Effects of Predators on Structure of the Burrows of Voles

To test the hypothesis that voles reduce the amount of time spent burrowing when risk of predation is low, we excluded predators from four penned populations of voles and allowed access by predators to four other penned populations. Voles responded as expected; pens without predators had fewer entrances to burrows and fewer simple burrows (short, blind tunnels and escape burrows). Spatial distributions of entrances to burrows remained random or clumped in both treatments. Multiple-nest burrows were larger and more complex than single-nest burrows or escape burrows, but the structure within each type of burrow did not differ between treatments. Although voles altered the types of burrows they constructed in response to risk of predation, some other factor apparently constrained them from changing the structure of their burrow systems.