Bats network to find food

Great noctule bat

Noctule Bat (Nyctalus noctula). © Carolin Scholz/ University of Potsdam

Many animals have developed social strategies to be successful in extensive hunting areas. As a result, they no longer have to look for a needle in a haystack on their own, but can rely on their peers. According to new studies, noctule bats also form such networks in order to find swarms of insects in particularly open areas. As a result, the bats are much more successful than individually hunting conspecifics.

Many carnivores such as the common noctule bat (Nyctalus noctula) face the daily task of finding new food. Their prey can be very irregularly distributed in the landscape and only available for a short time – a search for a needle in a haystack. Animals that depend on such adventitious occurrences have therefore often developed social strategies for foraging and are in contact, for example during the hunt, to exchange information about their environment.

“This can be studied particularly well in the common noctule bat, because its prey – swarms of insects – are distributed in the open air space in a completely unpredictable manner,” explains Manuel Roeleke from the University of Potsdam. “In addition, the distance over which the bats can locate the insects using ultrasound is relatively small at around 10 to 15 meters. This makes it difficult for them to track down their prey. In contrast, the animals perceive their own conspecifics over much greater distances, ideally up to 160 meters. So searching in the group should be easier.”

Bats form sensory networks

A team led by Roeleke has now specifically investigated the extent to which noctule bats work together when searching for food. To do this, they equipped a total of 81 bats with small GPS devices weighing around one gram, which they used to record the animals’ flight patterns. “With the state-of-the-art ATLAS system, we can record the movements of dozens of animals at the same time. Thanks to the great support of local farmers and private individuals, we have been able to operate the tracking technology in the Uckermark since 2018. It is a unique opportunity to research animal movements and biodiversity in the European cultural landscape,” explains Roeleke’s colleague Florian Jeltsch. For their investigations, the researchers had to set up several 15-meter-high receiving masts around the bats’ hunting grounds. Ultimately, this enabled them to monitor an area of ​​about 80 square kilometers.

“Our data was able to confirm the theory of the mobile sensory networks: while searching for insects, the bats fan out, but remain in acoustic contact. If necessary, they also adjust their trajectories to be able to search as large an area as possible,” explains co-author Christian Voigt from the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin. So if an animal finds a swarm of prey insects in the network, the neighbors will notice this through changes in the flight movements and through ultrasonic calls specially used for insect hunting. This gradually draws the attention of all animals in the sensory network to the worthwhile hunting area.

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Depending on group size and food distribution, the research team then compared the foraging efficiency of “networked” bats with that of individual hunters. To do this, they used a computer model based on the previously empirically determined movement patterns. “Networking and exchanging ideas proved to be particularly useful for the bats when the food sources were widely distributed,” explains Roeleke. “Our model shows that connected animals took 40 percent less time to locate prey than bats that ignored their fellows while hunting.”

By hunting in groups, bats can therefore also find prey in large-scale cultural landscapes. Thus, they effectively contribute to the control of agriculturally harmful insects. However, consistent protection of bats and their roost groups is also crucial. If the local population becomes too small, the animals are no longer able to form efficient networks. As loners, the animals then find it difficult to find food quickly and reliably.

Source: Leibniz Institute for Zoo and Wildlife Research (IZW) in the Research Association Berlin eV; Specialist article: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2203663119

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