Ruby-throated hummingbirds, jewel-like scarab beetles, and rainbowfish... These shiny, flashy animals aren’t just trying to razzle dazzle potential mates with their iridescence. It’s actually a very widespread anti-predation defense called interference coloration, according to a new study published in Biology Letters this week.
Interference coloration is when the color or brightness you see changes depending on the viewing angle and how light hits the surface. These changes can happen literally in a flash and within the wink of an eye. It’s evolved independently many, many times in groups ranging from squid to reptiles to at least one mammal (golden moles)—yet we’re still not sure about its function. It may have to do with sex, species recognition, or thermoregulation. Given its conspicuousness, it seems counter-intuitive that iridescence could serve as a defense against predators. But not all predator avoidance strategies are about blending in with the environment. For example, some experts argue that the vivid stripes of zebras confuse or distract would-be predators from attacking.
Bright flashes of color or sudden changes in brightness may also startle a predator, and if the changes were triggered by movement (a wing flick for example), it makes it harder for a hunter to pinpoint the right spot to strike. To investigate, Thomas Pike from the University of Lincoln created a virtual, dynamic prey on the computer and trained avian predators to "hunt" them. Specifically, seven female Japanese quail pecked at 20-millimeter-diameter iridescent shapes—modeled after the sometimes blue, sometimes green metallic sheen of the common greenbottle fly, Lucilia sericata—as they moved in a straight line at a constant speed of 150 millimeters per second across a gray background. The computer monitor was equipped with a touch screen and an automatic feeder that released mealworms when the birds pecked the fly.
The presence of interference coloration, he found, significantly reduced the success of the predator's attack, possibly by confusing them. It took the birds almost four tries on average to successfully peck a shimmery target that changed color and brightness depending on the angle. But when it came to the plain, uniformly colored controls, the birds successfully pecked them in fewer than three tries on average, Science News explains, and they struck closer to the target’s center as well.
That last bit means that attacks against interference-colored prey were less accurate, and that changes in color or brightness caused by prey movement hindered a predator's ability to pinpoint their exact location. Despite its counter-intuitiveness, interference colors may have evolved as an anti-predator mechanism.
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