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.