Stabilized vs. Unstabilized Barrier Islands: How Shoreline Engineering Shapes the Habitat, Prey, and Distribution of Red Knots, Black‑bellied Plovers, and Piping Plovers after Five Years

Abstract

Climate change-driven storms and sea-level rise are altering Mid-Atlantic coastlines at accelerating rates, particularly in barrier-island landscapes. Migrating shorelines threaten coastal infrastructure and create pressure on imperiled shorebirds that depend on high-quality foraging grounds year-round. Shoreline-stabilizing techniques, including beach nourishment, breakwaters, and revetments, are used to mitigate coastal erosion and protect local infrastructure, but their direct and indirect impacts on shorebird populations and their prey are poorly understood. The Virginia barrier island system, recognized for its ecological importance to shorebirds, is currently undeveloped except for one island, Wallops Island, which has undergone various stabilization measures to protect critical infrastructure. This system provides a unique opportunity to expand existing knowledge of how ecological and geomorphic factors influence shorebird foraging habitat use in the context of anthropogenically altered shorelines. The goals of my thesis were to quantify the ecological and geomorphological drivers of the federally threatened piping plover (Charadrius melodus), the federally threatened rufa red knot (Calidris canutus rufa) and the black-bellied plover (Pluvialis squatarola) and their prey in the context of stabilized and unstabilized shorelines in coastal Virginia. We evaluated 4 important foraging habitats (sandy ocean beach, peat banks, bay shoreline, and interior pools) on the 5 northernmost barrier islands in Virginia: partially stabilized Wallops Island and unstabilized Assawoman, Metompkin, Assateague Islands, and Gargatha Beach. In 2024 and 2025, we conducted monthly point count surveys from May 1st to August 31st for breeding season adult piping plovers and from April 15th to June 30th and August 1st to October 15th for migratory red knots, black-bellied plovers, and co-occurring shorebirds, and collected core samples to evaluate benthic prey availability. We also sampled terrestrial insects monthly from May to August due to their importance to piping plover foraging ecology during the breeding season. We implemented Bayesian mixed-effects modeling on a series of a priori candidate models to estimate the effect of distance to the nearest and each individual type of stabilization, along with important environmental and geomorphological covariates, on the presence of all three focal species and their benthic and terrestrial prey densities. We also compared our terrestrial prey densities and habitat distributions with historical data in Virginia and with 2 recent studies in New York and North Carolina to examine geographic or longitudinal differences in terrestrial prey availability for piping plovers in our study. We found that piping plovers were more likely to be present, and total benthic, worm and crustacean prey abundances were higher at greater distances from the stabilization actions during the piping plover breeding season at 4-5 years since the most recent activities. However, other factors such as habitat type and beach width were stronger predictors of piping plovers and their prey than distance to the nearest stabilization, with foraging piping plovers most likely to be present on peat bank habitats and on wider beaches. We found the opposite relationship with benthic insect larvae and terrestrial prey, which were more abundant closer to the stabilization actions during the piping plover breeding season; likely driven by their high abundances in the human-created borrow pool adjacent to the stabilization footprint. We found that red knot presence was more likely farther from the nearest stabilization features in all habitat types, but that stabilization was a weaker predictor of red knot presence than other ecological and geomorphic factors. Black-bellied plovers were strongly influenced by distance to stabilization, with contrasting relationships with stabilization depending on habitat type. Black-bellied plovers were more likely to be present farther from stabilized features when using peat, bay and pool habitats, all of which occurred outside of the footprint of stabilization. However, black-bellied plovers were more likely to be present closer to stabilization when foraging in sandy ocean intertidal habitat. Both red knots and black-bellied plovers were more likely to be present with higher abundances of other shorebirds and increased prey species richness, and black-bellied plovers were more present in areas where the shoreline change rate was negative (e.g., eroding or retreating). Our results showed that 4-5 years after shoreline stabilization actions on Wallops Island, benthic invertebrates in the sandy ocean intertidal zone had recovered to similar densities as the surrounding islands, but the highest densities occurred on peat banks outside stabilized areas. We suggest that future stabilization efforts both create high-quality foraging habitats, such as the borrow pool, within or adjacent to the stabilization footprint and conserve the potential for adjacent areas to respond to natural coastal processes that create bayside, pool, and peat habitats for foraging shorebirds. Future studies should deploy a before-after-control-impact design for at least 4 years pre- and post-action to better understand recovery times of avian and prey metrics, and to better tease out the impacts of individual stabilization actions.