Laura Erickson's For the Birds

Martin Luther King Jr.’s Birthday

(Recording of a Northern Cardinal)

Although Monday is the national holiday, today is Martin Luther King Jr.’s real birthday, which naturally set me to thinking about race relations in birds. A lot of bird species don’t have different races, since flight allows them to cross barriers that would separate earthbound mammals. But as in humans, avian races do develop when populations become isolated geographically. One example of this is the Baltimore and Bullock’s Oriole. These orioles look as different as two races of humans, yet, like people, taxonomists consider them to be a single species–that is, fully capable of interbreeding. The Great Plains separated the orioles for a long time, just as oceans and mountain ranges isolated groups of people long enough to develop racial differences. When European man settled the Plains and planted shade trees, the two orioles were both able to expand their ranges, and now they meet in the middle, where they interbreed indiscriminately. That’s why both orioles were combined into a single species called the Northern Oriole.

The cardinal also has different races. The southwestern form is glowing, brilliant scarlet, compared to the more muted but equally lovely red of Minnesota and Wisconsin cardinals. Geographical isolation limits interbreeding enough to maintain these differences, although again the birds can successfully mate and produce young wherever they do meet.

At present, the International Code of Zoological Nomenclature doesn’t use the term “race”–it calls these groups of birds “subspecies,” though many ornithologists believe “race” is more clear and accurate.

Sometimes a species of birds comes in different colors for a non-racial reason. Ruffed Grouse and screech owls, for example, come in reddish brown or gray. Snow geese come in white or blue. Many hawks come in dark and light colors. A single brood of these birds can include young of both colors. This kind of color difference within a species isn’t due to geographical isolation—it’s exactly analogous to brown and blue eyes in people. In each case one or two genes control the color. Ornithologists used to call these “color phases,” but that mixed up a lot of people who erroneously thought that, say, a dark-phased Red-tailed Hawk might change into a light phase later. Now they use the term “color morph”–so you’d talk about a gray morph Ruffed Grouse or a dark-morph Rough- leg. White-throated Sparrows also have two forms–the white- striped morph and the tan-striped morph. Females of all these species select their mates indiscriminately–the quality of a male’s song and territory are far more important to her than the color of his feathers.

Martin Luther King had a dream that “One day on the red hills of Georgia the sons of former slaves and the sons of former slaveowners will be able to sit down at the table of brotherhood;” and he had a dream that his “four little children will one day live in a nation where they will not be judged by the color of their skin, but by the content of their character.” I think Martin Luther King must have liked birds.

(Recording of a cardinal)

This is Laura Erickson, and this program has been “For the Birds.”