Temporal variation in survival and recovery rates of lesser scaup

Abstract

Management of lesser scaup (Aythya affinis) has been hindered by access to reliable data on population trajectories and vital rates. We conducted a Bayesian analysis of historical (1951–2011) band-recovery data throughout North America to estimate annual survival and recovery rates for juvenile and adult male and female lesser scaup to determine if increasing harvest or declining survival rates have contributed to population changes and to determine if harvest has been primarily additive or compensatory. Annual recovery rates were low, ranging from 1% to 4% for adults and 2% to 10% for juveniles during most years, with trend models indicating that recovery rates have declined through time for all age–sex classes. Annual survival (mid-Aug to mid-Aug) averaged 0.402 (σ ̂ 0.043) for juvenile males, 0.416 (σ ̂ 0.067) for juvenile females, 0.689 (σ ̂ 0.109) for adult males, and 0.602 (σ ̂ 0.115) for adult females, where σ ̂ represents an estimate of annual process variation in each survival rate. Annual survival rates exhibited no evidence of long-term declines or negative correlations with annual recovery rates (i.e., an index of harvest intensity) for any age–sex class, suggesting that declining fecundity was the most likely explanation for population declines during 1975–2005. We conclude that hunting mortality played a minor role in affecting population dynamics of lesser scaup and waterfowl managers could take a less cautious approach in managing harvest, especially if recruiting or maintaining waterfowl hunters are viewed as important management objectives.