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Direct effects of predation (i.e., killing of animals) can result in significant economic losses to livestock producers. A recent publication by the USDA, Wildlife Services (2002) identified the following losses: (1) livestock losses attributed to predators, predominantly coyotes (Canis latrans), reach about $71 million annually; (2) cattle and calf losses to predators in the United States totaled 147,000 head during 2000. A National Agricultural Statistics Service (NASS) study valued these losses at $51.6 million; (3) sheep and lamb losses to predators in the United States totaled 273,000 in 1999. A NASS study valued these losses at $16.5 million; (4) In Arizona, New Mexico, and Texas, the three major goat-producing states, 61,000 goats and kids were lost to predators in 1999. A NASS study valued these losses at $3.4 million. Although direct losses of livestock due to depredation are often conspicuous and economically significant, they likely underestimate the total loss to producers because they do not consider indirect effects of carnivores as a result of livestock being exposed to the threat of predation without being killed.
Laundré et al. (2001) suggested that behavioral responses by prey species to impending predation might have more far-reaching consequences for ungulate behavioral ecology than the actual killing of individuals by predators. Potential negative, indirect impacts associated with the mere presence of predators include, but are not limited to, increased vigilance and reduced foraging efficiency by prey species, and being forced by predators to forage in suboptimal habitats that contain lower quality or quantity of nutrients, and higher levels of toxins. Moreover, overuse of and lowered carrying capacity in suboptimal habitats could contribute to resource degradation (e.g., overgrazing in marginal habitats, increased erosion and sedimentation) and lower producer profits due to declines in livestock production (e.g., weight gain, body condition, lamb or calf crop). Thus, indirect impacts of predation may have negative impacts on the ecological integrity of the land, as well as negative impacts on personal, local, and regional economies that depend on livestock production. However, there is little or no published information that addresses indirect effects of carnivores on domestic ungulates.
The purpose of this paper is to discuss how the mere threat of predation might influence foraging efficiency and vigilance, diet and habitat selection, skin-gut responses, and social behavior in wild and domestic ungulate prey species. Because there is little or no published information on domestic ungulates concerning these subjects, we rely heavily on wild ungulate studies that have attempted to quantify or qualify the indirect effects of predation. Our aim is to use the wildlife literature as a springboard to stimulate discussion among producers, wildlife damage management professionals, and researchers regarding ways to quantify and address the indirect effects of carnivores on domestic ungulates. We first discuss the evidence from the wildlife literature that supports indirect effects of carnivores on wild ungulates, and then relate that evidence to its potential implications for domestic livestock foraging behavior and production.