Vampire Bat Adopts an Orphaned Pup

When a vampire bat died just 19 days after giving birth, another female bat adopted the orphan. Researchers documented the unusual relationship in a new paper in the journal Royal Society Open Science.

As part of a study on cooperative relationships, researchers combined three groups of wild-caught common vampire bats into one captive colony at the Smithsonian Tropical Research Institute in Gamboa, Panama. They noticed that two unfamiliar and unrelated female bats slowly formed a social relationship. The researchers named them Lilith and BD.

“This colony included bats that were captured from completely different sites, meaning that many of them were strangers when we created the colony,” lead author Imran Razik, a graduate student in evolution, ecology and organismal biology at Ohio State University, tells Treehugger.

“Two of these strangers, Lilith and BD, gradually formed a strong grooming relationship in captivity, such that they were primary grooming partners. BD also donated food (i.e. regurgitated blood) to Lilith more than any other bat.”

Vampire bats often groom each other and will regurgitate their meals in order to feed others that haven’t been able to get their own meals of live animal blood. The researchers fast the bat colony in order to trigger food sharing between the bats.

When the researchers first caught Lilith, she was pregnant with a single pup, which was born a few months later. About a week after giving birth, Lilith became ill, likely from gastrointestinal issues. As she was unable to care for her baby, BD began feeding and grooming the female pup.

When Lilith ultimately died, BD stepped in to care for the baby.

“What we found was that BD then ‘adopted’ the orphaned pup. BD groomed and donated food to the pup more than any other female in the colony, and she did not interact with other pups to nearly the same extent,” Razik says. “BD was also nursing the orphaned pup, even though she was not pregnant and did not have a pup of her own.”

Strong Social Connections

For the study, the researchers combined 23 adult and three juvenile common vampire bats captured from three distantly located roosts. For four months, three surveillance cameras recorded 652 hours of footage, recording any cooperative behavior that lasted at least five seconds.

The footage showed that BD and Lilith increasingly groomed each other on a nearly equal basis. BD shared her food with Lilith right up until her death, even though Lilith didn’t often share her food with BD. Lilith’s grooming of her pup began to decline right after the baby was born, and her food-sharing barely started.

After Lilith died, BD steadily groomed the pup and her food sharing with the baby increased. Even at the end of the experiment, BD was still caring for the pup.

“I was really sad when Lilith died. I was also immediately concerned for the pup's well-being, since it was only a few weeks old and still very underdeveloped,” Razik says.

“Because I knew that BD was likely closer to Lilith and her pup compared to other females, I went into the flight cage after Lilith died and picked out BD, at which point I found out that BD had already begun lactating. I was really surprised, but also relieved. BD began to care for the pup, and the pup survived.”

The researchers don’t know how BD started lactating or why she adopted Lilith’s pup, but it likely had something to do with the strong social connection that they had with each other.

Earlier reports of vampire bat adoption were recorded by a researcher in the 1970s , Razik points out.

“Both then and now are observations from captive colonies, so we really don't know if, or how often, these adoptions happen in the wild,” he says. “Non-kin adoption has been observed in other species; however, it is hard to estimate the probability of non-kin adoption in many species because observations of orphaned offspring can be rare.”