Prioritizing bird conservation under northern raccoon predation: assessing species vulnerability from nesting success

Résumé fourni par la source

In recent decades, the raccoon ( Procyon lotor ) has expanded its range through repeated human-mediated introductions in Europe and Asia. In North America, its native range has also extended northwards, with marked increases in population densities, driven by greater food availability, declines of apex predators, reduced fur harvesting, and changes in land use and climate. As an opportunistic predator with strong climbing, swimming, and digging abilities, raccoons readily access eggs and nestlings of many bird species, posing a growing concern for avian conservation in both native and introduced ranges (Larivière 2004). To specifically assess the effects of raccoon predation on bird species, we adapted the Environmental Impact Classification for Alien Taxa (EICAT) framework (IUCN 2020), a standardized and evidence-based scheme widely used to assess the severity of impacts of alien species on native biota. In particular, we refined the original EICAT categories by subdividing and translating them into a semi-quantitative vulnerability index that helps to better account for variation in the magnitude of effects on bird nesting success and population size. Our approach enables an assessment of predation consequences across bird species, environmental conditions, and spatial scales. We applied our approach to compare the predation effects of raccoon on a suite of North American bird species with contrasting nesting behaviours and life-history traits: great blue heron ( Ardea herodias ), mallard ( Anas platyrhynchos ), northern bobwhite ( Colinus virginianus ), American oystercatcher ( Haematopus palliatus ), American herring gull ( Larus smithsonianus ), ancient murrelet ( Synthliboramphus antiquus ) and prothonotary warbler ( Protonotaria citrea ). Quantitative information on raccoon effects on nesting success and population trends was compiled through a systematic literature search in scientific databases, yielding 80 relevant publications. The ancient murrelet, a burrow-nesting seabird nesting on islands, appears to be the most vulnerable species. Raccoons are known to readily excavate burrows and kill large numbers of eggs, chicks and adults after a few individuals were introduced on breeding islands. Predation caused a very sharp decline in the nesting bird population and led to its local extinction in some areas within less than ten years (Gaston and Masselink 1997). In great blue herons and American herring gull, raccoon predation and disturbance of nests lead to colony decline or abandonment, reducing local reproductive output; however, available evidence suggests only moderate population decline due to frequent changes in colony locations in response to disturbance. The impact of raccoon on the nesting success of American oystercatcher and prothonotary warbler is highly variable across time and space and strongly depends on environmental conditions that determine predator access to nests. By contrast, impacts appear less severe for mallard and northern bobwhite despite repeated nest predation by raccoons and other mesopredators; these species exhibit life-history traits, such as short generation time, high reproductive output and the ability to produce multiple broods within a single breeding season, that likely buffer population-level consequences of nest predation. Overall, we provide a standardized, evidence-based approach to classify the ecological effects of raccoon predation on bird species across different contexts. Its application across regions (i.e. native and introduced ranges) enables more consistent comparisons. In particular, patterns observed in North America can inform general predictions about the ecological conditions and species most vulnerable to predation in newly invaded areas. Furthermore, this framework can support monitoring and management by identifying bird species and contexts in which raccoon predation is most likely to drive population declines. In doing so, it helps anticipate high-risk situations and guide both early intervention and long-term control strategies.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.