Habitat

Seaside Sparrow singing, Jake's Landing, NJ, May

Figure 2. Breeding habitat of the Seaside Sparrow

Breeding Range

Occupies tidal marshes throughout most of range (Kale 1983, Robbins 1983; also see Fig. 2), but with discontinuous local distribution (Greenlaw 1983, 1992). Vegetation use varied and opportunistic (Greenlaw 1983, Post et al. 1983). Most breeding populations require (1) nest sites above spring tides, and (2) openings in vegetation, e.g., pools and creek edges, where birds can forage on open mud and at bases of rooted vegetation. Optimum habitats contain contiguous nesting and feeding sites (Fig. 2); otherwise birds commute between nest-centered territories and separate feeding areas (Tomkins 1941, Post 1974).

Nests above mean high tide mark, mainly in supratidal (high) and intertidal marsh zones, usually covered by fine-textured graminoid vegetation: salt meadow grass (Spartina patens), black grass (Juncus gerardi), and saltgrass (Distichlis spicata) as well as dwarf- and medium-height ecophenes of smooth cordgrass (Spartina alterniflora). Low marsh, dominated by tall form of S. alterniflora, is rarely used for nesting. Birds wintering in areas with high tidal amplitude move up estuaries to breed, in some cases as far as 20 km from ocean (Sprunt 1927, Bull 1974).

In Northeast, medium height S. alterniflora most important in irregularly flooded (mean tide 0.6 m) marshes, where territories are often grouped and small. At Oak Beach NY, where population density was 20 pairs/ha, 20% of nesting area consisted of shallow pools and tidal inlets; new-growth S alterniflora, averaging 80 cm, covered 47%; sparsely vegetated pannes with dwarf form of S. alterniflora and glasswort, 16%; salt meadow grasses (saltgrass and Spartina patens), 2%; mixture of persistent, medium-height S. alterniflora and S. patens, 5%; reed, 6%; unvegetated shallow pools, 4%; wrack, 2% (Post and Greenlaw 2006).

In Massachusetts high marshes, medium-height S. alterniflora is widespread, growing on the edges of creeks and ditches, thus providing a variety of foraging microhabitats. Here, the sparrows’ preference for medium-height S. alterniflora is demonstrated: 82% of early season nests were in this form of grass, although it comprised only 12% of the cover (Marshall and Reinart 1990). 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. Marsh elder (Iva frutescens) covered 4% of the area but was not found in any territories.

Coastal habitats in 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 needle-rush (Juncus roemerianus). In a S. Carolina high (irregularly flooded) marsh, where Seaside Sparrow population density was 7.5 pairs/ha, scattered patches of needle-rush covered 40% of the site; medium-height S. alterniflora 30%; saltgrass 10%; areas of sparse short vegetation 15%. (WP)

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 male Seaside Sparrows/ha: S. alterniflora 38%; needle-rush 26%; saltgrass, 23%; glasswort (Salicornia) 8%, saltwort (Salsola,3%) (Post et al. 1983)

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 Cape Sable Seaside Sparrow (A. m. mirabilis) was first found nesting in discontinuous stands of sand cordgrass (60% frequency of dominance, with average height of 3 m), intermingled with patches of sea-puslane (Sesuviam maritimum; 25%) and spike-rush (Eleocharis, 15%) (Howell 1919, Werner and Woolfenden 1983). This sub-species has recently nested in 4 distinct prairie habitats, composed of (1) clumped and (2) unclumped S. bakeri, (3) sparse sawgrass (Cladium jamaicense), (4) muhly grass (Muhlenbergia capillaris) (Werner and Woolfenden 1983, Kushlan and Bass 1983). The majority of the mirabilis population now inhabits muhly grass prairie, (Lockwood et al 1997).

Nonbreeding Period

Transients concentrate in tall stands of smooth cordgrass, usually in sheltered areas along waterways. Smooth cordgrass has higher concentration of arthropods (Davis and Gray 1966, Post et al. 1983), as well as higher yield of seeds (L. A. Wood pers. comm.), than other salt-marsh plants. ). Resident Seaside Sparrows in S. Carolina regularly winter in tall S. alterniflora growing in the intertidal zone along creeks and bay edges near nesting areas (WP). In winter, local movements made between feeding areas and roost sites on marsh islands, where vegetation, mainly groundsel (Baccharis halimifolia), wax myrtle (Myrica cerifera), and sea-ox-eye (Borrichia frutescens) is rarely flooded. About 30% of probable migrant birds on a S. Carolina hammock returned the following year (Austin 1966).

Winter home ranges of A. m. mirabilis did not shift with changes in water depth; when water rose, sparrows occupied parts of home range that had fewer openings and higher vegetation such as sawgrass. 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 (Dean and Morrison 1999).