Conservation
implications
North American avifauna have decreased in abundance by approximately
29% since 1970 (Rosenberg et al., 2019). Aerial insectivores are even
more threatened (Nebel et al., 2010; Spiller & Dettmers, 2019). Bats
face conservation threats globally and regionally (Frick et al., 2020).
Though many factors contribute to declining population trends, decreases
or changes in food availability play a role, making identification of
key food sources important (Rosenberg et al., 2019; Spiller & Dettmers,
2019). The 73 arthropod families, 165 genera, and 382 OTUs identified in
NAI diets in our study far exceed previous documentation, particularly
at high taxonomic resolution, for most NAI species. However, there is
still much work to be done with resolving the different taxa in the NAI
diets. Tipulidae (crane flies) especially, were often not resolved
beyond the family level here, yet were the most common order found in
the diet of 4 of the 7 NAIs.
Crane flies constitute the majority of prey for various wildlife,
including snails, salamanders, other Arthropoda (Lunghi et al., 2020),
in addition to the NAIs observed here. A recent study found that crane
fly abundance was a key predictor of the persistence of multiple
sympatric bird species, and explained 39% of observed bird abundance
(Carroll et al., 2015). This suggests that any decline in crane fly
populations may be paired with future declines in avian populations.
Monitoring crane fly populations may help identify high conservation
priority areas as these insects are susceptible to plant community
degradation and loss (Yadamsuren et al., 2015) and changes in water
quality (Morse et al., 1994). Crane fly larvae in particular, are
susceptible to desiccation (Pritchard, 1983), and prolonged drought or
extreme heat caused by future climate change may harm crane fly
populations (Carroll et al., 2011). The importance of crane flies in NAI
diets highlights the need for expanded analyses on crane fly ecology and
conservation, especially as many species have yet to be described
(Marshall, 2012).
Knowledge of NAI diets can also identify regulators of unwanted pests
such as western spruce budworm, cutworm moths, and Douglas fir tussock
moths that cause crop and forest damage. Western spruce budworm in
particular, is a common conifer defoliator that reduces tree growth in
the Pacific Northwest (Fierravanti et al., 2019). Because NAIs consume
pests like spruce budworm in high and variable proportions, future
research into the possible cascading effects on forest biomass and soil
carbon retention may have global implications (Schmitz et al., 2017).
Overall, our findings indicate that the evolutionary interactions
between bats and moths may promote the coexistence of multi-phyla
predator communities. Future management practices that promote both
eared and non-eared prey insects may add stability to already threatened
insectivore populations.