Northeastern bats are on the decline for multiple reasons, especially fungal pathogens that cause white-nose syndrome. To support bat conservation efforts, researchers at University of New Hampshire, led by Devon O’Rourke, studied what bats eat.
Over the course of two years, with the help of volunteer citizen scientists, they collected more than 4,200 guano samples at 20 locations in central and southern New Hampshire, including forests, wetlands, fields, and suburbs. DNA analysis of the samples revealed that all were from little brown bats, and that they were eating a diverse assortment of insect prey.
A molecular metabarcoding approach allowed O’Rourke, a graduate student at the time and now chief operating officer at Cornerstone Genomics, to identify more insects than researchers had previously been able to identify through visual examination of the remains of insect body parts in guano. The new method didn’t confirm precise species, but it enabled O’Rourke to identify more insects and spiders to the genus level.
The researchers detected DNA of beetles in 92 percent of the samples, crane flies in 73 percent, moths in 65 percent, caddisflies in 38 percent, and mayflies and fishflies in 32 percent. “One of the differences in our study is that the overall composition was different than previous studies in New Hampshire and in Canada, which showed little brown bats eating more moths than beetles; we observed the reverse,” said O’Rourke. In the study, published in Nature Scientific Reports in September 2022, O’Rourke and his coauthors wrote, “The inordinate fondness for beetles observed among these little brown bats in New Hampshire” is a result of their “flexible foraging.”
Little brown bats in the study changed their diets through the seasons as different insects were available: beetles in spring and early summer, flies in late summer and fall. Bats consumed some insects considered pests, such as white grubs of the scarab beetle genus Phyllophaga, the Asiatic garden beetle (Maladera castanea), and the forest tent caterpillar moth (Malacosoma disstria).
In addition to revealing the food habits of bats and habitat conditions for imperiled bat species, this method could serve as a relatively easy and inexpensive way to identify the presence of potential pests of concern, leveraging the expansive foraging capacity of bats as an early detection system. O’Rourke’s research also suggests that bats may have more adaptable diets than was previously known, information that could be useful for conservation efforts. “More research is needed to determine the extent of their foraging flexibility, but this study paints a promising picture that these bats can likely adapt to a varied menu from place to place,” said O’Rourke, who welcomes questions about the study and can be contacted at devon(at)outermostlab.com.