Not all bats are unbelievably, overwhelmingly adorable, like the one below. Many of them have wrinkly faces and large ears that help them “see” in the dark, using echolocation.
But all bats are, without a doubt, exceptional creatures. Not only do bats pollinate our crops, prey on pests like mosquitos, and spread seeds that help damaged ecosystems recover, but they also possess a superpower that’s unique among mammals: flight.
Indeed, bats are the only mammals on the planet that can fly. Yes, some squirrels and frogs can glide through the forest. That’s neat, but it’s not flight.
The power of flight demands an enormous amount of energy and a highly specialized physiology. While airborne, a bat’s heart rate skyrockets to as high as 1,000 beats per minute — several times above its resting heart rate — and its body temperature surges, often pushing past 105 degrees Fahrenheit. To maintain that high metabolism, bats need to eat an enormous quantity of food and plenty of water.
A body built for flight comes with some serious benefits. It likely helps these creatures avoid getting sick, for example, even when they’re infected with a number of viruses, such as coronavirus, as Vox explains in the video below.
But as scientists are starting to learn, it also comes with some serious drawbacks. Especially as climate change continues warming the planet. Bats’ flight-adapted physiologies make them highly susceptible to severe droughts and heat waves. Plus, the proliferation of wind turbines — a climate solution that provides energy without harmful greenhouse gas emissions, and one we’ll need more of to combat warming — is killing them in droves.
While bats remain highly understudied relative to birds and other mammals, scientists are sounding the alarm. In North America, more than half of all bat species are at risk of severe population declines, due to other problems like fungal pathogens and the plight of insects. Climate change, they say, threatens to only speed up their demise.
Bats “break all the rules”
Scientists are typically reluctant to generalize about bats because they comprise such a large and diverse group of winged animals. With nearly 1,500 species, bats make up about one-fifth of all mammal species on Earth.
But one thing that can be said about them as a group is that they are, in not-so-scientific terms, very odd. “They break all the rules,” said Cori Lausen, a bat expert at the environmental group Wildlife Conservation Society Canada.
Flight is just one of their oddities. Bats not only push their heart rate to extreme highs but to extreme lows — as slow as one beat per minute. Many species can go into a period of deep sleep, known as torpor, for a few hours a day or even for weeks to conserve energy when it’s cold or food is unavailable. And while most small mammals have short lives and lots of babies, some bats can live for two decades or more and typically have just one pup per year, Lausen said, making them more like grizzly bears than, say, rodents.
For how much energy they need, it’s also surprising that many bat species, including most of those in the US, rely on insects alone for food (elsewhere, bats consume fruit, nectar, or even blood). They have to eat ridiculous quantities of them. A mom that’s nursing a pup can catch more than 4,000 insects in one night. It’s basically like trying to eat your entire weight in bugs, night after night.
This is where echolocation comes in. Bats make high-pitched noises with their mouths or noses and listen for the return signals to home in on their prey. Most of them will then capture the bugs with their feet, or the skin between them, before swinging the prey into their mouths, said Winifred Frick, chief scientist at Bat Conservation International. That’s why bats often look kind of chaotic in the air, she said.
You can see these acro-bat-ics (sorry) in the GIF below.
Oddly, although bats can fly, they can’t easily take off from a stationary position, like most birds and insects do. That’s one reason why they hang upside down. Bats gain the momentum they need for lift by falling. “For them, it’s not upside down,” Frick said. “It’s flight-side ready!” (Adorably, a handful of bat species cling to leaves, instead of hanging upside down, using suction-cup-like appendages on their arms.)
Bats are so weird, Lausen said, it’s almost like these animals shouldn’t exist. “They’ve got these fascinating physiologies so that they can survive, though it doesn’t seem like they should,” Lausen said. Nonetheless, bats have existed for millions of years, so these traits are obviously working for them — or at least they have been.
Why bats and climate change don’t mix
Most bats are small with big wings, some weighing as little as 2 grams — less than a penny! — like the bumblebee bat shown below. This is obviously useful for flight, but it can become a problem during heat waves. Compared to other mammals, bats have a lot of surface area, and that means they tend to lose water more easily through evaporation across their skin, said Liam McGuire, an associate professor at the University of Waterloo who studies bat physiology. Essentially, bats are at risk of drying out and dying from dehydration.
“They will likely face dehydration in scenarios of increasing temperatures,” a team of researchers wrote in a recent study, which cross-referenced the number of bats admitted to wildlife rehab centers in Italy with weather data. The study, an analysis of roughly 20 years of data, found that more bats were brought in for treatment — typically because they fell from their roosts, or showed signs of injury or dehydration — in weeks when it was in the high 80s or hotter.
