Predator removal comprises one management strategy to increase the reproductive success of a prey species of concern, particularly within human-altered landscapes. The efficacy of such an approach, however, depends partly on the extent to which predation risk is additive or compensatory, which remains unknown for many systems. We experimentally reduced the local abundance of deer mice (Peromyscus maniculatus), a primary nest predator of three sagebrush-obligate songbirds—Brewer's Sparrow (Spizella breweri), Sagebrush Sparrow (Artemisiospiza nevadensis), and Sage Thrasher (Oreoscoptus montanus)—during May to August 2019 in western Wyoming, USA, to assess whether nest predation risk was additive or compensatory, and whether nest predator removal could comprise a potentially effective management tool. Deer mouse removal did not affect the daily nest survival of songbirds between experimental and control plots, despite a reduction of 68%–85% in deer mouse abundance within treatment areas. Therefore, nest predation in this system likely operated in a compensatory way, in which deer mice that escaped removal, new immigrants, or other species of nest predator maintained similar levels of nest predation risk regardless of the prevalence of a primary predator. We caution that predator removal may not be an effective management tool in systems that lack barriers to predator immigration or have several alternative species of predators, even when a single species typically is responsible for the majority of predation events.
LAY SUMMARY
Human-induced changes to landscapes can result in some predators of bird nests increasing in abundance, which can decrease the nesting success of avian species of concern. Such predators sometimes are considered by managers to be candidates for abundance reduction programs.
Understanding whether predator removal could comprise an effective tool to increase reproductive success is not well-known in many systems.
We experimentally removed deer mice (Peromyscus maniculatus) within a landscape altered by natural gas extraction to determine whether predation by this primary predator would decrease the nest predation rates of declining sagebrush songbirds: Brewer's Sparrow, Sagebrush Sparrow, and Sage Thrasher.
Despite significant reductions in deer mouse abundance, predator removal did not increase the nest survival of any of the songbird species.
We, therefore, urge caution when considering the use of predator removal as a management strategy geared towards the reproductive success of avian species of concern. Aspects to consider include the permeability of the study system to immigration by other individuals of the focal predator, and whether nests could be discovered and depredated by other predator species in a compensatory manner.
La eliminación de depredadores constituye una estrategia de manejo para aumentar el éxito reproductivo de una especie presa con estatus de preocupación, especialmente en paisajes alterados por la actividad humana. Sin embargo, la eficacia de tal enfoque depende en parte de hasta qué punto el riesgo de depredación es aditivo o compensatorio, lo cual sigue siendo desconocido para muchos sistemas. Experimentalmente redujimos la abundancia local del ratón Peromyscus maniculatus, un depredador primario de nidos de tres aves canoras obligadas de sitios con Artemisia (Spizella breweri, Artemisiospiza nevadensis y Oreoscoptus montanus), durante mayo a agosto de 2019 en el oeste de Wyoming, EEUU, para evaluar si el riesgo de depredación de nidos era aditivo o compensatorio, y si la eliminación de depredadores de nidos podría ser una herramienta de manejo potencialmente eficaz. La eliminación de P. maniculatus no afectó la supervivencia diaria de los nidos de las aves canoras entre las parcelas experimentales y de control, a pesar de una reducción del 68-85% en la abundancia de ratones dentro de las áreas de tratamiento. Por lo tanto, la depredación de nidos en este sistema probablemente funcionó de manera compensatoria, en la cual los ratones que escaparon de la eliminación, los nuevos inmigrantes u otras especies de depredadores de nidos mantuvieron niveles similares de riesgo de depredación del nido independientemente de la prevalencia de un depredador primario. Advertimos que la eliminación de depredadores puede no ser una herramienta de manejo eficaz en sistemas que carecen de barreras para la inmigración de depredadores o tienen varias especies alternativas de depredadores, incluso cuando una sola especie suele ser responsable de la mayoría de los eventos de depredación.
