Rapid responses of marsh birds to large‐scale tidal wetland restoration in California's Sacramento–San Joaquin Delta

Introduction Tidal wetland restoration is widely used to recover ecosystem function in modified estuaries, yet uncertainty remains about how quickly wildlife communities respond. Early trajectories are central to evaluating restoration success, guiding adaptive management, and building ecosystem resilience in engineered landscapes. Marsh birds respond rapidly to changes in hydrology and vegetation, making them effective indicators of habitat restoration. Objectives We assessed how marsh bird communities respond following freshwater tidal restoration in California's Sacramento–San Joaquin Delta within a living laboratory framework, where multiple co‐occurring habitat types enable comparative evaluation of wildlife responses across a restored landscape. Methods We analyzed a six‐year (2020–2025) dataset of standardized avian point counts across restored freshwater tidal marsh, managed non‐tidal marsh, and unrestored pasture habitats. Species richness was estimated at point and site scales using stratified nonparametric bootstrapping. Species‐specific densities for focal marsh‐associated birds were estimated with distance sampling and hierarchical bootstrap inference to account for imperfect detection and uncertainty. Results Restored tidal marsh supported higher waterbird richness than managed marsh or pasture within 1 year of restoration, while landbird species richness remained similar across habitats. Marsh‐obligate species colonized rapidly and reached densities comparable to or exceeding those in long‐established managed marshes within 1–4 years. Early successional shorebirds and waterfowl declined as emergent vegetation expanded. Richness remained stable over time, indicating rapid compositional turnover rather than gradual species accumulation. Conclusions Freshwater tidal restoration produced rapid, predictable bird community responses that tracked habitat development and succession during the first six years post‐restoration.