Seaside Sparrow Ammospiza maritima Scientific name definitions

Jon S. Greenlaw, W. Gregory Shriver, and William Post
Version: 2.0 — Published July 1, 2022


Habitat in Breeding Range

Occupies tidal marshes along coasts throughout most of range (49, 50), but with discontinuous local distribution (115, 113). Use of vegetation is variable and opportunistic (115, 3), but broad patterns of marsh intertidal patch use exist. Most breeding populations require: (1) nest sites above spring tides, and (2) openings in vegetation (e.g., pools, paanes, and channel edges, and sufficient space between grass stems where birds can forage on open mud and around bases of rooted vegetation with access to vegetation profile at edges). Optimum habitats contain contiguous nesting and feeding sites within a single territory; otherwise birds commute between nest-centered territories and separate feeding areas (53, 116, Laskaris 2016). Dense local populations in a natural (unditched) marsh on Long Island, New York, were associated with areas of medium-height Spartina alterniflora (smooth cordgrass) in upper intertidal where persistent grasses often form clumps (nest-sites in early spring) and breaks in ground cover provide access to ground-foraging sites; this pattern was noted elsewhere in the immediate region (115).

Nests above mean high tide mark, chiefly in Spartina alterniflora-dominated low-marsh of upper intertidal situations in most parts of range, although vegetation on territories can vary among marshes within and between regions depending on local and geographic circumstances (3, 117; see below for important exceptions in habitat of A. m. macgillivraii near Charleston, South Carolina, A. m. mirabilis, and A. m. sennetti). Higher sparrow densities (ca. 20 pairs/ha) in marshes with well-developed low marsh in the northeastern United States are restricted to intermediate height (~0.5–1.0 m) S. alterniflora with prevalent thatch that tends to form semi-erect clumps locally after winter snows melt. Densities of 30 pairs/ha or more (118, 116) can occur where territories are nest-centered and small (116). In ditched marshes dominated by supratidal graminoid vegetation, sparrow territories in New York were large and multiple-use. Clumps of taller grasses grew on ditch berms, sometimes near or in Iva frutescens that occasionally or rarely are used as nesting substrate (116; S. E. Reinert in Rhode Island, personal communication). In contrast in South Carolina, high densities occurred in an impounded marsh (1 of 3 plots) at an estimated 68 birds/ha (perhaps about 34 pairs/ha, but altogether on 3 plots, 61% of adults captured were males ), where activity spaces (foraging and nesting) were about 1.7 ha (68). In some ditched marshes where nesting sparrows are uncommon or very local, sparrows nest in areas of higher grass height and density with some high-marsh graminoids near the nests, such as Spartina patens, Juncus gerardi, and Distichlis spicata (saltgrass). Low marsh dominated by tall form of S. alterniflora flooded daily is avoided for nesting but may be used for foraging at low tide when mud is exposed. Where black needlerush (Juncus roemerianus) becomes dominant in upper tidal marshes from coastal Virginia southward to Florida , sparrows also breed in that vegetation type (119, 68). However, marsh rice rat (Oryzomys palustris), a dominant nest predator that favors Juncus for rearing young and are widespread in southern areas, can discourage sparrows from using this vegetation more than it does (119). Birds overwintering in areas with high tidal amplitude move up estuaries to breed in brackish marshes where tidal amplitude is low, notably in sparrows of the Charleston population (above) of A. m. macgillivraii, in some cases traveling as far as 20 km from the ocean (120, 121, 69, 70).

In northeastern United States, medium height S. alterniflora is most important in irregularly flooded (mean tide 0.6 m) marshes, where territories are often grouped and small. At Oak Beach, New York, where population density was 20 pairs/ha or more, 20% of nesting area consisted of shallow pools, open mud patches, and tidal inlets; new-growth S. alterniflora, averaging 80 cm (medium height ecophene; 122), covered 57%; sparsely vegetated pannes with dwarf form of S. alterniflora and glasswort (Salicornia), 16%; salt meadow grasses (saltgrass and S. patens), 2%; mixture of persistent, medium-height S. alterniflora and S. patens 5%; reed 6%; unvegetated shallow pools 4%; wrack 2% (123). In Delaware, along shore of Delaware Bay, nests in typical saltmarshes near the bay and in brackish marshes somewhat inland where shrubs and a sedge (Schoenoplectus americanus) are more prevalent closer to upland vegetative habitats. In both marsh types, nest sites commonly are in areas of Spartina alterniflora, but in the latter marsh type, 13% of nest sites included the sedge S. americanus (124).

