Before going into detail about results, let us put this region in context. Forests are an important component of the landscape, with more than 86 % of them being privately owned4. Working forests refer to forests that are actively managed to achieve specific goals, such as timber products, recreational activities, creation or maintenance of wildlife habitat, and carbon sequestration. Additionally, these forests are important for numerous bat species, including bat species devastated by white-nose syndrome, a fungal disease that is decimating millions of bats that use caves for hibernation, or migratory species affected by wind energy developments. Forests provide foraging and roosting resources for bats5. In turn, bats provide essential ecosystem services to forests, such as control of insects that feed on plants6,7.
During our first field season in 2020, we focused on evaluating the influence of forest characteristics and forest management on winter acoustic activity and bat foraging habitat use. We then decided to go further in understanding foraging bat winter ecology. After all, we are what we eat. Over the next two years, we also collected fecal samples from bats captured in working pine forest landscapes of Georgia, Louisiana, North Carolina, and South Carolina. Why did we do it? Our goal was to identify diet composition of overwintering bats relying on DNA metabarcoding techniques. We compared composition of prey consumed among different bat species and determined the potential role of forest bats as pest controllers. To our knowledge, our study is the first one to evaluate diet of overwintering bat communities in these forests, while documenting agricultural and forest pest consumption.
What did we find? Overall, our results showed great variability in food preferences among the seven bat species analyzed. As expected, we observed differences among species with different foraging strategies, but also among species with similar foraging strategies, such as eastern red and Seminole bats. In addition, we noted that prey diversity in winter bat diets was similar to, if not greater than, what bats consume in summer. Frequent consumption of Diptera (flies and mosquitoes) by all bats in our study could reflect prey availability, with more Diptera in winter compared to other insects. This finding corroborates previous work indicating that foraging opportunities in winter probably depend on prey availability, making bats more generalist during winter8.
So, what role do bat communities play as pest controllers in winter? We confirmed that bats consume at least 47 arthropod species considered to be agricultural and forest pests. Among them, the Nantucket pine tip moth and the pale weevil, serious pests of young pines and seedlings, were important food sources for bats in winter. We also observed many agricultural pests, such as the garden tortrix moth and the green clover worm. We believe that these pests probably inhabit agricultural areas adjacent to working forests. It was not a huge surprise; bats are highly mobile mammals, and the ecosystem services provided by them are expected to go beyond benefiting farmers and local communities. The green clover worm, although not the most consumed pest, was found in the winter diet of five bat species, including migratory eastern red and hoary bats. Green clover worms are migratory moths, with most populations overwintering south of the midwestern United States Corn Belt9. Although generally considered to be of minor economic importance, it is one of the most common defoliating insects in alfalfa and soybean fields. Thus, consumption of overwintering green worm populations may provide an ecosystem service by controlling populations of green clover worms outside of the growing season and outside major crop-producing areas of the Corn Belt.
Additionally, our study identified several species of flies and mosquitoes in overwintering bat diets that are recognized as nuisances or threats to human or livestock health. Mosquitoes in particular are important disease vectors of worldwide concern because of their impact on public health10, 11. Our analyses revealed a high diversity of vectors (e.g., Aedes and Culex) in many samples, including species that are common vectors of diseases such as malaria or West Nile virus. Finally, we highlight consumption of other dipterans, such as black flies, capable of transmitting pathogens to wildlife, livestock, and poultry.
By providing valuable information on winter diet composition and ecosystem services provided by bats, we hope to guide management decisions for forest attributes important to these species, thus increasing conservation opportunities within working forests.
Santiago Perea, from Madrid, Spain, is a Ph.D. candidate at University of Georgia. Broadly speaking, his main research interests focus on understanding ecological processes that drive animal population distributions and abundance within the conservation biology framework. His current Ph.D. research is on bat winter ecology in working forests of the southeastern United States Coastal Plain. Santiago is approaching these questions from different angles: applying hierarchical modeling to assess how different factors influence winter foraging activity and habitat selection at multiple scales, assessing direct and indirect relationships between bats, insect communities, and different forest management decisions, for example, by evaluating the bat diet composition by DNA metabarcoding. His Ph.D. dissertation is funded and supported by the National Council of Air and Stream Improvement, Inc., Resource Management Service, the Westervelt Company, the Weyerhaeuser Company, and the University of Georgia, Warnell School of Forestry and Natural Resources.
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