Translocation Biology of the Endangered Pacific Pocket Mouse in Southern California

The Pacific pocket mouse was emergency listed by the U.S. Fish and Wildlife Service (USFWS) as endangered in 1994. Today, there are only four known populations in existence: three on Marine Corps Base Camp Pendleton in San Diego County, and one at Dana Point in Orange County. As part of recovery efforts supported by the USFWS and the U.S. Marine Corps, CRES is researching methods to translocate pocket mice to augment existing populations and/or establish new populations in appropriate areas within the historic range of the species.

As part of a Conservation Research Postdoctoral Fellowship program, basic behavioral and ecological research will be conducted to learn about space use, social interactions, and dispersal of pocket mice. The CRES Genetics and Applied Animal Ecology divisions will work together to assess genetic variation in the populations.

A major problem affecting many translocation programs is that animals disperse too far from their release site, exposing themselves to dangers by moving beyond the bounds of protected areas. Many dispersing animals are known to select habitat preferentially if other members of their species are present, an indication that the area is likely to be safe and has adequate resources. One area of research will involve spreading pocket mouse scent around the release site to determine if translocated mice are more likely to remain in the most suitable area.

Often, when conducting translocation programs, differences in specific habitat types between the source and release sites are not evaluated as long as the release site contains suitable habitat for the species. Emerging scientific evidence suggests that animals develop preferences for the type of habitat in which they were reared and, when dispersing, they search for habitat similar to their natal habitat. Maturing in a particular habitat may increase an individual’s performance in that habitat compared with other suitable habitats. CRES staff will test the relative successes of animals released into habitat similar to or different from their natal habitat, using dispersal distance, settlement patterns, stress response, and survival rates as measures. Finally, the study will address other factors such as the number of animals released together, their kin relationships, and level of familiarity with one another as these factors have been shown to dramatically affect post-release success.