Vampire bats, those bloodsucking, flying critters with razor-sharp teeth, are rather social beings. They love grooming one another and sharing food supplies, which consists of regurgitated blood from some other unfortunate mammal. These bats also call out to one another when they’re apart from their group.
But when they’re ill, they call out less frequently and have fewer interactions with family and friends, new research suggests.
In 2020, such behavior sounds a lot like social distancing. But the scientists do not think the bats’ self-isolation is intentional. Publishing their findings last week in Biology Letters, the researchers believe that when bats are ill, they just have trouble mustering up the energy to call out.
“It’s like us,” said Sebastian Stockmaier, a doctoral candidate at the University of Texas, Austin, who led the study. “When they are sick and feeling bad, they are not interested in social interactions.”
Mr. Stockmaier and his fellow researchers say it is much like that miserable lethargy you feel when an illness settles in and all you want to do is lie in bed.
The researchers found that on average, when vampire bats are feeling sick, they call out 30 percent less frequently than when they are healthy. And whether intentional or not, it should have a beneficial side effect of limiting the spread of whatever pathogen is afflicting them.
“If they are sick, they groom others less,” Mr. Stockmaier said, “and that will theoretically reduce disease transmission.”
To measure this, the scientists went to the Smithsonian Tropical Research Institute in Panama, where vampire bats abound. They are generally found in Central and South America and feed off the blood of mammals, like cattle and horses.
While many people might recoil from the sight of a vampire bat — especially the terrifying close-ups of their bared teeth — Mr. Stockmaier calls them “cute.”
Finding, catching and keeping them in captivity is not hard, Mr. Stockmaier said, “if you know where to get blood.” (His team gets all it needs from local slaughterhouses.)
For the experiment, the scientists injected 18 female bats once with lipopolysaccharide (LPS), a compound that induces an immune response similar to a bacterial infection, without actually causing the illness — or threat of infection — in the bat. It usually lasts between 24 and 48 hours. Females were used because they are more social than males, engaging more often in grooming and communal feeding and maintaining bonds with their offspring for long periods.
The researchers later injected the same group of female bats with saline solution as a control. In both cases, they removed the bats from the larger group — but within hearing distance — and recorded and measured their calls.
They found that, on average, the bats made 30 percent fewer calls, with 15 of 18 recording fewer calls compared with the control group.
In another study, Mr. Stockmaier said, the researchers discovered that bats injected with LPS produced symptoms of illness, slept more, moved around less and performed less social grooming. He also noted that previous studies have shown that many similar animals require eight times more energy to call out than not to call out.
So, they concluded that it is more likely that the bats are just feeling too lousy to call out, rather than intentionally stifling themselves as a naturally selected, personal sacrifice to prevent pathogen transmission to the group at large.
Mr. Stockmaier laments that “bats are getting a lot of bad press right now,” mainly because it is widely believed that the new coronavirus, which causes Covid-19, originally jumped from horseshoe bats. He is quick to point out that is a different species from vampire bats, and that all of them offer something unique to study.
“I love bats,” he said. “I think they are fascinating animals.”