Among mammals, socially dominant individuals often make decisions for the whole group. (Think of your overbearing friend on a road trip who demands a stop at In-N-Out because he's craving an animal style burger.) But among pigeons, it's the submissive ones that often assume command when it's time for the flock to move, according to new research.
The findings, published Monday in Proceedings of the National Academy of Sciences, suggest a diverse social structure among pigeons in which different skills are valued for different tasks.
Dora Biro, an animal behaviorist at the University of Oxford in England, became interested in the nuances of pigeon protocol because she wondered how social animals ever manage to decide anything.
"The problem a group faces is integrating different preferences and coming up with a single solution that the rest of the group follows," she said. "It's a common problem for any socially living species, including humans. Every single day of my life I'll have some kind of decision-making problem."
Research on primates, such as mountain gorillas and chacma baboons, had shown that dominant personalities were usually the deciders. But the dynamics of other social creatures, like birds and fish, remained unknown.
With their ace navigation ability, gang tendencies, and familiarity with humans, the domestic pigeon (Columba livia) was a logical choice to test the relationship between dominance and decision-making.
Biro first needed to know the basics of pigeon flight. Did everyone in the flock contribute to decisions about where to fly? Or was it more of a dictatorship?
It turned out that only certain birds determined the flock's flight path, implying some hierarchy of leadership.
To test the theory that dominance determined leadership, Biro turned to technology.
She collaborated with a group of statistical biophysicists at Eötvös University in Hungary to first devise a computerized method for determining pigeons' pecking order. Rather than having to manually document every social interaction between birds, they wanted to try using video, computers and visual tracking cues to map the birds' behavior when exposed to a food source.
Biro's team established three groups of 10 pigeons each from a population reared at the university. They fitted each bird with a mini-backpack, on which they painted a three-color barcode using nail polish. ("We used more nail polish in this research than I ever have in my life," Biro noted.) Team members then set up a video camera on the ceiling of the loft where the birds were housed and set out a small ceramic cup containing bird food.
They taped multiple feeding trials and were able to reconstruct the movement and behavior of each individual in more than 22 hours of video.
The researchers measured dominance between all pairs of interacting birds in two ways: the amount of time individuals in a pair excluded each other from feeding, and the degree to which one bird approached the other versus the degree to which it avoided the other.
Compiling all of the interactions, they established that certain pigeons were always more dominant over others. Unsurprisingly, the dominants also tended to be the bigger individuals.
Next, Biro wanted to see if the dominant pigeons were also the leaders. They fitted each bird with an elastic harness complete with GPS device, which had to be custom-made for each bird. ("If it didn't fit comfortably, they did weird things like walk backwards," Biro said.) Then they tracked the flock as they took flight.
They measured leadership as the amount of time between two birds' directional movement, indicating the response of one bird following another.
When the researchers compared the dominance and leadership data for each pigeon, they found no correlation. That was an indication that some factor other than dominance determined who would lead the flock. It could be experience, it could be motivation, it could be flight speed—there are several untested possibilities, Biro said.
While the jury is still out, understanding how leaders are born is fundamental to any social animal, from pigeons to humans.
"It really matters how you choose your leaders," Biro said.
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