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Abstract

Saltmarshes dominated by smooth cordgrass (Spartina alterniflora) are currently rare in the Tampa Bay region and likely represent remnant patches of more extensive marshes that were extant during the nineteenth and twentieth centuries. We investigated small populations of two tidal marsh species, Saltmarsh (Ammospiza caudacuta) and Nelson’s (A. nelsoni) sparrows, on one such isolated marsh (Shell Key) in Pinellas County, Florida. We sought to characterize basic population characteristics of relative abundance and persistence of individuals of the two species over a seven-year period. We color-banded sparrows to be able to identify all returning individuals, including those that we saw and were not captured on subsequent visits. In most cases, we visited the marsh twice (late autumn, late winter) to examine within-winter season persistence. We captured a total of 51 sharp-tailed sparrows (45% Saltmarsh and 55% Nelson’s sparrows) from February 2010 to November 2016. We recaptured 11 individuals including three repeats in the same winter season and eight returns between years, thus providing wintering evidence (site tenacity) and evidence of philopatry, respectively, for both species. We estimated on average that four Saltmarsh Sparrows and six Nelson’s Sparrows overwintered in the marsh based on mean annual numbers of the two species captured and observed bypassing nets during the February visit. A female Saltmarsh Sparrow banded during our study was recaptured at a nest with four eggs in the ensuing breeding season on a saltmarsh in Warren, Rhode Island. This study is the first to document more than 4% of Saltmarsh Sparrows surveyed on the central Gulf coast of Florida in recent decades. It provides an explanation for why current field observers have found so few Saltmarsh Sparrows in recent decades along this coast where historically they were regarded as common and widespread in the late 1880s in Tampa Bay area tidal marshes. Saltmarsh Sparrows evidently are narrower habitat specialists along the Gulf Coast than are Nelson’s Sparrows. The former species locally prefers smooth cordgrass marshes, which have largely disappeared because of human development and black mangrove (Avicennia germinans) intrusion; the latter species uses the same marsh type and also large stands of black needlerush (Juncus roemerianus) that Saltmarsh Sparrows largely avoid. We hypothesize that Saltmarsh Sparrows perhaps established an old connection to tidal marshes dominated by S. alterniflora along the central Florida Gulf coast during the last Pleistocene ice age glaciation event when suitable tidal marshes were more widespread before mangroves spread northward into the region.

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