A Demographic model for ring‐necked ducks breeding in Minnesota

Abstract

ABSTRACTPopulation models can provide insights into how perturbations of demographic vital rates influence population growth rates (λ) and help prioritize efforts to achieve management goals. Although population models have been developed for numerous duck species, this tool has not been developed for ring‐necked ducks (Aythya collaris). Ring‐necked ducks are a late‐nesting species that may not be surveyed well by the May Waterfowl Survey, which is timed optimally for earlier nesting ducks like the mallard (Anas platyrhynchos). Information specific to ring‐necked ducks would help identify important influences on the rate of population growth and the direction of population change. We used data from our own research during 2008–2012, long‐term (1975–2016) survey data from northcentral Minnesota, USA, vital rate estimates from the literature, and long‐term (1987–2016) banding data to develop a population model for ring‐necked ducks. We estimated annual survival and recovery rates of after‐hatching‐year and hatching‐year female ring‐necked ducks in Minnesota. Survey results and our matrix models indicated that ring‐necked ducks are declining in the forested portion of Minnesota. Thus, we examined a boom‐or‐bust simulation scenario that might maintain a population through periodic occurrence of exceptional reproductive years in conjunction with high hatching‐year survival. Our results indicated that long‐term persistence is only expected in this population if reproductive output doubled at the same time that hatching‐year survival was at its highest value, or if the population is maintained through immigration. Sensitivity analysis indicated that unit changes in 30‐day brood survival will produce the most change in λ in the parameter space observed, although elasticity analysis indicated that proportional changes in annual survival of adult females will produce the largest proportional changes in λ. Management to improve brood survival to increase λ might include improving the habitat quality of brood‐rearing lakes, especially those with more open water and less nesting habitat than those used for nesting. Our findings might also help explain disparities between annual breeding waterfowl surveys, which indicate stable or increasing populations, and hunter experiences in the fall. In Minnesota, hunter experiences have not matched expectations based on historical fall numbers and this could occur if regional production declined and fewer young birds were available for harvest. Our findings highlight the need for further study to inform management in this rapidly changing region. © 2019 The Wildlife Society.