HETEROGENEOUS SURVIVAL RATES OF MALLARDS (ANAS-PLATYRHYNCHOS)

We analyzed data of adult mallards (Anas platyrhynchos) banded throughout North America during the past 30 years, using a model developed to estimate heterogeneity in survival rates of marked individuals. The model incorporating heterogeneity in survival rates was often the most parsimonious model for the data sets analyzed, thus constituting an advancement over previous band-recovery models. Likelihood-ratio tests indicated that significant amounts of heterogeneity existed in die data sets analyzed. We were unable to detect significant differences in heterogeneity between sexes or between birds banded prior to the hunting season (July - September) and after the hunting season (January - February) in the same areas. Heterogeneity varied widely among banding areas. Changes in reporting rates confound the estimation of heterogeneity. Adjustment of estimates of heterogeneity for differences in recovery rates in the first year after banding and subsequent years results in lower estimates of heterogeneity for mallards. Coefficients of variation of survival rates for adult mallards, adjusted for variation in recovery rates, varied from 18 to 25%.