Escaping intraguild predation: Mexican kit foxes survive while coyotes and golden eagles kill Canadian swift foxes
Moehrenschlager A., List R., Macdonald DW.
Although interspecific killing among carnivores can drive populations toward extinction, it is generally unknown how these intraguild interactions vary among populations, and whether the threat for vulnerable species can be mitigated. We studied imperiled populations of swift foxes (Vulpes velox) in Canada and kit foxes (Vulpes macrotis) in Mexico to determine potential differences in survival or predator-avoidance strategies. Survival rates were significantly lower in Canada than in Mexico because of mortality caused by coyotes (Canis latrans) and golden eagles (Aquila chrysaëtos), and the potential for population recovery is likely higher for the Mexican fox population. Differences in body size between coyotes and foxes, diet, group sizes, intraspecific home-range overlap, home-range sizes of coyotes, and movements of coyotes relative to foxes were similar among study areas. However, Canadian foxes had home ranges that were approximately 3 times larger than those in Mexico, and Canadian foxes were most frequently killed on their home-range peripheries. Home ranges of kit foxes decreased in size as the availability of black-tailed prairie dog (Cynomys ludovicianus) colonies increased and associated refuge holes, which foxes could use to escape predation, were significantly more abundant in Mexico than in Canada. Small home ranges of foxes probably reduced encounters with coyotes in Mexico, and a high availability of refuges likely allowed foxes to elude predators when such encounters did occur. Differences in survival of foxes relative to mortality caused by coyotes demonstrate that interactions between carnivores can vary greatly between populations and that, in some situations, vulnerable species may be able to coexist with dominant carnivores despite a lack of large-scale habitat partitioning. © 2007 American Society of Mammalogists.