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By Root 782 0

of separated milk idling unattended on front porches, the cream nearest to the top of the bottles. Up at dawn with the delivery men is much of Britain's bird population, for dawn is a propitious time to sing. One bird, the small blue tit, made a discovery: the foil on the bottles was susceptible to being pecked through, revealing a rich creamy drink just below. A few reports of vandalized milk bottles were lodged, soon a spate more, then a plague of them. Hundreds of birds had learned the milk-bottle trick. Cross with their skimmed milk, the Britons were not long in finding the culprits. For us, the question is not who but how: How did this discovery spread among the blue tits? Given the rapidity with which it spread, it seemed likely that some birds observed others getting the cream, and imitated them doing so. Clever, pudgy little birds.

By providing a captive population of chickadees with a similar setup, one group of experimenters observed the phenomenon recur step-by-step. Their studies suggest a more likely explanation than imitation. Instead of carefully observing and assimilating all that the first, cream-pilfering bird was doing, other birds simply saw that he was atop the bottle. This may have attracted them to the bottles. Once landed on the bottle tops, by doing a natural behavior—pecking—they discovered the foil's puncturability themselves. In other words, they were drawn to a stimulus, the bottle, by the first bird's presence. Its presence enhanced the likelihood that they too would become cream stealers, but it did not demonstrate how to do so.

This may seem nitpicky, but there is an important difference at work here. In a case of stimulus enhancement, I see that you are acting in some unspecified way on the door, after which it opens. If I amble over to the door and kick it, hit it, and otherwise maul it, I might get it to open, too. In a case of imitation, I watch exactly what you are doing with the door and reproduce just those actions—the seizing and turning of the knob, the application of pressure after turning, and so on—that lead to the desired outcome. I can do that because I can imagine that what you are doing is somehow related to your goal, your desideratum: to leave the room through the door. The blue tits, on the other hand, need not have been thinking about what the milk bottle tits wanted—and probably were not.

MORE HUMAN THAN BIRD

Dog researchers wanted to test whether the stick-flaunting dogs are acting more like a blue tit or more like a human being. The first experiment was designed to determine if dogs would imitate humans in a situation in which the people were acting to attain some desired object. The researchers were asking, in essence, whether dogs can understand that a person's actions function as a demonstration that can be followed if the dog is otherwise unsure how to get that desired object himself.

They set up a simple experiment in which a toy or a bit of food was placed in the crook of a V-shaped fence. The dog was seated on the outside of the point of the V, and was given a chance to try to retrieve the food. He couldn't go straight through or over the fence, but both routes around the fence—around the left stem or the right stem—were equally long, so equally good. When given no demonstration of how to get around the fence, the dogs chose randomly, preferring neither side, and eventually making their way to the inside of the V. But when given a chance to watch a person walking around the left side of the fence toward the reward—a person actively talking to the dog along the way—the observing dogs changed their behavior outright: they also chose the left side.

It looks as though these dogs were imitating. And what they learned by imitating stuck: when a shortcut through the fence was later introduced, they maintained the route they had learned by watching, ignoring the shortcut. The researchers ran a handful of other trials to be clear what exactly it was that the dogs were doing. They were not simply navigating by smell: laying down a scent trail on the