Abstract
Selenium accumulation in aquatic ecosystems poses a considerable threat to birds, particularly in wetlands primarily supplied with agricultural runoff. The Salton Sea, a terminal lake in southeastern California, relies heavily on drainage water from nearby agricultural fields. This influx has formed essential wetland habitats along the lakeshore, which are crucial for various bird species, including the endangered Yuma Ridgway’s rail (Rallus obsoletus yumanensis). During the breeding seasons from 2020 to 2023, we used GPS transmitters to monitor Yuma Ridgway’s rails and to compare selenium concentrations and nesting success among 3 wetland types: those fed by irrigation runoff, Colorado River water, or spring-fed groundwater.We examined blood, feathers, eggshells, unhatched eggs, and prey items to determine selenium exposure within the 3 wetland types. Our analysis revealed that selenium concentrations in rail tissues were strongly linked to the selenium levels in their prey. Additionally, selenium concentrations in eggshells were consistent with those in the blood of parent birds. The source of water (i.e., wetland type) and the rate of water flowing into the marshes significantly affected selenium levels, with the highest concentrations in marshes fed by irrigation runoff. Faster water inflow resulted in lower selenium levels. Nesting success was greater in river-fed marshes, while unhatched eggs from ag-fed areas had higher selenium concentrations.
We noted instances of embryo malpositioning, possibly associated with heavy metal exposure, but we observed no direct fetal abnormalities. Our findings suggest that increasing the use of Colorado River water in predominantly ag-fed marshes could reduce selenium buildup and improve the nesting success of Yuma Ridgway’s rails.