However, since birds differ strongly in how well they see ultraviolet light, the markings should only be visible to those bird species that have the right type of colour vision. (sciencedaily.com)
They will now have full colour vision and show effort to move to things that are brightly coloured and will be attempting to reach for things. (bounty.com)
However, they do not possess depth perception or a perfect colour vision, which is why they tend to get more attracted to highly contrasting colours. (smartbabyhq.com)