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Wildlife Monographs

Red Fox Predation on Breeding Ducks
in Midcontinent North America

Results and Discussion


History of Midcontinent Fox Populations

Application of our findings to other time periods and to local areas requires knowledge of fox population changes and densities. Red foxes were present in nearly all parts of the midcontinent area during the present study, though densities varied greatly among areas and years. However, they have not always been numerous, major population changes will likely occur in the future.

Apparently, red foxes were absent from southern and southwestern portions of the midcontinent area during pristine times and were not abundant in the remainder of the area (Sargeant 1982). After settlement of the midcontinent area by Europeans began in the late 1800's, fox populations declined to extremely low levels; from the late 1800's to the mid-1930's red foxes were absent or uncommon in most of the area (Johnson and Sargeant 1977: 38-40, Sargeant 1982). Thus, before the 1930's red foxes had little impact on midcontinent duck populations. The duck populations, however, were subjected to predation of unknown magnitude by other canids including wolves, coyotes, gray foxes (Urocyon cinereoargenteus), and kit foxes (Johnson and Sargeant 1977 36-38, Hall 1981).

In the 1930's red fox populations began to increase in eastern portions of the midcontinent area, and by the early 1940's densities were high in many places (Sargeant 1982). The expansions began almost simultaneously in Iowa, Minnesota, eastern North Dakota, eastern South Dakota, and southern Manitoba, and extended to western North Dakota, western South Dakota, and southeastern Saskatchewan in the late 1940's and early 1950's. Populations began to increase in western Saskatchewan in the early 1960's and in southeastern Alberta in the early 1970's (Johnson and Sargeant 1977:40). The species was most widely distributed in the 1960's and early 1970's, and during that period the population of the overall area was probably at an all-time high. Because of changes in fox density, the impact of red foxes on midcontinent ducks has increased markedly since the 1930's.

Fox densities are known for few places in the midcontinent area. Scott and Selko (1939) searched portions of 2 counties in Iowa and found a spring density of 1 fox family/41 km2. Although a low density by today's standards, it was probably indicative of fox densities in large parts of the midcontinent area at that time. The only comparable data are for the Prairie Pothole Region of North Dakota for 1963-80 (Table 13). These data place in perspective fox densities in eastern North Dakota during the present study period and probably reveal the nature of fox population changes in large parts of the midcontinent area during recent times. The highest populations during this 18-year period occurred during the early 1960's and in 1973 when the present study was completed. In 1964, the spring population was estimated at 1 fox family/5.7 km2. Many longtime residents remember foxes as being abundant in the early 1960's, indicating the population was higher than average. By 1969, when the present study began, the population had declined to 1 family/20.0 km2. This was believed to be one of the lowest spring densities since the 1930's (Allen et al. 1974). From 1969 to 1973 the population increased to 1 family/7.0 km2, but by spring 1977, it was again low (1 family/20.4 km2). It has been gradually increasing since that time. We believe the principal causes for the changes were variable human-inflicted mortality rates and interspecific canid competition (Sargeant 1982).


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