Note A — Front matter (continued 4)

Fourteen subspecies of this wide-ranging, variable form are now recognized in America, north of Mexico. Many of them are too closely related to be distinguished even by detailed descriptions. When breeding, they may be identified, in life, by a knowledge of the area which each form alone inhabits at this season. But during their migrations, and in winter, when several forms may be associated, it is usually not possible to identify them in the field. The reader is referred to admirable monographs of this group by J. Dwight, Jr. (The Auk, vii, 1890, pp. 138-150), and H. C. Oberholser (Proc. U. S. Nat. Mus., xxiv, 1902, pp. 801-884).