PS 18-137
Assessing the vulnerability of coastal marsh birds to sea level rise in South Carolina
Increases in storm severity coupled with rising seas and coastal development present major threats for southeastern coastal marsh bird species. Habitat alterations associated with these stressors can leave fragmented and isolated patches of habitat, potentially having adverse effects on species distribution, abundance, and survival. Marsh birds tend to occupy high trophic levels making them valuable indicators of habitat integrity. We investigated current marsh bird distributions along the South Carolina coast in relevant ecologically sensitive areas. Our goal was to see which landscape and local factors drive marsh bird distributions in the southeast and overlay current critical habitat areas with sea level rise models to prioritize key conservation areas. We conducted two different occupancy surveys: broad scale surveys for four marsh bird species and surveys specific for Black Rails (Laterallus jamaicensis). Broad scale survey sites were selected to assess a range of environmental gradients within the marsh. For Black Rail surveys we used a priori hypotheses to select sites based on literature, research questions, and accessibility. Each site was visited three times during April-August 2013 and 2014 and spanned 300 km2 of South Carolina coastal marshes. Occupancy and abundance data were related to a suite of local and regional environmental variables.
Results/Conclusions
Least Bitterns (Ixobrychus exilis) and Clapper Rails (Rallus longirostris) occupied 6.5% and 81% of our sites respectively. Our pilot Black Rail data demonstrated 7% of our sites were occupied, of which all had water levels of less than 5cm, indicating a preference for shallow water habitats. Least Bitterns were strongly associated with relative salt marsh cover within a 200-meter radius (AICwt 0.71), while Clapper Rail abundance was also strongly associated with local cover of S. alterniflora (AICwt 0.52). We used Sea Level Affecting Marshes Model (SLAMM) in the context of current habitat associations to project future habitat availability for focal species. Under a fossil-fuel intensive model for the year 2100, the amount of salt and brackish marsh decreases significantly, becomes fragmented, or is converted to open water. Understanding species sensitivity to habitat changes will help inform future local and regional conservation and management for these species. Data on the Black Rail, where there is a lack of information about the species distribution in South Carolina is especially critical, as anecdotal declines have been noted throughout the Atlantic Seaboard.