Productivity and Population Increase of Subarctic Breeding Canvasbacks

Abstract

Effective waterfowl management is dependent upon adequate population and productivity information from all portions of a species' breeding range, but productivity of canvasbacks (Aythya valisineria) breeding in the boreal forest has not been assessed adequately. We measured indices of productivity for canvasbacks breeding in the subarctic boreal forest near Yellowknife, Northwest Territories, during 1985-95. Mean clutch size was 7.05 ± 0.16 eggs. Size of broods was 4.25 ± 0.30 for Class I and 4.00 ± 0.37 for Class II. Brood size values generally were lower than those measured in parkland habitats. Apparent nest success averaged 69% and was consistently high. Production of broods per pair (0.3) and young per pair (1.4) was low but similar to values reported for some parkland breeding populations. Comparison of survey data between the periods 1962-65 and 1985-95 indicated a 10-fold increase in the number of canvasback pairs and broods on our study area. Productivity was inadequate to account for this increase, which suggests that high survival rates or immigration were contributing factors.