a) Blue? This ain’t blue. You don’t even know blue.
b) So that I match my mate, who looks just like me.
c) I eat blueberries and incorporate plant pigments into my feathers as they develop.
d) It has nothing to do with my diet: I eat bugs and make my own blue feather pigments.
e) I am a starling and need to show the world that not all starlings are as drab as my cousins in North America.
Yes, this is a starling–the greater blue-eared starling from Africa. And Mr. Starling does have the blues–electric blues, I would say, although he must be battery powered, because I didn’t see any wires connected to him when I snapped this photo. But you’ll get no credit for choosing (e) because our starlings (European starlings, to be exact) are gorgeous to the creatures whose impressions are most important to them: other European starlings, of course.
Bird feathers come in lots of different colors. Black, brown, pink, yellow, orange, green, and red are generally caused by some combination of three classes of pigments in the feathers. But blue feathers–including those of blue jays, bluebirds, indigo buntings, and blue grosbeaks–don’t have any blue pigment. Their color is the result of diffraction and diffusion of light caused by structural properties of the feathers, not pigmentation. In fact, there is no known blue pigment in any bird feather. This is amazing, is it not? What’s more is that this starling is iridescent blue. A slight change in the lighting, and he fades to dull in a heartbeat. He knows it, too, and uses the angle of sunlight to strut his stuff. So, we can cross out (c) and (d) as possible explanations for why he is so blue.
Ms. Starling does look exactly like Mr. Starling–to us, that is. Here’s something that I have been puzzled about for years: As anyone who has watched birds knows, the males and females of many species are identical. But birds never seem to have a problem immediately figuring out the sex of another bird from some distance away. We now know why.
Birds see colors that we are blind to. They have four different types of color-sensitive cones in the retinas of their eyes, compared to only three types of cones in human eyes (and just two in most mammals, like dogs). So birds see color in a fourth dimension quite beyond our grasp. In addition, the fourth cone allows them to see into the near ultraviolet end of the spectrum, which we can’t see. It turns out that most of the bird species with identical males and females who perplex birdwatchers are easily told apart by color patches that birds see but humans can’t. So while male and female starlings might look the same to us, they look very different to each other. So answer (b) is out too.
That brings us to (a) as the correct answer to the quiz question. Whatever kind of blue you can see in this photo or in nature just isn’t what birds see. My bet is that this guy is blazing in UV. And I bet greater blue-eared starlings are tuned in to that brilliant color. When the light is just right and potential mates are hooking up with each other, there must be blue magic in the air. Nothing can look as good to a starling as another starling. And we can’t appreciate the beauty of his colors the way that another starling does. In short, we aren’t seeing Mr. Starling’s true colors.
Here’s another example of plumage that must be sizzling in UV if you’ve got four color cones. Check out the close-up of this lilac-breasted roller. Our perceptual version of these colors is probably just a ghostly trace of what birds see. But it should not surprise us that bird feathers have evolved into such mind-boggling plumage. It now looks as if feathers evolved for colorful displays before they were ever used for flight.
White plumage is also created by the structural properties of feathers, not pigments, and spans a range of ultraviolet nuances not visible to us.
What other birds have you seen with these amazing colors?