Even the bird-brained can follow a leader. When pigeons fly in flocks, each bird falls behind another with better navigational skill, and the savviest among them leads the flock, scientists report in the April 8 Nature.
The research suggests hierarchies can serve peaceful purposes in the animal kingdom, where dominance by brute force is often the rule. “A pecking order tends to be just that — a pecking order,” says Iain Couzin of Princeton University, an expert in collective behavior who was not involved in the research.
The research also suggests that for pigeons, dominance isn’t set in stone. While one bird often emerged as the leader, other birds also stepped up. This flexibility in leadership had previously been seen only in some small groups of fish.
From schools to packs to swarms to flocks, collective behavior is widespread among animals. But in many cases, the important interactions are with nearest neighbors, and control of the group’s movement is distributed among members rather than hierarchical.
Biological physicist Tamás Vicsek of Eötvös Loránd University in Budapest and his colleagues studied flight dynamics in homing pigeons, which fly in flocks but conveniently return to their roosts. The researchers outfitted 13 pigeons with tiny backpacks carrying GPS devices that measured shifts in birds’ flight direction five times per second. Flocks of eight to 10 birds flew with the devices during homing flights (a roughly 14-kilometer trip back to the roost) and spontaneous “free” flights near home. Each bird also flew solo flights of about 15 kilometers each.
Analysis of GPS logs showed that for each excursion, the flock had one leader followed by at least three or four other birds. Each of these followers was in turn followed by other birds in the flock. Comparing the solo flight paths to the group flights showed that the birds with the best navigational skills led the flock.
While flocks have hierarchies, they’re not dictatorships, notes Vicsek. One bird led eight of the 13 flights, while other birds took the lead on the rest of the trips. Vicsek likens the dynamics to a group of peers deciding where to eat dinner. “Maybe someone knows the area restaurants best, or there is a person who’s a gourmand — or maybe they are the most outspoken,” he says. This one person might pick the place to eat for several nights, although another person might chime in now and then. And then there is the person with no say, whom everyone knows has terrible taste in food.
“These pigeons know each other. They know which is the smartest. The fastest bird will even follow the slower one who knows the way home the best,” say Vicsek. Videos of the birds’ positions during flight showed that if the best navigator moves a little to the left, it takes about a third of a second for other birds to do the same. But if the least savvy bird makes a move “the others don’t care,” Vicsek says.
Pigeons’ brains may be wired for follow-the-leader, comments behavioral neuroscientist Lucia Jacobs of the University of California, Berkeley. When the left eye sees something, for example, it sends all the visual information to the right brain hemisphere, and vice versa. This “extreme lateralization” may play a role in organizing flocks, the new work suggests. A pigeon following another was most likely to be flying on its partner’s right, seeing this leader with its left eye. “It’s very cool,” Jacobs says.
FOLLOW THE LEADER Pigeons flocks have followers and leaders, reveals an analysis of data recorded by GPS devices in the birds’ backpacks. While the flock member designated as red isn’t the fastest bird, his movements guide the flock on a homing flight.
Credit: M. Nagy, Zsuzsa Ákos, D. Bíró & T. Vicsek