If You Build It: Using Ground Squirrel Risk Perception to Test Wildlife Crossing Structure Success

Roads and traffic present many risks for wildlife, and animals must be able to accurately assess risks in their environment. Animals can often perceive the level of risk they face, and their behavioral responses can alter their fitness and potentially even whole-population dynamics. However, animals may be unable to properly measure the levels of risk near roadways because roads present novel environmental conditions and alter predators’ behavior. To mitigate some of the ecological problems created by roadways, wildlife crossing structures (WCSs) are being incorporated into transportation projects. To understand whether WCSs provide quality habitat for wildlife, we compared the levels of risk that small mammals perceive on under- and overcrossings on an interstate highway to the levels in natural habitats within the Cascade Range of central Washington. This study presents the first time that the behavior of resident animals is being used to assess the effectiveness of WCS. We quantified the risk perception of Cascade Golden-mantled Ground Squirrels (Callospermophilus saturatus) by setting out feeding trays and measuring general population-level foraging behaviors. We also observed the behaviors of individual squirrels at the feeding trays (via video imaging), and conducted in-person scan sampling on days when the trays were not present. Animals’ activity budgets away from the trays did not differ significantly between the WCS and natural habitats. Squirrels depleted the trays twice as fast on the WCSs, but individual squirrels’ frequency of vigilance behaviors did not differ between the two habitats. We found few clear differences in individual behaviors between the undercrossings and overcrossing, or between different microhabitats on the WCSs. These results indicate that the individuals on the WCSs perceived similar levels of perceived risk compared to the animals living in natural habitats. If properly planned and constructed, WCSs can provide quality habitat that wildlife populations can use without additional stress. Behavioral ecology presents a promising new technique to assess the effectiveness of road ecology projects.