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 Atlantic coastal North America. This species is composed of three geographically separated subspecies, all of which inhabit open country, wet meadows or tidal wetlands. The nominate sub-species, Ammodramus nelsoni nelsoni, breeds from north Alberta, central Saskatchewan, and south Manitoba to northeast South Dakota. A. n. alter is restricted as a breeder to the southern coasts of Hudson and James Bay, Canada. The maritime sub-species, A. n. subvirgatus, breeds along the coast from the Gulf of St. Lawrence to Parker River National Wildlife Refuge along the north shore of Massachusetts.
Prior to 1995, Nelson's and Saltmarsh 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. Nelson's is the only species of the two that breeds away from the Atlantic coast.
Nelson's Sparrow was named after Edward William Nelson, an American naturalist who conducted field surveys for the United States Department of Agriculture, Bureau of Biological Survey in Alaska, Death Valley, and Mexico. Nelson was Chief of the Bureau from 1916 to 1927.
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 migrating. While Nelson's Sparrow can adapt to a variety of habitats, typical fluctuations in rainfall and storm surges cause high nestling mortality rates during the breeding season. Mowing, draining, plowing, burning, and spraying for insects can all disrupt the sparrow's breeding cycle. This species generally requires mature, extensive, and undisturbed marshland habitat in order to achieve successful nesting and re-nesting. The conservation of extensive tidal marsh and interior northern grasslands is critical to the stabilization of the species.