Bats give each other ‘deep kisses’ to establish social bonds
There are all kinds of strange habits among animals related to the formation and strengthening of social bonds. Elephants use water holes, birds dance, and vampire bats (Desmodus rotundus) share "French kisses" bathed in blood.
There are three species of bats that feed solely on blood, which we know as hematophagy: the common vampire, the hairy-footed vampire, and the white-winged vampire. Now, a team of scientists at Ohio State University has discovered that, among vampire bats, regurgitation of blood into a partner's mouth is a sign of maximum confidence.
Blood-feeding animals (such as mosquitoes, ticks, fleas or lice) rely primarily on the blood of the animals, and as for vampire bats, if they cannot feed for three days, they may starve to death.
"It's not just sharing in the sense of 'I have a large portion of food and I'm also going to let you eat from the same plate as me,'" said Gerald Carter, a behavioural ecologist and leader of the work published in Current Biology magazine. "I'm actually going to take some of the food I've already eaten and give it to you as if you were my offspring," he said.
This deep kiss bathed in freshly drained blood thus serves to form social bonds with unknown members of his refuge. Although we find it shocking, it is excellent proof of how incredibly prosocial these creatures are.
"Sharing food for vampire bats is like the act of many birds regurgitating food for their young. But what's special about vampire bats is that they do this for other adults, eventually even with some strangers.
We could say that it would be the gesture of a true bond, something we could even call friendship. Social grooming and food exchange can build trust between unrelated bats to form life-saving bonds that can last a lifetime.
"We assume that food donations are an adaptive trait, which means there is some benefit to the donor in the long run," Carter continued. "Maybe that benefit is that they are creating a relationship that will feed them and bring something positive later.
To test how these links emerge, Carter and her colleagues examined a group of bats from Las Pavas and Tolé, Panama, two geographically distant sites, which meant the animals were unfamiliar with each other. The bats were placed in pairs, one from each location, or in small mixed cohorts. For each group, the researchers retained the food of one of the bats and observed how it interacted with its cage mates. The experiment lasted 15 months. Several bats, particularly those that were in pairs, began to preen more over time, and in some cases, this led to sharing blood with the more malnourished partners. Almost 15% of the bats were observed practising this deep blood kiss with a previously unknown partner. Being unfamiliar with each other increased the need for some bonding to share blood.
The researchers suggest that this technique of strategic friendship may also be unconsciously applied to humans, as human relationships may be more conditional than we would like to admit.
Reference: Current Biology, Carter et al.: "Development of new food-sharing relationships in vampire bats" https://www.cell.com/current-biology/fulltext/S0960-9822(20)30099-3 , DOI: 10.1016/j.cub.2020.01.055
