Last week I wrote about how birds get their colors—and that had me thinking about what birds do with all those colors.
Some hide. If you’ve ever searched for a striped sparrow in the underbrush, or a White-tailed Ptarmigan in a field of rocks, or a Common Pauraque along a south Texas trail, you know how effective their camouflage is.
But then there are Wood Ducks and Painted Buntings (top), Yellow Warblers and Western Tanagers. Aptly named Rainbow Lorikeets with every color displayed on each individual. Not to mention my favorites, the dazzling multi-hued bee-eaters. These birds have exchanged the safety of muted greens and stripy browns for colors that scream “Here I am!” It doesn’t seem very… sensible. Yet, the world is full of brilliantly colored birds. The rewards must be worth the risk.
My first thought was that maybe it isn’t as risky as I’m imagining. What we perceive as flamboyant, might other animals, notably predators, see differently? What eats these bright birds? I immediately thought of falcons, accipiters, and other birds of prey; bobcats, weasels, coyotes, and other predatory mammals; and large reptiles such as alligators and snakes. Could all these bird-eating animals be colorblind?
No, they’re not. Raptors have excellent color vision—better than ours! Alligators are red-green colorblind, but see other colors well. Snakes, at least the ones that eat birds, are able to see some colors, plus infrared. Even many mammals that I assumed were colorblind have limited color vision.
Then I considered that many colorful birds have colors that break up their outline so, at a casual glance, they don’t appear to be birds but perhaps flowers or fruit or colored leaves. Perhaps the colors aren’t as noticeable as they appear at first. That could (and likely does) apply to some species—various warblers with all those black and yellow stripes and patches, or the strong markings on a Black-headed Grosbeak, for example.
But what about the brightest birds, the ones that you can’t help but see? Brilliant red Vermilion Flycatchers, Summer Tanagers, and the Madagascan Red Fody. Screaming pink flamingos, coppery Rufous Hummingbirds, turquoise kingfishers. How can they justify being so obvious?
All those colors serve a purpose—actually, several purposes. Birders often use color to identify a species, and may birds do the same. Different colors help differentiate one species from another. This diversity is especially valuable in species-dense habitats, such as tropical forests (and may explain the multitude of colorful fish on a coral reef, another habitat with a lot of different species).
Bright colors can also serve to warn off the competition. Ruby-crowned Kinglets raise their red crowns when they’re feeling threatened. Other species, such as meadowlarks and many sparrows, flash white tail feathers.
Some colors actually do serve as camouflage. Try to spot a Yellow Warbler in a tall cottonwood when many of the leaves are the same color yellow. Rainbow Lorikeets hang out in shrubs and trees with brightly colored flowers, and they fit right in. (OK, sort of.) And colors may help regulate body temperature.
But the primary driving force behind all these colors, as with many things, is sex. Bright colors signify robust health. The brighter the color, the healthier the bird. And, as with many species, while the males do the advertising, it’s the females who do the choosing. As a result, the males with the most brilliant feathers pass on their genes, and the species gets progressively more colorful. At some point, the price of all that flamboyance, whether it be the metabolic cost or increased predation, balances with the selective pressure from the females’ mating preferences, and the species’ colors stabilize. The result? Colorful birds, and a delighted bird photographer.