学进去

A group of blue-faced birds step through the grass shoulder to shoulder, red eyes looking around. They look like middle schoolers seeking a cafeteria table at lunchtime. Perhaps they’re not so different.

A new study, led by Damien Farine, an ornithologist who studies collective behaviour, shows that the vulturine guineafowl of eastern Africa, like humans, have multilevel societies. In the past, scientists assumed such social structures required a lot of brainpower. But the pea-brained guineafowl are revealing the faults in that assumption.

These large birds wander across the landscape in packs, often walking so closely that their bodies touch. They may fight each other to maintain their strict hierarchies (等级制度), but at other times they engage in friendly behaviours like sharing food.

Suspecting the guineafowl might have a social structure, Dr. Farine and his colleagues began a thorough study of their society. For a whole year, they made daily observations of 441 birds. Coloured leg bands in unique combinations let researchers tell the black-and-blue birds apart. They also attached GPS devices to the backs of 58 birds, which let them see exactly where every group went, 24 hours a day.

The findings of the research suggest that the vulturine guineafowl have a multilevel society. There are groups within groups within the population as a whole. There even seem to be groups 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 tiny brain size: “They don’t only have small brains relative to mammals (哺乳动物), they also have quite small brains relative to other birds,” he said.

According to him, 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 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. Depending on what enemies or resources are around, it might make sense to travel in a combined group rather than a smaller one.

“Having a multilevel structure may not require having a large brain,” Dr. Farine said. There may be more birds and other animals out there that, although small-brained, have societies as many-leveled as our own.