The Raven's Game of Hide and Seek

During the annual Christmas bird count, volunteers at Prudhoe Bay typically see only one species of bird--the raven. On forty below mornings like this one, ravens glide by the Geophysical Institute on their morning commute to Fairbanks with no sign of being cold. Alaskans know the raven as one of the state's most adaptable birds. It's also one of the most intelligent, as is shown in a recent study by Bernd Heinrich, the author of Ravens in Winter.

Heinrich is a biologist at the University of Vermont who has spent 15 years in the Maine woods studying the behavior of ravens. He and John Pepper of the University of Michigan recently conducted an experiment on why ravens fly long distances to cache meat from animal carcasses when they could fly shorter distances and spend more time picking at the carcass.

Ravens and other related birds, such as crows, magpies, and blue jays, sometimes hide food and come back for it later. Chickadees also "scatter-hoard," stowing bits of food in random locations. Heinrich found that ravens were able to watch other ravens cache food and remember where that food was even though they didn't place it there themselves.

Using an aviary, an enclosure of chicken wire over the forest floor in Maine, Heinrich watched ravens as he gave them meat in a setting where they couldn't fly long distances. In one of the experiments, a recently captured raven was placed inside with four ravens that had been in the pen for more than a year. Though the birds accustomed to life in captivity wouldn't let the wild bird near meat and peanuts left by researchers, the wild bird watched with interest as the tame birds ate and walked away. When the tame ravens made their caches, they kept it in a pouch below their tongues and deposited it in the snow, hiding it from the sight of other ravens. Despite this secretive practice, minutes after the ravens made their caches, the wild bird started digging at the precise location where the food was hidden.

Ravens use their memory to raid others' caches, Heinrich said during a telephone interview from Burlington, Vermont. To test if ravens are using their sense of smell to find food, Heinrich made 40 artificial caches in the pen, burying 20 hunks of meat and 20 piles of unshelled peanuts in the snow. When 11 ravens were released into the pen, they found none of the 40 manmade caches, though they recovered caches they had made before.

Heinrich said he's seen similar results in the field, even with the most pungent of baits. "I buried skunks, which they love to eat, but they never dig up food they don't know about already," he said. Heinrich, who just finished a new book about ravens, says his study shows that ravens can remember where others hid food, an ability not noticed in other species of bird and one that impressed someone who has studied the birds for decades. "It surprised me a lot," he said.