By Dr. Becker
Monitoring biodiversity around the world is critical for conservation efforts in this era of rapid environmental change. Acoustic surveys, or compiling a library of sounds, are increasingly being used to identify animal species in need of protection, including bats.
Bats are small, fast and nocturnal, which means monitoring them by visual surveys isn't only impractical, it's nearly impossible. However, as bats use sounds to navigate, hunt for food and socialize, acoustic surveys have proven to be quite effective at revealing bats in a given area.
It's an emerging field, as researchers have only begun to characterize animal sounds, which often form complex sequences made up of "multiple distinct acoustic units."1 Further, in the case of bats, many species lack reference recordings to help researchers match bat calls with bat species.
Adding to the challenge is the fact that some bat species have very similar-sounding calls.
In Mexico however — a country with many bats, including some at risk of extinction — a team of international researchers were able to record thousands of bat calls in order to create a library of bat sounds to identify bat species and further conservation efforts.
Bat-Call Library Allows Automatic Identification of Species
Researchers from the University of Cambridge, University College London (UCL) and Zoological Society London (ZSL) recorded more than 4,500 bat calls representing 59 species of bats in Mexico (the country is home to about 130 bat species in all).2
The calls were taken in desert, jungle and tropical forest regions of Mexico to capture the sounds of a diverse range of bats. An audio library of the calls was created, and machine-learning algorithms and voice-recognition software were used to analyze the calls.
The system was able to identify about 70 percent of bat species based on their unique sounds. When it came to identifying bat families, it was correct more than 91 percent of the time.
"It is the first time automatic classification for bat calls has been attempted for a large variety of species, most of them previously noted as hard to identify acoustically," according to a University of Cambridge press release.
Dr. Veronica Zamora-Gutierrez, from the University of Cambridge Conservation Research Institute and UCL, continued:3
"Audio surveys are increasingly used to monitor biodiversity change, and bats are especially useful for this as they are an important indicator species, contributing significantly to ecosystems as pollinators, seed dispersers and suppressors of insect populations.
… By tracking the sounds they use to explore their surroundings, we can characterize the bat communities in different regions in the long term and gauge the impact of rapid environmental change …
Before now it was tricky to do as many bat species have very similar calls and differ in how well they can be detected. We overcame this by using machine learning algorithms together with information about hierarchies to automatically identify different bat species."
What Do Bats Sound Like?
Humans are unable to hear most sounds emitted by bats, which are ultrasonic (i.e., ranging in frequency from 20 to 200 kilohertz [kHz]. Humans can typically only hear up to 20 kHz.).
However, a device called a "bat detector" allows researchers and citizen scientists alike to record bats' ultrasonic calls and lower them to frequencies that are audible to humans. In the video above, you can hear bat calls for yourself. The chirps, beeps and whistles have been slowed down by about 10 times.4
What researchers have revealed is that sounds can help to distinguish between species that were otherwise indistinguishable. For instance, the common pipistrelle bat and the soprano pipistrelle bat were considered to be the same species for hundreds of years.
It was their unique calls that finally clued in researchers that they weren't as alike as they appeared.
"Genetically, they're as different as lions and tigers are, but they're hard to tell apart by looking at them," ecologist Kate Jones of the University of College London and the Zoological Society of London, who worked on the featured study, told the LA Times.5
Why Create This Bat 'Caller ID'?
Recording bat calls and creating an automatic caller ID of sorts is part of a larger effort to protect not only bats but also the greater environment. For starters, 1 in every 5 bat species is at risk of extinction in the next five decades, according to citizen-scientist project Bat Detective.6
In North America, the fungal disease white-nose syndrome (WNS) has led to the deaths of millions of bats, and they're also threatened by habitat loss and wind turbines. It's incredibly important to protect vulnerable bat species, as they provide many benefits to the environment.
In the tropics, for instance, over 500 different types of tropical plants are pollinated by bats every year. Examples of foods that are pollinated by bats include bananas, peaches, cloves, carob and agave (used to make tequila).7
Meanwhile, fruit-eating bats are sometimes called the farmers of the tropics because they are incredibly efficient at dispersing seeds. Bats cover large distances while feeding at night and defecate while flying, which means the seeds in their feces are scattered across the vast open expanses of clear-cut rainforests.
By eating insects and reducing fungal damage, bats even save farmers more than $1 billion worldwide — and that's only for corn crops. The value of bats to the agriculture industry is estimated at nearly $23 billion per year, but may range up to $53 billion a year.8
Not to mention that bats are regarded as "canaries in the coalmine" for environmental changes worldwide. Declines in bat populations are an early warning that many species may soon be in danger.
Get Involved to Help Save Bats
Bat Detective is looking for citizen scientists like you to help weed through audio recordings in search of bat calls. They explain:9
"Typically many hours of recordings are made at night by researchers using bat detectors and the most difficult part of the process is finding bat calls in these recordings! For example, for a [one] hour recording it will take [six] hours to go through the files to find all the calls and detail them."
If you have a bit of extra time on your hands, you can listen to a short audio clip online and help classify bat calls for Bat Detective. In addition, the following steps are also important for protecting bat species worldwide:10
- Avoid caves and mines where bats are hibernating during winter.
- Encourage natural bat habitats around your home by reducing outdoor lighting, minimizing tree clearing and protecting streams and wetlands. Install a bat house.
- Adhere to cave closures. Check with your state and federal agencies or a local chapter of the National Speleological Society for the status of caves and caving in your area.
Follow the national WNS Decontamination Protocol to clean and disinfect clothes, footwear and equipment used in caves or mines.
- Talk to your family and friends about the benefits of bats and the fact that white-nose syndrome is decimating entire populations of bats across North America.
- Report unusual bat behavior, such as bats flying during the daytime in late-winter months, or bat deaths, to your state wildlife agency.