Managing California Ground Squirrels on Levees Using Habitat Modification

Burrowing mammals such as ground squirrels are considered threats to levee integrity, and some authors have proposed that ground squirrel occurrence on levees might be reduced by habitat modification. We characterized the threat that California ground squirrels pose to levees by summarizing available information on burrow lengths and depths, and we reviewed available information about the efficacy of habitat modification to reduce squirrel occurrence on levees. Burrows of California ground squirrels averaged 8.2 m in length (range = 0.9-42.1 m) and 75 cm in greatest depth (range = 33-168 cm), indicating that most burrows are not long enough to transect most levees but nonetheless could contribute to “piping” of water through the levee and create voids that trigger collapses of levee soil. There is little evidence that managing for either short-stature grassland or shrubby vegetation on levees will reduce occurrence of ground squirrels, but further research is needed for both approaches. Managing for trees on levees likely will reduce the occurrence of ground squirrels, probably because tree-covered habitats create visual obstruction that is avoided by ground squirrels. The presence of nut and fruit crops adjacent to levees increases the occurrence of ground squirrels on the levee, probably because these crops provide a rich food resource