Birds of a Feather

There are no purple humans. There are no blue bunnies. There are no green deer. And there are no cyan lions.

Most mammals tend toward earth-colors. Beige, tan, ecru, brown, gray, russet, tawny, sienna… Why? Because they are either prey animals that have evolved camouflaging pelts in order to avoid being eaten, or they are predators from species which have evolved similar coloring in order to blend in with their surroundings - until it's time to pounce. No teal tigers either, but tawny stripes that fool the prey-animal's eye into thinking it's seeing blades of grass.

But birds have evolved a more complex strategy for survival of their species.

It's all about sex.

The color of bird plumage varies with habitat. For example, in the desert and in the forested areas of Australia, local birds also make use of camouflage. In the former habitats they are gray-backed and in the latter they tend to dark green. But in the arid inland regions, natural selection, in response to the short breeding season, has given the indigenous avian species bright, vibrant colors.

This visual message shouts "Look at me! I'd make a great mate!" But this is true mostly for males; females tend to be drabber. They can afford to be since, for these species, the females choose their mates and not vice versa. Females are more invested in the outcome of mating since their eggs are relatively few in number compared to male sperm.

Female and male cardinals

A difference in appearance or size between the genders is called sexual dimorphism and this difference may be great or small.

For some species, a bird's age is a factor in its plumage. A newly fledged European Starling, which is mostly black and brown, lacks the white dots at the feather-tips of its mature relatives.

And some species molt as the seasons change; new feathers may look just like the old ones, or they may be seasonally-specific. For example, in winter the male American Goldfinch is a mellow yellow and black fellow, but in May – the nesting season – the yellow becomes bright chartreuse. Presumably, female American Goldfinches find the new color scheme rather attractive.

American Goldfinch winter vs. summer plumage

So why do female birds go for the showy, ostentatious males? One theory is that saturated colors and extravagant plumage are biologically expensive to produce so they're an indicator of male health and virility. These attributes lead to healthier chicks.

Our perception of plumage color depends on 2 processes.

1) The feathers themselves (and the bird's skin) may contain pigments; their ratio to one another result in the final colors we – or, to be precise - other birds see. Melanin may make the feathers pale yellow or red-brown or deep black (ornithologists – scientists who study birds – also think that melanin strengthens feathers.) Carotenoid produces a bright yellow or orange. And the presence of porphyrin makes feathers red, pink, and green.

2) But there is another mechanism in play. The structure of a given feather also affects the perceived color. Feathers contain proteins and these proteins refract the incident light, in the same way a prism, when held up to a light source, creates a rainbow.

Common Ravens

Feathers may be iridescent – the angle from we view them changes the color perceived. Or they may be non-iridescent; light conditions can vary the color we see. And some birds have ultraviolet feathers; they reflect light within the UV range. This latter variation may not be visible to humans, but is quite eye-catching to another bird of the same species.








Would you like to read more about birds? Try these e-books, accessible free online using your library card: Bird e-books

Here are some photos of birds from around the world. Can you guess what pigments are at play? What feather structure?

Gouldian Finch	Spendid Fairy Wren	Yellow-Collared Love Birds
Indian Peafowl	Andean Cock-of-the-Rock	Paradise Tanager
Sun Conures	Violet-Backed Starling	Crimson Rosella