An earlier study in the Mediterranean linked drought to a drop in reproductive success, meaning bats were having fewer pups. And yet another paper, published in 2010 using data from bats in the southern Rocky Mountains, similarly indicated that bats had fewer offspring when water was scarce. “These data portend significant consequences for regional insectivorous bat populations in response to climate change in western North America,” Rick Adams, the author of the 2010 paper, wrote.
Dehydration can be devastating, but heat alone also poses a potential existential threat. Temperatures above roughly 105°F can cause heat stress or even death among many species, especially if the animals nest in trees outside, where they’re exposed to the ambient temperatures. Heat waves in Australia, for example, have caused dozens of mass die-offs of flying foxes, big fruit-eating bats that use their noses and large eyes instead of echolocation to find food. “They’re out, exposed, just sitting on a tree branch during the hottest part of the day,” McGuire said.
Over two days in 2019, temperatures reaching 107°F wiped out roughly 23,000 spectacled flying foxes, about a third of Australia’s population of the species. The number of heat waves in Australia, and around the world, are projected to increase in the coming decades due to climate change.
What’s more is that one of the main technologies meant to combat warming is also harming bats. Wind turbines kill hundreds of thousands of bats each year in North America alone, and globally they are known to harm more than 30 bat species. Typically, the bats — most of which are migratory species — die from colliding with turbine blades, though it’s not clear why these animals are drawn to them.
Making these threats more troubling is the simple fact that bat populations don’t recover quickly after die-offs, whether or not they’re climate-related. It goes back to their flight-enabled physiologies: Unlike birds, which drop their eggs off at a nest, bats have to fly while pregnant, which isn’t easy. That’s why most bats only have one pup per year, Frick said. “Their reproductive rates are really low, which makes it harder for them to recover from big catastrophic events [e.g., heat waves, big storms that wipe out habitat] that lower populations,” she said.
The uncertain future of bats
This would all matter a lot less if bats were doing fine otherwise. Yet they face a wide range of threats beyond climate change, including a disease known as white-nose syndrome, which has killed millions of bats in North America. The disease, caused by a fungus, can damage their skin and wake them up while they’re hibernating, causing them to burn off vital energy stores and either freeze or starve to death. The syndrome continues to spread and kill bats in North America. And while it’s also found in Europe and Asia, it doesn’t seem to cause mass mortality there.
Together, these problems are pushing many bat species closer to extinction. In North America, more than half of all species “are at risk of populations declining severely in the next 15 years,” according to a 2023 report by the North American Bat Conservation Alliance, a coalition of groups including government agencies and Bat Conservation International. This trend is mirrored globally. Importantly, the 2023 report found that climate change — namely, drought and extreme heat — could impact more than 80 percent of all North American species.
Some bat species may yet prove resilient in the face of warming. While flight can be a liability, it also gives bats the ability to move freely. Scientists suspect that warming is pushing populations of some species, like the Mexican free-tailed bats, further north, where it’s cooler. These bats — among the fastest animals in the world, capable of reaching speeds close to 100 miles per hour — were once confined to the Gulf Coast, McGuire said, but now they’re regularly found up in Tennessee. “Their range is expanding quite rapidly,” he said.
Bats that roost in caves, which amount to nearly half of all species, globally, may also be better off than those that rest out in the open or in trees. Rock crevices may shield these mammals from warming and drought, scientists say. It also helps that many species are able to go into torpor. “If you’re caught in a situation where the climate is changing, the environment is degrading, then the bats may be able to use torpor to reduce some of their energetic costs and help to buffer them a little bit against that,” McGuire said.
Yet scientists don’t know how effective these strategies will be over the long term. In fact, they still don’t know much about bats in general.
This lack of data is rooted, in part, in bats’ bad reputation, said Mark Brigham, a biologist at Canada’s University of Regina. “Until 30 years ago or so, studying bats was not viewed as a particularly good thing,” he said. “Most people viewed them as yucky, ugly, Dracula-type creatures that you didn’t want to go anywhere near. It’s only in the last five years, maybe, that anyone has shown any interest in heat effects on bats to be very honest.”
Bats clearly don’t deserve this bad reputation.
Exhibit A: Baby bats wrapped up in blankets like a burrito. They don’t exactly look sinister.
By eating agricultural pests, such as moths and beetles, bats also provide up to $53 billion in economic value each year in the US alone. They eat pests that bother us, too, including mosquitos. And of course, bats pollinate agave plants as they slurp up their nectar, which give us, among other things, tequila.
“But at the end of the day,” Frick said, “I come back to the fact that bats are just badass.”