Friday, September 24, 2010
Ravens are smart, and one is tempted to say they may be smarter than people. Or at least smarter than snowmobilers, which any Yellowstone XC skier will tell you sets the bar somewhat lower. In any event, the snowmobilers who come into Old Faithful during the winter have a difficult task protecting their lunches from the ravens. If you think keeping your backpack zipped is sufficient, you're likely to go hungry on the way home. Carefully fastened buckles can slow them down, but not for long: they've figured out how to open those, too.
Think about that achievement for a moment. How many dogs or cats, with careful training, do you suppose could learn to unfasten a buckle? Not many, if any, I would venture. Ravens, on the other hand, can work it out on their own.
How clever are ravens? In his wonderful book Mind of the Raven, the biologist Bernd Heinrich describes an experiment he conducted. What he did was this: he attached a piece of food to the end of a string, a little over two feet long, and hung it from a horizontal bar. The raven could stand on the bar, but couldn't reach the food from any available perch. By using a piece of hard salami, Heinrich also guaranteed that the bird could not tear off a piece while in flight. His problem was to figure out how to get the food within reach of his bill.
The only way to succeed was for the bird to reach down below the perch, grab the string and raise it above the perch, then -- and here's where it gets particularly tricky -- pin this loop of string against the perch with his foot, release the loop from his bill, reach down, and repeat the procedure until the morsel came into reach. Could a raven figure all that out?
The first day, they struggled some with the string and quickly gave up. The next day Heinrich put out the food again, in the same arrangement, and the first raven that tried it performed the entire procedure on his first attempt. It was no fluke:the raven had figured it all out and could repeat it every time thereafter. Other ravens got it right the first time, and the initial failure seems to have owed more to the birds being spooked by a weird and unfamiliar arrangement than with being stumped over what to do with it.
Once a biologist has some success with an experiment, he's likely to create many variations on the theme and Heinrich did exactly that. He put up two strings, one holding food and the other suspending a rock; that didn't take long to figure out. Then he crossed the strings: to get the food, a bird would have to stand over the rock and pull the nearest string. They could figure this out, too, but they it always gave them trouble: most of them would test the string above the food, see the rock jiggle, and then move to the other string. Heinrich, perhaps surprisingly, takes this as evidence that they were thinking and not just responding to positive conditioning: "[C]onsciousness of what they thought they knew* took precedence over trial-and-error learning, which was glacially slow even for this one extremely simple task."
It's a bold claim, because what Heinrich is saying is that the ravens weren't plucking the first string just out of habit; they plucked it because they had a mental concept of how the game worked and they had a hard time letting go of it - otherwise, they'd have learned the new system much easier.
To test this hypothesis, Heinrich next placed a rock on a familiar piece of string, and hung the food from a brand-new string, one of a different color, thickness, or texture than the birds had seen before. Had they been conditioned like mice pressing a button to get a reward, the ravens would have tested the most familiar string first; but that's not what happened. Instead, they always went for the novel string attached to the food and ignored the familiar-looking string. The fact that the old string was associated with past success did not impress them as you might think. This time, their mental concepts were leading them to the correct solution.
Clever birds. Clever experimenter, too, and a good writer. I highly recommend Heinrich's books ( Mind of the Raven and Ravens in Winter).
* These were birds who had already solved the one-string problem, in case that wasn't clear.