Behavioural evidence for ultraviolet vision in a tetraonid species – foraging experiment with black grouse Tetrao tetrix

In addition to wavelengths visible to humans (400–700 nm), many birds are able to detect near ultraviolet light (320–400 nm). Most studies of ultraviolet (UV) vision in birds have concentrated on the importance of UV vision in intraspecific signalling, especially in passerine birds. However, birds may also use UV vision for other purposes, e.g. foraging. We performed a laboratory experiment to test whether a tetraonid species, black grouse Tetrao tetrix , could detect the difference between UV-reflecting and non-UV-reflecting food items (two colour morphs of bilberry Vaccinium myrtillus ). Black grouse preferred UV-reflecting berries when UV light was used for illumination, but showed no preference in the absence of UV light. This observation establishes a potential UV sensitivity in this species; such a sensitivity should be considered in behavioural experiments with this species.