- A hundred experts from Mexico, the United States and Canada worked together for the past two years to release the first report on the state of the 154 bat species that live in North America.
- The researchers concluded that the main threats that bats face in the region are the loss and disturbance of habitat, climate change impacts, wind farms, and the fungal disease white-nose syndrome.
- Mexico is home to 142 species of bats, whose protection researchers say hinges on protecting their habitat, including at least 15 caves that they propose designating as bat sanctuaries.
- Rodrigo Medellín, a Mexican researcher who helped coordinate the report, spoke with Mongabay Latam last July about why bats are so important for both nature and humans.
The stories people tell about bats seem to come from novels, comics or science-fiction movies. They’re able to emit and hear sounds in frequencies inaccessible to other species. Some undertake epic migrations that take them across oceans. Others can fly as high as 3,000 meters (9,800 feet). They have an enviable immune system that makes them resistant to hundreds of viruses. Their list of qualities is as wide as their diversity: scientists today know of at least 1,460 species of bats throughout the world.
In all the stories about bats, there’s a common thread: bats are facing growing threats that challenge their survival. The populations of several species are declining considerably. And this threatens to turn many of these stories into tragedies.
Bats are excellent pollinators and pest control agents, helping in the cultivation of various types of crops. Their remarkable immune system could also hold the answer to the development of new treatments to fight illnesses like cancer. Losing even a single species of bat is therefore no minor issue.
“Protecting bats and their habitats helps create a healthier, safer world for our forests, our farmers, and ourselves,” says the “State of the Bats in North America” report, published in 2023 to catalog for the first time the situation of the 154 bat species found in Mexico, the United States and Canada.
For two years, 100 experts from the three countries got together to assess the extinction risk for bats in North America. According to their findings, of the 142 species that live in Mexico, at least three are critically endangered and 16 endangered; of the 44 species in the United States, seven are endangered; and of the 17 species in Canada, three are endangered.
The researchers found that the biggest threats to bats in the region are climate change impacts, loss and disturbance of habitat, wind farms, and the fungal disease known as white-nose syndrome. They warn that 52% of bat species in North America risk a severe population decline over the next 15 years as a result of these threats.
Rodrigo Medellín was among the scientists who helped coordinate the research for the report. A researcher at the Wildlife Ecology and Conservation Laboratory at the National Autonomous University of Mexico (UNAM), Medellín spoke with Mongabay Latam recently about the main findings from the report and some of the strategies are already in place to ensure that bats remain the central characters in their many stories.
Mongabay: What led you to complete the first report about the state of bats in North America?
Rodrigo Medellín: We realized that bat populations were suffering serious harm and that we were missing many opportunities of collaboration between the three countries.
That’s why, in 2015, we created the North American Bat Conservation Alliance (NABCA). The next step was to conduct an analysis about the state of the 154 species of bats that have been identified in North America and find the biggest threats they face.
With the help of Bat Conservation International, we started to design a protocol to identify the threats and assess how each of them was affecting the different bat species. That work took us two years.
In the case of Mexico, 48 experts participated to evaluate the 142 bat species that live in the country. There are only five countries with more bat species than Mexico. In addition, having such broad participation from Mexican experts positioned Mexico as a leading country in the conservation of bats.
Mongabay: The report shows a worrying scenario for different bat species.
Rodrigo Medellín: The research identified that 52% of the bat species in North America are at risk of suffering severe declines in the next 15 years.
Additionally, 98% of bat species in the region are losing their habitats, their refuges, the ecosystems where they move and where they migrate. If that wasn’t enough, 82% of them are threatened by climate change impacts.
There’s another factor. In the United States, there are bat populations that have lost 99% of their individuals due to white-nose syndrome.
Mongabay: What causes the disease?
Rodrigo Medellín: The syndrome is caused by a fungus that likes cold temperatures. It’s a fungus that dies when the temperature reaches 11° or 12° Celsius [52-54° Fahrenheit]. This fungus only attacks bats that are hibernating and whose temperature is 0-2°C [32-36°F]. The fungus grows in the bat tissues. Then the bats wake up halfway through winter using what’s known as “brown fat” [adipose tissue], which bats accumulate to survive the hibernation period all winter. The fungus ends up killing them. Many of the bats end up with their wings in tatters and also damage to some of their internal organs.
Mongabay: When was this syndrome identified and why is it a problem in North America now?
Rodrigo Medellín: The syndrome was identified in the state of New York in the winter of 2005-2006. The most accepted hypothesis until now is that a speleologist who had traveled to Europe entered a cave there and the fungus got stuck to his boots or his clothes. Upon his return to North America, he brought the spores of the fungus. When he entered a cave in New York, he introduced the spores accidentally.
With the fungus already on the American continent, humans stopped being the main vector, which is now bats moving from cave to cave spreading the fungus.
