Effects of cattle on habitat use and diel activity of large native herbivores in a South American rangeland

Abstract

Cattle grazing usually has negative effects on wildlife. We studied the effects of cattle on the patterns of habitat use and diel activity of three neotropical herbivores, capybara (Hydrochoerus hydrochaeris), gray brocket (Mazama gouazoubira) and marsh deer (Blastocerus dichotomus) across the savannas of northeastern Argentina. We conducted a camera-trap survey with 234 stations in three habitat types (grasslands, forests, pine plantations) with and without cattle. We used occupancy models to evaluate the effect of cattle (presence or recording rate), season (winter vs spring-summer, and its interaction with cattle), distance to water bodies, and density of vegetation, on the probability of detection (p) of the native herbivores. We also evaluated the effect of cattle, habitat type, structural complexity of the vegetation, proportion of marshlands and forests in the landscape, season, and relative accessibility by humans, on the probability of occupancy (ψ) of these species. Using kernel density functions, we estimated the overlap in diel activity pattern of native herbivores with that of cattle, comparing this overlap between stations with and without cattle. Several variables, but not cattle, affected ψ. For marsh deer p was lower when cattle were present. For brocket, p was much lower in winter when cattle were present. For the marsh deer and the capybara, ψ increased (but in brocket decreased) with increasing cost of human access, a proxy of hunting. For capybara and brocket, ψ increased with increasing structural complexity of vegetation. Cattle were more diurnal in grasslands than in forests and plantations. Native herbivores became more nocturnal, with lesser overlap with the diel pattern of cattle, in grasslands, when cattle were present. Cattle seem to exert interference competition on the native herbivores which used less frequently areas where cattle were present and avoided being simultaneously active with grazing cattle. Livestock production should strive to mitigate the negative competitive effects of cattle on wildlife by maintaining cattle free protected areas. It should also reduce some indirect effects of this activity on the native herbivores (e.g., hunting of wildlife and frequent burning of grasslands).