Tests of Compensatory vs. Additive Hypotheses of Mortality in Mallards

Band recovery data from over 410 000 adult Mallards (Anas platyrhynchos) banded in North America between 1950 and 1979 were analyzed to examine the effect of exploitation on annual survival rate. Two extreme hypotheses were defined; completely compensatory, and totally additive, and an explicit mathematical model was presented to represent each hypothesis. Comparison of the values of the log—likelihood functions at their maxima allowed discrimination between the two models (hypotheses). Extensive Monte Carlo studies were made on the performance of the discriminant test and the power of the test under the two extreme hypotheses and a range of intermediate hypotheses. The results of the discriminant tests on the data agreed closely with the expected performance of the test if the true underlying process was compensatory. We rejected the hypothesis of total additivity (P = .001). Instead, it appears that hunting mortalities are largely compensated for by other forms of mortality.