Marsh bird occupancy along the shoreline‐to‐forest gradient as marshes migrate from rising sea level

Abstract

AbstractOne mechanism by which coastal marshes may persist as sea‐level rises is to expand landward into existing forest, a process known as marsh migration. Though recent studies highlight the importance of marsh migration to the conservation of birds associated with coastal marshes, marsh bird responses to this transition from forest to marsh are poorly understood. To address this need, we conducted surveys of five focal marsh bird taxa at 92 points distributed across the gradient from the shoreline to the marsh–forest interface in one of the most vulnerable regions to sea‐level rise in North America where marshes have been migrating landward for at least several decades. Given this landward movement of the forest–marsh interface, we modeled focal taxa occurrence as a function of distance‐to‐forest, thereby assuming that marshes closer to the forest were newer than those closer to the shoreline. In addition, we investigated the effects of vegetation conditions and fire frequency. Occupancy probability of marsh birds decreased closer to the forest–marsh interface where woody vegetation was taller and herbaceous cover was dominated by Cladium jamaicense, suggesting migrated marsh may provide limited habitat for these bird species, at least in the short term. Though parameter estimate uncertainty for black rail (Laterallus jamaicensis) was high due to a limited number of detections, occupancy of this species may increase with the conditions associated with migrated marsh, specifically greater C. jamaicense dominance and decreasing distance‐to‐forest. Clapper/king rail (Rallus crepitans/elegans) occupancy was greater at sites that had burned more frequently over the past decade, and occupancy of all focal taxa was greater in areas with vegetation conditions consistent with the effects of fire in coastal marshes, including reduced herbaceous vegetation density and shorter woody vegetation. As such, prescribed fire may serve as an effective method of facilitating marsh migration and increasing the quality and quantity of habitat for coastal marsh birds as sea‐level rises.