In the thief-ridden world of western scrub jays, a bird storing food takes note of any other jay that watches it and later defends the hoard accordingly, says a new study.
A difference in hiding tactics showed up in lab tests where birds cached some of their favorite food in ice cube trays filled with pellets, says Nicola Clayton of the University of Cambridge in England. When the birds revisited these trays, they used elaborate ruses to hide the food again if the original watcher was hanging around once more, Clayton and her colleagues report in an upcoming Science.
“It is quite sophisticated,” says Clayton. The brain structures of birds and people differ, but recent research shows that they can manage a lot of the same tasks, she notes.
The new findings are “just the last step in a long series of experiments showing that birds do all kinds of things,” says comparative neuroscientist Tom Smulders of the University of Newcastle in England.
Scrub jays have a “very chimplike” social hierarchy, says Clayton. A high-ranking bird typically steals an underling’s food. Lower-ranked birds don’t pilfer from their superiors but do occasionally defraud each other. In a show of domestic cooperation, jays let their mates raid hoards with no protest.
In the latest series of tests, Clayton and her colleagues provided a jay with some waxworms, a desirable treat, and offered two trays for hiding. Under the beady eyes of a superior or fellow subordinate, the hider cached more of the waxworms far from the watcher than it did when it was alone or viewed only by its mate.
When the hoarders revisited the trays in private, the birds who’d been watched by a dominant bird during the first episode shifted more treats to other hiding places than did birds watched by a subordinate, a mate, or no other jay.
In a more complex test, Clayton and her colleagues chose birds that had similar ranks. The team let a bird cache waxworms in one tray in the presence of one observer, and then in a second tray while a different bird looked on. When the hider returned to the trays and found one of the original observers present, it focused on moving items from the tray in which it had buried food when that observer was around.
The data suggest that a nonhuman animal can remember and discriminate among individuals that possess different knowledge, Clayton says. People do this by what’s called “theory of mind,” that is, imagining plots running through someone else’s head. However, Clayton is careful not to go so far as to say that her team’s experiment shows scrub jays have theory of mind.
Thomas Suddendorf, a psychologist at the University of Queensland in St. Lucia, Australia, calls the birds’ powers “impressive” but agrees with Clayton’s caution.
Some other jays and crows might be as mentally agile as the scrub jays, speculates Smulders. He’s getting “promising results” in an investigation of magpies’ recall of food that they’ve hidden.