Here's a Starling on Mrs B's garden feeders. Male and female Starlings look identical to me. So how do they decide who is a girl and who is a boy? It turns out that the female Starlings have patches of ultra-violet on their heads. You need to think of ultra-violet as a different - just one that we can't see. It's counter-intuitive - a colour that you can't even imagine. But Starling eyes can see those frequencies. I wonder what it looks like? When we "see" ultraviolet or infrared, they are done as FALSE COLOUR images. Get it explained properly by watching this awesome programme soon whilst it is still on the iplayer
http://www.bbc.co.uk/iplayer/episode/b06pm7t8/colour-the-spectrum-of-science-3-beyond-the-rainbow
