Foraging efficiency and parasite risk in eastern grey kangaroos (Macropus giganteus)

Abstract

Large mammalian herbivores must balance foraging efficiency with multiple constraints, including the risk of gastrointestinal parasitism. The costs imposed by gastrointestinal parasites are likely to exert selective pressure on hosts to develop aversion behaviors. Fecal aversion, or the avoidance of foraging patches contaminated by feces, is one mechanism by which herbivores can reduce their exposure to gastrointestinal parasites transmitted through the fecal contamination of foraging grounds. As feces also fertilize the surrounding pasture, herbivores may face a choice between the benefits of increased nutrient intake and an increased risk of parasitism. We investigated fecal aversion in free-ranging eastern grey kangaroos (Macropus giganteus), including the potential conflict between fecal aversion and increased nutrient intake, through a combination of field observations and a field experiment. Kangaroos exhibited fecal aversion by moving through contaminated patches as they were encountered. The experiment revealed that both sward height and fecal contamination affected the kangaroos' choice of foraging patches: kangaroos preferred taller grass but would not accept a higher risk of parasitism for increased nutrient intake.