Selenium Risk to Yuma Ridgway’s Rails at the Salton Sea
March 2020 - May 2024
- US Geological Survey
- US Geological Survey
The federally endangered Yuma Ridgway’s rail (Rallus obsoletus yumanensis) inhabits emergent marshes throughout the Lower Colorado River Basin and around the Salton Sea in California. Emergent marshes around the Salton Sea support one of the largest remaining populations of Yuma Ridgway’s rails in the U.S. (U.S. Fish and Wildlife Service 2010, Eddleman and Conway 2018). Much of the rail habitat at the Salton Sea is managed by the U.S. Fish and Wildlife Service (at Sonny Bono Salton Sea National Wildlife Refuge) and California Department of Fish and Wildlife (at Wister Wildlife Management Area). Recently, unmanaged marshes have appeared at agricultural drainage outlets around the Salton Sea and are becoming more common as sea levels recede (Barnum et al. 2017). Marsh bird survey results suggest Yuma Ridgway’s rails are moving away from managed wetlands into the new unmanaged marshes around agricultural drainages (U.S. Fish and Wildlife Service, unpublished data). These new unmanaged marshes receive agricultural drainage water with varying concentrations of selenium, whereas managed marshes receive Colorado River water with relatively low concentrations of selenium. Selenium affects reproductive success (e.g., embryo development) of birds at elevated concentrations. Crucially, selenium concentrations exceed EPA water quality standards in agricultural drains feeding unmanaged marshes inhabited by Yuma Ridgway’s rails (Saiki et al. 2012). As such, rails within the unmanaged marshes may be at risk from elevated selenium concentrations and these unmanaged marshes may create an ecological trap for the rails. Alternatively, they may be helpful additions to rail habitat to support recovery of the bird. Managers and policy-makers need to know whether these new unmanaged marshes are benefiting or hindering recovery of the species.
We are monitoring rail demographics, selenium burdens in breeding rails, and selenium concentrations in rail prey items within managed and unmanaged marshes around the Salton Sea. Our research will help evaluate the habitat suitability of unmanaged marshes for Yuma Ridgway’s rails and assess the risk selenium concentrations in these unmanaged marshes may pose to Yuma Ridgway’s rails. Such information will help guide conservation efforts both locally (e.g., can managers safely use no-cost drain water to create marshes for Yuma Ridgway’s rails?) and throughout the entire range of this federally endangered rail.