Age Determination of Mallards

Abstract

A technique for distinguishing adult from yearling wild mallards (Anas platyrhynchos), from late winter through the nesting season, was developed by applying discriminant analysis procedures to selected wing feather characters of 126 yearlings and 76 adults (2-year-olds) hand-reared from wild eggs during 1974, 1975, and 1977. Average values for feather characters generally increased as the birds advanced from yearlings to adults. Black-white surface area of greater secondary covert 2 was the single most reliable aging character identified during the study. The error rate was lowest in females (3%) when discriminant functions were used with measurements of primary 1 weight and black-white area cf greater secondary covert 2 and in males (9%) when the functions were used with black-white area of greater secondary coverts 1, 2, and 3. Methodology precludes aging of birds in the field during capture operations. J. WILDL. MANAGE. 43(2):384-393 Although the mallard has been studied widely, only limited information has been published on age-related aspects of its life cycle, especially age-related productivity. This paucity of information can be attributed, in part, to the lack of a reliable aging technique applicable during the nesting season. Although keys have been developed on the basis of certain wing feather characters to determine age of mallards during the fall and winter (Carney and Geis 1960, Carney 1964), the reliability of these characters during the breeding season is diminished because of feather replacement and wear before and during the nesting season. The present study was undertaken to develop a technique for reliably separating yearling from older (adult) mallards from late winter to the onset of wing molt in late summer. Several feather measurements were chosen for establishing discriminant functions for each group. Wing feathers were selected on the basis of observed patterns of variation in feather characters, with knowledge of age-related feather variation based on published 1 Present address: Division of Wildlife Research, U.S. Fish and Wildlife Service, Washington, DC 20240. literature, and on the basis of pattern and timing of molt. Variation in primary feather lengths of yearlings and adults was recognized in blue-winged teal, Anas discors (Dane 1968), and redhead, Aythya americana (Dane and Johnson 1975). Wing covert markings were used to age yearlings of certain species, including gadwall, Anas strepera (Oring 1968); common merganser, Mergus merganser (Anderson and Timken 1971); redhead (Smart 1962, Dane and Johnson 1975); and blue-winged teal (Dane 1968). We thank C. W. Shaiffer, who made most of the measurements; B. A. Hanson for assistance in data collection; T. J. Dwyer for his encouragement and help during development of the study; D. C. McGlauchlin, Manager, Audubon National Wildlife Refuge, for support in obtaining mallard eggs for aging studies; F. B. Lee for supervising the rearing of known-age mallards; and R. J. Greenwood for critically reviewing the manuscript.