How do fish and birds get together? Researchers think the answer is a mat with purp



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Fish and birds are able to move in groups without separating or colliding due to a newly discovered dynamic: followers interact with the trail left by the leaders. The discovery offers new insights into animal locomotion and points to potential ways to harness energy from natural resources such as rivers or wind.

"Air or water flows naturally generated during flight or swimming can prevent collisions and separations, allowing even individuals with different flapping movements to travel together," explains Joel Newbolt, Ph.D. of the Department of Physics at New York University and principal author of the study. , which appears in the Annals of the National Academy of Sciences. "Notably, this phenomenon allows slower followers to follow the fastest leaders by surfing their trail."

More broadly, the study opens up possibilities for better capturing natural resources to generate energy from wind and water.

"While we use wind and water to help meet our energy needs, our work offers new ways to harness them more efficiently as we seek new methods to improve sustainable practices," notes Leif Ristroph, one of the co-authors of article and assistant professor at the Courant Institute of Mathematical Sciences at NYU.

It is well known that animals such as fish and birds usually travel in groups, but the details of these interactions in schools and herds are not fully understood.

In order to study the effects of flapping movements and flow interactions on the movement of members of a group, the researchers conducted a series of experiments at the Laboratory of Applied Mathematics of the Courant Institute. Here, they designed a robotic "school" of two aircrafts, which simulate wings and flippers, which fly up and down and swim forward. The flapping movement of each leaf was driven by a motor, while the forward swimming movements were free and resulted from the water pressure on the leaves as they beat.

The researchers, who also included Jun Zhang, a professor at the Courant Institute, NYU Physics Department, and NYU Shanghai, varied the speed of flapping movements to represent faster and slower swimmers and riders.

The process can be seen here: https: //little.ly /2U8fGl7 (credit: video courtesy of Joel Newbolt, Courant Institute of Mathematical Sciences, NYU).

Their results showed that a pair of blades with different flapping movements, which would swim or fly at different speeds when alone, may in fact move together without separating or colliding due to the follower's interaction with the mat left by the leader.

Specifically, the follower "surfs" in distinct ways on the mat left by the leader. If it is behind, the follower experiences a "push" forward by that trail; if you move too fast, however, a follower is "repelled" by the leader's wake.

"These mechanisms create some sweet spots for a follower when sitting behind a leader," notes Zhang.

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