Code

CCBTR-14-07

Publication Date

2014

Abstract

Knowing how many individuals there are of a species of conservation concern and where are they distributed are their most fundamental pieces of information required for their management. We estimated the winter population sizes of the Seaside Sparrow, Nelsons’ Sparrow, and Saltmarsh Sparrow within the Virginia tidal areas of the Chesapeake Bay and Eastern Shore of the lower Delmarva Peninsula. These three species are of special concern because their populations are restricted to marsh habitats that are regionally and globally in decline. Estimating their numbers creates a historical benchmark for monitoring and makes connections between breeding and winter areas. Connecting the breeding and wintering grounds of migratory bird species is essential for full life cycle conservation. We calculated the winter population sizes for these by multiplying the density of birds detected from surveys by the amount of available marsh habitat. The density of birds was obtained by averaging the standardized number of birds detected during rope-drag transects per area across 95 marsh patches. We also estimated the subspecies composition of the Nelson’s and Saltmarsh sparrows from additional capture surveys. We used GIS coverage of Virginia tidal marshes to sum for the total area of plant communities that are used by these sparrows. The Virginia portion of the Chesapeake Bay and Eastern Shore supports approximately 27,000 Seaside Sparrows, 65,000 Nelson’s Sparrow, and 50,000 Saltmarsh Sparrow in winter. Seaside Sparrows were found in greater density on the shores of the Chesapeake Bay compared to the seaside of the Eastern Shore. The overall population numbers indicate that a large portion of Virginia Seaside Sparrow population leave after the breeding season and are not commensurately replaced in number from the migration of more northern birds. The results also provide an estimate of the percentage of each population composed by subspecies thereby providing clues to geographic origin of populations using the region in winter. Further breakdown of these numbers by subspecies indicate that the region supports 53,000 of the interior Nelson’s Sparrow and 11,000 of the coastal breeding form. This may be considered a relatively large percentage of the overall known population for the coastal Nelson’s Sparrow and highlights the region’s importance to their survival. The Saltmarsh Sparrow was divided into approximately 42,000 of the northern-Atlantic breeding form and over 8,000 of the mid-Atlantic breeding form. The Virginia coastal region obviously receives a large influx of migrants from Saltmarsh Sparrow populations emanating from the northern Atlantic. These estimates provide an opportunity for relative comparison to other geographic regions so that conservation actions can be spatially prioritized. This study also provided a technique by which density values are obtained from a high frequency sampling technique while also using a unique double-pass rope drag technique refine estimates based on detection probability. This project could serve as a standardized protocol in which to collect data on bird density for these species in other regions during winter. 1

Topic

Abundance/Distribution; Habitat Quality/Use/Movement

Species

Nelson's Sharp-tailed Sparrow; Saltmarsh Sharp-tailed Sparrow; Seaside Sparrow

Source

The Center for Conservation Biology Technical Report Series, CCBTR-14-07. College of William and Mary & Virginia Commonwealth University, Williamsburg, VA.

Pages

12

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