Foraging under predation risk in the wild guinea pig : the effect of vegetation height on habitat utilization

Wild guinea pigs are neotropical, diurnal, herbivorous rodents which frequently inhabit field borders. They use borders as protection from predators and forage in adjacent fields. We studied the relationship between the height of field vegetation and cavy density along the border. Animal distribution was determined by an indirect method based on counting the number of faeces in circular sample units. We sampled 60 units on a 1800-m line transect placed on field borders five times between July and December 1991, at intervals of 32 to 43 days. Cavy density was highest where vegetation height in the foraging areas was lowest. This relationship was most strong in July (winter) and was progressively lost with plant growth. We interpretated these results as the population expression of individual strategies for solving the trade-off between foraging and predation risk: individual guinea pigs (1) should select a home range with shelter for daily inactive periods given by the field border, and with an adjacent rich area of very short grass to forage; and (2) should reduce danger in open areas by behavioural adaptations.