Effects of barrier island salt marsh restoration on marsh bird occurrence in the northern Gulf of Mexico

Abstract

In the northern Gulf of Mexico, salt marshes are threatened by sea level rise, erosion, and loss of protective barrier islands. These barrier islands provide critical habitat for wildlife, including globally significant populations of marsh and shorebirds. We investigated salt marsh restoration on two Louisiana barrier islands using presence of eight marsh bird species as an index to evaluate restoration success. Land loss was extensive for both islands prior to restoration, with submerged marsh restored by backfilling sediment into the marsh platform. Restoration methods were similar between the two islands, although Raccoon Island was built to a higher elevation (1.1 m) than Whiskey Island (0.8 m). Avian presence was estimated via passive acoustic monitoring and point counts. To evaluate restoration success, we modeled influence of habitat covariates on index species presence in restored and reference (intact) sites over three breeding seasons and modeled occupancy for six species. On Whiskey Island, index richness was higher in restored sites. Marsh specialists Seaside Sparrows (Ammospiza maritima) and Least Bitterns (Ixobrychus exilis) had higher occupancy in restored areas on Whiskey, while generalist species showed no response to site. These results are likely due to a strong association between habitat and vegetation type, with restored sites dominated by Spartina alterniflora and reference sites by Avicennia germinans. On Raccoon Island, species richness was low across all sites. Our results suggest that restoration efforts were successful in creating salt marsh habitat on Whiskey but not Raccoon as of the time of our study.

Coastal bird community response to dredge‐spoil tidal marsh restoration at New Round Island, Mississippi, U.S.A.

“…Field workers noted that marsh vegetation was limited on RNDI to the edges of the containment cells, with the cells still primarily filled with water. This might provide insufficient vegetation cover for Seaside Sparrows (Byerly et al 2020). The depth of containment cells has large impacts on the success of marsh restoration and subsequent colonization by marsh birds (Byerly et al 2020); in the case of RNDI, additional sediment would need to be added to the containment cells to encourage additional marsh vegetation growth.…”