Why do these fake eyes scare off predators?

Tom Grundy/iStockphoto

Why do these fake eyes scare off predators?

Eyelike spots on butterflies and caterpillars scare off songbirds and other predators, yet scientists don’t know exactly why they work. Do they startle potential attackers simply because they’re conspicuous, or do they mimic the eyes of a creature the songbirds truly fear? In a new study researchers lured great tits (Parus major) to a particular spot on the floor of their cage with a dead mealworm. When the bird swooped down upon its prey, the team flashed one of five images on a computer monitor lying directly beneath the worm: an owl (a tit predator) with open eyes, an owl with its eyes closed, a butterfly with prominent owl-like eyespots on its wings, a butterfly with eyespots whose colors had been reversed, or a butterfly whose eyespots had been digitally removed. About 68% of the birds shown the image with the eye-mimicking spots either flew away or showed signs of being startled such as chirping a warning call, the researchers report today in the Proceedings of the Royal Society B. That’s on par with the 57% showing the same reactions to the owl with open eyes, the team notes. But only 33% reacted similarly to the image that sported color—reversed eyespots—a difference that suggests it’s not the boldness of the image that’s startling the birds, it’s the mimicry of eye coloration in a predator the bird is likely familiar with. An even smaller percentage of the birds were startled by the butterfly with no eyespots. Interestingly, the image of the owl with no eyes seemed to spark more curiosity than fear among the would-be predators, triggering them to investigate the image more closely.