Culpeo (Dusicyon culpaeus) and South American grey fox (D. griseus) have comparable ranges, but the factors determining local and geographic distribution are unknown. I first review the best documented cases of sympatry in canids, and discuss the implications this analysis has on canid conservation. I then compare the behavioral ecology of grey and culpeo fox in Torres del Paine National Park, Chile and review hypothetical factors that determine their distribution when sympatric;The number of sympatric canids per area seems to be determined by a combination of biogeographical history, human intervention, and environmental diversity and productivity. Sympatric canid species either segregate in different habitats or utilize different food resources, but do not do both. Interactions among sympatric canid species may have important conservation and management implications because canid community structure often changes after a species' range expansion, extirpation, or reintroduction;From 1986 through 1989, 44 grey and 19 culpeo fox were monitored using radio telemetry techniques. European hare (Lepus capensis) was the most common vertebrate found in grey fox feces (45%), followed by guanaco (Lama guanicoe, 14%) and Akodon species (13%). European hare accounted for 69% of the prey items and rodents 20% in culpeo fox feces. Yearly diets were significantly different. Grey fox were more omnivorous than culpeo fox. I suggest that differences in feeding habits were attributable to differences in food availability;Home ranges of culpeo fox were significantly larger than those of grey fox, but did not differ between sexes or among seasons. Home ranges of both species were interspersed but did not overlap. There were significant differences in fox use of habitat. Grey fox were located more in upland shrub transition habitat and in areas of medium habitat-density. Culpeo fox were found more in thickets of trees and in areas of high vegetative-density. Habitat use was related to availability. Interference competition by culpeo fox or exploitation competition may have been important in determining fox distribution. Based on fox energy requirements, it seems that the distribution of grey and culpeo fox in southern Chile is determined in part by the distribution and local density of European hare.