Nelson’s Sparrow, Nelson’s Sharp-tailed Sparrow, Sharp-tailed Sparrow, Saltmarsh Sharp-tailed Sparrow, Saltmarsh Sparrow? They are a confusing lot! This blog post will try to straighten them out, concentrating on the Nelson’s Sparrow.
The Nelson’s Sparrow (Ammodramus nelsoni) and the Saltmarsh Sparrow (Ammodramus caudacutus) were formerly thought to be the same species. Old field guides (prior to 1998) refer to these two species as one species called the Sharp-tailed Sparrow. But their songs, plumage and genetics differed leading to further study and the separation of the two species, designated Nelson’s Sparrow and Saltmarsh Sparrow. Where the range of the Atlantic race of the Nelson’s Sparrow overlaps with the Saltmarsh Sparrow, occasionally hybrids occur.
It is thought that the two species diverged about 11,000 years ago as the glaciers from the last glaciation period retreated. The closest living relative of these two species is the Seaside Sparrow from which they separated about 600,000 years ago. The Nelson’s Sparrow is named after Edward William Nelson, Chief of the US Bureau of Biological Survey from 1916 to 1927. He was the first to collect this species in 1874 when he was 18 years old.
The Nelson’s Sparrow breeds in two distinct geographic areas of North America. The Atlantic race breeds on coastal areas of Maine, New Brunswick, Nova Scotia, Prince Edward Island and the St. Lawrence River area of Quebec. The interior race breeds in the prairie region of Manitoba, Saskatchewan, Alberta, the western coastal area of Hudson Bay and James Bay, southern Northwest Territories, North Dakota and Minnesota. They winter along coastal areas of Texas eastward to Florida and up the east coast of Florida to Virginia.
The preferred habitat is tidal wetlands with salt meadows of cordgrass, saltgrass and salt marsh rushes and sometimes wet grasslands next to rivers where slough grass and scaly sedge grow. Wintering birds can be found in tidal salt and brackish marshes near ocean coastlines. The interior population breeds in freshwater marshes dominated by tall grasses like cord grass, cattail, and bulrushes.
The Nelson’s Sparrow is a small secretive bird about 12 cm long (the Song Sparrow is 17 cm long). It has an orange-buff triangle on its face with a gray cheek, median crown stripe and nape. Its lightly streaked buff-coloured breast contrasts sharply with its white belly. It has black and white stripes on its back and its wings are tinged with rufous. Its tail is narrow and the tail feathers are sharply pointed. Both genders look similar.
For identification this species needs to be distinguished from the Saltmarsh Sparrow and LeConte’s Sparrow. The Saltmarsh Sparrow is very similar but it has more defined facial features, and crisply streaked under parts and a white throat. The face and breast of the Nelson’s Sparrow is an undifferentiated orange. Contrasting with the LeConte’s Sparrow, the Nelson’s has a grayish central crown stripe, an unstreaked gray nape, distinct white lines on the back, and a larger bill. Because these three species are so similar one needs to study the graphic depictions carefully for accurate identification.
The Nelson's sparrow forages and rests on or near the ground, making only short flights. The displaying males will make fast flights skimming over the marsh vegetation. The females will occasionally make lookout flights hovering over the vegetation. The males sing frequently at night but they will quit if another male appears. The males territorial ranges often overlap. This causes frequent fights and chases. The males often follow the females around protecting them from other males. The males do not participate in nest site selection, building or rearing the young. Scientists have found this species practices male-dominance polygyny in which a small proportion of males mate with a disproportionate share of females. This includes mating with unwilling females at times. LeConte’s Sparrows and Savannah Sparrows are known to chase Nelson’s Sparrows where their territories overlap.
Nelson’s Sparrows nest in marsh vegetation close to the ground. The female builds a cup-shaped nest of dry grass and stems and attaches it to vegetation. In it she lays 3 to 7 light green eggs heavily spotted with brown. The eggs are incubated for 11 days. After the young fledge small flocks feed on seeds of cordgrass. Nelson’s Sparrows eat mainly insects, aquatic invertebrates and seeds. They forage mainly on the ground or in the marsh vegetation and are known to probe the mud for food.
The song of this sparrow is distinctive. It has been described as a ‘hiss that drops off at the end’. It is a very raspy trill depicted as ptshhhhhhh-uk. The call note is tsik. The Nelson’s Sparrow is difficult to see because it often will run along the ground rather than flush. It does not usually respond to spishing.
The global population of the Nelson’s Sparrow is considered stable although there have been population declines due to loss of habitat from the draining of marshes, the development of shorelines and sea level rise due to global warming.
The Saltmarsh Sparrow is one we New Brunswick birders need to be watching for. Its breeding range is along the Atlantic coastline from Florida to southern Maine. I wouldn’t be surprised if it showed up here occasionally. It would be wise to learn to differentiate it from the Nelson’s Sparrow which is relatively common here.
We are fortunate to have healthy shorelines and marshes here in New Brunswick to support a population of the Nelson’s Sparrow. They must play an important role in the marsh and tidal shoreline ecosystem.
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