Diet composition of nestling Boreal Chickadee ( Poecile hudsonicus ) under drought and non-drought conditions

Climate change-induced droughts represent an exogenous shock to ecosystem functions and biodiversity. Boreal forests appear to be particularly susceptible to these climatic fluctuations. Droughts in boreal forests have the potential to disrupt food webs within the system. However, the interplay between drought events and food availability for boreal species is not well studied. Identifying key food sources and characterizing dietary breadth is necessary for understanding the ecology of a species and potential impacts of changing environmental conditions. The Boreal Chickadee (Poecile hudsonicus) is a generalist forager and boreal forest habitat specialist with documented population declines. There exists little research on the diet of Boreal Chickadees. To fill this knowledge gap, and better understand the dynamics of food availability for climate-threatened birds, we used DNA metabarcoding techniques to reveal the diet of nestling Boreal Chickadees in northern Minnesota in 2021 and 2022. We found that nestlings were primarily provisioned prey items from the orders Araneae, Diptera, and Lepidoptera. We compared prey items detected in diet to arthropod surveys to evaluate prey selection and found that Boreal Chickadees consumed Diptera and Lepidoptera prey items in greater proportions than expected based on availability from our surveys. Our results showed that arthropod communities and dietary diversity and breadth were lower in a drought year compared to a non-drought year. This is the first study to analyze Boreal Chickadee nestling diet and this information can be used as a baseline to evaluate diet shifts in response to ongoing anthropogenic disturbances such as climate change and land-use changes.