In the darkening weeks of late fall, Dolphin-Union caribou herds cross the stretches of frozen ice that seasonally connect Canada’s Victoria Island to the mainland. Each spring as temperatures begin to warm, the herds return to the northern island to calve.

In a paper published in Philosophical Transactions of the Royal Society, B, SFI Omidyar Fellow Andrew Berdahl, long-time collaborator Colin Torney (University of Glasgow), and co-authors, used drones to collect overhead footage of these migrating caribou. Then they extracted trajectories of each individual caribou and used those trajectories to quantify how social influence impacts fine-scale movement patterns within the herd.

This is the first paper to use drones to record the movement of individual animals within groups. It is also among the first to study social interactions within those groups as they migrate.

Until recently, scientists could only study animal migration by tracking a small subset of individuals through GPS collars. As a result, most studies focus on the individual, despite the fact that so many migratory animals travel in groups.

“New technologies, like the drones and computer vision we used in our study, are really exciting because they give us the ability to collect movement data on every single individual in a group simultaneously,” says Berdahl. “That means we can now unravel the important role that social interactions play in guiding migratory movements.”

The authors’ findings call into question one classic assumption in the field of collective behavior: that individuals within a herd all behave similarly. “We found enormous variation in sociality across sexes and age classes,” says Berdahl. “For instance, calves are highly social while adult bulls tend to be much more independent.”

The study also shows that caribou follow highly isotropic interaction rules — that is, they are more influenced by others in front of them rather than those beside them. “This leads to asymmetric information flow through the herd and, interestingly, agrees with the traditional knowledge of the Inuit, which states that a subset of ‘lead’ caribou effectively guides the path of the annual migration,” says Berdahl.

“Ultimately, collective behavior is important because social dynamics can have population-level implications,” write the authors. The framework they lay out could be used to explore individual and collective movement in a wide variety of animals and environments. 

Read the paper, "Inferring the rules of social interaction in migrating caribou," in Philosophical Transactions of the Royal Society, B (March 26, 2018)

Read the article, "Drones Are Spying on Caribou—for Science" in National Geographic (March 26, 2018)

Read the article, "Drones Spy Caribou on a Treacherous, Icy Crossing" in The Drive (March 26, 2018)

Read the article, "It’s Complicated: Drone Research Reveals Caribou’s Complex Social Dynamics" in Drone Below (March 27, 2018)

Read the article, "Drones Spy Caribou on a Treacherous, Icy Crossing" in The New York Times (March 28, 2018)

Read the article, "Computer Vision-Infused Drones Reveal Caribou Migration Patterns" in The New York Times (March 28, 2018)

Read the article, "Drones spying on secretive species in the name of science highlight importance of UAV technology" in Commercial Drone Professional (March 28, 2018)

Read the article, "Drohnenüberflug zeigt: Eine Rentierherde ist keine gleichförmige Masse" in Der Standard (March 30, 2018)

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