Seaside Sparrows spend their entire lives in the dense grasses of coastal salt marsh. Christmas Bird Count data show a steady decline since the 1960s in the central Gulf Coast states, where the bird was most abundant. BP oil persists in significant quantities in some coastal salt marshes, putting Seaside Sparrows at continued risk of direct oiling and contaminated or reduced food supplies, plus habitat loss in areas where heavy oiling actually killed marsh. The Dusky Seaside Sparrow, a Florida subspecies, went extinct in 1987 because of a combination of food chain contamination and habitat manipulation and destruction.
The Seaside Sparrow is a chunky songbird with a substantial bill. On average, the bird weighs almost 1 ounce and measures 6 inches in length, with a wingspan of 7.5 inches. Under most conditions, the Seaside Sparrow's plumage appears dark and blurry. The throat is whitish and the folded wings brownish, but the back and underparts are olive gray with indistinct streaks. In good lighting, a yellow patch may be visible in front of the eye.
With a long bill and large feet, the Seaside Sparrow can probe the mud, scratch the loose wrack, climb through dense stands of grass, and chase prey across the soft ooze exposed by the tide. These birds are fairly omnivorous and consume insects, spiders, snails, beach fleas, and worms during the breeding season. Seeds are eaten in the fall and winter. Seaside Sparrows have the ability to drink saltwater.
Along the Gulf of Mexico, scattered populations breed from the Texas-Mexico border to the mid-coast of Florida. Males sing a buzzy song from exposed perches. In territorial disputes, males fight vigorously from the ground and up into the air. Monogamous pairs bond with complex displays, and females defend their nests from rival species, like Marsh Wrens. The female sparrow builds a nest of course and fine grasses, and attaches it to a cluster of grass or a small woody plant. She lays two to five whitish eggs, splotched with brown, that hatch after about 12 days. The pair feed the chicks together. The young leave the nest in about nine days, though they cannot fly for at least another week. Following a nest failure, pairs often re-nest, or produce a second clutch. Juvenile Seaside Sparrows form loose flocks in taller vegetation and cooperate in their mutual defense.
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