Rutgers University–Camden Researchers Study Actions and Interactions Among Birds

Images of birds on a wire, processed by Matlab software

Photo processed by Matlab software to allow researchers to analyze the birds’ actions and interactions.

By Jeanne Leong

A study by Rutgers University–Camden researchers shows the spacing among birds perched on wires between telephone poles can be explained by the same social forces that describe other group actions.

Led by professors Benedetto Piccoli and Bill Saidel, the Rutgers University–Camden research team—including nine undergraduate, graduate, and postdoctoral students at Camden, Grenoble, France, and Salerno, Italy—found that how birds self-assemble can be explained by the combination of attraction (such as for mating or searching for food) and repulsion (to avoid collisions with group members or because of claustrophobia).

“It’s a lot like people standing in a movie line,” says Saidel, an associate professor of biology. “It’s an attraction. You want to talk to the person in front of you but you don’t want to be in their personal space. That’s a repulsion. It’s the same thing with birds.”

Bill Saidel, associate professor of biology, Rutgers University–Camden

Bill Saidel

The study also shows that interactions between birds are topological—the birds interacted with each other based on the closeness of their neighbors on the wire.

Over a two-year period, the team took hundreds of photos of starlings and pigeons sitting on telephone wires at various Camden County, N.J. locations.

After narrowing down the photos to a set of 114, they analyzed the photos, observing how and where the birds were positioned and measured the distances between the birds.

Using a systematic quantitative approach, the team developed a mathematical model to predict the pattern of spacing between individual birds.

“There are a few characteristics where we were able to capture, like, birds are dense,” says Piccoli, the Joseph and Loretta Lopez Chair in Mathematics at Rutgers University–Camden, where he also serves as associate provost for research. “If you have a large group, they sit more closely in the center and they are more spaced on the wings and this depends on the species and the bird’s size.”

Benedetto Piccoli, associate provost for research and Joseph and Loretta Lopez Chair in Mathematics at Rutgers University–Camden

Benedetto Piccoli

The task of gathering data on birds and analyzing their behavior is complicated because they’re up high, and locating and measuring their position is not so easy to do. The team came up with the idea of photographing birds on wires to conduct their research. “It’s just catch as we could,” says Saidel. “One of the rules of natural behavior is that you can’t tell them what to do.”

Sometimes, while Saidel was driving to his Rutgers–Camden office, he’d stop along the road to take photos.

“I carried my camera all of the time” says Saidel, “and if I saw birds on the wire, I would just swerve to the right to stop. There were at least two times where I avoided monumental accidents.”

Using Matlab software, the team scaled the photos, cropped the bird groups in the photos, removed the wires, and took measurements and analyzed the images and the data they found.

“There is a lot of image processing because you need to identify the birds, measure the distance between birds, and make sure you aren’t confused among the different wires,” says Piccoli.

Through funding from a National Science Foundation REU (Research Experiences for Undergraduates) grant, the team was able to hire students who assisted with the project, traveling through South Jersey and identifying locations to capture photos of birds perched on wires.

The study, “Modeling Birds on Wires,” is published in the Journal of Theoretical Biology.

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