Special Issue 1 • April 2021 By STEVEN E. REINERT, DEIRDRE E. ROBINSON, JAMES M. O’NEILL, MIRANDA B. ZAMMARELLI, & JOEL ECKERSON Abstract This report summarizes results after 4 years (2017‒2020) of a 5-year, comprehensive field study of Saltmarsh Sparrow breeding ecology and reproductive success in a 10-ha salt marsh in upper Narragansett Bay. We found 153 active nests and documented outcomes for 152: 55 (36%) failed due to flooding, and 42 (28%) failed due to predation. Nest success (as defined by at least one chick fledging from a nest) averaged 28% over four years, with a range of 24% (2020) to 38% (2017). We banded 316 Saltmarsh Sparrows, 48% of which were adults. As is typical for the species, most Saltmarsh Sparrows nested in marsh habitats dominated by grasses: 59% of nests were placed at sites dominated by stands or mixtures of the “salt meadow” grasses (Spartina patens, Distichlis spicata, Juncus gerardii), and 18% of nests were placed in salt meadow grasses mixed with Spartina alterniflora. Sparrows selected nest sites in S. patens more frequently than would be expected based on that species’ abundance on the marsh. Unlike findings from other published studies, Saltmarsh Sparrows at our study site nested regularly (24%) at the base of, or within 15 cm of, the erect, woody stems of Iva frutescens, and nest success in that microhabitat (38%) was significantly greater than at sites lacking I. frutescens plants (22%). Based on these findings, we suggest that on salt marshes targeted for management activities to combat the negative impacts of sea-level rise, sparrow biologists work in concert with marsh-restoration specialists to strategically place spoils from restoration operations so as to promote the growth of patches of I. frutescens for use by nesting sparrows. Introduction The Saltmarsh Sparrow (Ammospiza caudacuta, Fig. 1) breeds in patches of healthy salt marsh from Virginia to Maine—and nowhere else on the globe (Greenlaw et al. 2020). Its reliance on low-lying coastal habitats renders it vulnerable to the impacts of sea-level rise by two fundamental mechanisms: (1) sea-level rise is driving increased tidal inundation and erosion of saltmarsh (Donnelly and Bertness 2001, Raposa et al. 2017, Eckberg et al. 2017, Watson et al. 2017, Adamowicz et al. 2020), as well as changes to vegetation, specifically replacement of the Saltmarsh Sparrow’s favored high-marsh nesting vegetation types (Spartina patens, Distichlis spicata, Juncus gerardii) with Spartina alterniflora—the dominant low- marsh grass; and (2) increased frequency of nest-flooding events (DiQuinzio et al. 2002, Bayard and Elphick 2011, Ruskin et al. 2017). These two factors have decimated Saltmarsh Sparrow populations during the past two-plus decades. Field et al. (2017) conducted Saltmarsh Sparrow Relationships of Nest- Site Selection and Nest Success of Saltmarsh Sparrows (Ammospiza caudacuta) in Upper Narragansett Bay, Rhode Island Figure 1. Adult Saltmarsh Sparrow perched in a high-tide bush at the Jacob’s Point study site. Note the aluminum federal band and three plastic color-bands (photo by Deirdre Robinson).