Molecular tools reveal diets of insectivorous birds from predator fecal matter

The emerging field of molecular scatology enables critical testing of food web theory. The non-invasive application of molecular tools allows for sequencing of prey DNA from predator fecal matter, evaluating diet breadth and foraging guild. While insectivorous bats are obscure foragers compared to most insectivorous birds, more is known about which arthropod species bats consume because molecular techniques have been optimized for mammalian systems, not avian physiology. Our research objective was to use molecular tools to detect arthropod prey in the fecal matter of an insectivorous avian predator. We used Western Bluebird (Sialia mexicana) as a model predator due to its generalist foraging strategy. We compared two fecal DNA extraction kits: (1) Qiagen's DNA stool mini kits, used widely in dietary studies on bats and (2) Zymo's Soil/Fecal DNA MiniPrep kits, not currently cited in the molecular scatology literature. We successfully extracted DNA only with the Zymo kit, amplified mitochondrial cytochrome oxidase c subunit I genes, sequenced, and identified the arthropod prey. A spiked PCR experiment showed evidence of possible inhibitors remaining in the Qiagen kit extractions. Overall, arthropod prey from seven different orders and five different classes were identified. We discuss the ecological implications of these data and suggest areas of future research applying molecular techniques to avian fecal matter. Consistent methodological advancement will enable molecular scatology to identify ecosystem services provided by insectivorous birds, develop ecological theory, and inform predator conservation efforts.