Birds Keep Track of Time

National Wildlife, Feb-March, 1999

If you leave a glass of milk in a warm place for a day, you know to throw it away without bothering to taste it. That's because humans have an ability called episodic memory--an ability to recall events in the past that involves what, where and when. Now it appears we are not alone. Neurobiologist Nicola S. Clayton of the University of California at Davis found in experiments that the California scrub jay (above) can keep track of the spoiling time of stored food. Like chickadees, squirrels and many other species, scrub jays cache food for later retrieval. Past studies have determined that they find the items by memory, not smell--but there was no evidence the birds could remember when they stored the food.

Clayton first gave jays larvae of wax moths and had the birds discover that after a certain amount of time the larvae rot. Then she let the birds cache both new larvae and peanuts. When the birds grew hungry, they preferred to retrieve and consume first the larvae while the treats were still fresh. But when enough time had passed for the larvae to rot, the birds went straight for their hidden peanuts--just as we would bypass milk we were sure had spoiled.