Chalk one up for our fine, feathered friends: Behavioral scientists say that birds possess the ability to remember not only a past event but when it happened, the kind of memory previously thought unique to humans.
The study of scrub jays, published in Thursday's issue of the journal Nature, marks what the researchers said is the first demonstration of episodic, or event-based, memory in animals other than humans.This type of memory is jokingly referred to as "mental time travel" because it involves mental images of past events. To remember where you put your car keys, you might "see" yourself walking into the house the night before and dropping the keys on a table in the hall.
Birds and humans took different branches on the evolutionary tree 250 million years ago, so the finding suggests that fundamental mechanisms of information storage in the brain may have evolved even before the age of dinosaurs.
"It could be a big step in understanding how space, time and events are represented in the brain," neurobiologists Kathryn Jeffery and John O'Keefe of University College in London said in a review of the study. "It also helps solve a problem in the field of human memory - where and how is a memory for events formed and stored?"
Episodic memory functions in a fundamentally different way from and uses other parts of the brain than knowing a fact, such as what car keys are. That is a form of semantic memory. It's also different from having a more basic instinct, such as hunger.
In the bird study, researchers Nicola S. Clayton of the University of California-Davis and Anthony Dickinson of Cambridge University in England allowed scrub jays to store their favorite food, larvae of wax moths, or "wax worms," on one side of a sand-filled tray. The birds hid peanuts on the other side of the tray.
Birds chose to retrieve the wax worms if they were less than four hours old. Birds that had previously learned that the wax worms decompose within five days avoided the old worms in favor of peanuts. Making such decisions based on the timing of past events is a crucial element of episodic memory.
In a second test, the researchers removed the rotten 5-day-old worms. The birds learned that the wax worms were more likely to be gone the longer they had to wait to recover them.
Other scientists were intrigued but less convinced that the birds were displaying true episodic memory. And they noted that studies of monkeys and even rats have shown broadly similar results.