Population estimates for tidal marsh birds of high conservation concern in the northeastern USA from a design-based survey

Tidal marsh loss to anthropogenic environmental impacts and climate change, particularly sea level rise, has and will continue to cause declines in tidal marsh bird populations. Distribution patterns of tidal marsh birds are generally known, yet we lack detailed knowledge of local abundance and regional population sizes, which limits our ability to develop effective conservation strategies that will mitigate the impacts of marsh loss. We designed and implemented a probabilistic sampling framework to establish a regional marsh bird monitoring program, and collected baseline information for breeding tidal marsh birds in the northeastern USA (Maine to Virginia). We sampled 1,780 locations in 2011-2012 to provide regional population estimates for 5 tidal marsh-specialist birds. We estimated that there were 151,000 Clapper Rails (Rallus crepitans; 95% CI = 90,000-212,000), 117,000 Willets (Tringa semipalmata; 95% CI = 88,000-146,000), 5,000 Nelson's Sparrows (Ammodramus nelsoni; 95% CI = 1,000-9,000), 53,000 Saltmarsh Sparrows (A. caudacutus; 95% CI = 37,000-69,000), and 230,000 Seaside Sparrows (A. maritimus; 95% CI = 174,000-286,000) in northeastern tidal marshes. Our baseline assessment can be used to identify local habitat patches important to regional populations for each species and to prioritize conservation actions in targeted areas to maximize tidal marsh bird persistence. The flexibility and probabilistic design of our sampling framework also allow for integration with other monitoring programs (e.g., the U.S. Fish and Wildlife Service Salt Marsh Integrity Program and National Park Service Vital Signs Monitoring Program) so that inferences for these species can be made at multiple spatial scales.