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Bird Color Mysteries Explained

bird_coloration-cover.jpgWhy is a cardinal red or a bluebird blue? Why do some birds have plumage that is intensely colored—is it pigment, light, gender, robust health, or some combination of all four? What roles do disease, climate, and wear and tear play in this process? What does feather display signal about sexual attraction and social status? How has color camouflage evolved?

Noted ornithologist and author Geoffrey E. Hill explores these and other intriguing questions in National Geographic Bird Coloration (National Geographic Books; March 16, 2010; ISBN: 978-1-4262-0571-2; Hardcover), the first non-academic work on coloration and plumage, and their key role in avian life.

I invited Geoffrey to write a few remarks and share some of his photos with Nat Geo News Watch.

By Geoffrey E. Hill

One Saturday morning as I was casting about for a topic for my dissertation at the University of Michigan, I found myself in a pet store staring at three common canaries in a cage. I was already hooked on birds; I had just completed a master’s project at the University of New Mexico studying subadult plumage in male black-headed grosbeaks.

Plumage color was foremost on my mind, so I couldn’t help but notice that one of the canaries in front of me was brilliant uniform yellow, while the other two were drab yellowish green.

In my life, I’ve had only a few epiphanies–flashes of insight into the answers to complex questions. Standing in front of the canaries’ cage that morning, I had an epiphany.

Three disparate facts that were rattling around in my head suddenly merged into an explanation for why birds had red and yellow feathers.

  • Fact 1: the red and yellow feather coloration of birds results from carotenoid pigments.
  • Fact 2: birds, as well as fish, cannot make their own carotenoid pigments – they have to ingest these pigments.
  • Fact 3: guppies (small fish) that live in algae-rich portions of streams and eat a lot of carotenoids are oranger than guppies that live in shaded sections of streams with little algae.

I almost exclaimed out loud: “birds show their foraging ability through the brightness of their feathers!” Feather coloration as an honest signal of foraging ability explained why birds with red and yellow feathers are so variable in appearance.

Chilean-Flamingo-photo.jpg

A sleeping Chilean flamingo. The red coloration of both feathers and skin results from carotenoid pigments and the density at which the pigments are deposited determines how saturated–how pink or red–the color is. (Captive, February).

Photo courtesy of Geoffrey E. Hill

Metallic-Starling-photo.jpg

A male metallic starling. The beautiful iridescent coloration of feathers, as in the head and nape plumage of this starling, result from light interacting with microscopic structures in the barbs of the feather. Such structural coloration is an inherent property of the feathers and cannot be extracted from feathers in the same way that pigments can be extracted. (Captive, August)

Photo courtesy of Geoffrey E. Hill

My epiphany was 22 years ago, and I’ve been studying the coloration of birds ever since.

Along the way, my students and I have published over 100 scientific papers on topics related to the coloration of birds, and I’ve written four books on the subject.

My epiphany proved correct: birds do signal foraging ability through the color of their feathers, but that is hardly the full story.

Color can signal a diversity of information about a bird from its sex and identity to its social status and attractiveness.

Plumage color also regulates how fast a birds warms up or cools down, and the colors of feathers can have a large effect on how fast feathers wear out.

ray-Snowy-Plover-photo.jpg

A gray snowy plover on gray beach sand. Many birds have plumage colors and patterns that help them blend into their surroundings. Species that live in open featureless landscapes, like beaches, tend to have plain unpatterned back plumages that match the average coloration of their environment.

Photo courtesy of Geoffrey E. Hill

White-cheeked-Turaco-photo.jpg

Turacos and their unique green pigment. The soft green plumage color of this White-cheeked turaco results from turacoverdin, a pigment that is found only in the feathers of turacos. Most of the green coloration of birds results from yellow pigments in combination with blue structural coloration.

Photo courtesy of Geoffrey E. Hill`

The story of avian coloration is fun and fascinating, but until now it was known only to a handful of research biologists.

In National Geographic Bird Coloration this tale is finally told for an audience of bird enthusiasts. I present all functions that have been proposed to explain the colors of birds. I also explain the mechanism for color–pigments as well as the fine structures of feathers.

I end with some thoughts about how the colors and patterns of birds evolved. The text is unencumbered with citations and statistics, but it is comprehensive and intelligent. More than five hundred photographs of birds and feathers bring the chapters to life.

Geoffrey E. Hill is an ornithologist, seeker of the elusive Ivory-billed Woodpecker, and author of two books: A Red Bird in a Brown Bag and Ivorybill Hunters. He served as the consultant for the forthcoming National Geographic feature film The Lord God Bird. Visit his website.

royal-terns-photo.jpg

Courting royal terns. The brilliant red and orange bill coloration of these terns results from carotenoid pigmentation. The female has the redder bill in this pair, and among both males and females individuals with the reddest bills are the healthiest birds in the best condition. (Alabama, April).

Photo courtesy of Geoffrey E. Hill

Reviewed and posted by David Braun