Ever since Darwin, the vividly colorful feathers used by many male birds to attract females have been assumed to attract predators as well. However, a new study published in PLOS ONE indicates that these ornaments are not necessarily eye-catching to predators after all.
A team of scientists led by Suzanne Amador Kane used specialized imaging and computer modeling to show how colorful feathers from peacocks and parrots appear in the eyes of other animals. To female birds, these feathers are as conspicuous as ripe fruit — a good thing for a male bird hoping to catch the attention of potential mates. For wild cats and dogs, however, the researchers found that the flashy feathers were not easily detectable against a background of green leaves and grass.
These surprising results are due to differences between the visual systems of these animals. Cats and dogs are red-green colorblind — they have only two of the three types of color-sensitive cone cells that most humans have in the retina — so these predators perceive many yellow, orange, and red feathers as being similar in color to green leaves. By contrast, birds have four types of cones, each with sensitivities well-suited for distinguishing different feather colors. Compared to birds and humans, these predators also see the world as blurrier, with less variation between dark and light, so even vivid green and blue peacock feathers appear muted. Like birds, these predators have the ability to see ultraviolet light, a part of the spectrum that is invisible to humans, but that superpower isn’t enough to help them detect colorful plumage.
Darwin wrote that “[e]ven the bright colors of many male birds cannot fail to make them conspicuous to their enemies of all kinds,” but these new results show birds that appear vividly colorful to humans and other birds can appear drab and inconspicuous in the eyes of mammalian predators. Together with another recent study that showed conspicuously colorful plumage does not enhance the risk of attack by birds of prey, this suggests that being colorfully sexy is not the main risk these colorful birds face.
These findings are described in the article entitled How conspicuous are peacock eyespots and other colorful feathers in the eyes of mammalian predators? recently published in the journal PLOS One. This work was conducted by Suzanne Amador Kane, Yuchao Wang, Rui Fang, and Yabin Lu from Haverford College, and Roslyn Dakin from the Smithsonian Conservation Biology Institute.