Differentiating Yearling from Adult Northern Pintails by Wing-Feather Characteristics

Abstract

Several reproductive parameters vary with age in ducks, particularly between yearlings (birds hatched the previous year) and older birds (Kaltenhauser 1971, Batt 1979, Krapu and Doty 1979, Baillie and Milne 1982). Because yearling females of most species are potential breeders (Bellrose 1976), it is necessary to distinguish yearlings from adults when analyzing the reproductive potential of duck populations. During the late summer and autumn, juvenile ducks may be distinguished from adults by differences in the cloacal bursae (bursae of Fabricius), retrices, or tertials (Larson and Taber 1980). These criteria, however, are not valid during the following spring (Dane 1968). In a number of species, it has been possible to identify yearlings during the breeding season using various juvenile characteristics of the primaries, secondaries, and their coverts because these feathers are retained until the post-breeding (prebasic II) molt (e.g., Dane 1968, Dane and Johnson 1975, Blohm 1977, Krapu et al. 1979, Wishart 1981, Serie et al. 1982, Carney 1983, Gatti 1983). To date, there has been no comparative treatment of feather characteristics in yearling and adult northern pintails (Anas acuta), although Carney (1964) listed some features that were potentially useful in discriminating between these two age-classes. In this paper, I describe wing-feather characteristics that differentiate yearling from adult pintails during the breeding season.