First Confirmed Records of Parasitism of Seaside Sparrow Nests by Brown-Headed Cowbirds

Molothrus ater (Brown-headed Cowbird) is a known nest parasite for numerous North American passerines and has exacerbated the decline of many imperiled landbird species. However, Brown-headed Cowbird habitat preferences do not frequently overlap with many salt marsh-dwelling species. During intensive demographic research of Ammodramus maritimus (Seaside Sparrow) in the coastal salt marshes of Mississippi (2010-2012), we documented the first instances of confirmed nest parasitism of Seaside Sparrows by Brown-headed Cowbirds. We suggest that sea-level rise could increase instances of nest parasitism in marsh-dwelling passerines by increasing the perimeter-to-area ratio of marsh habitat and moving existing marsh in closer proximity to habitats preferred by Brown-headed Cowbirds.