In a Massachusetts tidal marsh, medium-height Spartina alterniflora, grew on the edges of creeks and ditches, thus providing a variety of foraging microhabitats. Here 77% of nests were placed in medium height S. alterniflora, although it comprised only 12% of the cover. Salt meadow grasses covered 50% of the area, while they comprised 34% of territory cover. The tall form of S. alterniflora (> 100 cm) was uncommon on the territories. Iva frutescens (marsh elder) covered 4% of the area, but was not found in any territories (117).

Coastal habitats in the Southeast and Gulf of Mexico have vegetative structure similar to that in the Northeast, although plant diversity is greater, and S. patens tends to be replaced by saltgrass, drop-seed (Sporobolus virginicus), and black needlerush. In a high (irregularly flooded) marsh in South Carolina, where Seaside Sparrow population density was 7.5 pairs/ha, scattered patches of black needlerush covered 40% of the site, medium-height S. alterniflora 30%, saltgrass 10%, and areas of sparse short vegetation 15% (WP). In another brackish marsh west of Charleston, South Carolina, the first subcoastal breeding population of A. m. macgillivrarii was found in 1924 in which nests were located in clumps of "bulrush" (Cyperaceae) (125). This early site is now vacated by sparrows and they currently nest farther down the same river on a marsh on Headquarters Island (see "WP" information above). This upriver site is about 10 km from the coast. At another breeding location in Georgetown County, South Carolina, farther north and closer to the coast, macgillivraii nested in three habitats covering a polyhaline range (salinity 18–30 ppt). Lowest density of sparrows was in an area covered chiefly by thick stands of black needlerush (estimated 5 birds/ha) while the highest density had roughly 13 times more birds (about 68 birds/ha) in a nearby area in an impoundment (non-tidal) with a few cm of standing water and a mixed plant cover of tall and short forms of S. alterniflora, saltgrass, and small stands of black needlerush. An intermediate density plot had plant cover comprised of a short-form of smooth cordgrass with interspersed large stands of black needlerush (68). In contrast to other coastal breeding locations, breeding habitat used by A. m. sennetti in Cameron County, Texas, is unlike the intertidal, Spartina-dominated habitat elsewhere in much of its range. Rather, favored habitat is in saltwort (Batis maritima) and sea oxeye daisy (Borrichia frutescens) (77, 78, 52). This isolated population is associated with a distinctive genetic population structure as is the isolated populations of A. m. mirabilis in the Everglades (12).

In east-central Florida, the Dusky Seaside Sparrow (A. m. nigrescens) occupied coastal salt marshes, as well as freshwater prairie, covered primarily by sand cordgrass (Spartina bakeri). The percent relative cover of vegetation at Gulf Hammock, Florida, an irregularly flooded marsh (average tide 0.8 m) that had a density of 1.6–2.6 males/ha: S. alterniflora 38%; black needlerush 26%; saltgrass 23%; glasswort 8%, and Salsola kali 3% (3). However, most sparrows nested in Distichlis and Salicornia (3). In south end of range of Scott's Seaside Sparrow, the species is resident only in black needlerush stands. Optimal conditions at one site, high count of 20 males registered, characterized by muck soil, tall black needlerush as high as 170 cm, no mosquito ditching, and presence of natural saltwater channels and pools. Ground cover at site consisted of 96% black needlerush, 2% S. alterniflora, and 2% black mangrove (Avicennia germinans) seedlings and other grasses (80).

