COTT E. HENKE, Campus Box 218, Caesar Kleberg Wildlife Research Institute, Texas A&M University- Kingsville, Kingsville, TX 78363.
Abstract: 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 (< 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, environmentalists, 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 resulting from coyote predation have increased the competition between human interests and coyotes (Scrivner et al. 1985)...... Texas Studies A total of 328 coyotes was removed during April, 1990 – January, 1992. Coyote abundance was reduced by 48% on the removal areas, as estimated from scent station lines, vocalization rates, and scat transect counts. After 9 months of removal effort, rodent species richness and diversity declined on removal areas, while rodent density and biomass, percent of kangaroo rats (Dipodomys ordii) within the rodent population, and black-tailed jackrabbit (Lepus californicus) density increased on the removal areas. Abundance and density of species on the non-removal areas remained fairly stable throughout the study. Cottontail rabbit density, and raptor richness, diversity, and density were relatively unaffected by coyote removal. Henke (1992) believed that kangaroo rat populations irrupted on coyote removal areas. This appeared to create intense competition among the 12 species of rodents found in the area, and eventually lead to the exclusion of the other rodent species from the area. Henke (1992) also noted that coyote removal appeared to cause a 320% increase in jackrabbit density and suggested that altered jackrabbit behavior due to a lack of coyote predation risk could increase competition with livestock for available forage. He speculated that such dramatic changes in the structural composition of the food web would lead to instability within the ecosystem..... Conclusion Although the results of these studies appear ambiguous at first glance, differences in methodologies among studies can explain the various outcomes. The Texas studies which involved short-term (< 6 months) coyote removal programs did not note differences in rodent and lagomorph populations. However, those studies which consistently removed coyotes throughout the year began to realize population-level changes after a minimum of 9 months of coyote removal. Although white-tailed deer and bobwhite quail reproductive success increased with coyote removal, overall population densities for both species remained unchanged. This implies that a compensatory mortality mechanism is involved with these populations and that potential population increases of certain game species due to coyote removal are short-lived. All studies indicated that coyote control caused an immigration of coyotes into the removal areas. Coyote population densities returned to pre-removal levels typically within 3 months after removal efforts ceased. Therefore, short-term coyote removal programs typically are not sufficient in reducing coyote density and, therefore do not alter ecosystem composition. However, intensive, long-term coyote removal has been successful in reducing coyote populations by over 40%, which has resulted in prey-base increases. The intended goals of coyote control need to be determined prior to the onset of removal efforts. If the management objective is to reduce livestock losses caused by coyotes, then an intensive, short-term removal program may provide immediate relief of depredation just before and after parturition. However, if the coyote removal is practiced year-round, microherbivore populations may potentially increase; increased competition for forage with livestock may result. Consequently, a reduced stocking rate then may be required to offset competition, which may negate the number of livestock saved from predation. If the goal is to increase the harvestable surplus of a game species, then it must first be determined that coyote control will increase the numbers of the target species. Next, can the additional animals be supported by the habitat? Finally, will predation as a mortality source be replaced with other mortality factors acting in a compensatory manner? Until these questions can be answered, then coyote removal would not be warranted. Click HERE for the full paper.