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Résumé :
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An historical, four-year study initiated in 1977 in New York (USA) found Saltmarsh Sparrows (Ammospiza caudacuta) nesting syntopically with Seaside Sparrows (A. maritima), both in some abundance, in atypical, natural (young), tidal low marsh habitat. Saltmarsh Sparrows mostly occupied an extensive area of intermediate height Spartina alterniflora, which covered 89% of the vegetated study area and harbored about 97% of the nests. We undertake a retrospective analysis of nest fates, nest heights, and comparative nest survival using current analytical tools to ask how successful nesting Saltmarsh Sparrows were in relation to Seaside Sparrows nesting in the same habitat, which was the latter species’ typical habitat. Fates of Saltmarsh versus Seaside sparrow nests in this low marsh habitat were similar; predation (38%, 37%) and nest flooding (18%, 14%) were the most important causes of nest failure. Saltmarsh Sparrows placed their nests higher above the mud surface in low marsh (7.4 ± 0.4 cm) than in their typical high marsh habitat (4.8 ± 0.6). Overall mean daily survival rate (DSR) of nests (n = 231) in Saltmarsh Sparrows was 0.974 ± 0.0017 and the probability of surviving the 25-day nesting period was 0.52 ± 0.02—as high as the rate achieved by Seaside Sparrows (n = 319; DSR = 0.970 ± 0.0021), and as high as the highest levels of mean daily nest survival in other studies of Saltmarsh Sparrows. DSR declined with nest age, but only for Seaside Sparrow, and DSR was low for both species in 1980 compared to the other years. Creating new, low marsh habitat may offer potential for innovative conservation efforts to avoid the threatened extinction, by mid-century, of Saltmarsh Sparrows.
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