Spring and Summer Age Separation Techniques for the Mallard

Abstract

A quantitative technique was developed to distinguish adult from yearling mallards (Anas platyrhynchos) during the breeding season using wing feather measurements of 423 fall-shot birds. Mean feather measurements of adults of both sexes were larger than those of immatures (yearlings). The best measurement for separating ages in both sexes was vane width at the tip of greater secondary covert 5. Four and 5 variables were required to correctly classify the age of 91 and 95% of the hens and drakes, respectively. Wing feathers were measured on 50 known-age wild mallards captured in southern Manitoba during spring and summer, 1975-77. All 4 of the yearlings and 22 (88%) of the adults captured in 1975-76 were correctly classified using discriminant functions developed from wing measurements of fall-shot birds. Use of the qualitative age characters, covert shape and primary covert coloration, resulted in the correct classification of all knownage wild yearlings and 91% of the known-age wild adults. Covert wear and bill spotting were poor indicators of age for breeding mallards. J. WILDL. MANAGE. 47(4):1054-1062 Carney and Geis (1960) presented a qualitative method using wing characteristics for identifying sex and age-classes of mallards in fall. Age (adult or immature) through December was assigned by shape, wear, and coloration patterns of tertials, greater tertial coverts, middle coverts, and primary coverts. Hopper and Funk (1970) evaluated mallard age-class separation based on wing examination and found it to be accurate for banding operations through February. Accuracy of this method was a function of observer experience and bias. Krapu et al. (1979) developed a quantitative mallard age classification technique based on wild-strain, captive birds. However, Blohm (1977) and Wishart (1981) showed that feather measurements of captive ducks may not be representative of free-flying birds. This paper presents an alternative method of age-class separation based on free-flying, wild mallards. Additionally, a qualitative method of age classification is evaluated for use during the breeding season. This study was supported by the North American Wildlife Foundation through the Delta Waterfowl Research Station, the D cks Unlimited Foundation, and the University of Wisconsin, College of Agriculture and Life Sciences. Lodging and research facilities in Manitoba were generously provided by the owners of East Meadows Ranch and L. King. R. A. Montgomery of the Max McGraw Wildlife Fou dation made their penned mallard flock available for study. S. M. Carney and L. D. Schroeder of the U.S. Fish and Wildlife Service cooperated in separation of age-classes. J. R. Cary consulted on statistical analyses and D. L. Patterson and C. Sauer typed the manuscript. R. A. McCabe advised my research, and along with O. J. Rongstad and D. H. Rusch, reviewed the manuscript. I especially appreciate the help and suggestions of R. J. Blohm through all phases of my work.