German and American biologists have found out that ordinary vampires (Desmodus rotundus) can form strong social connections that do not break down even when the surrounding conditions change and do not require mutual benefit. To do this, they caught 23 female common vampire bat and placed them for 22 months in the laboratory with other ordinary vampires under the condition of limited resources, in which individuals fed neighbors and cared for each other. When released into the wild, they were equipped with backpacks with sensors, the data from which showed that befriended individuals preferred to spend time with each other.
Some types of social animals do not just exist in groups but are looking for a special relative or relatives – in fact, animals are looking for friends. Depending on the species, such friends can go out together in search of food, raise offspring and defend themselves from the enemy. Evolutionarily to have friends is very profitable: for example, chimpanzees share food only with those relatives who are friendly to them.
However, two points are not always clear. The first is whether animals can form long-term bonds that will not depend on external factors. In other words, if, for example, an alliance is formed with an increased threat from a predator, then when it disappears, it can disintegrate. The second question is the profitability of communication for both participants: it is unclear whether the animals can be friends without receiving any benefit for themselves.
Scientists led by Gerald Carter of the University of Ohio decided to consider both of these issues on the example of ordinary vampires. To do this, they caught 23 females (17 adult females and 6 of their daughters) who were placed in laboratory cells along with other individuals raised in captivity. For 22 months, scientists restricted animals to food and noticed that individuals exhibit resource-specific behaviours: grooming, and as well as food sharing. The strength of the formed connections grew over time (p = 0.003) and was observed even if there were no family ties between the particulars.
At the end of the observations, the scientists released the captured vampires into the wild, equipping them with backpacks with sensors, that allowed to track the proximity of individuals to each other. Vampires, who were equipped with sensors, who were never kept in captivity, but lived in the same place – they acted as a control group.
Vampires who managed to make friends in the laboratory, kept their strong connections, being in the wild: they spent more time with each other than with other individuals and were also closer to each other than the individuals in the control group (p <0.001).
Interestingly, not all the strongest connections have survived: scientists noticed that during the study the connection between mothers and daughters was weakened. This aspect, the authors admit, is difficult to explain: perhaps the younger individuals could not form any important features of behaviour, being raised in captivity, and this reflected on their lives when they returned to their relatives. However, scientists conclude that ordinary vampires can not only form strong bonds, but also maintain them without their own benefit by giving food and caring, and then not forget their friends in changed conditions.
The formation of such kind of friendship among ordinary vampires has already been observed earlier: in 2017, scientists found that females of this species feed their friends to take care of their offspring if something happens.