Hamburg, Germany  - Hitchcock was right: Birds do cooperate to solve tasks which no individual bird could master alone, according to a team of German scientists.

Until now, such group problem-solving efforts have been thought to be restricted to humans and other primates, such as chimpanzees. But the team of scientists headed by Dr. Amanda Seed at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, discovered the same group techniques used among 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, according to the findings published in the Proceedings of the Royal Society and reported in New Scientist magazine.

The rooks could see the food through a slit but had to use string thread through peepholes 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.

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 involving chimpanzees have shown that chimps will wait for their partner before acting.

Ironically, rooks may fail to fully grasp the benefits of cooperation because individuals rarely compete, Seed says.

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.

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. (dpa)