Seasonal Food Habits of Swift Fox (Vulpes Velox) in Cropland and Rangeland Landscapes in Western Kansas

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ABSTRACT.-Food habits of swift foxes (Vulpes velox) occupying two distinct landscapes (dominated by cropland versus rangeland) in western Kansas were determined by analysis of scats collected in 1993 and 1996. Frequencies of occurrence of prey items in scats were compared between cropland and rangeland areas by season. Overall, the most frequently occurring foods of swift foxes were mammals (92% of all scats) and arthropods (87%), followed by birds (24%), carrion (23%), plants (15%) and reptiles (4%). No differences were detected between landscapes for occurrence of mammals, arthropods or carrion in any season (P - 0.100). Plants, specifically commercial sunflower seeds, were consumed more frequently in cropland than in rangeland in spring (P =' 0.004) and fall (P = 0.001). Birds were more common in the swift fox diet in cropland than in rangeland during the fall (P = 0.008), whereas reptiles occurred more frequently in the diet in rangeland than in cropland during spring (P = 0.042). Variation in the diet of the swift fox between areas was most likely due to its opportunistic foraging behavior, resulting in a diet that closely links prey use with availability.

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. …