Drones Are Spying on Caribou in Canada—for Science

Flying cameras are giving biologists an all-encompassing view of
migration that reveals how social interactions motivate the
animals’ every move.

Ecologists Andrew Berdahl, a Santa Fe Institute fellow, Colin
Torney of the University of Glasgow, and colleagues flew drones to
capture footage of Dolphin and Union caribou, a Canadian herd, as
the animals crossed from Victoria Island to the Canadian mainland
in the last stage of their fall migration.

Scientists have long pondered the dynamics of animal migrations,
but they’ve had limited ways to study them. “Tracking collars
revolutionized ecology by allowing researchers to quantify animal
movement in a rigorous way,” says Berdahl of the widely used GPS
and radio-collar technology. But GPS doesn’t capture the entire
herd nor the dynamics between animals—providing only a
snapshot, rather than a full-picture view.

In order to truly understand migration in detail, he says, “we
also need to know the social context driving movement decisions.
And for that we need to see the behavior of [more] of the herd at
the same time.”

So in 2015, the team put cameras in the sky. They captured 12
hours and 40 minutes of footage of the running caribou herd (in
short clips, limited by drone battery life). They then fed the
information into a computer vision program that identified the
unique caribou in each frame, then linked the animals’ positions
across frames to get their individual trajectories. This allowed
the scientists to see each animal’s behavior in relation its
neighbors—visualizing what were “essentially traffic rules for
caribou.”

The footage revealed great variation in the interactions within
the herd—who paid attention to whom, who stuck close to whom, and
whose moves were most influential on others—illustrating the
importance of age, sex, social status, and reproductive status in
the animals’ movement choices. For example, bull males were the
least likely to take cues from others, while young calves tended to
be copy-cats.

It also showed that caribou were more influenced by herd members
in front of them than by those beside or behind them. This unequal
influence supports traditional Inuit knowledge that as herds
travel, a subset of lead animals effectively determines the path of
the group. Presumably, Berdahl says, more experienced animals take
up front positions that let them teach younger individuals the
migration route.

“It’s very exciting to be able to use new technology to obtain
quantitative information about large animals [on the move],” says
Iain Couzin of the Max Planck Institute for Ornithology in Germany,
an expert on collective behavior not involved in the study. “These
are very difficult data to get. Drones are opening up a new
opportunity for us biologists, giving us access to systems that are
incredibly hard to study.”

The study authors see their technique as a means to examine how
social information is used at different life stages, how this
behavior varies throughout the year, and whether some individuals
are persistent leaders or followers.

“Every individual step an animal takes is a decision,” says
Berdahl, that depends on social cues in concert with environmental
ones such as obstacles and incentives along the path. He hopes that
zooming in on those cues can offer clues to the motivations and
pressures that drive caribou movement, plus insight into the
leadership dynamics of herds—especially as some are forced to forge
new paths in a rapidly changing environment.

Meanwhile, there’s great potential for drones to gather
additional layers of information—such as high-resolution, 3-D
images of the migration landscape—to put the animals’ behaviors
into even more detailed context. “These interactions don’t happen
in a barren environment,” says Couzin, who, in his own research,
looks forward to taking “a hybrid approach, using different
technologies at different scales to get a more comprehensive
picture” of animal movements in natural settings.

“This is a developing methodology that could be applied to many
animal systems,” Berdahl adds. “I’d be tempted to say it will
revolutionize studies of this kind.”