DNA barcoding reveals the diet of the chimney swift (Chaetura pelagica), a declining aerial insectivore

The global decline of insects is expected to have deep effects on insectivorous species in particular, and ecosystems in general. It is now observed that avian aerial insectivores, such as swallows and swifts, are in decline, perhaps due to decreasing abundance of insects. Until now, our knowledge of the diet of chimney swifts was based on identifying insect fragments in fecal samples. Unsurprisingly, harder-bodied insects such as beetles and true bugs were mainly identified using this method. We hypothesized soft-bodied insects were also being consumed but no recognizable fragments were making it though the digestive tract. Using general arthropod primers and DNA barcoding of fecal and regurgitant samples, we were able to produce the first molecular characterization of the diet of chimney swifts. Coleoptera, Diptera, and Hemiptera were the orders most commonly detected, with 96%, 86%, and 68% occurrence, respectively. Other prey orders detected include Lepidoptera, Ephemeroptera, Hymenoptera, Trichoptera, and Araneae. This analysis emphasizes the importance of beetles and true bugs in chimney swift diets, and also reveals the significance of flies as a prey item. Compared to the aerial insect community sampled using sticky traps, it also appears chimney swifts are selective in their feeding habits, particularly targeting beetles even though they are not the most abundant prey item present in the environment. If the availability of these preferred prey items is decreasing over time, it may be contributing to the decline of this bird across its range.