Newsome, C.N., and E.A. Hunter. 2022. Habitat edges influence the distribution of nest predators for Seaside Sparrows, but not nesting decisions or success. Ornithological Applications 124:duac023.
Nest failure for coastal marsh bird species is primarily caused by predation and nest flooding. As sea level rise makes nest flooding more likely, the threat of nest predation will constrain the potential adaptive responses of marsh nesting species. Thus, understanding the predictors of nest predation is important for conservation and management of birds inhabiting coastal marshes, such as Seaside Sparrows (Ammospiza maritima). Predator activity may be influenced by landscape features (particularly edges between marshes and other habitats), potentially making nest predation predictable. We aimed to understand the predictability of Seaside Sparrow nest predation relative to two major landscape features: distance to roads and distance to tidal rivers, as both of these edges may be entryways or attractants for predators in the marsh. In coastal Georgia, USA, we assessed mammalian predator activity relative to the two features of interest, and hypothesized that predator activity would be greater close to roads and tidal rivers. We also recorded Seaside Sparrow nest locations and nest predation events and hypothesized that nest predation events would increase with increasing predator activity. Consistent with our hypothesis, predator activity increased close to roads and tidal rivers, but mammalian predator distribution did not explain the spatial variation in Seaside Sparrow nest predation. Seaside Sparrows also placed their nests in locations with increased predator activity, indicating that the ability to avoid nesting in high risk areas may be constrained by habitat or resource limitations. Additionally, mammals may not be the primary nest predators, as we found that one bird species (Marsh Wren, Cistothorus palustris) contributed substantially to nest predation rates. Understanding the predictability of mammalian predator distribution can contribute to predation risk management for Seaside Sparrows, which could relax the constraint of nest predation on the species’ ability to respond to the intensifying threat of sea level rise.