Spatial and Temporal Changes in Emergent Marsh and Associated Marsh Birds of the Lower Mobile-Tensaw River Delta in Alabama, USA

Abstract

Sea-level rise, suppression of natural disturbances, and human development of coastal lands have influenced the capacity of tidal marshes to maintain quality habitat for wildlife, including coastal marsh birds. This study targeted the oligohaline marshes of the lower Mobile-Tensaw River Delta, Alabama, USA with the objective of assessing landcover and marsh bird distributional changes relative to two sampling periods, 2004 and 2015. We employed analysis of aerial imagery and standardized marsh bird surveys to derive information on the densities of common gallinule (Gallinula galeata), king rail (Rallus elegans), and least bittern (Ixobrychus exilis) during each sampling period. A gradient of land change was apparent where the northernmost and the southeastern portions of the study area lost land from 2006 to 2013 while the extent of emergent marsh wetland increased in the south and decreased in the north. Average densities of all three birds declined between survey periods (common gallinule 15%, king rail 50%, least bittern 38%). Changes in the distributions of these marsh birds reflected change in landform and emergent marsh habitat. This study reveals that tidal wetlands and associated communities do not change through linear processes. Rather, coastal wetlands may show distinct patterns surrounding areas of accretion, and loss.