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GEOGRAPHIC VARIATION AND TAXONOMY OF THE NORTHERN WATERTHRUSH

Abstract In this study we analyzed geographic variation in the Northern Waterthrush (Seiurus noveboracensis) and reassessed the status of the four subspecies described between 1880 and 1948, three of which were recognized by the AOU Check-list (1957) and Godfrey (1986). We examined 490 specimens that came from throughout the breeding range of the Northern Waterthrush and used four morphometric data sets and three color variables to investigate geographic variation. Males differed from females based on morphometric characters. Males, unlike females, showed a morphometric trend with latitude and longitude. Their wing chord, tail and tarsus lengths showed a gradual decrease in length from north to south, while their tail and tarsus lengths gradually decreased eastward. The body shape showed a longitudinal trend where western specimens tended to have proportionally longer tails than wings compared to specimens from the eastern part of the range. Color was more strongly related to geography than morphometric characters and showed both longitudinal and latitudinal trends. Specimens from the southeastern part of the range were more olive dorsally and yellow ventrally and had fewer underpart markings than most specimens from the northwestern part of the range. Only the wing length permitted us to discriminate between the most distant populations. These trends are clinal and cannot support the recognition of subspecies.