Little information has been published about the life history and behavior of the swift fox, Vulpes velox . This lack of information can be attributed, in part, to the fact that for many years there have been few swift foxes to observe. Swift foxes were nearly extirpated from a large portion of their range at one time. Some workers, including myself, are of the opinion that this depopulation was brought about by coyote control measures. Robinson (1953), on the contrary, states that populations of small predators are increased because of coyote control measures. Be that as it may, the observations herein reported are on the denning and associated behavior of the swift fox. These observations were made principally in Hansford County, Texas, at various times from December, 1953 to September, 1956. Approximately 25 occupied dens were observed. These dens were all in open, sparsely vegetated habitats, on sloping plains, hill tops, or other well-drained situations. Grater (1939), however, reported seeing a pair of kit foxes, Vulpes macrotis , move their whelps to a new den because the old den was flooded by high water. A mound of earth, from 2 to 12 inches high, typically extended from 2 to 4 feet from each entrance. There were one or two open entrances for each den in the spring and some dens, probably more than one year old, had also as many as four plugged entrances. The entrances were circular or slightly ovoid and were from 7 …