Visual modelling suggests a weak relationship between the evolution of ultraviolet vision and plumage colouration in birds

Birds have sophisticated colour vision mediated by four cones types that cover a wide visual spectrum including ultraviolet (UV) wavelengths. Many birds have modest UV-sensitivity provided by violet-sensitive (VS) cones with sensitivity maxima between 400-425 nm. However, some birds have evolved higher UV-sensitivity and a larger visual spectrum given by UV-sensitive (UVS) cones maximally sensitive at 360-370 nm. The reasons for VS-UVS transitions and their relationship to visual ecology remain unclear. It has been hypothesized that the evolution of UVS-cone vision is linked to plumage colours so that visual sensitivity and feather colouration are “matched”. This leads to the specific prediction that UVS-cone vision enhance the discrimination of plumage colours of UVS-birds while such an advantage is absent or less pronounced for VS-bird colouration. We test this hypothesis using knowledge of the complex distribution of UVS-cones among birds combined with mathematical modelling of colou...