SSS 2010-01-05（在线收听）

Sometimes it pays to look like a pile of poop. At least if you’re a tasty caterpillar trying to avoid getting eaten by hungry birds. Because a study in the journal Science shows that even young chicks tend to overlook caterpillars disguised as dung.

Animals have come up with some pretty clever tricks for keeping themselves off a predator’s dinner plate. Some use camouflage, adopting colors and patterns that help them blend into the environment. Others masquerade as something inedible, like bird droppings or twigs. But scientists got to wondering whether the two approaches are really so different. Maybe critters dressed as twigs also “blend in” so that predators just don’t see them. To find out, scientists presented some twiggy-looking caterpillars to two sets of hand-reared chicks. They found that baby birds that had never seen sticks before gobbled those bad boys right up. But chicks who were shown real twigs first took much longer to peck at the mimics, and did so more gingerly than their naïve friends.

That means the birds could see the caterpillars, but were fooled by the costume, at least temporarily. Which, for a caterpillar on a leaf in the wild, could mean the difference between eating and being eaten.

—Karen Hopkin