Fox-Prey Relationships in Eastern South Dakota

Relationships between red foxes (Vulpes fulva) end their principal prey, particularly ring-necked pheasants (Phasianus colchicus), were studied on four units in eastern South Dakota from December 1964 to September 1966. Each unit was composed of a 100-square-mile reduction area, on which fox populations were reduced, and a 100-square-mile check area, on which fox populations were not reduced for the study. Indices to populations of foxes, pheasants, mice, eastern cottontails (Svlvilagus floridanus) and whitetail jackrabbits (Lepus townsendi) were obtained and used to evaluate food habits and the effect of predator reduction on prey populations. Four-hundred seventeen stomachs and 104 female reproductive tracts from foxes taken in reduction areas and in or near check areas were examined. Fox densities in the study areas in 1966 were low compared to past densities in certain other states. Aerial den counts showed that active fox dens were 67% fewer on the reduction than on the check areas in 1966. Fox reproductive rates increased in the year following population reduction. Soils, topography, and cover type were the most important factors determining the suitability of an area for denning. The breeding season of foxes in South Dakota began earliest in the southeastern part of the state and progressed northwestward. Initially, high pheasant populations were present in Units 2 and 3, whereas Unit 4 was intermediate in pheasant numbers and Unit 1 was considered to be in marginal pheasant range. Sumner indices of adult pheasants and of broods declined considerably in all but one instance on one unit from 1964 to 1965. Winter storm mortality contributed to further declines in adults in Units 1 and 2 from the summer of 1965 to the summer of 1966; however, indices for adults during this period increased in Units 3 and 4. Number of broods declined or re111ained the same from 1965 to 1966. Results of night spotlight counts of jackrabbits and cottontails were highest in Unit 3 and the reduction area of Unit 4. Significant increases were observed in jackrabbit indices from 1965 to 1966 in the reduction area of Unit 3. Deer mice were the most abundant small mammal in the study units. Total numbers taken in the snap-trap surveys declined from 1965 to 1966, particularly in Units 3 and 4. Meadow voles were locally abundant, depending on the occurrence and distribution of suitable habitat. Frequency of meadow vole sign increased from 1965 to 1966 in all units except Unit 2. Mice, pheasants, rabbits and insects were the most important fox food items. Mice and rabbits were staple foods at all seasons. Heavy predation on young rabbits during the denning season was noted. Pheasants were important in the diet in 1965 when the birds were fairly common. The high incidence of pheasant in fox stomachs from eastern South Dakota probably reflected the availability of the birds. It appeared that foxes had an easy time obtaining pheasants due to the low degree of competition between individual foxes and the large number of pheasants. The decline of pheasants from 1964 to 1965 was reflected by a considerable decrease in occurrence of pheasant remains in fox stomachs. A spring survey of food remains at active fox dens gave a biased impression of feeding trends as compared to results of stomach analyses. Mice young rabbits and insects were under-represented or absent from den debris but were present in stomachs taken at this season