Colorful Birds
Why are some male birds so colorful; females so dull? The simple answer is that the male’s vibrant colors help him defend territory and attract a mate; the female’s drab coloration allows her to blend in with her surroundings.
Nothing in nature is simple though, is it? The variations in color and markings of a bird are so complex that ornithologists will probably never fully understand all the factors involved. For the purpose of this essay we’ll explore two color pattern categories: epigamic colors bring the sexes together; cryptic colors help conceal the bird.
The bright yellow breeding plumage of the American Goldfinch, an example of epigamic coloration, warns rival males of territorial lines and helps attract a mate. During the breeding season, most species’ pair-bonding begins with the male defending territory and behaving aggressively towards all intruding members of his species. The male will be less aggressive towards a female if the species is sexually dimorphic, which means there is a visual (color) difference between the males and the females. Some male birds have colorful markings that may be fully or partially hidden except when used in display to either advertise territory boundaries to other males or for courting females. Examples of this are the red/buff shoulder epaulettes of the Red-winged Blackbird and the spectacular tail display of the Peacock.
Within sexually dimorphic species, the female’s coloration is usually cryptic. Their plumage is dull and resembles or blends into the background so well that when they sit motionless on their nests they are practically undetectable. In many species the male assumes a cryptic color after the breeding season: they blend in better with their surroundings, making them less of a target for predators. This is true for the Goldfinch and most warbler species. Many male ducks, including the Mallard, assume cryptic coloring when they are flightless during a full molt.
Almost every color or color pattern has some significance in the birds’ natural history. The survival of the species has been ensured by the evolutionary forces that have worked on thousands of generations attaining the best adaptations for the birds’ various environmental situations.