The Sound of Nature: How Bioacoustics is Changing the Way We Identify Birds

In the quiet corners of forests, fields, and backyards, a revolution is taking place, not one you can see, but one you can hear. Bioacoustics, the science of recording and analyzing sounds in nature, is giving birders, researchers, and conservationists a powerful new way to study birds. Instead of relying solely on visual sightings or field guides, people are now using technology to listen to the landscape, identifying species by the songs, calls, and even subtle flight noises they make.

At the heart of this technology are sensitive microphones, recorders, and software programs that can capture and interpret bird vocalizations. Tools like BirdNET, BirdNET-Pi, and Merlin from the Cornell Lab of Ornithology allow anyone from backyard birdwatchers to professional ornithologists to identify birds in real time using nothing more than a smartphone or a Raspberry Pi. These systems analyze the unique frequency patterns and rhythms in bird calls and match them to an extensive database of known species.

This shift to sound-based birding opens up new possibilities. Many birds are heard more often than they are seen, especially species that hide in thick brush, sing from the tops of trees, or migrate at night. With bioacoustic monitoring, we can now track these elusive species, monitor bird populations over time, and even detect changes in biodiversity caused by climate change or habitat loss. Bioacoustics doesn’t just help us hear birds better, it helps us understand them in ways never before possible.

Merlin App: Bringing Bird ID to Your Pocket

Merlin, the free bird identification app developed by the Cornell Lab of Ornithology, has soared in popularity since its 2014 launch. As of December 2024, it surpassed 23 million downloads, with over 12 million users active in just one year, and its Sound ID feature has already helped make over 1.3 billion identifications

Why It’s So Popular

Merlin has become especially popular because it empowers beginners and makes birding more fun and approachable. According to a coordinator at the Cornell Lab of Ornithology, many users describe the app as unlocking a kind of “superpower”, the ability to identify birds by sound and sight with ease. Interest in birdwatching also soared during the COVID-19 lockdowns, providing a major boost to Merlin’s user base. In fact, the app saw a 67% increase in users during the first spring of the pandemic, and its popularity continued to rise with the launch of its Sound ID feature in 2021. What makes Merlin even more powerful is the community behind it. The app is fueled by hundreds of millions of bird observations from eBird and millions of photos and audio recordings contributed by citizen scientists to the Macaulay Library, making it one of the most robust and community-driven tools in modern birding.

How Merlin Work

The Merlin Bird ID app offers several powerful ways to help users identify birds. With Photo ID, users can upload or snap a picture of a bird, and Merlin uses artificial intelligence and computer vision trained on millions of bird images to suggest possible matches. The Sound ID feature allows users to simply tap the microphone icon and let the app “listen” to bird calls in real time. Merlin converts the audio into a spectrogram and uses the same type of AI vision algorithms found in photo recognition to identify species, even distinguishing between overlapping songs. If neither a photo nor a sound is available, the Bird ID Wizard can still help. By answering five simple questions: location, date, size, color, and behavior users receive a list of likely species, drawing from eBird’s massive database of over 750 million bird observations. Finally, the Explore Birds feature lets users browse beautifully illustrated species lists tailored to their region and time of year, complete with photos, range maps, bird calls, and seasonal occurrence charts, making it a valuable tool for both beginners and seasoned birders alike.

Seeing Sound: How Spectrograms Help Us Identify Birds by Ear

In the world of bioacoustics, a spectrogram is one of the most powerful tools for visualizing and analyzing sound, especially bird songs. While most people are familiar with the traditional waveform display, which shows sound as a line that rises and falls with changes in volume over time, this view only tells part of the story. A waveform shows how loud a sound is but not what frequencies are being used. In bird identification, the pitch, tone, and pattern of a song are just as important as its volume, and that’s where the spectrogram becomes essential.

A spectrogram adds a crucial layer of information by displaying sound in three dimensions: time (left to right), frequency (bottom to top), and intensity (shown as color or brightness). This allows researchers and now everyday birders to “see” the unique acoustic signature of a bird’s call. For example, a fast series of high-pitched chips might appear as a series of short, bright streaks in the upper portion of the graph, while a low, drawn-out hoot shows up as a thick band near the bottom. These visual patterns are often more reliable and easier to analyze than listening alone, especially when dealing with overlapping calls or subtle variations between species.

What makes the Merlin Bird ID app especially innovative is that it brings this technology directly into the hands of users. When using the Sound ID feature, Merlin displays a live spectrogram in real time as the app listens to the soundscape. Users can watch the bird sounds appear visually as they happen bright lines, curves, and pulses moving across the screen with every chirp and whistle. This real-time feedback not only shows which birds are singing, but also helps users start to recognize the visual “fingerprints” of common species. It’s a perfect example of how complex scientific tools are now being adapted into intuitive, user-friendly formats that make birding more accessible, educational, and fun.

Beyond Merlin: How BirdNET-Pi Takes Bird Listening to the Next Level

While the Merlin Bird ID app is a fantastic tool for identifying birds by sight and sound, it does have its limitations especially when it comes to continuous data collection. Merlin relies on a person being present, phone in hand, and ready to record. Most people only use it while they’re actively birding, usually during good weather and daylight hours. That means you’re only capturing a small window of the bird activity happening around you. As great as Merlin is for quick, real-time identifications, it doesn’t provide a complete picture of the bird life in your area over longer periods of time.

For those who want a deeper, more consistent understanding of bird activity especially researchers, educators, or serious backyard birders tools like BirdNET-Pi offer a much more robust solution. BirdNET-Pi is a free, open-source application that runs on a small, affordable computer called a Raspberry Pi. Once installed and set up with a microphone, BirdNET-Pi passively listens for bird vocalizations 24/7, rain or shine, day or night. This always-on approach means you’re capturing the full range of bird activity in your location, including species that may be more active at dawn, dusk, or even during inclement weather when people are less likely to be outside.

One of the standout features of BirdNET-Pi is the ability to review and verify the detections it captures. Every bird call is logged along with a spectrogram a visual representation of the sound which allows users to go back and confirm or study the identifications. Merlin, while incredibly user-friendly, doesn’t offer this kind of review functionality. In addition, BirdNET-Pi provides detailed statistics and graphs that show trends in bird vocal activity over time. You can see which species are vocalizing the most, track migrations, and even monitor how bird activity changes by hour, day, or season insights that simply aren’t available through Merlin.

For anyone interested in long-term monitoring, research, or just getting a deeper understanding of their local bird population, BirdNET-Pi complements Merlin perfectly. It’s a more advanced tool that puts the power of bioacoustics into a permanent, automated system—no phone or fair weather required.

Hearing is Believing: How Bioacoustics is Transforming Bird Identification

As technology continues to evolve, so too does our connection with the natural world. Bioacoustics has opened up an entirely new dimension of birdwatching—one where we no longer need to see a bird to know it’s there. Whether you’re using the Merlin app on a sunny morning walk or setting up a BirdNET-Pi station to monitor your backyard soundscape 24/7, these tools are helping us listen more closely and learn more deeply. The songs of birds are more than just beautiful background music they’re data, they’re identity, and they’re clues to the health of our ecosystems. By embracing bioacoustics, we’re not just identifying birds we’re tuning in to the rhythm of the wild.