Systematics

Figure 1. Breeding and year-round ranges of the Seaside Sparrow, by subspecies

Geographic Variation

Plumage color and pattern vary somewhat clinally along the Atlantic Coast and Gulf of Mexico, but two populations—the Dusky Seaside Sparrow (A. m. nigrescens) and Cape Sable Seaside Sparrow (A. m. mirabilis)—formerly were classified as species (e.g., Am. Ornithol. Union 1957). Along the Atlantic Coast, birds are paler from south to north, with darkness peaking in central Florida (Griscom 1944, McDonald 1988). Genetics (Avise and Nelson 1989, Nelson et al. 2000) and biogeography (Funderburg and Quay 1983, Werner and Woolfenden 1983) imply two phylogenetically distinct groups, one on the Atlantic Coast and in the Everglades and the other along the Gulf of Mexico east to nw. Florida, but plumage does not fall neatly into such a grouping. Rather, Gulf birds most closely resemble Atlantic birds, and two geographically intermediate populations isolated on peninsular Florida (one now extinct) are the most distinctive (McDonald 1988). Size generally diminishes from north to south along the Atlantic Coast (McDonald 1988). On the Gulf coast, size generally decreases from north to south on the Florida peninsula and from east to west from the Florida panhandle to s. Texas, although differences are slight (McDonald 1988). Song also varies geographically, with populations isolated on peninsular Florida the most divergent (Hardy 1983).

Subspecies

Seven subspecies (Fig. 1), generally following Mary V. McDonald (1988) who, with Herbert Kale II, examined >1300 specimens from throughout the species’ range. Treatment here differs in that -- until a more refined examination of Atlantic Coast birds is performed -- the broadly similar nominate subspecies and A. m. macgillivraii are retained.

A. m. maritimus (Wilson, 1810). Breeds coastally from New Hampshire (occasionally Maine) south to n. North Carolina (type locality = Great Egg Harbor, New Jersey, fide Oberholser 1931); winters coastally from Virginia south to ne. Florida. Dorsum gray, with or without relatively pale streaking; ventrum grayish white with buff breast band pale.

A. m. macgillivraii (Audubon, 1834). Includes A. m. waynei (Oberholser, 1931), A. m. pelonotus (Oberholser, 1931), and A. m. shannoni (Bailey, 1931). Resident coastally from n. North Carolina to s. Georgia (type locality = Charleston, South Carolina) and, formerly, ne. Florida. Like A. m. maritimus but streaking dorsally and ventrally thicker and darker; averages slightly smaller. Birds of intermediate plumage in hybrid zones with A. m. martimus to the north and A. m. nigrescens to the south were named as subspecies by Oberholser (1931), but these individuals generally fall within the broad range of variation of A. m. macgillivraii (Tomkins 1937, Kale 1983, McDonald 1988).

A. m. nigrescens Ridgway, 1873. Extinct resident of coastal mid-Atlantic Florida (type locality = Indian R., Florida). Dorsum dark fuscous; ventrum white, lacking a breast band and streaked heavily with fuscous.

A. m. mirabilis (Howell, 1919). Endangered resident of Everglades region of Florida (type locality = Cape Sable, Florida). Dorsum greenish olive; ventrum white, lacking a breast band and streaked lightly with brown; with A. m. sennetti, the smallest subspecies (McDonald 1988). Unlike all other subspecies, A. m. mirabilis occurs in freshwater habitats rather than salt marshes (Post and Greenlaw 2000).

A. m. peninsulae Allen, 1888. Includes A. m. junicola (Griscom and Nichols, 1920). Resident of Gulf coast of peninsular Florida, from the panhandle to Tampa Bay (type locality = Tarpon Springs, Florida). Dorsum brownish black; ventrum gray with buff breast band faint. Birds in w. Florida panhandle are intermediate between A. m. peninsulae and A. m. fisheri.

A. m. fisheri Chapman, 1899. Includes A. m. howelli (Griscom and Nichols, 1920). Resident coastally along Gulf of Mexico from Alabama west to ne. Texas (type locality = Grande Isle, Louisiana). Dorsum olive gray, with or without dark brown streaking; ventrum grayish white with buff breast band bright.

A. m. sennetti Allen, 1888. Resident coastally in s. Texas, from Aransas Bay to Boca Chica (type locality = Corpus Christi, Texas); winters south to mouth of Rio Grande, Tamaulipas (Howell and Webb 1995). Dorsum greenish gray, generally lacking streaks; ventrum grayish white with buff breast band faint and tinged yellow; averages smaller than A. m. fisheri (McDonald 1988). Birds in central Texas are intermediate toward A. m. fisheri.

Related Species

Among the passerines with nine primaries (see Klicka et al. 2007), the Emberizidae (Old World buntings and New World sparrows and seedeaters) is closely related to the Cardinalidae (New World grosbeaks and buntings), Thraupidae (tanagers), and Icteridae (New World blackbirds and orioles). Within the Emberizidae, the sparrows and towhees form a distinct clade (e.g., Grapputo et al. 2001), in which Ammodramus groups with other “grassland” genera such as Passerculus and Pooecetes.

On the basis of skeletal characteristics (Robins and Schnell 1971), mitochondrial DNA and allozymes (Zink and Avise 1990, Avise and Walker 1998, Klicka and Spellman 2007, JSG), and behavior and vocalizations (JSG), the Seaside Sparrow’s nearest relatives are the sharp-tailed sparrows (A. caudacutus and A. nelsoni). An apparent female hybrid A. maritimus -- A. caudacutus was collected near New Haven, Connecticut (Sage et al. 1913), and the two species have been observed copulating (Montagna 1942).