Seasonal Food Habits of Swift Fox (Vulpes velox) in
Cropland and Rangeland Landscapes in Western Kansas
Introduction
The swift fox (Vulpes velox) once occupied most of the shortgrass and portions of the mixed-grass prairies of the Great Plains in North America (Egoscue, 1979). Settlement of the prairies led to declines in swift fox populations; their numbers were dramatically diminished in parts of the region by the late 1800s (Baker, 1889; Long, 1965; Lechleitner, 1969; Hillman and Sharps, 1978; Zumbaugh and Choate, 1985). Many factors were likely responsible for the decline including inadvertent poisoning (aimed at wolves [Canis lupus] and coyotes [C. latrans]), intense trapping, and habitat changes with an associated loss of prey species (Jones et al., 1983:257; Scott-Brown et al., 1987). Currently, the swift fox is a candidate species with a "warranted but precluded" recommendation for listing as endangered under the Endangered Species Act (Federal Register 60(116):31663-31666).
Factors limiting expansion of swift foxes into unoccupied portions of their historic range are unknown and may be a key to the conservation of this species. Optimal habitat for swift foxes is believed to be shortgrass prairie with relatively level terrain and available holes for shelter and protection (Scott-Brown et al., 1987). However, apparently healthy populations also occur in the agricultural landscape of western Kansas (Sovada et al., 1998). This successful occupation of a highly cultivated landscape may be unusual in the current distribution of swift foxes in North America (see Swift Fox Conservation Team, 1997). It is not clear why mixed agricultural areas in other parts of the swift fox distribution are not supporting populations of swift foxes. It has been suggested that the practice of dryland winter wheat/fallow rotation characteristic of the agricultural landscape that sustains swift foxes in Kansas may be important to the persistence of foxes in the area (Fox and Roy, 1995). Recovery plans and efforts for swift fox conservation require an understanding of the relative importance of various factors limiting swift fox from establishing, maintaining, and expanding their distribution throughout their historical range.
Swift foxes, like other North American canids, are opportunistic foragers, feeding on a wide variety of mammals, arthropods, birds, plants and carrion. Available information about food habits of swift foxes is limited and has largely been documented for populations occupying shortgrass prairies (Cutter, 1958a, b; Kilgore, 1969; Zumbaugh et al., 1985; Uresk and Sharps, 1986; Hines and Case, 1991). Information is not available for swift foxes occupying areas that are largely cultivated. The generalist foraging behavior of swift foxes make food an unlikely limiting factor, yet there is no evidence to refute or support food availability as a reason for limiting population expansion. Evidence from kit foxes (Vulpes macrotis) suggests that food scarcity may result in temporary or local declines (White and Ralls, 1993). It is not known if lack food resources or other factors inhibit swift foxes from pioneering into agriculturally mixed landscapes located adjacent to grasslands that support swift fox populations.
We compared food habits of swift fox populations occupying both highly cultivated and predominantly rangeland (shortgrass prairie) landscapes in western Kansas. We analyzed the contents of swift fox scats to determine if food habits were different for swift foxes occupying each landscape and identify food resources that might be distinctive to a cultivated landscape. We compared diets in the cropland and rangeland landscapes by season.
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