A northern mockingbird mimics the songs of many other birds. Credit: Courtesy of Bob Duchesne

Merlin is magic. I am referring to a bird identification app that I recommended to you a few weeks ago. It’s a free download from the Cornell Lab of Ornithology, at Merlin.AllAboutBirds.org. After another few weeks of testing, I’m now certain it could help a lot of people identify birds that they are hearing.

Its magic does not equal the wizardry of Gandalf in “Lord of the Rings.” I’d put it down somewhere around Harry Potter’s first year at Hogwarts — strong potential, but still learning. As it turns out, continuous learning is the whole point. I called the Cornell Lab seeking information on what makes Merlin tick. Drew Webber filled me in.

It works like this. You open the app on your smartphone, hit Sound ID, and point the phone in the direction of the bird you want to identify. Merlin compares the bird with its huge database of songs, and predicts which bird is most likely yours. The prediction is only as good as the scope and accuracy of the database. If the song you are hearing doesn’t quite match up with what’s in the database, Merlin could guess wrong.

Fortunately, the database upon which Merlin relies is awesome. Cornell’s Macaulay Library is the repository for nearly 41 million bird photos, videos and audio recordings, with more coming in every day. As additional songs come in, Merlin gets smarter.

Smarter is good, because the birds don’t make it easy. Some individuals are terrible singers. There are regional differences in song within some species, and some dissimilar species sing similar songs. Also, birds make other noises. That’s a lot for Merlin to remember.

Furthermore, it’s possible that some of the songs in the library are incorrectly identified, leading to Merlin errors. Drew walked me through the pains the Cornell Lab takes to make sure that songs stored in the Merlin database are accurately identified. But it’s nigh impossible to weed out all the miscues, at least in the early years of this rapidly developing app.

As Merlin continues to listen, it displays every bird it hears, nearly as fast as it hears it. That’s because the app is constantly sampling the sound in short bursts. That works great for relatively short songs, but mimics like northern mockingbirds can cause trouble. They are so talented at imitating other birds, they sometimes sing better than the original.

Fortunately, they tend to sing the same imitation five times or so, and then switch to another imitation. That makes it easy for humans to recognize the pattern, but Merlin’s short attention span can struggle. I intend to go to the Bangor Mall and try it out on the mockingbirds there.

Merlin is also learning call and alarm notes — the short sounds that birds use for communication, or to express alarm. Some notes are long enough to give Merlin a fighting chance. Some are so short and similar that Merlin has to guess between many candidates. It’s improving, though, as more sounds are added to the database.

I asked Drew about woodpecker drumming. On the one hand, drumming patterns vary by species, and an experienced birder can usually differentiate between them. On the other hand, drumming rhythm also varies somewhat by individuals. And, of course, it’s not a vocalization. It’s just the sound of a tree being whacked. Merlin is getting better at drummer identification but it is still far from perfect.

The Merlin app is not an energy hog. That’s deliberate. The programmers took great pains to design it for extended use. You can leave it running and let it record hours of audio, identifying everything it hears over that period. I look forward to taking a long walk in the woods, and then comparing my list to Merlin’s. We’ll see who wins.

Merlin can store audio files, where they may be uploaded to the Lab. Confirmed identifications can then be added to the database. Cornell’s eBird app can also store and upload audio files. Thus, Merlin can be taught new songs and variations as they are sent in, increasing its speed and accuracy.

That’s my new mission in life. I hear birds singing badly all the time. Some of them are so bad, they’re an embarrassment to their mothers. I intend to record the ones I positively identify, and send them in.

I’m sure I can teach Merlin a thing or two. Until then, it’s best to take every Merlin ID as a suggestion, not a confirmation. It’s still learning.

Try it.

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Bob Duchesne, Good Birding

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.