Unfortunately, estimates say that from the moment the syndrome was identified in North America until the last time there was a census, between 6 million and 8 million bats died. In Europe, bats have already developed resistance to the fungus, so it doesn’t affect European bats anymore.
Mongabay: What are the species most affected by this syndrome?
Rodrigo Medellín: It only affects species that hibernate. The most affected one is the northern long-eared bat [Myotis septentrionalis]. This species isn’t found in Mexico. Its population has declined by 99%. There are other species that have had declines of between 94 and 96%.
I was able to see the decline of the population firsthand. I carried out the BioBlitz in New York’s Central Park [an activity where volunteers and scientists get together to identify species of plants and animals]. The first time we did it was in 2003, before the syndrome arrived, and there were plenty of little brown bats [Myotis lucifugus], which is another of the species that’s greatly affected by the syndrome. In 2013, I went back to Central Park and we didn’t find a single bat of that species.
Mongabay: Does the syndrome also affect species in Mexico?
Rodrigo Medellín: We believe that the syndrome is about to enter Mexico. In the time of Bernardo Villa [a renowned Mexican bat expert], in the ’50s and ’60s, we knew of about 14 bat hibernation sites in Mexico and four species that hibernated there. Today, there are 130 sites identified and we know there are nine species that hibernate there. These are the ones that could be at risk.
For five years we have tracked the hibernating populations of bats in Mexico, and to date we haven’t found the syndrome. But it was identified very close to the Rio Bravo [known as the Rio Grande in the U.S.], so its appearance in Mexico is imminent.
Mongabay: How can we prevent the disease from causing so much damage to bat populations?
Rodrigo Medellín: That’s what different labs are working on. There’s a lot of research to understand if the immune system of bats could be strengthened, if we can prevent them from getting infected. But there isn’t a solution yet.
It’s ironic. We always said bats have a really impressive immune system because it’s very hard to find sick bats. However, this fungus does cause them a lot of harm.
There are elements for hope. In the northeastern United States there are colonies of bats that were decimated but that are recovering now because they’ve grown resistant to the fungus. No one knows how it happened, but in Europe, for example, bats also developed resistance to the fungus, and it’s happening in America too.
Mongabay: In the report, you highlight that a growing threat is the climate change and its impacts. How does this affect bats?
Rodrigo Medellín: We have records of certain droughts, very high temperatures, or the famous Santa Ana winds, in the southwestern United States that have affected bats.
I’ll tell you what I’ve seen in my experience: I’ve been going to the Pinacate Desert [in the state of Sonora, northern Mexico] for 20 or 25 years, and we’ve recorded certain climate events that caused impacts. For example, atypical rains caused saguaro cacti [Carnegiea gigantea] to bloom earlier in the Sonora Desert. When the bats got there, they found the saguaros were finishing their blooming and there was no food for the females to eat to produce milk for the babies. When I got to the cave where they live, I found a carpet of baby bones.
The females decided evolutionarily to lose the babies because they’re the production units of the species. They prefer to stay alive and lose that year’s baby rather than risk their own death. This is the lesser long-nosed bat [Leptonycteris yerbabuenae], one of the species that pollinates agave, and therefore to which we owe mescal and tequila.
The second event we registered was in 2013. The Santa Ana winds hit. The wind starts blowing at 5 p.m. It’s a very hot wind, very dry, very strong. The next day, we found bats impaled in the saguaro thorns because the wind had pushed them. When we got to the cave, there were many dead females on the ground.
We’ve had two different climate events in the past 25 years. We can’t say that’s an impact of climate change but it’s true that the trends are pointing to less rain and more heat. That, without a doubt, will affect bats.
Mongabay: In the case of Mexico, what’s the biggest threat to bats?
Rodrigo Medellín: The destruction of their refuges. And that’s because of people’s lack of awareness. We’ve fought this by talking to landowners and explaining to them how fascinating, fundamental, important and essential bats are for people’s daily lives and for the functioning of ecosystems. When people have that information, they become the biggest defenders of the caves.
However, there are still caves where bats are being disturbed. We need to double our environmental education efforts and join forces with the federal, state and municipal governments to make sure that these caves are protected, not only by landowners but also legally protected. That’s what we’re trying to do.
We’re working with the National Commission of Natural Protected Areas (CONANP) to designate some caves as sanctuaries. In Mexico, we have sea turtle sanctuaries on some beaches. We want to do the same thing but with bat caves.
We’re also working with CONANP to strengthen the management plans for natural protected areas. We’re including regulations so that the caves in these areas are really protected. What we want is the caves not to be touched under any circumstance.
Mongabay: How many caves would have more protection?
Rodrigo Medellín:In a first analysis we’re focusing on 15 priority caves: caves that have a lot of bats or a nursery colony that’s particularly sensitive.
