Fecal metabarcoding reveals differences in nestling diet across years with extreme variation in climate and arthropod availability in a montane songbird

Abstract Animal diets are shaped both by the availability of resources and preferences for certain food items over others. Environmental conditions can affect the availability of arthropod prey, and animals that rely on arthropods for food may need to shift their diet across years with different climatic conditions. Here, we tested for differences in Poecile gambeli (Mountain Chickadee) nestling diet between 2 elevational sites and years with extreme climatic differences. We present the first study characterizing P. gambeli nestling diet using fecal DNA metabarcoding. Fecal samples were obtained from nestlings across 2 years at high- and low-elevational sites in the northern Sierra Nevada mountains, USA. We also sampled arthropods on conifer trees during the fecal sampling period. The first year was characterized by low-to-average snow accumulation, while the second year was a heavy snow year. We used these naturally occurring climatic extremes to test for differences in diet and food availability between years and elevations. There were significant differences in the family-level community composition of available arthropods between elevations and years except for at low elevation, where community composition was not significantly different between years. There were also significant differences in the community composition of nestling diet between elevations and years. Differences in diet were associated with differences in food availability for commonly sampled arthropod families, but chickadees exhibited both selection for and avoidance of some prey families. Overall, chickadees utilized prey resources from a diverse suite of taxa and showed flexibility in provisioned diet both across small spatial scales and between years, potentially making them highly resilient to climate-related changes in prey availability.