Researchers at the University of Southern Mississippi and the Max Planck Institute for Ornithology in Germany conducted an experiment to determine how well wild vampire bats (Desmodus rotundus) form bonds with each other. The study found that even when they were not living together, “friendships” formed in captivity would persist into their natural environment. The researchers also discovered that these pairs will meet up over a meal after independent departures from the roost.
“We wanted to see how important relationships are in the wild,” said Dr. Gerald Wilkinson, an Assistant Professor of Biology at the University of Southern Mississippi and one of the researchers in this study. “It’s interesting that captive bats that formed bonds with each other also had relationships when they were released into their natural habitat.”
The experiment involved recording the echolocation calls of free-ranging vampire bats. The researchers were able to identify individuals by their call, which is a unique identifier similar to a human fingerprint. Bats emit a small number of calls and each individual’s is slightly different from any other’s. Once individuals were identified, Wilkinson and his team searched for them in their natural environment and recorded any interactions among these bats and between other vampire bats and other species (humans, cows and chickens) that may not have been part of the original captive study.
When the researchers found a free-ranging bat feeding on its own, they would wait to see if another bat appeared within about 20 minutes. If one did, they would then wait to see if the two bats flew off together.
“We were looking for independent departures of bats that formed friendships in captivity,” says Wilkinson. “These are good indicators of friendship because these bats will only come back to a roost after feeding if they have met up with another individual.”
The researchers found that the vampire bats that were friends in captivity returned to the roost independently, but quickly found each other when they met up at the roost. Even though these bats could be hundreds of meters away from one another when they separated after feeding, they would return only about 20 minutes later and always fly back together.
“It’s so amazing how they find each other,” says Wilkinson. “It’s like they can’t stand to be apart.”
The researchers also discovered that these friendships were not limited to the captive study colony or even to bats in general. Researchers found that vampire bats will make friends with different species, such as chickens and humans, and maintain those relationships outside of captivity.
“We often found vampire bats feeding on chickens at the same time, but not because they were forced to,” says Wilkinson. “They seemed very happy about it because they always flew away together.”
The researchers believe that friendships could play a vital role in the success of individual vampire bats and their colonies by helping to maintain a cohesive society, especially during challenging periods. Wilkinson and his team hope to conduct future studies that focus on the how these friendships evolve over time and under varying conditions. Dr. Wilson says, “We want to know what qualities a bat must have in order to be a good friend.”
Vampire bats were once believed to suck blood from the necks of sleeping animals, but now we know that they actually lick a small wound. This behavior evolved because these bats cannot chew and digest solid food. Instead, they need a liquid diet in order to live. It was also discovered that vampire bats will not suck blood from all mammals or even all mammals that they feed on. Instead, they will seek out specific species and individual animals to prey upon.
This study was funded by the National Science Foundation. You can read more about this research in “Vampire Bats Maintain Long-Term Individual Friendships Outside of Bat Groups” in Ethology Ecology & Evolution .