Color Key to North American Birds / with bibliographical appendix

by Frank M. Chapman

Family Turdidæ Thrushes.

Subfamily Turdinæ Thrushes.

Genus, Planesticus, Thrushes.

Species, migratorius American Robin.

The Robin's distinctive scientific name, therefore, which it alone possesses, is Planesticus migratorius. There are numerous other members of the genus Planesticus, but not one of them is called migratorius and this combination of names, therefore, applied to only one bird.

The questions Why use all these Latin terms? Why not call the bird "Robin" and be done with it? are easily answered. Widely distributed birds frequently have different names in different parts of their range. The Flicker (Colaptes auratus), for instance, has over one hundred common or vernacular names. Again, the same name is often applied to wholly different birds. Our Robin (Planesticus migratorius) is not even a member of the same family as the European Robin (Erithacus rubecola.) If, therefore, we should write of birds or attempt to classify them only by their common names, we should be dealing with such unfixed quantities that the result would be inaccurate and misleading. But by using one name in a language known to educated people of all countries, a writer may indicate, without danger of being misunderstood, the particular animal to which he refers. Among people speaking the same tongue, where a definite list of vernacular names of animals has been established, they can of course be used instead of the scientific names.

Such a list of North American birds has been prepared by the American Ornithologists' Union. It furnishes a common as well as scientific name for each of our birds, and is the recognized standard of nomenclature among American ornithologists. The names and numbers of birds employed in this Color Key are those of the American Ornithologists' Union's 'Check-List of North American Birds.'

It will be observed that in this 'Check-List,' and consequently in the following pages, many birds have three scientific names, a generic, specific, and subspecific. The Western Robin, for example, appears as Planesticus migratorius propinquus. What is the significance of this third name?

In the days of Linnæus, and for many years after, it was supposed that a species was a distinct creation whose characters never varied. But in comparatively recent years, as specimens have been gathered from throughout the country inhabited by a species, comparison frequently shows that specimens from one part of its range differ from those taken in another part of its range. At intervening localities, however, intermediate specimens will be found connecting the extremes.

Generally, these geographical variations, as they are called, are the result of climatic conditions. For instance, in regions of heavy rainfall a bird's colors are usually much darker than they are where the rainfall is light. Song Sparrows, for example, are palest in the desert region of Arizona, where the annual rainfall may not reach eight inches, and darkest on the coast of British Columbia and Alaska, where the annual rainfall may be over one hundred inches. In going from one region, however, to the other the gradual changes in climate are accompanied by gradual changes in the colors of the Song Sparrows, and the wide differences between Arizona and Alaska Song Sparrows are therefore bridged by a series of intermediates.