Bats such as the common noctule consume pest insects over intensively managed arable land and thereby support sustainable agriculture. A new study led by scientists from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) and the University of Potsdam shows that 23 percent of the insect species consumed by common noctules in north-eastern Germany are pests. Yet, agriculture can only benefit from this free service provided by bats if there are sufficient near-natural habitats in the vicinity of agricultural land. This is where common noctules hunt disproportionately often; only in combination with near-natural habitats can bats find sufficient prey in an intensively farmed landscape, according to the scientists in a paper just published in the journal “Agriculture, Ecosystems and Environment”.

Over a period of three years, the team equipped a total of 128 common noctules (Nyctalus noctula) in the Uckermark district in north-eastern Germany with miniaturised transmitters and used an automated radio tracking system to follow the bats’ movements during their foraging flights. The intensively farmed landscape in the Uckermark is dotted with small natural habitats such as grasslands, woodlands, water bodies, and wetlands of varying sizes. Although these make up less than 5 percent of the total area, the scientists assumed that they are crucial for the bats as foraging habitat. To determine the composition of the bats’ diet, the team used the method of metabarcoding, which allows the insects consumed to be identified from the remains of insect DNA in bat faeces.

Bats prefer natural habitats when hunting – and often feed on insects that are harmful to agriculture
The analysis of the bats‘ movements shows that common noctules do not use the habitats in the landscape proportionally to the abundance of these habitats.: 55 percent of the foraging locations were recorded in this habitat. All other habitats, such as water bodies (14 percent), settlements (14 percent), grassland (10 percent) and forest (9 percent), were visited much less frequently during foraging. “However, if we compare the proportionate habitat use with how frequently this habitat type occurs in the landscape, it becomes clear that bats only visit agricultural areas out of necessity and clearly prefer other landscape types,” explains Marit Kelling, lead author of the paper and PhD student at the Leibniz-IZW and the University of Potsdam. Agricultural land accounts for almost 95 percent of the area around the bats’ daytime roosts, while wooded areas and water bodies, for example, each cover only about 0.5 percent of the area. The common noctules therefore make disproportionate use of the small remnants of near-natural landscape, presumably because they find food there much more reliably.

Because intensively used agricultural land is the dominant habitat type in the Uckermark region, common noctules still hunt most frequently over these areas. “We classified the flights into commuting and foraging based on their characteristics and found that 55 percent of foraging flights still take place over farmland – which also means that a significant portion of the bats’ prey is consumed there”, says Kelling. The team identified 295 different insect species in the bats’ faeces, an average of 11 different species per sample. 23 percent of the identified insect species – 67 species – are known to be harmful insects: 28 as agricultural pests, 20 as silvicultural pests and 19 as nuisance insects that can potentially transmit diseases. Agricultural pests such as the common cockchafer (Melolontha melolontha), the European crane fly (Tipula paludosa) and the summer chafer (Amphimallon solstitiale) were found most frequently in the samples, on average almost 1.5 times per sample.

Small natural habitats – big impact on wildlife and agriculture
“The observed foraging behaviour of common noctules shows how valuable it is to preserve even small, near-natural habitats within intensively used agricultural landscapes”, says Prof. Dr Christian Voigt, head of the Department of Evolutionary Ecology at the Leibniz-IZW, professor for Evolutionary Ecology at the Institute of Biochemistry and Biology at the University of Potsdam and senior author of the paper. “The bats avoid agricultural land, yet they most frequently feed on insects there. Their strong preference for small remnants of near-natural grasslands or water bodies when foraging suggests that they find food there more reliably. Only in combination with these near-natural habitats can the bats find sufficient prey insects, as the insect biomass over agricultural areas is generally lower owing to the use of pesticides.” The preservation of these habitats, for example at glacial kettle holes in the Uckermark, therefore not only contributes to bat conservation, but is also of great importance for the preservation of the services provided by bats in consuming pest insects. Near-natural habitats in an agricultural landscape thus promote sustainable agriculture.