Blane Klemek: Bird plumage more than just beautiful
In the world of birds, plumage color patterns are essential to individual species survival. In fact, one of the many functions of plumage color is concealment. Abundant and familiar examples exist right here in our own backyards, forests, and fields.
A couple of common gamebirds that readily come to mind are ruffed grouse and American woodcocks. At a glance it may appear that these birds are basically one color. But at close examination, many shades and patterns of those fundamental colors emerge. Clearly, however, the reason for such arrangement of plumage color pattern is the environment the birds inhabit. Both species of birds sitting in a motionless posture on the forest floor mixed with fallen leaves, brush, and trees are nearly impossible to see.
The American bittern is another bird with an interesting plumage color pattern. Here’s a bird that spends its life within the tall vegetation and shallow waters of specific wetlands. Not just any old wetland will do for the bittern. Its lifestyle is one in hiding and so wetlands with cattails, tall grasses and sedges, as well as reeds and other vegetation, attract bitterns.
Observing a bittern out in the open or in flight does little to illustrate just how cryptic their plumage color pattern is, until, the bird steps into the tall vegetation and performs its little disappearing act. As a bittern slinks, almost sloth-like, into the herbaceous neighborhood it inhabits, stretches its neck upward, and points its bill straight up, it is suddenly just another clump of grasses or cattails. The body contour, the striped breast plumage, and all the surrounding vertical stems make for a bona fide Houdini act that’s tough to follow, let alone see at all.
The ptarmigan, a gallinaceous bird of mountainous snow country and tundra, is a bird well suited for the changing landscape of the northern frontier. During the wintertime ptarmigans are colored almost pure white in order to match its harsh surroundings. In the spring as snow melts and patches of earth, rocks, and ground vegetation are visible once again, ptarmigans plumage resembles this change as well. Ptarmigans take on a mottled look, displaying patches of both brown and white. And by summertime, ptarmigans are finely barred in browns and blacks.
Disruptive patterns also help to conceal birds. Bold markings, often associated with the head and neck region, effectively lessen the difference between the shape of a bird’s body or outline and its normal habitat type. The black bands on a killdeer’s head, neck, and breast are examples of bold patterns that help to “disrupt” the contrast that would exist without the bands, which makes the bird difficult to detect on the ground.
Countershading is another pattern common in birds. First described by Abbott and Gerald Thayer in 1909, countershading helps to disguise a bird’s outline. We see this typically in shorebirds; that is, darker plumage above and lighter plumage below.
Shorebirds normally forage in open spaces along beaches and shorelines of riparian areas. In so doing the birds are exposed and somewhat vulnerable to predation. However, strongly contrasting colors of the dorsal and ventral surfaces of most shorebirds act in partnership with sunlight. Dark plumage on a bird’s back does not reflect light very well, and this contrasts sharply with the bird’s lighter colored bellies. The visual interaction helps to blend a bird’s outline with the background and thus, reduces its visibility.
That withstanding, countershading, as intuitive as it is, also occurs in its opposite form. Some birds such as male bobolinks, golden plovers, and black-bellied plovers display dark plumage on their underparts and lighter colored plumage on their upperparts. This seemingly maladaptive color pattern’s primary purpose is to enhance visibility rather than reduce it. The reason? Such color patterns are more important during the breeding season for attracting mates than it is for concealment.
But what about the showy and colorful breeding plumages of most male songbirds? How do bright colors survive in a species? Aren’t colorful birds more vulnerable to predation? While it is true that bright colors are sexually selected (brightly colored males tend to mate more often and hence spread their genes), predatory selection might also be contributing to bright colors in birds and, thus, increased survivorship.
Some research has shown that more colorful birds, usually males, are more difficult to catch or, as some other research also suggests, unpalatable, or determined to be unpalatable by some predators. The latter suggests that some predators will forgo preying on brightly colored birds because of past bad experiences with other brightly colored prey such as truly unpalatable/distasteful species such as salamanders and toxic colorful insects like monarch butterflies, wasps, and hornets. These predators have learned that colorful prey equals bad tasting and painful prey.
Why animals possess the color patterns they do is a fascinating subject to observe and study. In regard to birds, plumage color patterns did not come about randomly. Such diversity in coloration and pattern evolved over time and is what it is because it helps birds survive, reproduce, and to pass on their genes to the next generation.
Indeed, the next time you go birding, take note of the dazzling number of different plumage color patterns amongst birds and other species of wildlife. This awareness enhances our days afield as we get out and enjoy the great outdoors.
BLANE KLEMEK is a Minnesota DNR wildlife manager. He can be reached at firstname.lastname@example.org.