What’s the first thing you see when you look at these birds? For me, it’s their incredible diversity of color! And it’s not only tropical birds—even cold climates produce blue Steller’s Jays, red House Finches, yellow goldfinches, and pink rosy-finches. Or consider the ruby gorget on a Broad-tailed Hummingbird, flashing its iridescent hue when the sunlight hits it just right. How can feathers be all these colors? It varies.

Blue birds, jays, bluebirds, and the like, get their colors from the way their feathers are structured. It’s not a pigment, but rather a result of the way keratin crystals and tiny air pockets scatter blue light. The first time I ever saw a Blue Jay, it appeared monochromatic—black, white, and gray. I hunted through my field guide, but couldn’t find the bird. Then the sun came out from behind the clouds, and the bird was transformed from dull gray to brilliant blue. Aha!

The brilliant metallic color of a hummingbird’s gorget works the same way. Those throat feathers actually lack any pigments; the colors come from microscopic crystals in the feathers. That’s why the color of the gorget changes according to the light shining on it.

Birds with yellow, orange, pink, and red feathers get their colors from the food they eat—in this case, carotenoids. Carotenoids are what make plants orange—fall leaves, yellow sunflowers, and of course, carrots. There are over 600 kinds, and they are all produced by photosynthesis. When birds eat plants (or a few types of fungi) containing these pigments, they are incorporated into their feathers. Since carotenoids are actually yellow, orange and red birds have to convert the chemicals to the other colors, courtesy of a specific set of genes. If you’ve ever seen a yellow male House Finch or cardinal, for example, it’s because that individual has a mutation in the genes that do the conversion. They’re limited to the yellows of the original pigment.

You may have seen pale gray or white flamingos in zoos. That’s because these and other boiled-lobster-pink birds, such as Scarlet Ibises and Roseate Spoonbills, get their pigments, in this case the carotenoid canthaxanthin, either directly from an aquatic blue-green algae, or from the crustaceans that eat the algae. The more intense the feather color, the more direct the source. Often, the food provided for captive birds lacks canthaxanthin, and the birds show their underlying drabness instead.

There are a few exceptions. Turacos get their bright red color from a different type of pigment. Porphyrins contain about 7% copper, which is why it’s so red. Another pigment, turacoverdin, is green. And parrots get their tropical colors from another group of pigments, the psittacofulvins. (Parrots are in the order Psittaciformes.)

What about black and brown birds? They get their dark hues from the same molecule that colors human hair and skin—melatonin. I’ve always wondered why black birds, such as crows and ravens, are black. I can see how it would help keep them warm in winter, but what about summer? Don’t they swelter? Well, it turns out that melatonin has another purpose. It’s strong. Feathers high in melatonin don’t wear out as quickly. That’s an important consideration, especially for flight feathers, which take the most punishment. In addition, flight feathers high in melatonin are more aerodynamic, perhaps because they hold their shape better.

So how does this all fit together? Consider the Green Jay. The feathers on its head are blue due to their structural make-up. Its body is covered by feathers with that same structure, that also contain yellow carotenoids that the bird has eaten. The green is more pronounced on the back, with yellow on the belly and underside of the tail. Finally, the black head and tail feathers contain melatonin. The result is one gorgeous bird!