The Cape Sable Seaside Sparrow (A. m. mirabilis) today is a freshwater species. Where it formerly occurred in the Cape Sable area of coastal Everglades National Park, it evidently also occurred in brackish habitat with discontinuous stands of sand cordgrass (60% frequency of dominance, with average height of 3 m), intermingled with patches of sea-purslane (Sesuviam maritimum, 25%), Distichlis, and spike-rush (Eleocharis, 15%) (81, 7). This subspecies has nested in 4 distinct inland prairie habitats, composed of (1) clumped S. bakeri, (2) unclumped S. bakeri, (3) sparse sawgrass (Cladium jamaicense), and (4) muhly grass (Muhlenbergia capillaris) (7, 126). Currently, the majority of the population now inhabits muhly grass prairie (marl prairie) (8), although individuals will select nest sites in areas that have mixed composition of muhly grass, Rhynchospora (beaksedge), and Schizachyrium scoparium (9). High sparrow densities occur in patchy areas of high coverage of muhly grass, ground litter, and tall vegetation heights where sparrows build nests and where in other parts of a male's territory openings around grass bases and clumps of grass allow sparrows to forage (9). Specifically, A. m. mirabilis only nests within the grass layer of these prairies, while avoiding shrubs. Fires are a natural occurrence in A. m. mirabilis habitat. Hypothesized benefits of fire for sparrow numbers under 'normal' hydrologic conditions are believed to be soil depth, vegetation growth rates, and prevention of excessive litter depths. Prescribed fires occur at about 4 year intervals (9). Extreme hydrologic conditions resulting from excessive flooding (too short hydroperiods) impacts vegetation composition, which influences sparrow numbers negatively; hydroperiods of 90–180 days appear to be best for sparrows in muhly-dominated, seasonally wet marl prairie (127).

Automated broadcast of primary (territorial) songs of A. m. mirabilis in unoccupied, suitable habitat at the beginning of territory establishment provided support for the hypothesis that direct public information (conspecific song) influenced habitat selection and territory establishment by individual males (128). See Vocalizations: Social Context and Presumed Functions of Songs.

Habitat in Nonbreeding Range

Habitat in Migration

Little is known about habitat use during migratory stopover. Of 40 individuals that overwintered on Kiawah Island (south of Charleston, South Carolina) and marked with GPS dataloggers to track local and regional movements, 2 individuals migrated north to spend the summer in tidal marshes along the Delaware Bay in New Jersey (70). All stopover sites used by these two birds during fall migration were salt marshes varying in size from the expansive marshes of Bombay Hook National Wildlife Refuge in Smyrna, Delaware, to a relatively small, isolated salt pond in Bethany Beach, Delaware.

Habitat in Overwintering Range

Transients concentrate in tall stands of Spartina alterniflora, usually in sheltered areas along waterways. S. alterniflora has higher concentration of arthropods (129, 3), as well as higher yield of seeds (L. A. Wood, personal communication), than other saltmarsh plants. Resident individuals in South Carolina (A. m. macgillivraii) regularly overwinter in tall S. alterniflora growing in the intertidal zone along creeks and bay edges near nesting areas (WP). Resident populations of Scott's Seaside Sparrow (A. m. peninsulae) at south end of range in west-central Florida (Pasco County), occur only in black needlerush stands (80). In contrast, about 100 km north in Gulf Hammock (Levy County), A. m. peninsulae was resident in a plot where ground coverage of S. alterniflora was 38% and black needlerush 26% (130, 3). In winter, local movements were made between feeding areas and roosting sites on marsh islands, where vegetation, mainly groundsel (Baccharis halimifolia), wax myrtle (Myrica cerifera), and sea oxeye daisy, floods rarely (WP, South Carolina).

Habitat suitability in winter is perhaps important in determining sparrows' choice of habitats occupied year round. Most suitable are areas containing a variety of vegetation types and structures under varying water depths (131).

Recommended Citation

Greenlaw, J. S., W. G. Shriver, and W. Post (2022). Seaside Sparrow (Ammospiza maritima), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.seaspa.02