UV sensitive vision in cardinals and tanagers is ubiquitous

Short wavelength visual sensitivity in birds is determined mostly by the type of photopigment present in the short-wavelength sensitive cone 1 (SWS1) which varies between clades and takes two main forms: the violet sensitive type (VS) and ultraviolet sensitive type (UVS). The common ancestor of passerines is thought to have been UVS, but there were at least 8 transitions between both types of visual sensitivity, even within species of the same family (Maluridae). The type of visual system a species has is a key parameter of avian visual models employed to describe chromatic visual perception and assess if colour differences are discernible by birds. Cardinalidae and Thraupidae together include more than 400 very diverse species that were model organisms in many bird colouration studies. However, visual sensitivity has been characterised for only one species of each of these families so far. Here, we obtained partial genetic sequences of the SWS1 opsin gene that determines the spectral sensitivity of the photopigment for a phylogenetically broad species sample of these families. All cardinals and tanagers studied here have SWS1 sequences corresponding with UVS sensitivity, suggesting that this character is conserved in these bird families despite their highly diverse range of plumage colours and habitat types.