Hunting Virtual Moths, Blue Jays Offer Eye on Evolution

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Strategy for Evasion

Bond said the study is one of the first experiments to show how the psychology of the predator—the hunting strategies of the blue jay—can affect the diversity of wing patterns in nature and the complexity of the camouflage.

"People have the impression that animals of the same species all look the same, but they show tremendous variation just like humans," said evolutionary biologist John Endler of the University of California at Santa Barbara. An important reason for this variation in appearance is to evade predators.

Diversity in appearance is common throughout the insect world. Grasshoppers, stick insects, praying mantids, and moths all show tremendous diversity in appearance—different coloration and patterns—within the same species.

The extraordinary variation in moths' appearance—"almost no two are alike," said Bond—also occurs because among moths themselves, appearance is irrelevant. "Moths don't look at one another, they detect each other by smell," said Bond. So altering appearances does not affect their sex lives and opportunities for breeding.

After about 30 generations in the experiment with blue jay and virtual moths, the moths were too well camouflaged for Bond to find. "The entire screen just looked like gravel," he said.

"But the blue jays were amazing," he added. Even as the moths became harder to detect, the blue jays were about 80 percent accurate in detecting the moths throughout the entire trial, said Bond.

Blue jays have a rather straightforward predatory strategy. They focus on one specific feature of a wing design, called a searching image—perhaps a pair of whitish dots. They then hunt all moths with this feature until that particular design is rare and the birds get hungry. Moths without the particular image the blue jays are seeking that day avoid detection. This strategy helps the birds compensate as wing patterns become more cryptic.

"This is a really neat computer simulation of how things work in the wild," said Endler.

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