Just for interest sake, swans have the most number of feathers of any bird, in excess of 22 000. Hummingbirds on the other hand have the least, just over 900.
There are 2 main pigments out of 4 present in bird feathers, namely melanin and carotenoids. The only other bird with its own two pigments is the turaco, which has green (turacoverdin) and red (turacin) pigments. Melanin as we know is the dark pigment whereas carotenoids produce red, yellow, or orange colors and these are obtained mainly through the bird's diet. A Flamingo is an example of a bird whose pinkish coloration will be enhanced by the algae they consume (Pink would be a red carotenoid on a feather lacking melanin which will be explained in more detail later on, so don't slit your ankles just yet).
Also present in the feather is keratin, a protein which is also found in the beak and claws of birds. Keratin is usually combined in two ways, either scattered or layered. Scattering is present in bee-eaters for instance and layering is present in sunbirds, giving them their spectacular iridescence.
If you were to take this Marico sunbird photographed by Andy Pay, now you would see that their feathers are made up in the following way illustrated by the picture :
1. The green and blue iridescence is created by a very tight layered keratin in the feather that only allows low frequency colors from the sun like the green and blue to "bounce off" or reflect if you like and the rest of the color spectrum being absorbed by the feather. The sun thus plays a vital tole in enhancing these birds' colors.
2. The red scattering is created by the red carotenoid and a scattered keratin.
3. The black is the dominant dark melanin pigment.
If you were to look at the following white-fronted bee-eater here: you will note the following:
1. The white is a result of the lack of melanin.
2. The red scattering is as described above, created by the red carotenoid and a scattered keratin.
3. The blue scattering is once again created by the scattered keratin reflecting blue light from a different part of the feather.
4. The black facial mask is created by the melanin.
5. The orange and yellow are created by the carotenoids.
6. And finally, the green, one of the most complex colors produced by birds, is a combination of yellow carotenoid on a scattered keratin, reflecting blue!