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The world's largest carnivorous bat has a surprisingly rich social life, displaying affectionate greetings and providing food to family group members, according to a study by Marisa Tietge at Museum für Naturkunde—Leibniz Institute for Evolution and Biodiversity Science in Germany, and colleagues, published in the open-access journal .

Many bats are highly social, living in groups and working together to find food. However, their nocturnal lifestyle makes it challenging to study these behaviors in the wild.

Researchers installed a motion-sensitive infrared camera inside a hollow tree in a tropical forest in Guanacaste, Costa Rica, where a family group of four spectral bats (Vampyrum spectrum) were roosting. These carnivorous bats, which can have a wingspan of up to 3ft (1 meter), were previously thought to be solitary foragers.

After three months of filming, the researchers identified that the bats were in fact far more sociable than was previously suspected. They categorized eight main types of behaviors, including social interactions, food provision, and play. Within the roost, bats would often groom each other and make social vocalizations.

The videos also revealed a social greeting similar to a hug, where one bat would greet another by wrapping its wings around the returning bat's body.

Adult bats returning to the roost with prey were observed voluntarily transferring the food to a younger bat in the colony. This behavior may allow adult bats to gradually transition their offspring from milk to a carnivorous diet and help young bats to develop their prey-handling skills before they leave the roost.

Although spectral bats were previously thought to be solitary foragers, the researchers recorded bats leaving or returning to the roost together, and prey transfer from the adult male to the lactating female was observed as well, suggesting that they sometimes undertake cooperative foraging trips, perhaps as a way for younger bats develop their hunting skills.

The study is the first to describe food provision and other complex social behaviors in a wild group of spectral bats. The findings suggest that both parents help to care for the young, a strategy that is relatively rare among mammals. The presence of two young bats in the colony—which are likely to be the breeding pair's pups born in different years—indicates that spectral bats remain in the roost for an extended period.

Together, these observations show that the social structure of this rare bat species is more complex than previously thought. Developing and maintaining strong social bonds is likely to be important for the bat's survival, the authors say.

Tietge adds, "Spectral bats exhibit a level of cooperative behavior and biparental care that is rarely documented in bats—a fascinating area for future research."

"We were astonished by how gentle and cooperative these apex predators are."

"The most endearing behavior was forming a tight cuddle-ball when falling asleep: each bat wrapping one wing around its nearest neighbor, all snouts touching."

"Rather than hunting and raising young in isolation, V. spectrum shows complex cooperation behavior, strong monogamous pair bonds, as well as extended parental investment and biparental care—traits highly unusual in carnivorous mammals, especially bats."

"I was astonished to find that the bats seemed to recognize me after several consecutive weeks of visiting the roost. At first, I was greeted with threat-like calls, and the bats broke their roosting formation to hide in the corners.

"But over time, their response shifted to just a few curious looks—no vocalizations, and they remained in a relaxed roosting formation. Even after nine months away, they appeared to recognize me immediately when I returned the following season."