Long-Term Wetland-Waterfowl Trends in Saskatchewan Grassland

Abstract

Wetland numbers, breeding duck populations, and brood production were monitored on a relatively pristine tract of grassland in south-central Saskatchewan from 1950 to 1975. Yearly numbers of wetlands (an index of wetland conditions) decreased an average of 55% between May and August 1950-75, but yearly numbers of May and August wetlands were positively correlated. Correlations among yearly numbers of adult ducks, their production, and yearly wetland numbers suggested that waterfowl recruitment from prairie environments with dynamic wetland regimes is a consequence of breeding population size, individual reproductive performance, and the persistence of suitable wetland conditions between spring and late summer. Duck populations that exploit variable prairie environments may exemplify temporally dynamic reproductive strategists and perhaps should not be labeled as either ror K-strategists. Long-term duck population trends for the grassland site were compared with those from parkland areas in Alberta, Saskatchewan, and Manitoba. Both grassland and parkland populations increased with favorable wetland conditions during the 1950's but decreased during the drought of the early 1960's. Wetland conditions improved markedly during the late 1960's and early 1970's at the grassland site, and pair densities of most duck species were higher in the early 1970's than in the 1950's. In contrast, parkland populations generally decreased between the 1950's and 1970's. Relative abundances of mallard (Anas platyrhynchos) and bluewinged teal (A. discors) were similar during the 1950's and 1970's at the grassland site, whereas blue-winged teal outnumbered mallard at the parkland sites. The relatively pristine upland and wetland habitat of the grassland site, unlike the agriculturally impacted parkland sites, may have positively influenced duck populations in the grassland site, implicating increased need for complexes of quality wetland and upland habitat for enhancement of duck production. J. WILDL. MANAGE. 49(1):212-222 Aerial and ground surveys of waterfowl populations have been conducted annually in North America since the 1940's to provide data on population levels for management of waterfowl hunting. Intensive ground surveys also have been conducted on selected important waterfowl breeding areas in prairie-parkland Canada and northern United States. These intensive studies were designed to fulfill several objectives: (1) appraise breeding population size and brood production; (2) assess habitat conditions; and (3) make air-ground comparisons of the counts. However, of 15 intensively studied areas identified by Anderson and Henny (1972), few studies were long-term. Paramount among these long-term efforts were the studies of waterfowl and habitat trends in the Canadian parklands between the early 1950's and late 1970's by Smith (1971) and Stoudt (1971, 1982). Here we document trends in wetland conditions, breeding duck populations, and brood production for a Saskatchewan grassland area surveyed annually between 1950 and 1975. Unlike much of Canada's southern prairie, this area has remained relatively undisturbed. To reveal fac ors associated with population trends, we also test for correlations between selected population and environmental variables and compare trends in duck populations and production fo the grassland area with trends documented by Trauger and Stoudt (1978) for Canadian parkland areas. This project and publication costs of the manuscript were funded by Ducks Unlimited Canada. The senior author sincerely thanks the Campbell families for granting permission to conduct the study on their lands and for their generous hospitality throughout its duration. The following people contributed to the project whi e it was in progress: J. R. Caldwell, D. F. Hooey, A. J. and J. Macaulay, D. Peterson, A. Spelay, G. H. Staines, R. T. Sterling, L. Sutton, and E. M. Wright. We are grateful to M. G. Anderson, D. H. Arner, E. A. Gluesing, E. P. Hill, J. D. Nichols, T. D. Nudds, M. W. Weller, and R. A. Wishart for comments.on the manuscript. J. W. Nelson and T. P. Sankowski execut d statistical analyses. P. E. Alvestad, J. T. Glenn, and M. L. Hilland typed the manuscript. Both authors contributed significantly to this paper. W.G.L. administered the study, collected the data, and prepared a preliminary re'Present address: Department of Wildlife and Fisheries, Mississippi State University, P.O. Drawer LW, Mississippi State, MS 39762.