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The relationship of vegetation-snow-small mammal demographics was investigated in swift fox (Vulpes velox) habitat along roadside ditches, coulees, and uplands in the mixed-grass prairies of southern Alberta and Saskatchewan during early (November), mid (January-February), and late (March-April) winter of 1995-1996. Mark-recapture methods of trapping resulted in a total of 163 small mammals in 9,360 trap-nights. Species diversity was low and deer mice (Peromyscus maniculatus) comprised 96% of the total catch, while shrews (Sorex sp.) constituted the remaining 4%. Peromyscus populations were localized during the winter and reproduction ceased from early November to early April. In early winter, P. maniculatus was more frequently captured in uplands, but in late winter, it was more abundant in linear (roadside and coulee) habitats in regions with less snow cover. Early winter trapping resulted in highest abundance values while there was a significant decline from early to late winter, except in one study area, where spring-like-conditions arrived sooner, at which time males traveled greater distances. It was hypothesized that low prey abundance, especially during the latter part of winter, probably contributes to higher swift fox mortality.