Skewed Age Ratios of Breeding Mallards in the Nebraska Sandhills

• Published in: The American midland naturalist 2016-04, Vol.175 (2), p.280-285
• Main Authors: Cunningham, Zach J, Powell, Larkin A, Vrtiska, Mark P, Stephens, Scott E, Walker, Johann A
• Format: Article
• Language: English
• Subjects: Age; Age discrimination; Age distribution; Age distribution (Demography); Animal age determination; Animal behavior; Bias; Bird nesting; Breeding; Breeding sites; Demographic aspects; Ducks; Ecosystems; Female animals; Females; Grasslands; Mallard; Note and Discussion Pieces; Notes and Discussion Piece; Ornithological research; Population; Ratios; Studies; Waterfowl; Wetlands
• ISSN: 0003-0031; 1938-4238
• DOI: 10.1674/0003-0031-175.2.280

Understanding demographic structures of populations allows managers to better evaluate factors affecting populations and increase efficiency of conservation efforts. Recent studies suggest low productivity, but high survival characterizes mallard (Anas platyrhnchos) populations in the Nebraska Sandhills. We studied age ratios of decoy-trapped and observer-shot mallards in the Sandhills during 2007–2008. Observed age distribution (second-year:after-second-year) of mallards was 2.8:1 for females and 0.8:1 for males. Age ratios of trapped females were skewed towards young females relative to other studies, and the age ratio of trapped females was not different than the age ratio of the sample we collected by shooting. The skewed age ratios we observed provide additional context to the low reproductive success that has been reported for nesting mallards in the Sandhills. Second-year mallard females tend to invest fewer resources and take fewer risks associated with nesting. As a result the Sandhills population may not contribute significantly to productivity of the continental mallard population but act as a reservoir of young female mallards available to disperse to more productive breeding areas in future years.