Nature Notes: Color Schemes

Nocturnal birds are mostly brown and dull-colored when compared to day birds
While the color of a flamingo’s feathers is influenced by what it eats, an indigo bunting’s color is the result of blue light refracting and reflecting off its feathers. Terry Sullivan

The summer birds are back in full force. Most are day birds, but some are nocturnal — the owls and the nightjars such as the nighthawk and whippoorwill. 

Friday evening Stephanie Krusa, who lives in Montauk, visited one of her favorite spots for night birds, not to see them, but to hear them load and clear while listening through her open car window. It was near the end of Navy Road, which runs to Fort Pond Bay. No sooner had she arrived and turned off the ignition and the lights than the chorus started. A whippoorwill here, a whippoorwill there. From just about every corner came the eerie chant of the whippoorwill. They may have become scarce elsewhere on the South Fork, but thank God, they are still holding their own in Montauk.

Nocturnal birds are mostly brown and dull-colored when compared to day birds. The males are selected on the basis of the calls and other signs, not by color. Males and females are rarely sexually dimorphic, and instead look like each other. On the other hand, almost all day birds, especially the songbirds, are sexually dimorphic. The males are showily colorful, the females drab and almost nondescript. In fact, it has been shown that for a few species, for example goldfinches, the brighter yellow the males, the more favorable they are in the eyes of the females.

The most colorful bird in my yard is the male cardinal. It would be hard to find a more spectacular red bird in the Americas. The red comes from pigments, most of which are gleaned in the male’s diet. The redder the fruit, the redder the male cardinal. However, the brilliance of the redness is also genetic. Feed females red fruit day after day and they still remain pale in comparison to the average male.

Some of a bird’s color is attributable to what they eat. Pink flamingos eat shrimp that tend to have pinkish carotenoid pigments. If you feed a flamingo with a commercial mix that lacks those pigments, it will eventually become a very pale pink, even white. If you grind up male cardinal or pink flamingo feathers in blender, the resulting powder will still be reddish.

However, if you grind up the feathers of an indigo bunting, a sparrow-size species in which the males are almost solid blue as the name suggests, you get a brown powder. Why? The blue color is a matter of the scattering and re-radiation of impinging light. It is not from blue pigments, but is said to be structural rather than chemical. The male indigo bunting’s brilliant hue has little to do with its diet. The male goldfinch’s bright yellow plumage is both chemical and structural. If you feed him on yellow birdseed rich inriboflavins, he will become yellower. 

The bizarre and wonderful colors of male birds begs the question: Why are mammals so dull in aspect? The human is one of the few mammals that is somewhat colorful: His or her hair may be yellow, brown, black, or even orange, with many variations of each color. Native Americans and other groups enhanced their outer appearances with applied pigments and various attachments. Modern men and women wear colorful clothes, while the women often apply lipsticks, rouges, and other colorful coatings. They are the closest thing to birds in the mammalian group. What if humans were as uncolorful as most other mammals? The New York Times would not have a Style section twice a week; there would be no Glamour or Elle magazines.

Fish are considered to be the first vertebrates to evolve, beginning 450 million years ago when the first sharks and rays appeared. They are cartilaginous. Bony fishes followed. Sharks and rays are not colorful, suggesting that the first bony fish were likewise not colorful. But modern fish species are just as colorful as modern birds. And in the large majority of cases, the females are just as colorful as the males. Fish forms gave rise to the amphibians and early reptiles, the dinosaurs and therapsids, which in turn gave rise to the mammals, and then birds.

The early dinosaur line that produced Archeopteryx is thought to have given rise to the first birds, which were toothed and had claws on their wings. They glided before they developed active flight. There is a bird in the wet areas of central and coastal South America called the hoatzin that may be a throwback to those first birds. When born, the young have two claws on each wing that they can use in climbing from limb to limb.

When all of the earth’s land mass was gathered in one continent, Pangea, the first amphibians, reptiles, birds, and mammals occupied most of it. However, as the continents drifted apart, the mammals that evolved, say in Eurasia, did not have an easy time getting to other continents, while the fishes could swim to them and the birds could fly to them. Today, fishes are the most ubiquitous vertebrates, followed by birds. Fish are cold-blooded, or ectothermic, so the temperature of the water is not a big problem for them, while birds are warm-blooded, or homiothermic. They can avoid frigid conditions by flying away from them, thus the seeds of migration.

The more species of birds, the more chance for species to interbreed, unless characters developed that set them apart. The first character to keep one species from breeding with another was size, the second and third were colorful males and the sounds they made. Because they resembled each other in size, New World warblers evolved intricate color patterns and distinct songs to keep them from interbreeding.

Female birds pick their mates in various ways, but apparently, in most cases, by their songs and plumage.

It is easy to see why males are so colorful and sing different songs. But what about fish, when males and females are colorful and look alike? Coral reef fishes are the most colorful of all. With few exceptions, Caribbean species are more colorful than their Pacific counterparts. It is argued that this is because the waters of the Pacific at similar latitudes are more opaque. It is also argued that reef fishes are particularly colorful because of their colorful habitat. As the reefs around the world continue to degrade, will colors of the fish and invertebrates inhabiting them become duller? It remains to be seen.

Apparently other cues, like phero­mones, are used in breeding, and in many cases females are fertilized by more than one male in a mix of broadcasted spermatozoa. It has also been argued that fish are colorful because of their diets, but experimental feeding in which certain species got very colorful diets did not make them more colorful, as it does for flamingos. 

Primitive humans left diagrams and pictures of familiar beasts on the walls of their caves, while modern humans build large museums to house their artists’ works, which are multiform and three-dimensional as well as two-dimensional, some combining both graph­ics and sounds. Is the aesthetic sense that motivates both artists and museum visitors the sense that also makes us appreciate the colors of tropical fish and the colors and songs of birds? I would think so. Then I also must ask, are colors in fishes and butterflies, as well as colors and songs in birds, the beginning of the aesthetic sense that has become so highly developed now in modern men and women?

I wonder if the white-tailed deer that hears the mating song of the male bluebird defining its nearby territory or sees a male red-breasted grosbeak flit by is as impressed as we would be?