Remote Audio-Recording Devices Hear Birds When We Can't

New technology makes it possible to record hundreds of thousands of songs in a short time. That could make protecting wild birds and other at-risk animals easier.

By Megan Tomerlin

About this article

This article was originally published in the "Perspectives" section of Park Science magazine, Volume 37, Number 1, Summer 2023 (July 31, 2023).

Great horned owlet (Bubo virginianus)

Image credit: NPS / Jim Peaco

In the cool dark of the desert morning, the world is quiet. Aside from an occasional cricket or the distant yip of a coyote, the only sound is the breeze. A big-eared bat flits by, clicking as it makes its way to its daytime resting place. The first rays of the Texas sun reach up over the horizon. The birds begin to emerge, just a few sparrows at first, and then a few more. Tentatively, the morning stretches and yawns. More and more birds fly out to greet it with their songs. The sun comes up, and the dawn explodes with light and sound. The desert hums with life, speaking to us. We can learn a lot if we listen to it.

But it’s becoming harder to hear those sweet bird songs. Our feathered friends face many rapidly increasing threats, including from climate change and habitat loss. North American bird populations have declined by about 25 percent in the last 50 years, and they’re continuing to decline at alarming rates. With the help of some early-career scientists, new remote, audio-recording technology can help us figure out how birds and other animals are faring—and how to help them—faster and more efficiently.

Open-Source Tools Give Researchers Powerful Options

Monitoring birds long term is essential. It can tell us much about individual bird species and their habitats. This makes it easier to address the things that threaten them. Normally, researchers monitor birds by using point counts, walking a transect, and counting how many species and individuals they observed along the way. But this method requires significant effort and expertise. Passive audio recording devices require less effort, can be quickly deployed, and can remain in place for months. These devices, combined with automated analyses, help make bird monitoring more efficient and cost effective.

---

Computer tools like BirdNET Analyzer and NSNSDAcoustics allowed us to automate our analysis of the recordings, identifying hundreds of bird species by their recorded calls.

---

The National Park Service’s Chihuahuan Desert Inventory and Monitoring Network is testing how well passive acoustic detectors and automated computer processes can keep track of birds long term. International volunteers and Scientists in Parks interns like me are helping the network with this task. In 2022, the network set up pilot projects to test this new technology at several locations in the Chihuahuan Desert. Using low-cost AudioMoth recording devices, we collected bird calls remotely. Computer tools like BirdNET Analyzer and NSNSDAcoustics allowed us to automate our analysis of the recordings, identifying hundreds of bird species by their recorded calls.

Sunrise at Fort Davis National Historic Site. Many species of birds are most active around sunrise. This makes it the best time of day for recording, monitoring, and bird-watching.

Image credit: NPS / Jason Mateljak

The initial results of this project are promising. We’ve learned more about these recording devices and computer tools and how to use them to our advantage in the Chihuahuan Desert parks. Monitoring birds using these new methods is affordable and saves researchers valuable time. Using this technology, we can monitor birds more often and in more places than in the past.

Piloting a Project through Collaboration

In summer 2022, International Volunteers in Parks intern Wesley Reverdy worked with the Chihuahuan Desert Network on a pilot project at Fort Davis National Historic Site. The project’s first goal was to record bird calls using the AudioMoth devices. Wesley researched different deployment methods at the Desert Research Learning Center, collaborating with staff from the Sonoran Desert Inventory and Monitoring Network. Once he found the most suitable methods, he deployed recording units at Fort Davis, collecting sounds every morning from late July through late August.

An AudioMoth acoustic recorder strapped to a tree at Fort Davis National Historic Site.

Image credit: NPS / Jason Mateljak

The second goal of Reverdy’s project was to automate the analysis of the recordings. With help from natural sounds biologist Cathleen Balantic, Reverdy developed a workflow to process and analyze the recordings. The analysis uses BirdNET Analyzer and NSNSDAcoustics to match sounds from the recordings to known bird calls. This allows researchers to identify the different species.

---

The first round of analysis of the month-long dataset found over 120,000 bird calls from more than 180 different species.

---

In spring 2023, Scientists in Parks interns Adam Pingatore, Rachel Struhs, and I completed the first step in analyzing the recordings from Fort Davis. The first round of analysis of the month-long dataset found over 120,000 bird calls from more than 180 different species. The next step in the analysis was to manually verify the accuracy of the results. This helped confirm the data’s quality.

