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

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 passi