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We studied the ecology of swift fox on the Pinon Canyon Maneuver Site (PCMS) in southeastern Colorado from March 1986 to September 1987. Forty-two foxes were captured 162 times; 23 were radio-collared. Mean minimum convex polygon home range size of 5 adult swift fox was 29.0 km2 (range = 12.8 to 34.3 km2) and although home ranges of adjacent social groups overlapped, core areas described by 50% harmonic means were almost entirely exclusive. Swift fox diet (as determined from scats) consisted primarily of small and medium-sized mammals (monthly mean % volume = 64%), arthropods (Χ̅ = 19%), and small birds Χ̅ = 8%). Mean litter size (n = 5) was 3.4 (range = 2 to 5) and not all females produced litters. Kaplan-Meier estimates of annual survivorship were 0.45 for adults (n = 8) and 0.126 for juveniles (n = 14). Predation by coyotes was the primary cause (63%) of fox mortality. Fox carcasses collected off of the PCMS (where coyote hunting and trapping were permitted) indicated that juvenile mortality due to predation by coyotes was lower there than on the study site. We conclude that where coyotes are abundant, predation by coyotes is a significant source of mortality for swift fox and that den availability might be an important aspect of swift fox management.