Nelson's Sparrow (formerly Nelson's Sharp-tailed Sparrow) is a secretive and highly localized species largely restricted as a breeding bird to wet meadows, edges of freshwater marshes, and salt marshes in recently deglaciated regions of interior and the Atlantic coast of North America. This species is composed of 3 geographically separated subspecies, all of which inhabit open country, wet meadows or tidal wetlands. The nominate subspecies, Ammospiza nelsoni nelsoni, breeds from north Alberta, central Saskatchewan, and south Manitoba to northeast South Dakota. A. n. altera is restricted as a breeder to the southern coasts of Hudson and James Bay, Canada. The maritime subspecies, A. n. subvirgata, breeds along the coast from the Gulf of St. Lawrence to northeastern Massachusetts.
Nelson's Sparrow was named after Edward William Nelson, an American naturalist who conducted field surveys for the U. S. Department of Agriculture, Bureau of Biological Survey in Alaska, California, and Mexico; he was Chief of the Bureau from 1916 to 1927. Prior to 1995, Nelson's and Saltmarsh (Ammospiza caudacuta) sparrows were considered the same species, the Sharp-tailed Sparrow (Ammodramus caudacutus), but are now separated based on differences in plumage, song, size, behavior, and genetics. Of the 2 species, only Nelson's Sparrow breeds away from the Atlantic coast.
At least three-quarters of the Nelson's Sparrow population breeds in Canada. With the precipitous destruction of coastal marshland and the continued drainage of inland grassland, this species has suffered acute loss of habitat for breeding, wintering, and migratory stopover. Although Nelson's Sparrow can adapt to a variety of habitats, typical fluctuations in rainfall and storm surges cause high nestling mortality during the breeding season. Mowing, draining, plowing, burning, and spraying for insects can all disrupt the breeding cycle. This species generally requires mature, extensive, and undisturbed marshland habitat in order to achieve successful nesting and renesting. The conservation of extensive tidal marsh and interior northern grasslands is critical to the stabilization of Nelson's Sparrow populations.