Birds calculate their own speed limits

Birds develop set their own speed limits to avoid colliding with obstacles, according to new research from the Massachusetts Institute of Technology (MIT).

Scientists there found that Goshawks have to follow a theoretical speed limit to enable them to avoid trees and other obstacles as they dash through a forest.

While that might seem like common sense, the research may have important implications for the design of unmanned aircraft.

Researchers found that, given a certain density of obstacles, there exists a speed below which a bird or any other flying object, has a fair chance of flying collision-free. Any faster, and a bird or aircraft is sure to smack into something, no matter how much information it has about its environment.

Emilio Frazzoli, an associate professor of aeronautics and astronautics at MIT, is part of an interdisciplinary team that includes biologists at Harvard University, who are observing flying behaviour in Goshawks and other birds, and roboticists at MIT, who are engineering birdlike UAVs.

Most UAVs today fly at relatively slow speeds, as they’re programmed to fly just fast enough to be able to stop within the field of view of their sensors.

If Goshawks did the same, though, they would be much slower than they actually are. Instead, Frazzoli says, they’re likely to gauge the density of trees and know intuitively that, given a certain forest density, they can always find enough openings.

Frazzoli added: “When you go skiing off the path, you don’t ski in a way that you can always stop before the first tree you see. You ski and you see an opening, and then you trust that once you go there, you’ll be able to see another opening and keep going.”

It’s now thought that robots could be programmed with this same speedy ‘intuition’, setting their own speed limits after being given some general information about the density of obstacles in a given environment.

Frazzoli and PhD student Sertac Karaman calculated that, for any given forest density, there exists a critical speed above which there is no “infinite collision-free trajectory”. In other words, the bird is sure to crash. Below this speed, a bird has a good chance of flying without incident.

The researchers are now seeing if the theory bears out in nature. Frazzoli is collaborating with scientists at Harvard, who are observing how birds fly through cluttered environments, and comparing the birds’ behaviour with what Frazzoli’s model can predict. So far, preliminary results in pigeons are “very encouraging”.

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