The Seaside Sparrow is a habitat specialist of salt and brackish marshes. First described by Wilson (1), it has attracted the interest of systematists since the late 1800s. Occurring in relatively small, localized populations along the Atlantic and Gulf coasts of the United States, this species has been divided into several morphologically distinct subspecies.
The Seaside Sparrow is socially monogamous, though extrapair matings have been reported from South Carolina. The species is territorial, but often feeds long distances from the defended space around its nest, a response to the wide separation of nesting and feeding areas in tidal zones it inhabits. Under ideal conditions, it may occur at high population densities, a reflection of the high productivity of salt marshes. Optimal habitat is found in marshes with expanses of medium-high cordgrass with a turf of clumped, residual stems. Especially suitable are spots not subject to extreme flooding that have open muddy areas for feeding. Nest mortality of northern populations is caused mainly by storm flooding; flooding is a significant mortality factor among southern groups, but predation is also important, and its intensity is often related to changes in water levels.
As a maritime wetland specialist, the Seaside Sparrow is a potentially valuable “indicator” of ecological integrity of certain types of coastal marshes and has already proven sensitive to habitat modification in Florida; e.g., the melanistic Dusky Seaside Sparrow (A. m. nigrescens) of east-central Florida is now extinct, and the pale Cape Sable Seaside Sparrow (A. m. mirabilis) of the Florida Everglades is endangered. Other populations are as likely to be susceptible to habitat disturbance and restriction as those in Florida. The species has been studied in detail in the Northeast (2, 3) and Florida (3, 4, 5).