In the corona pandemic, it is well known that you should avoid contact with other people if you are already feeling sick. According to a study, there is a parallel with an animal with a “Halloween character”: Sick vampire bats spend less time near their own species, evaluations of distance meters on the back of test animals show. It is probably a form of passive social distancing, in which there is no active isolation, but the consequences of being ill lead to reduced social contacts. Nevertheless, there is an effect that can slow the spread of infections among socially living vampire bats, the researchers explain.
Their literally bloodthirsty diet has inspired many a horror story: The vampire bats (Desmodus rotundus), which are native to warm regions of America, secretly land on their victims at night and then bleed them. With their sharp teeth they scratch a piece of the skin and then lick the blood that flows out. In addition to their special diet, these animals have another interesting aspect to offer at night: Vampire bats live in colonies with astonishingly complex social structures. Studies have shown that every animal has its own personal network of social contacts. These individuals help and care for one another – vampires evidently develop intensive friendships.
In this context, researchers working with Simon Ripperger from the Museum für Naturkunde Berlin are interested in the question of how bats react to diseases. It is known that changes in social behavior in response to a pathogen can strongly influence the spread of a disease in a population. In the context of the Covid 19 pandemic, we humans are currently focusing heavily on this aspect. However, the spread of pathogens can also change in animals if they react to infections with a form of social distancing, which reduces contacts between sick and healthy individuals.
Vampires with proximity sensors
In an earlier study, the researchers have already found indications that sick vampire bats also keep their distance due to illness. So far, however, these have been observations on animals kept in captivity. Now Ripperger and his colleagues have carried out an experiment in the field to get a closer look at social distancing in vampire bats.
To do this, they caught 31 females from a hollow tree in Belize and simulated a bacterial infection in half of these animals: They administered a substance to them that caused mild symptoms of illness for six to twelve hours. The control animals, however, only received a saline solution. The researchers then equipped all test animals with proximity sensors. These are devices that are lighter than a one-cent coin and can therefore be carried by the animals like a kind of backpack. These devices can record the interactions between the bats of a social group in detail, the researchers explain.
Passive social distancing
Using this high-resolution data, the researchers identified the bats’ dynamic social network, which allowed them to understand changes in the social contacts between sick and healthy animals. It was found that, compared to the control bats, sick animals spent significantly less time with other group members. Overall, they were less tied to the community, considering both direct and indirect connections, emerged from the analysis of the data. Ultimately, this means: The probability that a healthy animal came into contact with a sick one decreased. The researchers say that social distancing is apparently a simple but effective mechanism that can curb the spread of pathogens in vampire bats as well.
But on what principles is the disease-related distance in vampire bats based? As the researchers explain, it is more likely to be a passive effect. One speaks of an active form of social distancing when sick individuals are specifically avoided or when they move away from others even after being infected. In the passive form, the reduced contact is more of a direct consequence of being sick: The sick are often lethargic, which is associated with reduced mobility and activity and thus fewer social contacts. As the researchers report, it emerges from their previous observations that sick bats are primarily less involved in the mutual grooming between the animals, which leads to less contact. They also give fewer contact calls that normally call conspecifics, the scientists write.
Source: Oxford University Press, Museum für Naturkunde – Leibniz Institute for Evolution and Biodiversity Research, specialist article: Behavioral Ecology, doi: 10.1093 / beheco / araa111