Rooks appear to have a better understanding of how gravity works than do chimps and babies under 6 months old.

A common way of finding out whether animals and babies understand complex concepts is to show them images of impossible events. The rationale is that viewers spend longer looking at those which defy their expectations, presumably as they try to work out what’s going on.

Chris Bird of the University of Cambridge and Nathan Emery of Queen Mary, University of London, showed rooks computer-generated images, half of which were impossible according to the laws of gravity, such as an egg floating in mid-air above a table. Almost without exception, the rooks spent more time looking at the “impossible” images than the possible ones. They also took more second glances.

The responses were the same when the “familiar” egg shape was replaced by a cork, proving the birds’ insight applied equally to any object, familiar or not. The researchers say the result is consistent with rooks being able to solve complex problems from knowledge of cause and effect, rather than by trial and error.


Chimp beaters

“The results illustrate the richness of the information processing underlying bird behaviour, and especially corvid behaviour,” says Alex Kacelnik, who studies corvid intelligence at the University of Oxford. “The team used a very elegant procedure to detect whether rooks form expectations regarding the action of gravity.”

But Kacelnik said he was surprised that chimpanzees “failed” the same test. “It could be that chimps may respect gravity but fail to infer its presence in a virtual scene between external objects, but I also find this a striking inability,” he says.

In other recent experiments, researchers have shown that crows can use simple tools in sequence to obtain food rewards, and can even use tools in the wild. They’ve also shown their ability to use tools to stop rewards falling into a hole, something great apes were unable to master.

Rooks, meanwhile, can collaborate together to solve problems, and scrub jays appear to be able to undertake “mental time travel”.

Journal reference: Proceedings of Royal Society B, DOI: 10.1098/rspb.2009.1456