Habitat edges influence the distribution of nest predators for Seaside Sparrows, but not nest placement or success

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Oxford University Press

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 the conservation of salt marsh-dwelling bird species, such as the Seaside Sparrow (Ammospiza maritima). Predator activity may be influenced by landscape features (particularly habitat edges), potentially making nest predation predictable. We aimed to understand the predictability of Seaside Sparrow nest predation relative to two major landscape features: roads and tidal rivers, as both of these edges may be entryways or attractants for predators in marshes. In coastal Georgia, USA, we assessed mammalian predator activity relative to the two features of interest, and hypothesized that mammalian 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 first hypothesis, mammalian predator activity increased close to roads and tidal rivers, but mammalian predator distribution did not explain the spatial variation in Seaside Sparrow nest predation thus not supporting our second hypothesis. Seaside Sparrows also placed their nests in locations with high mammalian 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 allow for focused predator management efforts, such as exclusion, to habitat edges where we found the highest mammalian predator activity, which could relax the constraint of nest predation on Seaside Sparrow's ability to respond to the intensifying threat of sea level rise. Lay Summary center dot Seaside Sparrows (Ammospiza maritima) nest in salt marsh grasses. If a nest fails from flooding, they elevate their next nest. However, nests higher from the ground experience increased predation risk. center dot Understanding the spatial pattern of nest predation across Seaside Sparrow habitat is critical in the face of increased nest flooding from sea level rise. center dot We predicted that mammalian predator activity would increase along habitat edges adjacent to roads and rivers in Glynn County, Georgia, and that Seaside Sparrow nests would experience increased predation in these areas. Mammalian predator activity increased near road and water edges, but Seaside Sparrows placed their nests in locations with high predator activity, and nest predation was not correlated with mammalian predator activity. Marsh Wrens depredated Seaside Sparrow nests and may have had an important impact on nest predation patterns. center dot Our results suggest that future predator management be focused on habitat edges along roads and waterways.

Ammospiza maritima, coastal marsh, nest predation, predator, Seaside Sparrow