A random sampling of salt marsh harvest mice in a muted tidal marsh

摘要

Successful conservation of an endangered species, such as the salt marsh harvest mouse (SMHM; Reithrodontomys raviventris), requires detailed knowledge of the species' habitat and microhabitat associations. Identifying critical habitat features, however, can be problematic. We designed and implemented a randomized sampling regime with a large sample size of sites (n = 40) to identify potential microhabitat requirements or habitat constraints affecting the localized distribution of the southern subspecies of SMHM (R. r. raviventris). We used the random trapping technique to determine SMHM distribution across a muted-tidal, predominantly pickleweed (Salicornia virginica) marsh at the Don Edwards San Francisco Bay National Wildlife Refuge, California, USA. We tested the null hypothesis that this species' distribution is not associated with pickleweed salinity, sympatric rodent species, or the site location (peripheral vs. interior). We found SMHM throughout the marsh and detected no association with interior versus peripheral sites. We detected no associations between SMHM and sympatric rodent species. Pickleweed salinities ranged between 200 and 899 mmol/kg Cl-. In the prebreeding phase, SMHM were randomly dispersed. However, in the breeding and postbreeding phases, the population was clumped and associated with sites having mid-range (500-699 mmol/kg Cl-) salinities in pickleweed. Managers and biologists attempting to conserve SMHM in managed marshes need to be concerned with maintaining this mid-rangc salinity level in pickleweed. We found that SMHM were absent from areas of low salinity (200-499 mmol/kg Cl-) and were rare in hypersaline areas (699 mmol/kg Cl-). Mid-range pickleweed salinities can be created and maintained in managed SMHM habitat only via fresh infusions of sea water on a natural tidal basis.