Northern Prairie Wildlife Research Center
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
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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