Birds with a criminal past hide food well.

In the underworld of avian crime, scrub jays that have pilfered other birds' food caches hide their own with extra care.

When jays cached food as an onlooker jay lurked nearby, the birds with a thieving past were more likely than more innocent counterparts to retrieve the food again and hide it in a new place when the onlooker had left. That's one of the findings that Nathan Emery and Nicola Clayton of Cambridge University in England report in the Nov. 22 NATURE.

The test suggests that the jays may do fancier mental acrobatics than have previously been demonstrated for birds, says Emery. "It takes a thief to know a thief," he says.

The experiment grew out of some big questions about the capacities of animal cognition, as well as from Clayton's lunching habits during a year in California, where scrub jays forage for crumbs. Several times, Clayton noticed what she later observed in the lab--birds that had cached food when other jays were around returned later, alone, and hid the food in a different place.

In the lab, the researchers offered seven scrub jays the irresistible larvae of wax moths. For a scrub jay, "they're like Belgian truffles," Emery says. The birds eagerly snatched up larvae and buried them in an ice cube tray filled with sand. Sometimes the researchers allowed another jay to watch. Three hours later, the researchers presented each bird with its tray of hidden treats plus a spare ice cube tray. The jays that had been watched when they first hid their treats were more likely to dig up larvae and rehide them in a new tray.

To test whether the birds could later distinguish trays that they had used while onlookers were around from those they used while alone, the researchers watched the birds cache food under both circumstances. The investigators found that the birds later researchers watched the birds cache food under both circumstances. The investigators found that the birds later rehid food more often from the trays that had been observed.

To see what might make a bird suspicious of its comrade's intentions, researchers divided the group into those that had been allowed to pilfer in the laboratory and those that hadn't. The pilferers were more likely to rehide their food in private. To the researchers, this re suit suggests that the birds that had stolen relate their experience to other birds and respond accordingly.

From such feats, Emery draws evidence to challenge longtime assumptions about animal cognition. For years, people have assumed that "animals are stuck in time, that they work in the here and now," he says. In a previous study, Clayton found evidence that jays could remember specific episodes of food hiding in their past (SN: 9/19/98 p. 181). "I think the [new work] is very strong evidence for mental time travel," says Emery.

He also contends that the new findings suggest that a bird might be able to figure out what another individual is thinking, a capacity that has proved very hard to demonstrate outside of people.

Sue Healy, who studies bird cognition at the University of Edinburgh, agrees that the work demonstrates a new height of avian mental processes. The jays "seem to be attributing intent to other individuals based on their own experiences," she says.

"In the good old days, people were amazed that pigeons could remember anything," Healy recalls. Now, pigeons get credit for remembering a lot, and the supposed boundary between people and other animals has blurred more.