How conspicuous are peacock eyespots and other colorful feathers in the eyes of mammalian predators?

Feathers perceived by humans to be vividly colorful are often presumed to be equally conspicuous to other mammals, and thus to present an enhanced predation risk. However, many mammals that prey on adult birds have dichromatic visual systems with only two types of color-sensitive visual receptors (one sensitive to ultraviolet light), rather than the three characteristic of humans and four of most birds. Thus, understanding how these predators perceive color requires quantitative visual modeling. Here, we use a combination of reflectance spectroscopy, multispectral imaging, color vision modelling and visual texture analysis to compare the visual signals available to conspecifics and to mammalian predators for multicolored feathers from the Indian peacock (Pavo cristatus) as well as red and yellow parrot feathers; we also take into account the effects of distance-dependent blurring due to visual acuity. When viewed by tetrachromatic birds against a background of green vegetation, most of the feathers studied had color and brightness contrasts similar to values previously found for ripe fruit. By contrast, when viewed by dichromat mammalian predators, the color and brightness contrasts of these feathers were only weakly detectable and often did not reach detection thresholds for typical viewing distances. We furthermore show that the peacocks erect train has undetectable color and brightness contrasts and visual textures when photographed against various foliage backgrounds. Given the similarity of photoreceptor sensitivities and feather reflectance properties across relevant species, these findings are consistent with many feathers of similar hue being inconspicuous, and in some cases potentially cryptic, in the eyes of their mammalian predators. These results suggest that many types of colorful feathers are likely to be cryptic to mammals while providing a communication channel perceptible to birds, while emphasizing the importance of understanding diverse sensory receivers in the evolution of animal coloration.