The swift fox (Vulpes velox) was classified in 1995 as a candidate for listing under the Endangered Species Act. Since then, several studies have addressed survey methods for monitoring swift fox populations. The purpose of this paper is to assist field researchers in documenting the presence of swift foxes by identification of recently active den sites. We propose that swift foxes have unique external den characteristics that can be distinguished during aerial surveys. We collected data from 30 swift fox den complexes on both continuous rangeland and landscapes fragmented by cropland in northwest Texas. There were no differences in den characteristics between landscape types (P > 0.10). The number of openings per den ranged from 1 to 8 and had an average opening height of 20 cm. As number of openings increased, the maximum distance between openings also increased (r = 0.88, P < 0.001). One of the most distinguishing characteristics of swift fox dens was their dirt tailing. Of 74 den openings examined, all but 3 had conspicuous dirt tailings that averaged 267.0 cm long by 63.4 cm wide. We found that swift fox den openings were smaller than those of coyotes (Canis latrans) and red foxes (Vulpes vulpes), 2 species that can be sympatric with swift foxes. We suggest that aerial den searching followed by ground verification may be an effective technique for determining presence of swift foxes in areas of short-grass prairies and fragmented habitats.
McGee, Brady K.; Nicholson, Kerry L.; Ballard, Warren B.; and Butler, Matthew J.
"Characteristics of swift fox dens in northwest Texas,"
Western North American Naturalist: Vol. 66
, Article 10.
Available at: http://scholarsarchive.byu.edu/wnan/vol66/iss2/10