Why do running emus keep one foot on the ground

Computer-generated emus have helped solve a long-standing mystery of why birds sometimes run with at least one foot touching the ground.

This movement, called “grounded running”, was thought to use more energy than “aerial running”, where all feet are in the air for a moment at the same time.

Biomechanist Pasha van Bijlert of Naturalis, the Netherlands’ natural history museum, said the “foundational confusion” was surprising because animals were generally trying to conserve. as much energy as possible.

“So it appears that these birds are choosing a more energy-efficient running style,” he said.

Another theory of why birds use ground running is to increase stability and prevent accidents at the cost of using more energy.

But new research from Mr van Bijlert and his colleagues, published in Science Advances, suggests that the structure of emus and other birds allows for an energy-efficient way of moving at speed. you said.

To make an example

Mr van Bijlert was working on his PhD on whether Tyrannosaurus rex he could run, and what it would look like, when he deviated from the emu movement.

To simulate the way a dinosaur would walk, he had to test the software of a modern animal that is somewhat related to T. rex to use as a metaphor.

“One of the logical choices is an emu or an ostrich,” Mr van Bijlert said.

“Emus have three toes, so it’s probably a little bit like that T. rex [which also had three toes].”

Emus are one of the fastest animals in the world. They can run at a speed of 48 kilometers per hour for more than a kilometer, according to observations in 1963.

Before finding out whether T. rex could run, Mr. van Bijlert and his colleagues thought about questions about emus that needed to be addressed first, such as: why was it ground runners?

To answer this, the researchers built a digital marionette with an emu skeleton and muscles.

They can make its muscles stretch or tighten, or put the bird in an upright or bent position.

Mr van Bijlert said: “The model needs to learn to walk and run, and we do this with a good physics and mathematics approach.”

“Basically, you tell the model to go from A to B with as little expenditure of energy as possible or with as little muscle as possible… or both.”

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The group found the simulated emus would use ground running at medium speed as the most energy efficient way.

Mr van Bijlert says the emu’s upright form, which reflects its true nature, uses a narrow, narrow gait, just like a real bird.

“[The emus] you don’t necessarily pay more energy as a result. This is just, strictly speaking, it’s still a good thing they can do at some speed,” he said.

“We’ve created a big but curved bird, and if you simulate a different speed, it will choose to run at a wider speed.”

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The study found that the emu’s posture restricts full leg extension like human runners, so running can sometimes be more efficient than running on air.

On the other hand, people and other animals waste energy trying to run with their feet on the ground all the time.

That’s why we get into running air, both feet off the ground, when we go from walking to running.

Although birds such as emmus can also go completely airborne while reaching high speeds, they also use the ground to run from walking.

Mr van Bijlert said: “The long, straight tendons are an important part of what allows emus to run as fast as they do.

An ancient drink connection?

Birds are direct descendants of long-dead dinosaurs that relied on webbing tails to move.

Those tails may be lost in modern birds, but a new study suggests that running on the ground may have been used by their ancient ancestors.

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Not everyone agrees.

John Hutchinson, a lecturer in biomechanics at the Royal Veterinary College who was not involved in the study, said that although he did not think the research provided direct evidence of dinosaur movement , was a good inspiration to make similar comparisons in extinct animals.

“The body structure of extinct dinosaurs was different from that of living birds, so it is difficult to know whether they would have used bird-like movements or more like humans,” he said. .

“Yet the emu simulations suggest that other dinosaurs may have used running, which an independent study of the fossil footprints also suggested.”

While working on dinosaurs doesn’t solve the science, Mr van Bijlert says the emu model can offer other benefits, apart from his ongoing work. T. rex study, in areas such as robotics.

“There’s a lot to be gained by understanding how animals power their movements and what evolutionary strategies have come and saved the ultimate energy to build your robots, ” he said.