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How iridescent colors protect animals from predators

Some animals, such as rosemary beetles and starlings, possess brilliant iridescent colors that constantly change in the light. In a new study from the University of Bristol, researchers have found that this iridescence serves as a form of deceptive warning coloration. The experts report that it is the key feature of iridescence –  changing colors – that supports its ability to protect animals even after they have been detected by predators. 

The hue and intensity of metallic iridescent colors vary depending on the angle of the view and the direction of the light. Researchers in Bristol University’s CamoLab set out to investigate why iridescence has evolved so many times in the animal kingdom. 

The research team had previously demonstrated that iridescence is a highly effective type of camouflage. Now, the experts wanted to know whether iridescent colors may help provide any protection from predators post-detection.

“One of the challenges when studying the functions of such highly reflective structural coloration has been to separate the effects of the changeability of colors, the hallmark of iridescence, from the effects of simply having multiple colors at the same time, and also to separate the effects of gloss from the effects of iridescence,” explained study lead author Dr. Karin Kjernsmo.

To investigate, the researchers presented wing cases of real and artificial jewel beetles to birds that had no previous experience with this particular prey. The wing cases used for the experiment were iridescent, non-iridescent, glossy and matte. The experts then observed the birds’ willingness to attack the prey.

“Here, we tested the effects of both iridescence and surface gloss (i.e. specular reflection) on the attack behavior of prey-naïve avian predators. Using real and artificial jewel beetle, Sternocera aequisignata, wing cases, we found that iridescence provides initial protection against avian predation by significantly reducing the willingness to attack,” explained the researchers.

“Importantly, we found that the main factor explaining this aversion is iridescence, not multiple colors per se, with surface gloss also having an independent effect. Our results are important because they demonstrate that even when prey are presented up close and against a mismatching background, iridescence may confer a survival benefit by inducing hesitation or even, as sometimes observed, an aversion response in attacking birds.”

The study is published in the journal Animal Behaviour.

By Chrissy Sexton, Staff Writer

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