Ten years ago, a group of biologists from the Federal University of Pernambuco (UFPE) became intrigued by the variation in the number of naked-back bats (Pteronotus gymnonotus) in a cave in the Catimbau National Park, about 290 kilometers (km) from Recife. If on one day 120,000 animals were there, on another there were just over 200. With the help of a thermal sensor and software that record the entry and exit of the animals, they monitored other caves in the Northeast region of the country and realized that the phenomenon repeated. “We knew it wasn’t mortality. They were going somewhere”, observes Enrico Bernard, group coordinator.
Based on the analysis of the genetic material of bats from nine of these caves, the researchers found clues to the riddle: the data suggest that the animals form a large and connected population, with genetic proximity between colonies that live in caves that are up to 700 km apart from each other. states of Sergipe and Ceará. “The data suggest that these animals may be moving over long distances,” explains Bernard. Previously, the maximum recorded distance between connected populations was 150 km. The analyzes indicated two connected genetic clusters. “This indicates that, despite the existence of distinct groups, there are reproductive encounters between colonies”, says the biologist.
“These bats are using a network of caves and that means no longer looking at them in isolation”, observes biologist Fernanda Ito, first author of an article that presents these data, published in October in the journal Frontiers in Ecology and Evolution. She carried out the genetic analyzes during her doctorate at the Graduate Program in Animal Biology at UFPE, recently completed under the guidance of Bernard, co-author of the article also written in partnership with two researchers from the University of Helsinki, Finland. It was at the European university, during a sandwich fellowship, that Ito carried out the genetic sequencing of samples from 93 females and 84 males of this species, which have reddish-brown fur and whose length can reach 7 centimeters (cm). Their wings come together on the backline, which gives the impression that they have no fur on their backs.
Enrico BernardResearchers from the Laboratory of Applied Science to Biodiversity Conservation, linked to the Department of Zoology at UFPE, capture bats at Caverna do Gato, near the Catimbau National Park, in PernambucoEnrico Bernard
Little is known about the movement of bats in Brazil, since there is no specific monitoring program for these animals such as the National System for Ringing Wild Birds (SNA), through which it is possible to understand the routes and areas by where the birds go. Despite this, data from international surveys indicated that other bats, such as the lesser magueyero (Leptonycteris yerbabuenae) and the house bat (Tadarida brasiliensis), would be moving between caves in the United States and Mexico, with the first species traveling around 1,600 km and the second 2,500 km. In Europe and Africa there are also records of bats moving for more than 2,000 km.
And why would Brazilian bats fly so far? “We still need to find out why,” says Bernard. But Ito and he have their hypotheses: Nakedbacks may use the network of caves in search of reproductive partners. The researchers suspect a temporal segregation between the sexes in this species, since sometimes they find more males in the so-called satellite caves, sometimes males and females are together – at these times, the places would be used for copulation. According to the researcher, the females spend more time in the nursery caves, where there are warm chambers where they can give birth. In them, the group has already found some males, but more often those who are there are females with cubs that are born in these chambers and stay there for up to four months. “The nursery caves tend to be full all year round, on a regular basis; the satellites have more fluctuation”, describes Bernard. “We need to investigate these variations further to understand reproductive behavior.”
They may also be looking for clouds of insects, the species’ main food. And these bats eat a lot: in one night, they devour 20% of their body weight – it is as if a 70 kilogram (kg) person ate a 14 kg dish in a self-service restaurant. According to Bernard, one of the next steps in the study is to understand when insects are most abundant in cave regions, in order to infer whether that would be enough to stimulate displacement.
Other questions need answers: Molecular analysis shows that gene flow took place, but researchers have not yet determined how long ago this occurred. “The material we extracted allows us to obtain this data, but we are still carrying out the analyses”, explains Ito.
Pattabi / iNaturalist Brazilian Tadarida San Antonio, Texas, USAPattabi / iNaturalist
network conservation
If the caves are connected by the flow of animals and if they play an essential role in their reproduction, it implies that the whole network needs to be protected, suggests Bernard. Therefore, according to him, the environmental licensing for exploration of areas with underground cavities, defined in Resolution n° 347/2004 of the National Council for the Environment (Conama), would need to be discussed. Today it is possible to temporarily limit the so-called area of influence of the cave to a radius of 250 meters (m) from its surroundings. “This size may be insignificant, since the area of influence of the caves for bats may be much larger than previously thought”, observes the biologist.
“There is a lot of pressure to reduce this footage to a radius of 100 m, 150 m”, observes him, one of the 90 researchers from different countries who signed a letter in the scientific journal Science alerting to the risk of destruction that Brazilian caves are running after the publication of Decree n° 10.935, of January 12, 2022, which authorizes the construction of public utility projects in areas of caves classified as of maximum relevance. In the same month, the Minister of the Federal Supreme Court (STF) Ricardo Lewandowski suspended part of the decree, by means of a precautionary measure, but the Brazilian Society of Speleology (SBE) published a note in which it recommended its total suspension.
For biologist Paulo Bobrowiec, in a postdoctoral internship at the National Institute for Research in the Amazon (Inpa), who did not participate in the research, the study raises other questions. “Where are these bats moving? Are these areas that have been impacted by human activity?”, he asks. “In addition to the caves, it is necessary to know and preserve this route they take. If there is a change in vegetation, for example, this can impact the supply of insects. What impact can this have on this flow?”, he adds.
It is already known that in the Amazon region, for example, bats avoid previously deforested areas that have already been recovered, because they find less food there and face more predators than in the original forests.