Ammodramus nelsoni
Nelson's sharp-tailed sparrow

Ammodramus nelsoni, or Nelson's sharp-tailed sparrows, have three separate distributions within the Nearctic region. One population resides around Hudson Bay in Canada. The other two inhabit both Canada and the United states: one population ranges along the north Atlantic Coast from Quebec down to Maine and the other is in the center of North America, ranging over Minnesota and northwest North Dakota to Alberta and southern Mackenzie, Canada. All populations migrate to winter along the southern Atlantic and Gulf of Mexico coastlines. Small numbers are also found wintering in a similar habitat along California’s coast. (Cooper and Beauchesne, 2004; "Ammodramus nelsoni", 2011)

Ammodramus nelsoni prefer grassy areas that are within wetlands. Common sites are freshwater marshes at the edge of woodland lakes, brackish marshes, sedge bogs, and regions between creeks and wet meadows. Willow trees are the preferred nesting site for this species, so they are often found in habitats where these woody plants are abundant. Within these habitats, a water depth between 1 to 10 inches is ideal. Water depths are most important during the breeding season. If a site is too wet or too dry, Ammodramus nelsoni will most likely not live in that location. Ammodramus nelsoni winters in saltwater and brackish marshes. (Cooper and Beauchesne, 2004; "Ammodramus nelsoni", 2011)

Ammodramus nelsoni is noted for its sunny, golden-orange color extending from the eyebrows to the breast, where it is mottled with darker stripes. The sparrow’s gray-striped crown is bordered with dark brown, and the ear coverts are gray. The olive-brown upper body and neck are notably streaked with white or gray. White extends down the abdomen to its brown, tapered tail. They are small birds; weighing in at 19 to 21 g. They measure 11 to 13 cm in length and feature a 20 cm wingspan.

This species is sexually dimorphic. Both sexes look similar, but males are slightly larger than females. Juveniles have brown ear coverts and less distinct facial markings.

The more common Le Conte’s sparrows (Ammodramus leconteii) have a similar appearance to Ammodramus nelsoni. Differences include Le Conte’s sparrows' striped gray napes and more subtle sandy-streaked backs.

Three subspecies exist, based on location. Two subspecies are found in the United States and one inhabits British Columbia. (Cooper and Beauchesne, 2004; "Ammodramus nelsoni", 2011)

Male sexual behavior is a form of “scramble competition polygyny”. Males will actively survey an area in search for females. Once a female is found, the male will intercept them and attempt to copulate with the female, which is usually a forced mating. One to several males may attempt to mate with a single female at one time, or several males may mate with a single female one after the other in a short period of time. This breeding method suggests that sperm competition is an important factor in this species.

Although mating is forced by the male, receptive females will perform a mating invitation display during the time she is building a nest. She will crouch with her tail and bill raised, wings folded and slightly raised, and make no vocalizations. (Greenlaw and Rising, 1994)

Ammodramus nelsoni breeds annually during the spring and summer months. Females construct a cup-shaped nest attached to low-lying reeds or willow branches. Location of the nest is critical in habitats where water levels fluctuate, and females must select a height at which nests will not be flooded. Clutches of three to seven eggs are laid in late spring or early summer. The eggs hatch after about 11 days of incubation and 10 days later, the young are able to leave the nest. The young receive continued care from the female for an additional 20 days after fledging, when they become independent. (Cooper and Beauchesne, 2004)

Females alone build the nest and incubate the eggs. Initially the female broods the nestlings frequently after hatching and then less frequently after 4 to 5 days. Brooding episodes may last up to 14 minutes, but usually are 2 to 6 minutes.

There is very limited data on nestling feeding. It has been observed that young feed almost exclusively on invertebrate prey. Food items are mostly found by the mother in nearby vegetation, mud and water. The male has been observed to occasionally bring food to the nest. Fledgelings remain near their mother who continues to care for them for 20 days post-fledging.

Females do not defend the nest if a predator is nearby. They fly off the nest and stay quiet and hidden nearby. When the nestlings are in the fledgling stage, females will give alarm calls to warn their offspring of predators. (Shriver, et al., 2011)

Using banding data, the maximum observed lifespan is 10 years for males and 6 years for females.

Estimates of minimum annual survival of adults in 2 cohorts (in New York) were 60.3% and 54.7% in males, and 63.3% and 53.0% in females. Offspring survival into first fall is estimated as 31.1%.

