keep their center of mass, a sort of balancing point, more stable, and drop their bodies a bit). Each vaulted its way towards the obstacle, crouched on top of the obstacle, and extended its legs to step back down. There were slight variations in each bird’s way of moving, but the basic pattern of vaulting and crouching remained the same between them. Those findings were surprising to the team, which expected the smaller birds would display more crouching behavior and extend their legs to keep their motion smoother than their taller counterparts.
Those strategies for negotiating the various steps mimic those the birds would likely use to deal with uneven terrain in the wild, and it seems they weren’t concerned to keep their bodies from lilting in different directions in the process. Did that make their gait a poor example for the robotics engineers whose equipment might need stability?
"The priorities of birds are exactly what you'd want in your robot: get where you need to go, without wasting energy, and be safe!” said Christian Hubicki, graduate student at Bucknell University. "We typically tell robots to aim for steady motions because we know that's a stable way to move. But not only are there other ways to be stable, birds don't appear to show any preference toward being steady at all... and birds are far more stable than the best legged robots.
"Birds don't seem to care how steady their gait is, and neither should our robots.”
This practice of dissecting an animal’s motion to improve robotics technology is so helpful to engineers it’s likely here to stay.
"In our case, we are explicitly trying to understand what the animals do and why they do it, so the reasons can be evaluated when designing robots,” said Dr. Jonathan Hurst, associate professor in the School of Mechanical, Industrial, and Manufacturing Engineering at Oregon State. "This is called bio-inspiration, and it is different from bio-mimicry: We are not trying to copy what animals do for the sake of being like an animal. We are trying to understand how animals work, so we can make robots better.”
Read more about the study in The Journal of Experimental Biology.
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