New Publication: Flying Foxes Going About Their Bat Business
Fruit bats play a vital role in tropical ecosystems as pollinators and seed dispersers but are also potential vectors of zoonotic diseases. Many species of bats are known to host a range of zoonotic viruses, several of which have proven fatal to humans including rabies, Marburg, Nipah, and Hendra-viruses. More recently, bats have been identified as the natural host of several coronaviruses responsible for human fatalities including severe acute respiratory syndrome (SARS-CoV-1) and Middle East respiratory syndrome (MERS-CoV) (Calisher et al. 2006; Machhi et al. 2020). Moreover, bats are largely speculated to be the primary host for SARS-CoV-2, the causative agent for the COVID-19 pandemic (Zhou et al. 2020).
Myanmar sits at the intersection of different bioregions and contains habitats that are important for many endangered species. This rapidly developing country also forms a connection between hotspots of emerging human diseases. Back when I was working in Myanmar for the Smithsonian I started a collaboration with the Smithsonian Global Health Program who work all over the world as part of the “PREDICT” program which uses the expertise of medical doctors, veterinarians and ecologists to identify potential pandemic diseases arising from human/animal contact and build capacity in developing countries to monitor them. I talked a bit about it here, and that collaboration has finally borne fruit (bats).
I worked closely with my good friends Dr. Marc Valitutto and Jen Kishbaugh on this project. In this work we studied Indian Flying Foxes (Pteropus giganteus). With an average wingspan of 1.3m and body mass ranging from 0.6 kg to 1.6kg it is one of the biggest bats in the world. The bats roost in trees in the middle of villages, close to schools and small pig farms. They could potentially be shedding pathogens all the time and Marc and his team had a good idea of what they might be carrying but the missing piece was where are they coming from and going to. By attaching GPS devices to them we could answer some key questions. How far do they travel in a day, a week, a month? How many different locations do they visit? What kind of mixing occurs between groups of bats? What are the environmental conditions in the places they visit?
The bats were captured around their roost tree using mist nets. The netting and extraction was handled expertly by our local partners who have been catching bats for many years . The bats had measurements, swabs and blood samples taken and a GPS collar attached. They were given some sugar water to keep them happy during the short handling period. The samples were tested for a raft of different pathogens and we analyzed their foraging movement behavior and evaluated selected foraging sites for their potential as human-wildlife interface sites.
In what was good news for the bats and people they live amongst, we found no positive results for any of the things we tested for. Our paper focusses on the movement behaviour of the bats and identifying interface sites with humans where the potential for transfer of zoonotic disease is more likely. We used clustering analysis to identify foraging sites and high-utilization areas. We found that our 10 bats would often fly to 10 different locations on a given night, only rarely heading to the same spot as another tracked bat. They mostly travelled around 14km to feed each night with one individual heading off 72km away for a three day trip. Clustering analysis revealed six broad clusters of bat foraging locations within which core areas of usage were identified. Analysis of individual foraging sites revealed 207 unique locations visited across all tracked bats.
Although it's unlikely that every individual bat in the colony travelled alone to forage every night, the individual nature of foraging site selection we observed in our sample suggests that, if extrapolated to the total number of bats at this one roost, this could mean the entirety of the roost could be traveling to hundreds of locations over a short period of time.
We sent out a team of local experts to investigate the three biggest hotspots of activity and they found large fruiting trees directly over human houses and small pig enclosures that were also frequented by large numbers of pigeons and rats. This all makes for perfect conditions for interface between wild bats, domestic animals and humans and that is before you consider that people regularly hunt and eat these bats for supplementary food.
Our results highlight the importance of understanding the movement behavior of bats in order to identify human-interface sites and assess their potential for the spread of zoonotic disease. GPS tracking allowed us to determine the flow of individuals from roosts to foraging sites and to assess the conditions on the ground at these sites. Public health programs should target areas with sizeable bat roosts and foraging areas for education, outreach, and vaccination. Further work is needed to fully understand the risk of disease transmission between bats within a colony as well as between bats and humans and livestock at these interface sites.
Fruit bats are of huge ecological importance in tropical ecosystems and their populations are under threat from many directions including hunting, deforestation, the introduction of exotic predators, and environmental disturbances such as natural disasters and climate change. By more fully understanding the links between their movement behavior and the potential for interface with humans we can protect human health while ensuring that bats can continue to thrive in these landscapes.
Read our full paper here