Estimating movement and production rates in American black ducks
Zimpfer, Nathan Lawrence
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American back duck (Anas rubripes) populations declined dramatically throughout much of the 1970’s and 1980’s, and recently have appeared to stabilize at wintering populations of approximately 300,000. Models were developed to estimate movement rates of black ducks among multiple breeding areas, migrations rates from Canadian breeding areas, to US harvest areas, and fidelity rates of individuals back to their respective breeding areas. We utilized banding and recovery data from 1965–1998 to estimate movement rates based on a model developed in program SURVIV. The best model as determined by AIC suggested that movement rates were sex specific. The movement pattern was similar among males and females. Black ducks banded in the western breeding area, exhibit the greatest movement rates to the Mississippi Flyway, and southern Atlantic Flyway, while black ducks banded in the eastern breeding area predominately move to the northern Atlantic Flyway. Fidelity rates were estimated in Program MARK using banding, recovery, and recapture data. The best model identified in Mark, suggested age- and sex-specific fidelity rates. Fidelity rates for adults were very high (>0.95), and rates for young were only slightly less with young females exhibiting the lowest fidelity rate, at 0.8870. Second, we developed a model to predict production rates, as indexed by fall age-ratios, as a function of environmental and other intrinsic factors from 1990-2001. We utilized an exponential model which was log transformed. A model that included breeding area specific intercepts, black duck density, mallard density, spring temperature, and spring precipitation best predicted fall age-ratios. These models developed herein and their results can all be incorporated into an AHM strategy for American black ducks. Adaptive Harvest Management (AHM) offers the inherent strength of reducing uncertainty about the system through time, thus improving management capability, while striving towards a common objective.