The gregarious, small-brained vulturine guineafowl (Acryllium vulturinum) forms complex, multi-level societies, according to new research.
Published in the journal Current Biology, it challenges previous notions that only animals with large brains – such as humans, primates, elephants, giraffes and dolphins – are capable of such social structures.
Lead investigator Damien Farine, from the Max Planck Institute of Animal Behaviour in Konstanz, Germany, says he was curious to know how groups of animals resolve conflicts and make collective social decisions.
While doing field work in Kenya, he found the vulturine guineafowls presented an ideal opportunity to explore this, as there were many clusters that moved together and were large enough to fit with tracking devices.
So he joined forces with Danai Papageorgiou, the study’s lead author, who established how to trap them, and their team attached individual combinations of colours onto more than 400 birds’ legs to track their group membership.
“Over the course of a year, we then captured what, I believe, is the most complete picture of the social structure in a complex animal society ever – at least in the wild,” says Farine.
They continuously observed the same individuals sticking together, forming 18 distinct social groups with highly stable membership. Yet, Farine says, the birds didn’t demonstrate territorial behaviour – “instead, groups would often encounter each other, move together, and sleep together at night”.
“This suggested to us that there’s a lot more going on here than meets the eye. Watching these birds moving through the landscape, it is striking how cohesive they are.
“Members of the same group will often walk shoulder to shoulder, literally touching one another.”
By fitting all members of two groups with solar-powered GPS tags, Papageorgiou found that the fowl remained within 20 metres of every member of its group 95% of the time.
“Keeping in mind that groups can be up to 60 individuals, and that groups will walk up to 10 kilometres in a day, this shows that vulturine guineafowl really stick together,” says Farine.
He notes that many groups of birds show cohesive behaviour, such as the amazing flocking of starlings (Sturnus vulgaris), but they rarely remain stable in their membership.
Other more stable groups are often small, such as geese that migrate together, or territorial, keeping out other groups.
“What is striking about the vulturine guineafowl,” says Farine, “is that they show cohesion at multiple social levels – groups are very stable, keeping the same members over years, but comprise multiple breeding units between them.”
The researchers are mystified as to how the groups reform into their stable memberships when up to eight different ones all sleep together at a roost.
And rather than being territorial, the fowl actively engage with other groups – which is not unusual in itself, but it’s the first time this suite of behaviours has been observed in one species.
Farine says he rather expected to find unusual behaviour in these remarkable birds. “But I was surprised on how clear this social structure is.”
By definition, a complex society is one where individuals repeatedly interact with others across a variety of different contexts and maintain those relationships at different levels.
“The logic here is that keeping track of multiple types of relationships and the identify of many individuals requires a big brain,” Farine says.
Yet guineafowl have small brains, even compared to other birds, let alone mammals with much larger brains, and could give clues to how such social structures evolved.
“This discovery raises a lot of questions about the mechanisms underlying complex societies,” says Farine, “and has opened up exciting possibilities of exploring what it is about this bird that has made them evolve a social system that is in many ways more comparable to a primate than to other birds.