Impact of Red Fox Predation on the Sex Ratio of Prairie Mallards
Mallard Population Trends
History tells little of the actual number of ducks present during early times. We presume that populations fluctuated greatly, primarily in conjunction with climatic conditions but because the environment was unaltered and hunting was very limited, mallard densities at times probably exceeded those observed during recent years. Yet, we do not know how the mallard, noted for its adaptability, responded to agriculture, which altered the fertility of many wetlands and provided the grain crops now used extensively by mallards during spring and fall. Kiel et al. (1972) summarized descriptions of waterfowl abundance in the Prairie Pothole Region, with emphasis on Manitoba, for the 1800's and early 1900's. Their accounts suggest that ducks were abundant during most years, but that during occasional drought periods populations were reduced.
No one knows the magnitude of the various mortality factors that affected mallards during Resettlement times, but many of the factors important today were either absent or of different consequence then. In particular, the mallard was unaffected by the activities of modern man; there were no shotguns, mowing machines, power lines, or automobiles. Furthermore, the composition and density of predators were unlike those of today. Mallard densities and sex compositions were thus determined by mechanisms of a different sort and magnitude than operate now. Agriculture and predation are now believed to limit production severely, but other factors such as limited food supplies on wintering and breeding grounds may have had an even more stringent effect during pristine times.
Beginning with settlement, mallards and other waterfowl were extensively hunted for food, sport, and profit (Johnson 1961). Man's ability to harvest waterfowl increased dramatically with improved hunting paraphernalia and transportation. The impact of hunting on populations during the late 1800's and early 1900's is unknown, but it was of sufficient public concern to cause legislators to enact increasingly restrictive laws and regulations to control the harvest (Anderson and Henny 1972). The first waterfowl regulations in North Dakota, written into the territorial laws of 1887, stipulated that no more than 25 birds could be killed in one day (Johnson 1964). Early photographs provide vivid evidence that then as today the mallard was a favored bird and often taken in large numbers (Fig. 11).
During the severe drought years of the mid-1930's, waterfowl populations in North America reached their lowest numbers in recent history (Anderson and Henny 1972). Systematic waterfowl counts were not made until the mid-1950's when large-scale annual surveys were initiated. Since then, estimated spring populations of mallards have ran from a low of 7.1 million in 1965 to a high of 1 million in 1958 (Pospahala et al. 1974). Densities during 1955-73 ranged from 1.5 to 4.2 pairs/km2 in the Prairie Pothole Region of North Dakota and up to 9.7 pairs/km2 in prairie provinces of Canada.
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