RESUMEN
Light detection and ranging (lidar) has emerged as a valuable tool for examining the fine-scale characteristics of vegetation. However, lidar is rarely used to examine coastal wetland vegetation or the habitat selection of small mammals. Extensive anthropogenic modification has threatened the endemic species in the estuarine wetlands of the California coast, such as the endangered salt marsh harvest mouse (Reithrodontomys raviventris; SMHM). A better understanding of SMHM habitat selection could help managers better protect this species. We assessed the ability of airborne topographic lidar imagery in measuring the vegetation structure of SMHM habitats in a coastal wetland with a narrow range of vegetation heights. We also aimed to better understand the role of vegetation structure in habitat selection at different spatial scales. Habitat selection was modeled from data compiled from 15 small mammal trapping grids collected in the highly urbanized San Francisco Estuary in California, USA. Analyses were conducted at three spatial scales: microhabitat (25 m2), mesohabitat (2025 m2), and macrohabitat (~10,000 m2). A suite of structural covariates was derived from raw lidar data to examine vegetation complexity. We found that adding structural covariates to conventional habitat selection variables significantly improved our models. At the microhabitat scale in managed wetlands, SMHM preferred areas with denser and shorter vegetation and selected for proximity to levees and taller vegetation in tidal wetlands. At the mesohabitat scale, SMHM were associated with a lower percentage of bare ground and with pickleweed (Salicornia pacifica) presence. All covariates were insignificant at the macrohabitat scale. Our results suggest that SMHM preferentially selected microhabitats with access to tidal refugia and mesohabitats with consistent food sources. Our findings showed that lidar can contribute to improving our understanding of habitat selection of wildlife in coastal wetlands and help to guide future conservation of an endangered species.
RESUMEN
Disease may limit recovery of endangered species. We surveyed parasites in the federally endangered salt marsh harvest mouse (SMHM; Reithrodontomys raviventris halicoetes) and sympatric rodents in Suisun Marsh (Solano County, California, USA) from April 2018 through March 2019. We investigated individual SMHM risk factors (age, sex, reproductive status, and body condition) for infection and relationships among the estimated parasite prevalence and season and habitat management (natural tidal habitats versus diked, nontidal habitats). We captured 625 individual rodents, including 439 SMHM, and tested these for infection with Bartonella spp., Borrelia spp., Rickettsia spp., Francisella tularensis, Leptospira spp., Cryptosporidium spp., Giardia spp., and Toxoplasma gondii by PCR. Over one-third (34.6%, confidence interval [CI], 30.2-39.3%) of SMHM tested positive for at least one parasite. Four percent (CI, 2.8-6.3%) of SMHM were infected with F. tularensis holarctica, a virulent bacterium that causes mortality in rodents shortly after infection. Additionally, we detected three species of Bartonella (B. henselae, B. rochalimae, B. vinsonii arupensis), Leptospira borgpetersenii serovar Ballum, Cryptosporidium sp. (deer mouse [Peromyscus maniculatus] genotype), Cryptosporidium parvum, Giardia intestinalis, and an unidentified Borrelia sp. The only parasite that was associated with habitat management was Bartonella spp., which was more prevalent in diked than tidal areas. Male SMHM were more likely to be parasitized than females, and individuals in modestly poor body condition were most likely to be infected with Bartonella spp. The estimated sample prevalence of multiple parasites varied by season and by host species. This is the first major parasite assessment in a long-endangered species, and these results will assist managers to incorporate parasitic disease into recovery planning and provide a critical baseline for future investigations, including how climatically induced habitat and species composition changes could alter disease dynamics.