Video: Watch rooks team up to win a food reward doing tasks they couldn’t complete on their own

Who ever heard of birds cooperating on a project together? Sure, a pair may build a nest together, but cooperating on a single task to get food is something only primates have been thought capable of. Now it turns out that rooks, like chimps, can cooperate with each other – although they may lack the competitive edge needed understand teamwork properly.

Amanda Seed at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and colleagues tested cooperation between pairs of rooks.

They placed a 60 centimetre-long tray laden with food just out of the reach of two rooks placed inside a box. The rooks could see the food through a slit but had to use string thread through eyeholes at the back of the tray to drag it through the slit towards them.

To get their meal, however, the rooks were also forced to team up. Pulling just one end of the string simply unthreaded it without moving the tray. Only when the birds each pulled one end of the string simultaneously did the tray move.


Early bird

Seed’s team found that, with very limited training, all eight birds they studied mastered this act of cooperation – a specialisation previously thought unique to primates. But the rooks came unstuck when Seed’s team tested the birds’ understanding of cooperation in more depth.

In a second experiment, they presented one rook with an out-of-reach tray but placed the second rook in an adjoining room. The second rook had to scrabble through a hatch before getting into a position where it could pull on the string.

However, the first rook almost invariably pulled its own end of string instead of waiting for its partner to arrive. Similar studies have shown that chimps will wait for their partner before acting.

Paradoxically, says Seed, rooks may fail to fully grasp the benefits of cooperation because individuals rarely compete. In polygamous chimp society, an individual interacts with others chimps and so has to quickly learn about cooperation as a “commodity” on the “biological market”, she says. If a chimp never cooperates, it simply loses out.

Competitive cooperation

By contrast, Rooks form monogamous relationships and seldom interact with other individuals, so they never learn the true value of cooperation, says Seed. “It may be that the sort of cooperation we see in humans [and chimps] could only evolve in response to a very particular combination of pressures that lead to an awareness of when cooperation is worthwhile,” she adds.

Alicia Melis, also at the Max Planck Institute for Evolutionary Anthropology but not involved in the study, thinks the results tie in with previous studies.

“The idea that competition might also promote cooperation has been out there for a while,” she says. “In fact, many of the cooperative interactions among chimps take place to outwit others.”

But Ronald Noë of the University Louis Pasteur in Strasbourg, France, is more cautious. “We are talking about a comparison of only two species, [chimps and rooks], that are distantly related,” he says. “And in both cases, few subjects were used in the experiments.”

Unknown interactions

Noë thinks that rook pair bonds might not preclude interaction with other birds – and those interactions could open up a market for cooperation as a commodity.

“Rooks go out and forage in different size flocks,” he says. “Nobody really knows to what level they live in societies comparable to chimps – mainly because it’s damn hard to follow hundreds or even thousands of birds simultaneously.”

Seed thinks a better test of the competition-cooperation theory might be to compare chimps with Bonobos – a more peaceable ape that lives in egalitarian societies. Because competition may be less important in Bonobo societies, they may lack a strong understanding of cooperation, he suggests.

But Melis is not convinced. “I’m not sure I would expect Bonobos to show less understanding than chimps in this type of task, since so far there isn’t any evidence for cognitive differences between the two species,” she says. “But I agree with the authors – more comparative studies are necessary.”

Journal Reference: Proceedings of the Royal Society B (DOI: 10.1098/rspb.2008.0111)