2006-06-10 / Columnists

Nature Notes

Brilliant Coloration Is Not To Impress People: It's for the Birds
By Patricia Martin

Almost every morning, when I head up the East Bluff to feed my horse, I hear the birds singing in the trees. Lately, as I've looked up to spot them, I've been struck by the myriad colors found in the bird world. Yes, some of them are dull; however, quite a few are painted with bright colors. Most animals are colored to blend in with their environment so that they will not become someone's dinner, or so that they will not be spotted by those that they wish to eat, but with some birds, particularly the males, it seems that camouflage is of secondary importance. Brilliant bird coloration did not evolve to please the human eye, rather it came into being to impress other members of the same species, and it's the males who want to attract the less colorful females.

Around here we're used to seeing the bright blue of the blue jay or the red of the cardinal, two of our birds who are in the area year-around, but there are other colorful birds that are only here in the summer, or are merely passing through. One such summer bird I heard and saw yesterday. It was an indigo bunting. The male is an iridescent blue on his body with black feathers on his wings and tail and a short, gray, conical beak. On the top of a cedar tree where I saw him, he appeared almost black, but when he flew, the brilliant blue appeared. Blues and iridescent colors are not produced by pigments in the feathers or skin, as are the other colors in birds. These are structural colors. Blues are produced by minute particles in the feather that are smaller in diameter than the wavelength of red light. These particles are able to influence only shorter wavelengths, which appear blue and are scattered, reflected in all directions. Thus structural blue colors remain the same when they're viewed at different angles in reflected light. If, however, they're viewed by transmitted light (that is, with the feather between the light source and the observer), the blue disappears. The female indigo bunting, on the other hand, is soft brown in color with a whitish throat. It is only the male who sings, again to attract the female or to ward off other males. His song consists of paired warbled whistles sounding like "fire-fire, wherewhere, here-here, see-it see-it." The male learns his musical song not from his father but from neighboring males during his first spring.

These birds live and nest in deciduous forests and woodland edges, regenerating forest clearing, shrubby fields, the edges of mixed forests, and orchards. On the Island, I often see them along the East Bluff and near Sugar Loaf along Juniper Trail and Fern Way. The female builds the cupshaped nest of grasses, leaves, and bark in the fork of a small tree or shrub. As far as food goes, the indigo bunting likes to glean insects and seeds from the ground. Some of the favorite insects include grasshoppers, weevils, beetles, and larvae. The seeds that it likes include those from dandelions, goldenrod, and thistles.

Another colorful bird that I saw this spring, after a friend told me that he had seen them along the Bluff, is much more elusive than the bunting. It is the scarlet tanager. Often it is only their song that alerts you to their presence, despite the fact that the breeding male has a bright red body, as their name suggests. The male's wings and tail are black. In the fall the male loses some of its color and becomes rather patchy red and greenish yellow, but the black wings and tail remain. The female, on the other hand, is uniformly olive on the upper parts and yellow on the lower parts with grayish, brown wings.

The coloration of the scarlet tanager is the result of pigmentation. Pigments in the feathers absorb some wavelengths of light and reflect others; it is the wavelengths that are reflected that reach our eyes. The color we perceive is a function of the wavelength of light stimulating the receptors of our retinas. In the visual part of the spectrum, we see the shortest wavelengths as violet and the longest as red. Thus the body of the breeding male scarlet tanager has feathers that have pigments that absorb all of the wavelengths of light except for those which we perceive as red.

Of the more than 200 species of tanager that are found in the Americas, the scarlet is the only one who nests regularly in Michigan. By the way, the other species are equally colorful, with almost every color of the rainbow represented.

The song of the scarlet tanager is a series of four to five sweet, clear, whistled phrases that are similar to a slurred version of the American robin's song. The most frequently heard sound that they make is a soft, low-pitched buzzy "tipchurr" given by both sexes. These birds breed and nest in fairly mature upland deciduous and mixed forest and large woodlands. The female tanager usually builds her nest high in the branches of a deciduous tree, well away from the trunk. It is a shallow, cup-shaped nest made of weeds, grass, and twigs. This placement of the nest makes sense, as they often glean insects from the tree canopy, but they may also hover-glean, or hawk, insects in midair. It also explains why we don't often see these birds. During cold weather they may forage at lower levels of the forest and will also eat seasonal berries. These are only a couple of

the beautifully colored birds who visit or live on our Island. Keep an eye out for them as you walk or ride Mackinac's trails and roads.

Trish Martin is a yeararound resident of Mackinac Island, has earned a master's degree in botany from Central Michigan University, and owns Bogan Lane Inn.

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