Fascinating facts and insights from John Downers book
"The plumage of many birds sparkles with hidden ultraviolet signals. Even familiar birds such as starlings use UV as a lighting effect in their plumage and females choose males with the most alluring ultraviolet shimmer. More exotically, parrots, cassowaries and zebra finches all have ultraviolet plumage patterns. These signals are so important that, when a male bluethroat had an ultraviolet block applied experimentally to his plumage, he immediately lost his attractiveness to the opposite sex, even though the visible colours were unaffected. Older birds tend to reflect ultraviolet most, and these more experienced birds also have the most success in courtship."
"To enable them to detect UV, birds have an extra colour cone in their eye. In addition, they can see the same range of colours that we can and this must give them an incredibly enhanced impression of the world."
Wauw... imagine all that's in front of our very eyes but in a world unseen to us!