Mallard Recruitment in the Agricultural Environment of North Dakota

Determination of Age and Condition of Hens

Age was determined from discriminant functions developed by Krapu et al. (1979a). We used the function for black and white surface area of greater secondary coverts 2 and 3. Birds were aged as second year (SY) or after second year (ASY) unless the discriminant function lay between +1 and -1. We did not believe that in the latter situation that birds could be accurately aged, and we recorded them as after hatching year (AHY). AHY birds were deleted from analyses dealing with age.

Krapu (1981) demonstrated the importance of nutrient reserves in mallard re production and showed that weight is positively correlated with lipid content of mallard carcasses. We used weight at capture ÷ length of wing chord as an index to condition and compared this index to known reproduction effort.

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