Birds Learn to Skip Fast Butterflies and Their Look-Alikes

Flashy-colored butterflies are sending a message to would-be prey. They’re letting birds know that they are really fast and agile and they shouldn’t waste their time trying to catch them.

A new study finds that birds learn to recognize these colorful signs and not only avoid those rapid butterflies but species that look similar to them. The results were published in the journal Proceedings of the Royal Society B.

Bright colors play many potential roles in the animal world, according to study co-author Keith Willmott, curator and director of the Florida Museum of Natural History's McGuire Center for Lepidoptera and Biodiversity.

They are thought to be key in sexual selection to recognize potential mates or to warn off same-sex competitors. An animal can also quickly flash a bit of a bright color to distract a predator or call attention to a less vulnerable part of the body to attack, like the tail of a butterfly.

Or they can be aposematic, which means they use signals to advertise to predators that they are dangerous and they should stay away. In some animals, they may have stinging spines or chemical defenses, but in the butterflies the researchers studied, the bright colors were a signal that they had the ability to quickly evade their predators.

Researchers found that birds not only learned to avoid the elusive butterflies but stopped chasing species that even resembled them. This concept, called evasive mimicry, had been proposed for decades but had been difficult to study.

“I think because of the logistical difficulties, it’s much harder to study an animal that is fast and agile, and studying a system that involves one individual rapidly moving away from another is logically hard to do in a confined area!” Willmott tells Treehugger.

Wilmott started studying the classification of a group of fast-flying tropical butterflies known as Adelpha about 20 years ago for his PhD. He wondered if evasive mimicry could explain why so many species of Adelpha butterflies evolved to look so similar.

Is Bitter Better Than Nothing?

In the new study, Willmott and his colleagues devised an experiment using wild blue tits, birds that had never encountered Adelpha butterflies. They learned to catch a paper butterfly with an almond treat attached underneath.

Later, the birds were presented with a plain paper butterfly (bottom left in the photo above) or one with three common Adelpha wing patterns. The Adelpha-patterned butterflies either had an almond soaked in something bitter, which was meant to simulate chemical defense, or they evaded the bird’s attack and managed not to get caught.

The birds learned to associate wing pattern with distastefulness or escape, eventually avoiding the patterned butterflies and going after the plain paper butterfly instead. When put in a situation where they had all four options, they avoided the butterfly pattern they associated with the bitter taste or speedy getaway and often avoided those with a similar pattern or color.

Researchers found that birds were 1.6 times more likely to strike the bitter butterfly than the evasive ones, maybe because they had different abilities to withstand the bad-tasting almond.

“We hypothesize that it may be because chemical defenses can vary within individual butterfly species, so just because one individual proves to be unpalatable, the next one might not. We also suggested that an unpleasant-tasting butterfly may still provide some nutritional benefit (which all parents wish their children would understand as they try to get them to eat vegetables), while a butterfly that cannot be caught provides no benefit at all,” Wilmott says.

“Finally, it’s not possible to ascertain whether a butterfly is unpalatable or not without attacking it, whereas rapid movement away from a predator is an ‘honest’ signal that the prey is likely good at escaping, and therefore not worthy of even initial pursuit.”