Separating effects of spatial location and microhabitat density on perceived predation risk in small mammals

Prey animals must balance the benefits of foraging in a particular area with their risk of predation in that area and often prioritize indirect cues to predation risk over direct cues of predators when making decisions about foraging under the risk of predation. Researchers using giving-up density (GUD) as a metric to assess perceived predation risk have found that it is affected by microhabitat, with certain animals willing to spend more time foraging (i.e., lower GUD) in relatively dense microhabitats and less time foraging (i.e., higher GUD) in relatively open microhabitats. This phenomenon has been attributed to those animals perceiving less predation risk when near or under shelter. However, the measurement has often confounded microhabitat density with distance from shelter in species without conspicuous dens. We measured GUD in foraging small mammals while experimentally manipulating microhabitat density and controlling for spatial location of the forager. Small mammals increased foraging (i.e., decreased GUD) as expected when we increased microhabitat density, but they did so despite those manipulations being randomly permuted spatially over the course of four rounds of data collection. Our results indicate that experimentally controlling for the potentially confounding effect of the forager's distance to a safe location, such as dens, nests, or other shelters, did not remove the effect of microhabitat density on perceived predation risk. Thus, our results suggest that an animal's perception of risk is likely mediated by both their location in their home range and the microhabitat at that location. We provide suggestions for further work.