Abstract

We report on the foraging behavior of three small-mammal species over 21/2 years using experimental foraging trays. Trays provisioned with oat seed were set out in the field at dawn and dusk, and the amount of seed consumed (with re-provisioning) was determined over three consecutive nights and days. Experiments simultaneously evaluated the role of lunar phase, season, and microhabitat (shrub vs. open); additionally, artificial exclosures (?0.56 ha) were employed to evaluate the influence both of mammalian and avian predators and of a dominant competitor species, the large diurnal degu (Octodon degus). Other principal small mammals included Darwin's leaf-eared mouse (Phyllotis darwini) and the olive field mouse (Akodon olivaceus). Trays were enclosed by hardware-cloth cages with either small or large holes in the side to exclude avian consumers and provide selective access to all small mammals (large holes) or to exclude the largest species (small holes). Small-mammal population sizes varied greatly throughout the study. Principal factors affecting seed consumption rates were population size, followed by season (winter ? summer), and microhabitat (shrub ? open). The role of the latter factors was relatively minor in 1999 and 2000 but amplified greatly in the final year of study when small-mammal numbers increased five-fold. In contrast to earlier work at this site, predation had minimal direct effects on foraging activities, although significant effects of microhabitat, lunar phase, and season suggest the importance of perceived predator risk. Both Phyllotis and Akodon foraged more in the absence of degus, and two- and three-way interactions further supported an important role for competition in this system. The combination of large-scale predator/competitor manipulations with fine-scale foraging experiments and long-term replication illustrates the importance of utilizing such approaches to gain insights to behavior and foraging strategies in variable environments.