Influences of tidal flooding, plant composition, and habitat openness on saltmarsh songbird occupancy

Saltmarshes are dynamic coastal ecosystems that provide critical breeding habitat for a suite of songbirds, including both obligate saltmarsh specialists and more generalist marsh nesters. These species’ reproductive success depends on nesting in areas subject to regular tidal flooding. However, sea-level rise is increasing flooding frequency and severity while driving marsh migration into adjacent uplands, where newly formed marshes often support vegetation distinct from older areas. We evaluated how plant community composition, tidal flooding, and surrounding environmental features, like elevation and proximity to forest or open water, affect occupancy of four focal marsh bird species across a latitudinal gradient in coastal Virginia. Predictors associated with nearby forested cover were consistently associated with lower occupancy while other species-specific associations were tied to different broad scale geography, landscape cover, and nearby vegetation cover parameters. Obligate saltmarsh-nesting species, such as Ammospiza caudacuta (Saltmarsh Sparrow) and A. maritima (Seaside Sparrow) also showed strong associations with latitude, while more generalist marsh nesters like Cistothorus palustris (Marsh Wren) and Melospiza melodia (Song Sparrow) did not. Vegetation associations reflected different nesting strategies, with Iva frutescens (marsh elder), Sporobolus pumilus (saltmeadow hay), and Juncus roemerianus (black needlerush) contributing positively to occupancy depending on the species. Our findings underscore the importance of conserving marshes that support a variety of conditions, particularly for specialist species.