Long-term winter food supplementation shows no significant impact on reproductive performance in Mountain Chickadees in the Sierra Nevada Mountains

ABSTRACT Supplemental feeding of wild animal populations is popular across many areas of the world and has long been considered beneficial, especially to avian taxa. Over 4 billion dollars are spent by hobby bird feeders in the United States each year alone. However, there is mixed evidence whether wildlife feeding is beneficial, including when it is implemented as a conservation management tool, a targeted experimental design, or an avocation. Much of the current evidence suggests that providing supplemental food is advantageous to the reproductive output and general survival of focal taxa. However, many of these studies are limited in scope and duration, leaving possible negative impacts unaddressed. This is particularly true regarding passive backyard feeding, which describes the majority of supplemental feeding, including the immense effort of millions of public enthusiasts. Here we show that winter supplemental feeding prior to reproduction had no significant impact on a range of reproductive parameters in a resident, montane passerine species, the Mountain Chickadee (Poecile gambeli). This population resides in an intact natural environment with no exposure to supplemental food beyond our experimental treatments, and individual birds were tracked across six years using radio frequency identification technology. Our results add to the growing evidence that supplemental feeding alone, isolated from the effects of urban environments, may have little to no impact on the population dynamics of some avian taxa. LAY SUMMARY Supplemental feeding of avian species has been linked to beneficial, negative and neutral outcomes. Understanding the drivers behind these differences are important for understanding human impacts on avian populations as well as developing future conservation management plans. We tracked a population of Mountain Chickadees from two elevations in the Sierra Nevada, USA for nine years and compared the breeding performance of pairs that used versus those that did not use feeders available throughout the winter. The provisioning we provided is likely similar to the passive backyard feeding observed by many across the world but was conducted in an isolated natural coniferous forest environment. Despite the robust long-term dataset and intensive reproductive monitoring, we found no significant differences in the reproductive performance of chickadees that accessed feeders and those that did not. Our results add to the evidence that the effects of passive or targeted supplemental feeding are context and species dependent. RESUMEN La alimentación suplementaria de las poblaciones de animales silvestres es popular en muchas áreas del mundo y durante mucho tiempo se ha considerado beneficiosa, especialmente para los taxones de aves. Cada año se gastan más de cuatro mil millones de dólares en comederos para aves por parte de aficionados en los Estados Unidos. Sin embargo, existe evidencia contradictoria sobre si la alimentación de la vida silvestre es beneficiosa, incluso cuando se implementa como una herramienta de gestión de la conservación, un diseño experimental específico o un pasatiempo. Gran parte de la evidencia actual sugiere que proporcionar alimentos suplementarios es ventajoso para el desempeño reproductivo y la supervivencia general de los taxones focales. Sin embargo, muchos de estos estudios tienen un alcance y una duración limitados, lo que deja sin abordar los posibles impactos negativos. Esto es particularmente cierto con respecto a la alimentación pasiva en los jardines, que representa la mayor parte de la alimentación suplementaria, incluido el inmenso esfuerzo de millones de ciudadanos entusiastas. Aquí mostramos que la alimentación suplementaria de invierno antes de la reproducción no tuvo un impacto significativo en una variedad de parámetros reproductivos en una especie de paseriforme residente montano, Poecile gambeli. Esta población reside en un entorno natural intacto sin exposición a alimentos suplementarios más allá de nuestros tratamientos experimentales, y se realizó un seguimiento individual de las aves durante 6 años utilizando tecnología de identificación por radiofrecuencia. Nuestros resultados se suman a la creciente evidencia de que la alimentación suplementaria por sí sola, aislada de los efectos de los entornos urbanos, puede tener poco o ningún impacto en la dinámica poblacional de algunos taxones de aves.