Social Distancing… Among Vampire Bats?

While it is known that eusocial insects such as ants and termites altruistically self-isolate or are excluded by others when they are sick, similar phenomena are at play in mammals, too. ‘Sickness behavior’ – a rather simpler mechanism whereby infected individuals behave more lethargic, spend more time asleep, and are less social, is also said to result in reduced pathogen transmission rates. Such behaviors have previously been recorded in captive bats, our flying mammalian fellows. There, the immune-challenged animals indeed slept more, moved less, performed social grooming with fewer partners and for less time, and produced fewer calls to attract groupmates.

To find out how sickness behavior affects social behavior in vampire bats in their natural habitat, a group of researchers from the U.S., Panama, and Germany carried out a field experiment, by determining and comparing social networks created using high-resolution proximity data. Two groups of bats from Belize were monitored: a healthy control group and one that emulates sickness among the individuals. Proximity sensors allowed for tracking associative changes between the animals after they had been released back into their wild colony.

Compared to the control group, “sick” bats were in close contact with fewer groupmates, spent less time with others, and were less associated with more well-connected groupmates. Among the most significant findings was the duration of close contact. Here, the “sick” bats spent 25 fewer minutes per partner and 5 minutes per hour less on average. Furthermore, the reduction in associations was very consistent – the interactions between any given two “sick” bats were even fewer than between a pair of a “sick” and a control bat.

It has been shown that sickness behaviors can slow down the spread of a pathogen that typically is transmitted easily via physical contact or close proximity. Such behaviors in other animals include individuals actively avoiding contact with infected conspecifics as is observed in lobsters and mice, the latter even refusing to share refuge in free-range conditions. Meanwhile, human and eusocial animal societies are also seen to restructure social networks (think telling people/ants to self-isolate). Meanwhile, in an attempt to counteract such measures, parasites can manipulate host behavior to favor higher parasite transmission. Here, examples such as “zombie ants” and “fatal attraction” in plants come to mind.

The study shows that upon realizing that a pathogen has emerged (and, hopefully, even before the outbreak in the future), scientists can learn how it will spread spatially and temporally between individuals. Animal advocates will be glad that such data-based approaches are being tested, with high hopes set on increasing the survival rates of animals and species in danger. Of course, to fully evaluate the spread, we must develop and validate minimally invasive tracking technology that would allow monitoring animal movements between roosts and sites as well, to inform effective interventions aimed at stifling outbreaks such as viral rabies in vampire bats.