Thieving birds show it takes one to know one

British scientists say thieving birds watch their backs more than honest birds do.

Experiments by animal-behavior researchers at the University of Cambridge show that scrub jays that have been previously observed stealing food from others tend to move their own food to different locations to hide it from other sneaky predators.

The researchers say it is the first demonstration that a non-human animal can remember the social context of specific past events and adjust its behavior accordingly. This form of episodic memory -- known to scientists as "mental time travel" -- was assumed to be primarily a human trait.

"The jays seem to have transferred their previous experience of being a pilferer to the current situation in which their own caches might be stolen," reported N.J. Emery and N.S. Clayton. "They can recall specific past events, and the results raise the possibility that they can plan for the future."

Emery and Clayton's study appears in this week's issue of the journal Nature.

In the study, 21 birds were hand-raised in the laboratory. The birds were kept in cages separated by plexiglass so they could observe each other as they took worms from a tray and buried them in different trays with sand-filled compartments.

Some of the birds had experience in pilfering worms in previous experiments, while others had none. The experienced thieves quickly dug up buried worms when given access to their neighbors' trays.

Also, the experienced thieves that knew they were being observed by other birds through the plexiglass repeatedly reburied their own worms in different sand compartments in an apparent effort to find new hiding places that their competitors might not have noticed.

The experienced thieves did not rebury their food if the plexiglass was covered by a towel and their food caches were not observed by other birds.

Birds that were not experienced thieves also did not re-hide their worms.

Scrub jays are bold, noisy birds that grow to be about a foot long. In nature, they hide seeds and nuts by hammering them into the ground or into the crevices of trees with their sturdy black beaks. A single scrub jay will gather and bury as many as 8,000 acorns and other seeds each year, sometimes by spying on other birds and pilfering their food when it is left unguarded.