Dietary partitioning corresponds with predation of eared insects
Moth families that contain species with ears (Miller & Surlykke, 2001) were associated with the diets of NAIs that hunt visually but not bats that use echolocation or gleaning (p <0.01; Figure 1a; Table 2). The most abundant eared family, Noctuidae moths, occurred in the diets of 82% of Common Poorwills, 69% of Flammulated Owls, and 32% of Common Nighthawks sampled. Long-legged Myotis fecal samples contained Noctuidae moths 35% of the time. However, just 16% of Long-eared Myotis, 4% of Big Brown Bats, and no Silver-haired Bats consumed Noctuid moths. Other eared moth families, including Geometridae, Sphingidae, and Erebidae, also occurred significantly more often in visual hunters’ diets, but rarely in bat diets. One other family of eared moths, Drepanidae, associated with the diets of Flammulated Owls and Common Poorwills (p < 0.05, sit-and-wait predators, Table S2), but not Common Nighthawks.
Conversely, the non-eared moth family Tortricidae (mostly spruce budworm), was the most abundant family consumed more often by echolocators than by visual hunters (p < 0.001). We found Tortricidae in the diets of 65% of Long-legged Myotis, 63% of Long-Eared Myotis, 48% of Big Brown Bats, 23% of Silver-haired Bats, but only 11% of Common Nighthawks, 5% of Common Poorwills, and 31% of Flammulated Owls. Ten other insect families were consumed more often by predators that use echolocation (Table 2, p < 0.02). Insect families that were recovered more often in diets of NAIs that hunt by aerial hawking (bats and nighthawks) corresponded with those associated with echolocation strategies (bats only, Table S2). All insect families and OTUs consumed significantly more often by each individual NAI species can be found in Tables S3 and S4.

Dietary Partitioning among species

In general, we saw low dietary overlap among species (Table 3) regardless of foraging behavior or prey detection method. The highest OTU overlap in diets occurred among bats, with the two smallest species, Long-legged Myotis and Western Long-eared Myotis overlapping the most (22%). Big Brown Bat diets also overlapped considerably with all other bat species (18-21%). Among nocturnal birds, the highest overlap occurred between sit-and-wait predators, Common Poorwills, and Flammulated Owls (17%). Diet overlap between bats and birds was the lowest, with Flammulated Owls and Silver-haired Bats overlapping by just 2%.
Controlling for differences between years, Permanova analyses on presence/absence data indicated that NAI species identity explained the largest variation in diet (R2 = 0.23, p = 0.001). Pairwise comparisons indicated that the diets of all NAIs differed from each other (p < 0.006), except for Big Brown Bats, Long-eared Myotis, and Long-legged Myotis, which had more similar diets (Figure 1d; Table S6). Diet composition also varied due to whether NAIs detect prey visually or with echolocation (R2 = 0.12, p = 0.001) and whether they use aerial hawking or sit-and-wait strategies (R2 = 0.12, p = 0.001). Because species was the best predictor of diet, we included it in the full model with collection month (R2 = 0.18, p = 0.001) and plant community (R2 = 0.05, p = 0.001), which were also influential as main effects. The interaction between species and month was a strong predictor of composition (R2 = 0.17, p = 0.001), highlighting the importance of seasonal variation within each NAI diet. The total variation among insectivore diets explained by the model was 70%. We also performed Permanova analyses on Bray-Curtis distances of compositional data. Relationships were similar, with species (R2 = 0.10, p = 0.001), month (R2 = 0.09, p = 0.001) and their interaction (R2 = 0.14, p = 0.001) explaining the most variation among NAI diets (Table S3). Overall, the model using compositional data explained 55% of the total variation among NAI diets.
At the order level, Common Nighthawks and Long-legged Myotis consumed mostly Diptera (true flies, 75% and 43% of diets, respectively). Common Poorwills and Flammulated Owls consumed mostly Lepidoptera (moths/butterflies; 63% and 88%, respectively). Silver-haired bats were the only NAI to mostly consume Ephemeroptera (mayflies, 45%). In comparison, Big Brown Bats and Western Long-eared Myotis consumed similar abundances of Lepidoptera (30% and 44%, respectively), and Diptera (31% and 43%, respectively). The top insect orders consumed by all NAI species combined were Lepidoptera followed by Diptera, Ephemeroptera, and Coleoptera (Figure 1b). Except for Long-legged Myotis, the top insect families consumed for each NAI were consistent between 2017 and 2018 (Figure 2).
We found craneflies belonging to the genus Tipula in 35% of samples overall, more frequently than any other insect genera recovered. The most abundant and common prey OTU matched 100% with the family Tipulidae (BOLD:ADC2461, crane flies, Table 4). Morphological examination of specimens associated with this OTU confirmed it asTipula (Lunatipula) splendens Doane 1901 (personal communication, Dr. Jon K. Gelhaus, June 26th, 2021). This OTU occurred in 26% of all samples, in all NAI species diets except for Flammulated Owls, and was one of the most frequent and  abundant prey items consumed by Common Poorwills, Common Nighthawks, Big Brown Bats, Long-eared Myotis, and Long-legged Myotis (Table 3).
The second most abundant OTU matched locally to Choristoneura freemani (western spruce budworm; BOLD:ABX5883) and was detected in 16% of all NAI samples. It was one of the top two OTUs consumed by most bat species but occurred in just one Common Nighthawk sample and two Common Poorwill samples.

Dietary breadth and turnover

From the fecal samples of all seven NAI species, we identified 73 arthropod families, 165 genera, and 382 OTUs. Silver-haired bats had the widest diet breadth at the order (10) and family (36) levels (Table S7), whereas Common Poorwills consumed the greatest number of insect genera (75) and OTUs (154). We detected the fewest total OTUs in Common Nighthawk samples (50). Flammulated Owls and Common Poorwills had the highest variation or turnover among samples, whereas Silver-haired Bats and Western Long-eared Myotis had the lowest (Table 1). Long-legged Myotis had the most OTU-rich diet on average (Figure 1c), consuming more prey OTUs than Common Nighthawks, Big Brown Bats, and Long-eared Myotis (p < 0.001; Table S8). NAI species, collection month, year, and plant community were significant predictors of dietary richness. Species identity had the greatest influence.