A MODEL OF NORTHERN PINTAIL PRODUCTIVITY AND POPULATION-GROWTH RATE

Our objective was to synthesize individual components of reproductive ecology into a single estimate of productivity and to assess die relat ive effects of survival and productivity: on population dynamics. We u sed information on nesting ecology, renesting potential, and duckling survival of northern pintails (Anas aouta) collected on the Yukon-Kusk okwim Delta (Y-K Delta), Alaska, 1991-95, to model the number of duckl ings produced under a range of nest success and duckling survival prob abilities. Using average values of 25% nest success, 11% duckling surv ival, and 56% renesting probability from our study population, we calc ulated that all young in our population were produced by 13% of the br eeding females, and that early-nesting females produced more young tha n later-nesting females. Further, we calculated, on average, that each female produced only 0.16 young females/nesting season. We combined t hese results with estimates of first-year and adult survival to examin e the growth rate (lambda) of the population and the relative contribu tions of these demographic parameters to that growth rate. Contrary to aerial survey data, the population projection model suggests our stud y population is declining rapidly (lambda = 0.6969). The relative effe cts ori population growth rate were 0.1175 for reproductive success, 0 .117.5 for first-year survival, and 0.8825 for adult survival. Adult s urvival had the greatest influence on lambda for our population, and t his conclusion was robust over a range of survival and productivity es timates. Given published estimates of annual survival for adult female s (61%), our model suggested nest success and duckling survival need t o increase to approximately.40% to achieve population stability. We di scuss reasons for the apparent discrepancy in population trends betwee n our model and aerial surveys in terms of bias in productivity and su rvival estimates.