Tidal flooding caused 60% of egg and nestling mortality in a 2 year study conducted in Rhode Island. Flooding was also found to be the main cause of egg and nestling mortality in Canada and New York. There is little known regarding causes of adult mortality. (Shriver, et al., 2011)

Ammodramus nelsoni spends most of its time foraging, except during breeding season when males spend large amounts of time singing and searching for females. Foraging birds will run in short spurts, walk, or hop while searching for insects. Ammodramus nelsoni will often run and stop, climb vegetation and survey the area when not foraging. When alarmed, these sparrows will run crouched down with their heads lowered.

Their flight characteristics vary depending on social context, associated behavior, or destination. Most flights are relatively short and local.

Observed meetings between males is usually only when one male actively forces another male off a perch or one male retreats as another approaches. Dominance between males during breeding season has yet to be better understood. A singing male may cease singing when another male approaches or sings nearby, but counter-singing has not been observed. There is a loose dominance hierarchy apparent within different subspecies of Ammodramus nelsoni.

In New York, females have been observed fighting with males or chasing them off when the male tries to force the female into mating. Females will often chase males out of the immediate nesting area. They will use threatening calls or displays to ward off males. In New Brunswick, females have been observed to be more passive towards males.

Ammodramus nelsoni is a migratory species that brees in select regions of the northeast half of the United States and near the Hudson Bay in Canada. In fall, this species flies south to marsh habitats across the Gulf Coast or the southern Atlantic coast of the United States. During migration, Ammodramus nelsoni is often observed feeding in groups of 10 to 40 individuals, but at optimal locations they may amass in groups of up to 100. (Greenlaw and Rising, 1994)

Males are non-territorial. They typically concentrate their daily activities in large overlapping home ranges. Flight paths of males will cross and perching sites are often shared by several males.

Male home ranges are estimated to be between 1.2 to 1.6 ha in New Jersey and 3.0 to 5.7 ha in New York. The home range size for males in Canada is unknown, but believed to be much larger than the southern populations. (Greenlaw and Rising, 1994)

Males use songs to attract females, but unlike many songbirds they do not use this song to establish territory. They often sing in flight. Their most common song can be mnemonically described as 'k-chinnnng doot' and sounds like two short chips with a dry hiss in between.

Females use warning calls to alert offspring of danger and threatening calls to ward of males from nests. No observations of female songs have been made. Females also use body posture to communicate willingness to mate. When a female encounters a male and is ready to breed, she may crouch with her tail and bill raised, and hold her wings folded and slightly raised. Like most birds, Ammodramus nelsoni perceives its environment through visual, auditory, chemical, and tactile stimuli. (Greenlaw and Rising, 1994)

Ammodramus nelsoni is an omnivore, and procures the bulk of its food from grass stems or on the ground. In warmer months, their diets include insects, spiders, amphipods, and other small invertebrates. During winter months, seeds and grains provide the sparrows' sustenance. (Shriver, et al., 2011)

Females silently abandon their nests and hide when a potential ground predator comes near. She will give warning calls when dependent young are present and fly within 10 to 15 m of nest. Females return to the nest after the potential predator leaves the immediate nest area. An alarm call may be given when an aerial predator approaches, but typically the sparrows silently find cover. No nest-distraction displays have been recorded. Like most sparrows, their plumage features stripes in shades of brown, gray, and black that blend in well with their grassy environments. Known predators on adults and nests include northern harriers, short-eared owls, fish crows, Norway rats, and garter snakes. Though not confirmed, suspected predators include herons, egrets, glossy ibises, American crows, and black snakes. (Greenlaw and Rising, 1994)

As omnivores, these sparrows likely affect local seed distribution as well as insect populations. The adults and young also serve as food for several areal and land predators. Nest parasitism sometimes occurs in Ammodramus nelsoni nests. The only documented brood parasites for this species are brown-headed cowbirds (Molothrus ater). (Greenlaw and Rising, 1994)

Nelson's sharp-tailed sparrows do not have any economic benefits for humans.

There are no known negative effects of Nelson's sharp-tailed sparrows on humans.

The main threat to Ammodramus nelsoni is habitat loss due to human destruction; mostly because of conversion of grassland and marshes for agricultural uses. Because specific water depth is important to the species, it is essential to protect large areas of habitat to make certain that the ideal water conditions are present in at least a few areas within a wetland. Currently, the International Union for Conservation of Nature and Natural Resources lists this species as Least Concern and considers the population to be stable and widespread. However, increasing human development and resulting habitat loss should be monitored closely. As a migratory species, Ammodramus nelsoni is protected under the United States Migratory Bird Act. ("Ammodramus nelsoni", 2011)