Coyotes in the United States and Canada affect the populations, habits, and habitats of different varieties of foxes in different ways. Many studies have been conducted in the past decade attempting to understand the relationships between the coyotes and different species of foxes, including the kit fox, the red fox, and the gray fox. The results of these studies have provided some interesting correlations between coyote and fox populations and lifestyles.

P.J. White and Robert A. Garrott (1994) hypothesize that prey abundance seems to be the major factor that regulates kit fox populations. White and Garrott cite previous studies from the past two decades that mark the decline of the San Joaquin kit fox population coinciding with declines in the abundance of rodents and rabbits, which comprise the diet of kit foxes in the San Joaquin Valley of California. They explain that biologists thus posited that prey declines eventually led to decreased fox abundance. Yet White and Garrott believe that other factors must be involved that account for the sometimes ambiguous and fluctuating data involving fox population and prey availability. They conducted a study measuring rabbit abundance and kit fox density, which showed a strong positive correlation between the two factors and established that kit fox populations may fluctuate in response to extrinsic environmental factors that alter the abundance of their primary prey. For kit foxes, prey abundance seems to be affected little by coyotes because kit foxes have adapted to coexist with coyotes in several ways. One of these ways involves the differences coyotes and kit foxes display in habitat use. Using evidence and testimony from well-known researchers on the subject, P.J. White and Brian Cypher, Jeffrey Cohen (1998) explain that coyotes spend more time in the hills whereas kit foxes are found mostly often in the valleys. He goes on to explain that these habitat differences lead to varying food preferences. A coyote's diet consists mainly of rabbits, which are found for the most part in hilly areas, as well as larger prey such as deer. Kit foxes, however, prey mostly on small animals such as rodents, as well as insects. P.J. White, Katherine Ralls, and Robert Garrott (1994) also explain that kit foxes coexist well by exploiting certain prey species better than coyotes. They go on to explain that the red fox, a larger species of fox than the kit fox, has not adapted to living in the same area as the coyote partly because of its high dietary overlap with that of the coyote and its inefficiency at exploiting unfamiliar prey types. Like the kit fox, the gray fox can an over-lapping habitat with the coyote in part because its diet consists mainly of forest rodents, whereas the coyote's consists of larger prey species.

In addition to affecting the kinds of and amount of prey different species of foxes eat, coyotes also affect where and how the foxes live. Just as kit foxes use habitat and diet adaptations to facilitate coexistence with coyotes, they have also adapted behaviors to help them live more harmoniously with coyotes. Jeffrey Cohen (1998) cites that kit foxes dig many dens throughout their home range and use them year-round as escapes from the much larger coyotes. Cohen explains that gray foxes have learned a similarly effective technique for avoiding coyotes while still remaining in the shared territory. They climb trees, a skill that coyotes lack, to avoid danger. Again, red foxes lack these adaptive advantages that allow kit and gray foxes to maintain the same habitats as coyotes while also allowing them to often avoid direct physical attacks. They neither burrow dens nor climb trees. They also have a strong dietary overlap with that of the coyote. Thus they are more vulnerable to competitive exclusion by coyotes and as the coyote population increases, the red fox is pushed from more and more of its natural habitat, leading to a decrease in the red fox population.

Yet besides these indirect affects coyotes have on fox population size, competition among canids can be deadly. Jeffrey Cohen (1998) explains that competition in which individuals of one species prevent or limit the use of a resource (food or land in this instance) by individuals of another species is called interference competition. This interference competition manifests itself in individual coyote attacks on foxes, attacks that are sometimes fatal. Yet Cohen notes that coyotes do not usually kill foxes for food. Coyotes do not eat most of the kit foxes they kill, and even when they do eat them, they do not eat the entire animal. While admitting that prey abundance is the most important factor affecting kit fox population density, P.J. White (1997) notes that coyote attacks constitute the single major cause of death among kit foxes. In their study, White, Ralls, and Garrott conclude that during extended times of prey scarcity, coyote-induced mortality could contribute greatly to kit fox population declines, yet with the increase of prey abundance, the affects of coyote-induced mortalities on kit fox population dynamics would be greatly reduced. Similarly, White and Garrott (1998) describe coyote-induced fox deaths as an additive rather than compensatory mortality factor. For, as coyote-related mortalities increased, the proportion of fox fatalities due to causes other than coyotes remained constant. White and Garrott also find in their analysis a strong indication that the proportion of foxes killed by coyotes may be highly density-dependent at low to moderate fox population densities. White and Garrott conclude that the major factors regulating kit population dynamics are prey abundance and behavioral spacing mechanisms. They also conclude that coyote- induced mortality is a less direct, less dominating factor, but that it still may keep kit fox populations at lower densities, especially in low density fox populations and during times of prey scarcity.

Literature Cited:

Cohn, J. 1998. A dog-eat-dog world? BioScience 46: 430-434.

White, P.J., and Garrott, R.A. 1997. Factors regulating kit for populations. Canadian Journal of Zoology 75: 1982-1988.

White, P.J., Ralls, K., and Garrott, R.A..1994. Coyote-kit fox interactions as revealed by telemetry. Canadian Journal of Zoology 72: 1831-1836.