Managing the Threat of Subsidized Predators for a Threatened Shorebird

ABSTRACT Subsidized predators—present at higher densities due to anthropogenic activity—pose a significant conservation challenge to many at‐risk species and are often one of the main factors influencing the decline of many beach‐nesting birds. This study evaluates the efficacy of nest exclosures as an anti‐predator management intervention for western snowy plovers ( Anarhynchus nivosus nivosus ). We base our analyses on 8 years of intensive monitoring of two populations located on military bases in southern California. After placing nest exclosures on a subset of monitored nests, we surveyed all nesting areas at least twice weekly to document nest outcomes and, when possible, infer causes of nest loss. Our findings provide strong evidence supporting the use of exclosures in systems experiencing high predation pressure from subsidized predators. Without exclosures, nest predation rates reached approximately 27% across the nesting cycle, whereas nests protected by exclosures experienced predation rates of less than 2%, representing a ~16‐fold decrease. This intervention significantly improved nest survival, increasing the probability of hatching from 65% to 89% over a 32‐day nesting period. Additionally, we found no significant difference in nest abandonment rates between protected and unprotected nests, suggesting that exclosures did not contribute to increased adult mortality in this study system though it has been documented in other systems. Importantly, nest exclosures complemented, rather than replaced, predator control measures and habitat management strategies aimed at reducing predation risk. Furthermore, ecological factors, such as nest crypsis, were associated with reduced predation, reinforcing the importance of natural camouflage. Our findings underscore the effectiveness of exclosures in protecting nests and highlight the need for integrated conservation strategies that incorporate multiple protective measures to manage threats from subsidized predators.