----Docking Maneuvers


IF YOU’VE EVER WATCHED A HUMMINGBIRD zip from flower to flower at hyperactive speed, you may have wondered how it avoids bonking its beak.

 Anyway, David Lee wondered. Lee, a University of Edinburgh psychologist,photographed hummingbirds as they docked at a plastic feeder and analyzedthe high-speed film frame by frame.He found that the birds did not slow down gradually. Instead they streaked right brakes just a tenth of a second before they would have slammed into the contraption.

This pattern, Lee says, shows that a hummingbird does not go through complex calculations during its approach, constantly estimating its distance from the feeder

and its time of arrival. Instead the humming bird keeps track of some thing simpler: ---the angle formed at one of its eyes by two lines of sight— one extending from the eye to the target, the other from the eye to the tip of the bird’s beak. When the bird is far from the feeder this angle is large; when its beak is touching the feeder the angle is zero. At that point the bird wants its speed to be zero, too.

The hummingbird can dock safely by simply decreasing the rate of change in the angle—a directly perceivable quantity that depends on the bird’s speed—in the same measure as the angle itself decreases. Since the angle doesn’t decrease much until the final approach, that’s when the bird decelerates. “The hummingbird starts to slow down when it detects it’s about to collide into a thing,” says Lee. This method suits hummingbirds because it allows the maximum time for eating, which is a priority of theirs. But Lee says the method is widespread in the animal kingdom: drivers use it every time they brake for a stop sign.

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