Age Determination of American Black Ducks in Winter and Spring

Abstract

Age-specific studies pertaining to survival and productivity of American black ducks (Anas rubripes) are constrained by the fact that no technique has been developed to reliably determine age as second year or after second year from late winter to late spring. We developed a qualitative age-class scoring technique that can be readily used in the field. When tested on 5 independent observers, known-aged birds (n = 106) were correctly classified with 94–98% accuracy. To reduce subjectivity and provide an objective corroboration of age estimates, we also developed multivariate models from measurements of wing feather variables (weight and length of greater secondary covert 9, and width of tertial covert 5) that determined age with ≥90% accuracy (n = 255). There was ≥94% agreement between qualitative and quantitative age assignments of wild birds caught in spring (n = 172). The application of these age determination techniques should be useful in a host of life-history studies conducted on wintering, spring staging, and nesting grounds.