wHen Natasha Walter was first curious to know about the birds around her, she recorded their songs on her phone and tried her best to match each song with the online recording. When a friend recommended Merlin Bird ID, a free app, she tried it in her London garden and was delighted to find that the birds she had assumed to be female blackbirds – “what a bad birdwatcher I was” – were actually song thrushes and mistle thrushes.
“I’m obsessed with Marilyn – she’s wonderful and she’s a joy to me,” says author and human rights activist Walter. “That’s what AI and machine-learning were invented for. It’s a good thing!”
Marilyn is spending some time. app, Developed by Cornell Lab of Ornithology New York, which listens to birdsong and identifies singing species, has been downloaded 33 million times in 240 countries and territories around the world. The UK has the second largest number of total users – more than 1.5 million in 2024, an increase of 88% from 2023. Every month, there has been a 30% increase in new users of the app, whose voice recognition function was launched in 2021.
Merlin has been trained to identify the songs of more than 1,300 species worldwide, with more birds added twice a year. Different songs create different patterns on the spectrogram and Merlin is trained to recognize these different shapes and associate them with a species.
For those arriving late for bird watching, or those who don’t have a knowledgeable friend, the app has become their teacher. “My fear at first was that I wouldn’t really learn because I was outsourcing my understanding of birds to this app,” says Walter. “But it didn’t. This helped me continue my learning journey.” Nowadays, she speculates, and uses Marilyn to confirm her guesses. “It’s wonderful if you’re coming to bird watching late and don’t really have a mentor,” she says.
Angela Townsend from Bedfordshire started using Merlin after going on a nightingale walk one spring and being overwhelmed by the range of bird sounds in the evening chorus. He has found that this has steadily increased his birding knowledge. “The warblers used to be just little brown jobbies, but now I can identify Ceti’s warblers and willow warblers when I’m outside without turning on the app,” she says.
Marie Novakovich, author of My Family and Other Enemies, is another recent adoptee. She has found it especially useful when traveling to Croatia, where her parents live. “I like putting names on faces and names on sounds,” she says. “It really brings you closer to the natural world, rather than separating it from your life. It’s part of what makes life enjoyable.”
However, Merlin is not blameless. 12-year-old Caspar Wall first tried it in his Norfolk garden, discovering a northern cardinal and a brown-headed cowbird – North American species not found in Britain.
“I think it was figuring out where we live,” says Wall, who enjoys using it, even though he is now an extremely knowledgeable bird expert. “A few weeks ago we were watching a big group of Goldcrests and this one came up along with a Firecrest. I thought, ‘Oh, there must be a Firecrest here too’ and 30 seconds later we saw one, which was the first time I’d seen one. I like it and it’s very cool but I wouldn’t say it’s any better than the best people like (naturalist) Nick Acheson at identifying bird-calls. It can definitely be fooled.”
Wall enjoys fooling Merlin with his unique impressions of the curlew, barn owl, and greenshank.
Acheson does not use Merlin. He welcomes this, but points out that it can take the place of learning. “Anything that gets people thinking about and responding to nature is a great thing,” he says. “But there’s definitely a risk that people don’t learn and leave the responsibility for learning to Merlin.”
He has observed a glitch where merlins interpret a particular type of chaffinch call as that of a redstart, leaving people completely convinced that there is a rare bird in their garden. “There’s no replacement for a real person explaining to you what it feels like to hear birdsong, and encouraging someone to connect with it emotionally,” he says.
John Williamson, who works as a guide Norfolk Wildlife Trusthave found that merlins repeatedly identify high-pitched calls as those of the spotted flycatcher, a bird that is very unlikely to be found among Hickling Broad Nature Reserve Large reedbed. “Merlin can’t do housing,” he says.
Merlin has excited visitors by identifying a rare migratory Golden Oriole that occasionally visits the Hickling Forest, but no one has actually seen the species. Williamson is convinced that it is misinterpreting the quite unusual “catcall” of the female jay, a common woodland bird.
That said, Williamson considers it a “good tool” and welcomes how it is encouraging new people to enjoy birdsong and especially its mental health benefits. He knows someone who suffers from intense anxiety, but Marilyn has led him back into the world and into nature, allowing him to focus on quiet trips outside. “I find it impressive that an app can empower people to go out into nature,” he says.
Research has found that birdsong is particularly beneficial for mental health, and has lasting positive effects on health. For millions of people around the world, Marilyn is doing exactly that.
“It reminds you that birds are connected to your daily life,” says Walter. “It’s not about, ‘Now I’m going to do a bit of bird-watching’, you’ll just be walking around in the park and you’ll hear something and it makes you realize that these birds are singing all the time, even in London.”
