A pack of baldheaded, boldly plumaged birds steps through the grass shoulder to shoulder, red eyes darting around. They look like middle schoolers seeking a cafeteria table at lunchtime. Perhaps they’re not so different.
A study published Monday in Current Biology shows that the vulturine guineafowl of eastern Africa, like humans, have many-layered societies. In the past, scientists hypothesized that such social structures require a lot of brainpower. But the pea-brained guineafowl are revealing the flaws in that assumption.
Damien Farine, who led the research and is an ornithologist at the Max Planck Institute of Animal Behavior who studies collective behavior, first worked in Kenya during his postdoctoral research on baboon societies. Baboons are a model for researchers trying to understand how human society evolved. Some kinds of baboons live in groups within groups, a structure that’s called a multilevel society.
“Humans are the classic multilevel society,” Dr. Farine said.
Imagine a human family living in a village: The family might be friendly with other families within the village, which in turn might have ties to neighboring villages, and so on.
Keeping track of these relationships can be complicated.
“People have long hypothesized that living in complex society is one of the reasons why we’ve evolved such large brains,” Dr. Farine said. Researchers have found evidence for multilevel societies in some other large-brained mammals, such as monkeys, elephants, giraffes and sperm whales. But as Dr. Farine studied baboons, he also watched the vulturine guineafowl wandering around his study site.
“I was really struck by the social behavior that they exhibited,” he said.
These hefty birds can fly, but rarely choose to. Instead, they stroll across the landscape in packs, often walking so closely that their bodies touch. They may chase each other or fight to maintain their strict hierarchies. But at other times they engage in friendly behaviors like sharing food. Their groups are unusually large for birds, sometimes including 60 or more individuals. And while most other social birds are very territorial, Dr. Farine says, groups of vulturine guineafowl don’t mind sharing turf.
He suspected the guineafowl might have a social structure just as interesting as baboons. So he and his colleagues began an intensive study of vulturine guineafowl society at the Mpala Research Center in Nanyuki, Kenya. For a year, they made daily observations of 441 birds — nearly every adult in the local population. They counted 18 groups in total. Colored leg bands in unique combinations let researchers tell the black-and-blue birds apart. Scientists also attached little solar-powered GPS devices to the backs of 58 birds, including one or more in each group. This let them see exactly where every group went, 24 hours a day, for a whole year.
They found that group membership was stable; birds stuck with their pack.
Each group included multiple breeding pairs, along with other birds. Groups often met and interacted — in fact, certain groups seemed to prefer hanging out together. Some groups even bunked together at night.
“Even though they did not share the same home range during the day, they seemed to seek each other out at night and roost together,” Dr. Farine said.
The birds would all fly into the trees to sleep, then alight in the morning — hundreds of birds milling around in one place — and gradually sort themselves back into their original groups for the day.
The vulturine guineafowl, in other words, have a multilevel society. There are groups within groups within the population as a whole. Dr. Farine says there even seem to be clusters of friends within the small groups. This is the first time anyone has observed such a society in a bird.
And Dr. Farine emphasizes this particular bird’s poor intellectual endowment: “They don’t only have small brains relative to mammals. They also have quite small brains relative to other birds,” he said.
Larissa Swedell, a biological anthropologist at Queens College in New York who studies baboons, finds the results convincing. “It looks like they have demonstrated a multilevel society, which is really interesting in these small-brained birds,” she said. “But it’s not completely surprising.”
That’s because even among primates, Dr. Swedell says, it’s not always the brainiest species that have multilevel societies. Living in this kind of society might actually make it easier to keep track of the social order. For example, if groups are stable and a bird or baboon can identify just one or two individuals within a group, it knows which group it’s looking at — no need for a brain that can recognize every single animal.
Multilevel societies also let animals adjust their group sizes based on whatever challenges they’re facing, Dr. Swedell says. Depending on what predators or resources are around, it might make sense to travel in a conglomerate group rather than a smaller one. She notes that baboon groups may also come together to sleep, like the vulturine guineafowl.
Dr. Farine agrees that the vulturine guineafowl might not be all that unusual.
“Having a multilevel structure may, in and of itself, not require having a large brain,” he said.
There may be more birds and other animals out there that, although cognitively unimpressive, have societies as many-layered as our own. “What else is out there in nature?” he asked. “I suspect that probably this species is not unique.”