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We hypothesize first that the current distribution and demography of prairie foxes in North America is significantly affected by interspecific competition and, second, that intra-guild competition, for example, can be moderated by environmental factors. Although ideally desirable, ethical and logistical constraints pre-empted the possibility of testing these hypotheses through a major field manipulative experiment. We therefore designed a comparative study, contrasting the behavioural ecology of prairie foxes with and without abundant escape terrain provided by prairie dog towns. The two situations doubtless also differed in other respects, so the design of our natural experiment was not clear-cut, nonetheless, the results allow us to take a more informed view to two questions: first, can foxes evade coyotes and second, if they cannot, would coyote control be beneficial for swift/kit foxes? Although the fragmentation, perturbation, and loss of native prairie habitat is recognized as the prime factor responsible for the continental decline of the swift/kit fox complex, the consequent alteration of prairie ecosystems has also had deep indirect repercussions. The widespread changes of species richness and abundance are reflected in the shifts of the prairie canid equation. There is mounting evidence that intra-guild aggression is a major factor in carnivore communities in general, and between canids in particular. As coyotes have increased in range and numbers, they have been recognized as the main mortality factor of swift/kit foxes in most studies. If ecosystem restoration to pre-colonial conditions is limited, it is important to study intra-guild aggression involving prairie foxes, and specifically their relationship with coyotes.

We address these issues by comparing fox/coyote dynamics between two geographically and ecologically distinct study sites. The first spans the Canada/United States border encompassing portions of Alberta, Saskatchewan, and Montana. In this region, swift foxes forage in a homogenous habitat where they cope with climatic extremes on a seasonal basis. The second study site is located in the Janos-Nuevo Casas Grandes complex of Chihuahua, Mexico where the world's largest remaining prairie dog community provides food and escape terrain for kit foxes. Since 1994, seventy-six swift foxes and ten coyotes have been radio-tracked in Canada, while eleven kit foxes and eight coyotes have been monitored in Mexico. We compare several scales of interactive space utilization, den parameters, and diet between foxes and coyotes in our respective study areas. In addition, we contrast swift/kit fox survival rates and the impacts of coyote control on fox demography in Mexico and Canada.