California restored grazing land to tidal marsh; bird density jumped over 12,000%

California’s efforts to restore wetlands in the Sacramento–San Joaquin Delta are showing measurable benefits for marsh-dwelling birds, with a newly published study documenting a dramatic rise in Marsh Wren numbers after tidal flows were reintroduced to former agricultural land. According to the journal Restoration Ecology on June 8, 2026, the research by Jason Riggio and colleagues tracked bird populations from 2020 to 2025 at restoration sites managed by the California Department of Water Resources (DWR). The findings build on the state agency’s Dutch Slough Tidal Marsh Restoration Project, which converted former grazing and dairy land into freshwater wetland habitat. The study found that Marsh Wren density at Dutch Slough rose from 0.15 birds per hectare in 2020 to 18.47 in 2025, an increase of more than 12,000%.