Remember middle school? Well . . . maybe you don’t want to. It turns out, humans aren’t the only ones who go through agonizing rounds of teasing and torment to find their place in the pack. Other primates and mammals create social hierarchies, too, as do fish, hermit crabs, and birds.
A study published today in PLOS Computational Biology shows how one species of bird forms its pecking orders. The researchers focused on the Monk Parakeet, a bright green South American native that has invaded parts of the southern and eastern United States over the last 40 years.
Lead author Elizabeth Hobson, a postdoctoral fellow at the National Institute for Mathematical and Biological Synthesis, was studying social relationships among brand new groups of captive parakeets in Florida when she noticed how often the birds brawled. “We think about aggression as being fights between pairs of individuals,” Hobson says, “but it often takes place in a social context, with all of these other ones hanging out and watching.” So she got to wondering: Were the spectators learning something that could help them figure out their own place in line?
To find out, Hobson released two successive groups of captive parakeets, each containing about 20 individuals, into an outdoor flight pen that she describes as “a kind of circus tent made of chicken wire,” and monitored them over the course of 24 days. The conflicts that ensued were more like a chess club than Fight Club. Typically, Hobson says, “One bird edges over to the other guy, eyes him, kind of swipes him with his beak, and then the other bird flies away.” When she and co-author Simon DeDeo of the Santa Fe Institute counted up the parakeets’ wins and losses and entered them into complicated mathematical models, they discovered the birds weren’t taking cues from more obvious factors like size, but were rather playing a sort of “aggression telephone game,” Hobson says. In other words, parakeet A might fight parakeet B, then watch B fight C, C fight D, and D fight E, and then use that pattern to determine how to interact with parakeet E.
Once they had a sense of their place in the pecking order, the birds tended to challenge only those ranked close to them. That may be because those individuals posed the most immediate threat to their status, and provided the least risky opportunities for climbing the social ladder. Bullying the weakest guys at the bottom could waste energy, while aiming for the top slot would be rash.
It’s still unclear if parakeets benefit from higher social status, Hobson says; the birds forage for widespread resources like seeds and aren’t in direct competition with each other. But the findings underscore how humans aren’t alone in their social awareness and complexity. “It’s really neat to try to watch birds with new eyes," Hobson says. "What are you thinking about out there? What’s going on in that little bird brain of yours?”