What’s That Bird Song? Merlin Bird ID Can Tell You

Originally published in the Summer 2021 issue of Living Bird magazine. Updated May 2024.

It’s an almost universal feeling: the thrill of hearing a mysterious new bird song. And it’s usually followed up by the question: What was that bird?

In 2021, the question got much easier with the introduction of Sound ID in the Cornell Lab’s free Merlin Bird ID app. At the time of the feature’s launch, Merlin could recognize the sounds of 400+ species from the U.S. and Canada, and has since expanded to cover more than 1,300 species across parts of the Americas, Europe (Western Palearctic), and India. More about Sound ID coverage.)

Automatic song ID has been a dream for decades, but analyzing sound has always been extremely difficult. The breakthrough came when researchers began treating the sounds as images and applying new and powerful image classification algorithms like the ones that power Merlin’s Photo ID feature. The Merlin team was led by Grant Van Horn, who is now an assistant professor at University of Massachusetts Amherst.

“Each sound recording a user makes gets converted from a waveform to a spectrogram—a way to visualize the amplitude [volume], frequency [pitch], and duration of the sound,” Van Horn says. “So just like Merlin can identify a picture of a bird, it can now use this picture of a bird’s sound to make an ID,” Van Horn says.

This pioneering sound-identification technology is integrated into the existing Merlin Bird ID app, meaning Merlin offers four ways to identify a bird: by a sound, by a photo, by answering five questions about a bird you saw, or by exploring a list of the birds expected where you are.

How to Use Sound ID

Download Merlin. To get Sound ID, simply download our free Merlin Bird ID app and follow the prompts. If you already have Merlin installed on your phone, tap Get Sound ID.

Find a Singing Bird (or Birds). If you’re hearing bird song, just select Sound ID from the main menu and press record. Merlin will instantly start listing the birds it hears. On your phone screen you’ll see a list of possible species, complete with a thumbnail photo of the bird and examples of songs and calls for each species. Each subsequent time a bird sings, Merlin will highlight the corresponding bird in yellow.

Adjust Your Setup If Necessary. If Merlin has trouble identifying your bird, try getting closer without disturbing it, and check these tips to help you minimize extraneous noise.

Take Time to Review. When you’ve finished recording, you can go back and select a section to see which species are singing which songs. Or tap on any of the species in Merlin’s list of possibilities, and you’ll zip back to the point in the recording where that sound occurs. That way you can see and hear what separates it from other birds you’re hearing, and easily compare each sound to recordings from Merlin’s sound library.

Merlin automatically saves each recording to a folder on your device so you can access it anytime—and those recordings can be deleted or uploaded elsewhere if storage space is an issue.

Double-Check and Add to Your Life List. You can save each bird species Merlin helps you identify to your life list using Merlin’s Save My Bird feature. Just remember that identifying birds by sound is tricky for humans and machines alike. Think of Sound ID as a starting point—it’s always a good idea to verify a new ID by finding the bird and watching it sing.

If you’re still having trouble installing or using Sound ID, check the Merlin help pages.

Try These Other Fun Ways to Use Sound ID

Try these specific uses of Sound ID, recommended by Merlin project coordinator Drew Weber, to make your birding by ear even more enjoyable:

Decode the Dawn Chorus: In spring and early summer, mornings overflow with bird song—sometimes a dozen or more species at once. Merlin can tease apart these threads and reveal the identity of each individual in the soundscape. And because you can go back and dial in to the sound and image of each bird that was identified, you can listen again and again. Sound ID is a great tool to help you learn bird songs and calls.

Decipher Tricky Chip Notes: As if bird songs weren’t difficult enough, birds often communicate with little more than a few short, unmusical chip notes. Weber says that for many common species, such as Northern Cardinal, White-throated Sparrow, Song Sparrow, and Dark-eyed Junco, Merlin should be able to make the ID from a clear recording. Give it a try and see how Merlin fares.

Use Merlin as a Set of “Super Ears”: Some bird songs are easier to hear than others. Birds that are singing in the distance—or ones with stratospheric songs such as Blackpoll Warbler, Blackburnian Warbler, and Cedar Waxwing—can be hard to pick up and even harder to ID. You’ll feel like you have a superpower as Merlin detects and displays those difficult-to-discern calls, and checking what Merlin hears can be a great way to train your own ears.

Does Sound ID Really Work?

To train Merlin to identify bird sounds, the team assembled a minimum of 100 recordings for each species. (In total, the most recent Sound ID model was trained using 45.6 years of sound recordings.) Working on computers, volunteers trimmed and classified each recording by hand before it was fed into a machine-learning model that learned each song and its variations. The app also uses eBird observations to know which birds are most likely to be found at a particular place and time.

Even with all of Merlin’s computing power, some species present more of an ID challenge than others. “A bird like Willow Flycatcher where all the individuals have a very similar song across all of North America, is easier for Merlin to identify,” says project coordinator Weber. “Compare that to something like a Baltimore Oriole, where each bird has its own twist on the typical song. For species like that, it can be difficult for Merlin to make the correct ID with very high accuracy. Fortunately, we have thousands of examples of oriole songs and calls to draw on in the Macaulay Library and the model will get better and better over time.”

Weber says future updates to Merlin will continually sharpen its skills. “Users will eventually be able to directly upload audio from Merlin to Macaulay Library, which will complete the circle and allow Merlin recordings to directly train future Merlin machine-learning models.”

Merlin project leader Jessie Barry says that Merlin Sound ID marks a great leap forward in the ability for people to connect with and understand the sounds of the natural world around them. Macaulay Library web designer Matt Schloss, who describes himself as an advanced beginner and beta-tested the app, agrees.

“Merlin has helped me find birds that I might have overlooked before. It actually makes me feel like I have a superpower, or at least enhanced skills,” Schloss says. “I truly think this is going to change the way people bird.”

Merlin’s new sound identification capability is the product of years of work by the Merlin team, and was made possible thanks to the enormous collection of bird observations and sound recordings contributed by tens of thousands of citizen scientists who use eBird and the Macaulay Library. Thank you.