Northern Prairie Wildlife Research Center
Patterson (1979) contrasted the life histories of canvasbacks and mallards (Anas platyrhynchos) and described canvasbacks as "k-strategists" on the basis of their longevity, more specialized habitat requirements, use of more stable wetland habitats (Stoudt 1982, Johnson and Grier 1988), and lower probability of female breeding success as yearlings. Thus, canvasbacks were expected to have a lower reproductive potential than mallards or other "r-strategists." Bailey (1981) assumed younger canvasback females to be less persistent or successful breeders than older females, but also predicted that reproductive rates of a population should improve with habitat conditions.
Factors affecting breeding performance and productivity of canvasbacks are poorly understood due to insufficient information about known-aged individuals and lack of long-term studies. Earlier assumptions of lower reproductive effort or success by young females (Patterson 1979, Bailey 1981) were based on few data (Olson 1964) and similarity to related species. Hochbaum (1944) and Stoudt (1982) suspected that most yearlings nested but lacked direct evidence. The purpose of our study was to test whether return rates, arrival and nest initiation dates, clutch size, nest parasitism, nest success, hen success, and ducklings/brood were independent of the age of canvasback females and various environmental factors during the breeding season in southwestern Manitoba.
This project was funded by a Special Canvasback Research Program initiated in 1972 by the U.S. Fish and Wildlife Service. We are grateful to H. K. Nelson, W. R. Goforth, and R. C. Stendell, former Directors of Northern Prairie Wildlife Research Center, for their support throughout the study. The long-term studies of canvasback breeding habitat requirements conducted by J. H. Stoudt provided direction for this work. Stoudt's interest, encouragement, and assistance during the study are greatly appreciated. A. S. Hawkins provided invaluable historical perspectives on waterfowl populations and habitat conditions in the study area. Field assistance was provided by R. Bromley, J. Cameron, L. Deede, H. A. Doty, T. Fondell, D. S. Gilmer, T. Jasikoff, D. J. Johnson, M. R. Miller, J. H. Noyes, F. Roetker, G. Simard, and L. W. Vanderhoef. We are grateful to M. G. Anderson and the Delta Waterfowl and Wetlands Research Station for their assistance throughout the study. T. L. Shaffer, D. J. Twedt, and K. M. Kraft provided statistical assistance and reviews. Discussions with, and manuscript review by, H. F. Duebbert, G. M. Haramis, C. E. Korschgen, J. T. Lokemoen, and J. Y. Takekawa are appreciated.