Northern Prairie Wildlife Research Center


Home	About NPWRC	Our Science	Staff	Employment	Contacts	Common Questions	About the Site

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.

Previous Section -- Capture and Radio Marking
Return to Contents
Next Section -- Habitat Conditions and Climate

Accessibility FOIA Privacy Policies and Notices

U.S. Department of the Interior | U.S. Geological Survey
URL: http://www.npwrc.usgs.gov/resource/birds/recruit/henage.htm
Page Contact Information: Webmaster
Page Last Modified: Friday, 01-Feb-2013 19:50:52 EST
Menlo Park, CA [caww54]