These 15 priorities caves must have one of these three criteria: They must host many bats of one, two or three species. Or they must be a nursery or mating cave on which the future of the species depends. Or else they’re a cave with many bat species, which then becomes a priority for all those species.
Mongabay: The report highlights that half a million bats die every year from colliding with wind turbines. In Mexico, what happens with a place like the Isthmus of Tehuantepec, where there are more than a dozen wind farms?
Rodrigo Medellín: Around 15 years ago, one of these wind power companies asked me to assess how many bats were dying in their wind farms, which as it happens is on the isthmus. We found that many bats were dying, including endangered species. The company took the data and told me: “Many thanks, Dr. Medellín, for working with us. That’s were our collaboration ends. Please, consider this data under embargo and you can’t do anything with it.” And they fired me.
Unfortunately, they found a biologist who did the “easy work” — a person who says there’s nothing wrong happening with bats.
A few years ago, we published an op-ed [in The New York Times] that shows that in the United States, 600,000 to 900,000 bats are dying yearly because of wind turbines. Especially hoary bats [Lasiurus cinereus]. This species migrates along areas where the wind is strongest, the areas where companies place their wind turbines. Many bat species die, but this one is the most sensitive, the most vulnerable.
Mongabay: What mitigation measures do you propose?
Rodrigo Medellín: We’ve tried to knock on doors to explain to the wind power industry how important it would be for them to adopt mitigation measures against these harms. These are easily achievable, cheap and effective measures. It’s only about modifying the speed at which wind turbines work. This change means sacrificing 1% of the energy generated by the wind turbine, but it cuts 70% of the bat mortality.
In the United States, there are constant tests. In Germany, they’re implementing it very well. In Mexico, there’s no action at all.
During the previous administration [of Enrique Peña Nieto], we worked closely with SEMARNAT [the Secretariat of Environment and Natural Resources] and we had the guidelines to mitigate mortality. We were close to releasing them, but after that six-year term, the new administration had no interest. That’s where our initiative ended.
Mongabay: With the current scenario for bat species in North America, what steps are you contemplating to reverse the declines?
Rodrigo Medellín: We have a three-pronged strategy: using environmental education; carrying out research applied to conservation; and taking conservation-specific actions.
When we focus our efforts on protecting caves and protecting particular species, we’re acting directly on those threats that affect bats.
Mongabay: What research are the three countries currently working on jointly?
Rodrigo Medellín: We have a beautiful initiative in collaboration with other researchers. We’re using small chips, the size and shape of a grain of rice, that we insert under the bats’ skin. We do it with the lesser long-nosed bat. We put the chip readers at the entrance of the caves and that’s how we know that a bat has gone in and out, at what time and on what date. Thanks to that, we now have a record of the bats that have traveled from the Pinacate Desert to Arizona, the Baja California Peninsula and Jalisco. We recorded one particular bat travel more than 1,600 kilometers [1,000 miles]!
That’s helping us map bat migrations. We already knew they winter in the center and south of Mexico, but we don’t know what migratory route they follow exactly.
We’d published that the species’ population in the Baja California Peninsula increases to about 100,000 bats, but that in winter they disappear from there. We didn’t know where they were going.
Now, with the information we have, we know that in May, they get to Baja California and spread around the islands of the Gulf of California. In the fall, they cross the Sea of Cortés. Some still go to the Pinacate, others go to the south, to Sinaloa and Jalisco. In the next few years we’ll strengthen this data because we’ll have more transponders in more caves and we’ll be able to map each step.
Mongabay: What other scientific research is providing tools to protect bats?
Rodrigo Medellín: There’s a program where we show how protecting bats that eat insects is beneficial for rice, corn and cotton farmers. We’re showing the economic value of bats in pest control.
In Morelos [in southern Mexico], for example, a researcher showed that the presence of bats reduced the moths that plague the rice crops by up to 50%. If there are bats in the area, farmers can reduce the intensity of their insecticide use, and therefore the cost as well.
This made us work with rice farmers in the region to develop a strategy for protecting bats.
Mongabay: The report invites people to join the campaign to protect bats. What actions can people take to participate in the initiative?
Rodrigo Medellín: We can all help bats recover their populations and continue to be a beneficial element in our lives.
First, people can take care of hollow trees, old trees that have some dead branches. Those trees are crucial as bat refuges.
Second, we can create bat-friendly gardens with native plants that are pesticide-free.
Third, anyone who’s near a green space, whether it’s a park or something different, can create water sources for bats.
Another action is for people who have cats to prevent them from leaving the house because they’re very good predators of wildlife, not only of bats but also birds.
And, more than anything, people need to become a voice for bats: they need to speak of how wonderful and necessary they are for our daily lives.
Banner image: Antrozous pallidus is a bat that eats insects and cactus flower nectar. Image courtesy of Marco Tschapka.