Variation in Seiurus noveboracensis

THE NORTHERN WATERTHRUSH is one of the New World's most widely ranging warblers.It is a characteristic breeding bird by waters associated with our boreal forests, may be seen on migration in every state of the Union, and winters as far south as Venezuela (Wetmore, 1939).Three subspecies have been recognized by the A.O.U.Committee on Nomenclature: the nominate race, notabilis Ridgway (1880), and limnaeus McCabe and Miller (1933).Burleigh and Peters (1948) have recently described a fourth race, uliginosus, from Newfoundland.This paper attempts to analyze critically the variation indicated by these trinomials and to point out severe weaknesses and misconceptions regarding them.Variation in birds may be of several types such as individual, sexual, age, and geographic.Only after a study of the first three can the fourth adequately be determined.The approach here follows that order.