The dynamics of a kit fox, Vulpes macrotis nevadensis, population in western Utah was studied for four years coincidental with a population decline and initial recovery stages of the black-tailed jackrabbit, Lepus callfornicus desericola. The study began at least one year after the rabbits began decreasing. The presence of nonbreeding adult vixens seemingly represented the initial response of the foxes to a failing food supply. This was followed by a decline in the numbers of adults and then by smaller and fewer litters. The first sign of recovery was a return to normal sized litters. Data on natality, sex ratios, age structure, and population turnover are presented. Foxes were apparently unable to sustain themselves on available secondary prey such as kangaroo rats and appeared incapable of making adjustments in their hunting habits that enabled them to take advantage of diurnal prey.