Data for: Sexual dichromatism may not be a good index of sexual or natural selection in the blue cardinalids (Aves: Passeriformes).

More than a century ago, Darwin and Wallace started a still ongoing debate over which are the predominant forces driving sexual dichromatism (i.e., differences in body coloration between males and females): is it sexual selection on males to become more attractive, or is it natural selection on females to become more cryptic? While these are not mutually exclusive, the degree of sexual dichromatism has been extensively used as a proxy of the intensity of one type of selection (sexual) on one of the sexes (males). Here, we evaluated the relationship between sexual dichromatism and two body-color features that can be under natural and/or sexual selection in each sex: conspicuousness against the background and colorfulness (which we defined as the variety of colors and mechanisms to produce them within an individual’s plumage). We focused on the ‘blue clade’ of the Cardinalidae bird family and considered the properties of their own visual system and those of potential raptor predators. We ...