To do this, a scientist with experience identifying birds by ear listened to a small sample of calls from each bird species we recorded. They used the sounds of the calls, along with spectrograms—visual representations of sound frequency and intensity—to make sure the birds they heard were identified correctly during the analysis. If any birds were misidentified, we removed them from our results to update the species list.

---

Without this technology, a project of this scale would have taken more than 800 hours of in-person point-count monitoring.

---

After this verification process, the number of bird species detected at Fort Davis was narrowed down to 115. These included many striking species of sparrows, grosbeaks, and buntings, among others. Without this technology, a project of this scale would have taken more than 800 hours of in-person point-count monitoring. Instead, we were able to set up the recorders at Fort Davis in just one afternoon, and the data were analyzed and verified in under two weeks.

Bats at Carlsbad Caverns National Park. The park is in the Chihuahuan Desert Inventory and Monitoring Network.

Image credit: NPS

Expanding the Project to Record Bats and Amphibians

Climate change, disease, and competition from invasive species also threaten bats and amphibians, so the Chihuahuan Desert Network hopes to expand this project to include them. To monitor different types of animals, we need to consider their behavior and vocalization frequencies. We can adjust the recorder settings to make sure they capture the high frequency calls of many bat species.

---

Bats and many amphibians are most vocal at night, so we would have to set our recorders for different schedules to pick up their calls.

---

Bats and many amphibians are most vocal at night, so we would have to set our recorders for different schedules to pick up their calls. The network also plans to set up monitoring locations in more park units. The more we can learn about the status of these animals in our parks, the better equipped we’ll be to protect them.

We deployed many of the AudioMoth recorders in Boquillas Canyon along the Rio Grande in Big Bend National Park.

Image credit: NPS / Megan Tomerlin

A cup-shaped nest spotted near the Rio Grande in Big Bend National Park.

Image credit: NPS / Megan Tomerlin

Southern Bird Hotspot

Big Bend National Park is an incredible hotspot for bird diversity because it is large and has many distinct habitat types. Over 450 bird species have been reported in the park.

---

When the recorders are collected in April 2024, they will contain much more information than we could have gained using point-transect monitoring.

---

In April 2023, the Chihuahuan Desert Network’s team of Scientists in Parks interns set up AudioMoth recorders in Big Bend at several places along the Rio Grande. Biologist Missy Powell worked closely with the team to determine the best times of day to record bird calls. We put the recorders in locations where we monitor the vegetation and morphology of the river annually. This will make future retrieval and re-deployment of the recorders convenient and efficient.

The goal of the Big Bend project is to record the park’s birds over the course of a full year. When the recorders are collected in April 2024, they will contain much more information than we could have gained using point-transect monitoring. This will help us better understand the bird communities that live along the Rio Grande or visit the river during migration. By comparing our results to previous data, we can learn if new species have arrived, or if birds we expect to find are no longer present. Park staff can use this information to understand the health of the river ecosystem and make decisions about managing it.

Chihuahuan Desert Network technician Kiki Fahey and Scientist in Parks interns Sam Olivares-Mejia and Adam Pingatore hiking through the desert of Big Bend National Park to deploy acoustic recorders.

Image credit: NPS / Megan Tomerlin

Enhancing Our Ability to Preserve the Natural World

Urgent threats such as climate change and habitat loss make it critical to monitor park species. But that isn’t always an easy task. Resource managers have a lot on their plates. They need information not only about birds, but the whole ecosystem. The National Park Service’s inventory and monitoring networks collect data about soil, plants, water, and more. By gathering lots of data quickly, scientists can give parks the latest information when they need it.

---

Interns and international volunteers play important roles in this work. They’ll be the next generation of scientists and public land stewards.

---

Interns and international volunteers play important roles in this work. They’ll be the next generation of scientists and public land stewards. The National Park Service appreciates their contributions and the new ideas they bring to each project. Collaborative projects like these are essential for preserving our rapidly disappearing songbirds, bats, and other at-risk animals.

---

Want to know more about this work? Contact the Chihuahuan Desert Network Inventory and Monitoring Program.

---

About the author

^{Megan Tomerlin is an ecological assistant and Scientists in Parks intern for the Chihuahuan Desert Network. Image courtesy of Megan Tomerlin.}