Effects of Coyote Control on Their Prey: a Review

Coyotes (Canis latrans) are often removed from an area because of their predatory nature, regardless of the effect such removal may have on the ecosystem. Research results concerning ecosystem changes due to coyote removal appear ambiguous; however, differing lengths of coyote control can produce different results. Short-term coyote removal efforts (5 6 months) typically have not resulted in increases in the prey base; however, long-term, intensive coyote removal reportedly has altered to alter species composition within the ecosystem. A dichotomy of views exists concerning the role of coyotes in ecosystems. Ranchers, wildlife biologists, env~ronmentalists, and urbanites have different views concerning the same animal Historically, livestock managers have been the group most concerned with coyotes because of their depredation However, with the advent of game ranching, lost wildlife revenues result~ng from coyote predation have increased the competition between human interests and coyotes (Scrivner et al. 1985). Coyotes have been linked to the decline of white-tailed deer (Odocorleus virginranlrs) (Cook et al. 197 1, Harnlin and Schweitzer 1 979, Hamlin et al. 1984), mule deer (0 . Irenrionus) (Truett 1979), and prongholm (Airtilocapra artzerrcana) (Neff et al. 1985) through predation on fawns. Coyotes were responsible for 86% of annual white-tailed deer fawn mortality in Oklahoma (Gainer et al. 1978). Although rarely observed, coyotes have been reported to prey upon adult deer (Hamlin and Schweitzer 1979, Tlvett 1979). To resolve the problem of predation on domestic livestock and wildlife, various coyote control programs have been htiated; however, most techniques have resulted in limited success (Connolly 1978). To further enhance the problem of disparate views, coyote control is not a widely accepted practice by the populace at present. A growing concern for anunal welfare has caused the American public to re-assess its attitude toward coyote control All lethal methods, and most nonlethal methods, of coyote control receive little acceptance from the general public (Arthur 198 1) Vaious animal activist groups have questioned the accuracy of the number of livestock reported lost to predators and contend that ranchers exaggerate their losses to justify the need for predator control (Baker 1985). Defenders of Wildl~fe (1978) contended that not all coyotes prey on livestock, and that mass eradication is like "randomly killing large numbers of people when a murder IS committed in the hopes of killing the murderer " Animal Damage Control (ADC) personnel argue that coyote eradication is not their intended goal and that they only kill about 18-29% of the coyote populat~on in 13 cooperating western states (U S. F ~ s h and W~ldlife Service 1978) Connolly and Longhurst (1 975) examined the effect of control on coyote populations using a simulation model and dete~mined that a minimum annual removal of 75% of the breeding population was needed to consistently lower the coyote density. Wayne Pacelle, national director of The Fund for An~mals, has used this information as an argument against ADC, stating that because ADC only removes 18-29% of the coyote population, the entire coyote removal program 1s not only doomed to fail, but is also a waste of tax dollars. Defenders of W~ld l~fe (1 978) estimated that the average cost of killing coyote is approximately $1,000. Consequently, in their view, it would be less of an economic burden on the taxpayers to pay ranchers for livestock killed by coyotes. C e ~ t a ~ n a imal activist groups argue that the coyote IS a valuable p a t of the ecosystem and should not be persecuted by man (Defenders of Wildlife 1978, Humane Society 1978, S~en-a Club 1978). Such groups contend that even ~f coyote control programs were successfhl, it would increase overgrazing and ultimately decrease livestock productivity (Defenders of Wildlife 1982). Their reasoning is that reduced coyote populations allow rodent and rabbit populations to increase, which in turn, will increase competition with livestock for available forage, decrease livestock productivity, and promote rangeland degradation. Ranchers have countered this argument by stating that coyote control has no effect on ecosystems. Coyotes are resilient; they respond to control efforts with gl-eater litter sizes (Knowlton 1972). Therefore, coyote removal could never reach eradication levels which would affect the ecosystem Failure of ranchers to accept coyote predation as a natural process within a healthy ecosystem, and failure of environmentalists to realize that coyote predation can be an economic burden to some ranchers has polanzed these 2 groups (O'Gara 1982). This dichotomy is detrimental to solving the issue of coyote control because efforts of each group are directed at countering the other group's opinion, rather than at a cooperative effort to solve this environmental pi-oblem Few studies have been designed to investigate the effects of coyote removal on the remaining ecosystem It is the objective of this paper to give a review of the literature concerning coyote-prey interactions and attempt to explain why I-esults from these studies appear ambiguous.