When a bird sings, you may think you’re hearing music. But are the melodies it’s making really music? Or is what we’re hearing merely a string of lilting calls that appeals to the human ear?

Birdsong has inspired musicians from Bob Marley to Mozart and perhaps as far back as the first hunter-gatherers who banged out a beat. And a growing body of research is showing that the affinity human musicians feel toward birdsong has a strong scientific basis. Scientists are understanding more about avian species’ ability to learn, interpret and produce songs much like our own.

Just like humans, birds learn songs from each other and practice to perfect them. And just as human speech is distinct from human music, bird calls, which serve as warnings and other forms of direct communication, differ from birdsong.

While researchers are still debating the functions of birdsong, studies show that it is structurally similar to our own tunes. So, are birds making music? That depends on what you mean.

“I’m not sure we can or want to define music,” said Ofer Tchernichovski, a zoologist and psychologist at the City University of New York who studies birdsong.

Where you draw the line between music and mere noise is arbitrary, said Emily Doolittle, a zoomusicologist and composer at the Royal Conservatoire of Scotland. The difference between a human baby’s babbling versus a toddler’s humming might seem more distinct than that of a hatchling’s cry for food and a maturing bird’s practicing of a melody, she added.

Wherever we draw the line, birdsong and human song share striking similarities.

How birds build songs

Existing research points to one main conclusion: Birdsong is structured like human music. Songbirds change their tempo (speed), pitch (how high or low they sing) and timbre (tone) to sing tunes that resemble our own melodies.

Other features, like cadence and tension, are also used in both birdsong and human music, said Tina Roeske, a behavioral neurobiologist who specializes in birdsong. Just as the familiar tune “In the Hall of the Mountain King” gradually builds speed “accelerando,” as the compositional notation is known, some birdsong does too, like that of the nightingale.

While earlier studies focused on syntax, or how notes were ordered, newer research is integrating rhythm, too, by analyzing how notes are timed. In human music, rhythm is often thought of as a constant beat, like the one that opens “We Will Rock You” by Queen. But in birdsong, rhythm refers to patterns of notes, regardless of whether they are repeated.

To humans, birdsong may appear to have “a random structure,” Dr. Roeske said. Because of the speed at which birds sing — up to four times as fast as most human music — that rhythm is “hard for us to grasp and appreciate,” she added.

Dr. Roeske and her co-author Dr. Tchernichovski researched birds’ musical structure and found that birdsong rhythms fell into three general categories. The first is isochronous, in which intervals between notes are equidistant.

Alternating, in which a note is longer than the previous one.

And ornament, an exaggerated form of the alternating pattern.

Human music contains these rhythmic patterns, too.

In their 2020 study, Dr. Roeske and Dr. Tchernikovski compared recordings of thrush nightingales across Europe with examples from musical genres all over the world, including Western classical piano, Persian drumming and Tunisian stambeli. They found that birdsong and global music forms had the same types of timing components, integer ratios, which form the foundation of most melodies.

In music, these ratios are the amount of time between notes. A 1-to-1 ratio means notes are evenly spaced, like in “Twinkle, Twinkle, Little Star,” but a 1-to-2 ratio means the time from one note to the next is uneven, like in “Itsy Bitsy Spider,” Dr. Roeske explained.

When they charted integer ratios from birdsong and human music, the plots all produced a similar shape resembling a long-stemmed flower. This indicates that some birds build songs using patterns similar to those found in human music.

Other researchers are gaining insights by focusing on birdsong rhythm.

“We found that rhythm and syntax have a relationship that nobody has really thought about before,” said Jeffrey Xing, a graduate student in psychology at the University of California, San Diego, and an author of a September 2022 paper analyzing the song structure of the Australian pied butcherbird.

Pied butcherbirds “seem to prefer some song rhythms over others,” such as isochronous rhythm, Mr. Xing said. In some ways, these rhythmic patterns follow rules like forms of poetry that have strict meter. A good example is a sonnet.

“It’s a very rigid rhythmic structure that you have to follow, and somehow the syntax of the words you use has to conform to that,” he said.

Human brains and bird brains

Hollis Taylor has dedicated her life’s work as a violinist and ornithologist to the pied butcherbird, a species she deems a fellow musician.

Ms. Taylor, who analyzed the bird’s rhythmic structures with Mr. Xing, records the birds’ songs in Australian deserts and savannas in the middle of the night. Then, she transcribes their notes into musical notation.

“The musician in me recognizes the musician in them,” Ms. Taylor said.

She has observed what appear to be warm-up sessions, rehearsals and singing contests. Other than humans, there’s only a “small club” of species with an observed capacity to learn songs and vocal patterns, Ms. Taylor said, including songbirds, parrots, hummingbirds, bats, elephants and some marine mammals.

Ms. Taylor has performed her birdsong-like compositions with orchestras around the world. She draws inspiration from the French composer Olivier Messiaen, who also transcribed birdsong into musical notation.

Musicians’ fascination with birdsong has deep roots. Mozart, historians recount, kept a European starling in his Vienna apartment for three years. In a letter to his father, Mozart remarked at the “lovely” and precise way in which the starling learned and repeated one of his concertos.

While there is no concrete evidence that Mozart’s starling influenced his compositions, the idea that birds affect the work of composers endures.

The French composer François-Bernard Mâche, a founder of zoomusicology, speculates that birds may have influenced Igor Stravinsky’s compositions during summertime stays in what is now Ukraine. According to Dr. Doolittle’s research, the song patterns of Eurasian blackbirds found in that region resemble Stravinsky’s compositional style.

Neuroscience research points to the idea that this affinity between birds and humans is not so unusual. In terms of musical ability, we are more like birds than we are like our primate cousins or other mammals, said Johan Bolhuis, a zoologist who specializes in the cognitive neurobiology of birds and humans.

Our brains and songbirds’ brains have a similar way of learning musicality. But the brains of monkeys and non-songbirds, like gulls, are organized in a different way, Dr. Bolhuis said. It could be a sign of shared creative abilities: Like humans, some songbird species seem to improvise based on the song patterns they have learned.

For example, both humans and birds can produce smash hits that evoke feelings in their listeners, the psychologist Dr. Tchernichovski explained.

“When you hear music, what do you feel? Well, it depends on the music,” he said.

For instance, listening to a funeral march might make you sad even if you’re vacationing on the beach, and a romantic song might fill you with love even if you’re working on your taxes. Birdsong can affect the behavior of other birds by luring in a mate or scaring off an unwanted foe, similar to how we might turn up the volume when we hear our favorite song or skip to the next track if the vibe is off.

“This is the magic in music,” Dr. Tchernichovski said. “Bird songs seem to have some of this magic, too.”

But there’s no evidence that their songs have meaning, Dr. Bolhuis said.

“In the mind of the great composers, they actually meant something” with music, he said. “It’s not so much the case in birdsong.”

Also, birds have a limited repertoire, whereas with only a limited number of items, the human mind “can be infinitely creative,” Dr. Bolhuis said.

Researchers agree, however, that birdsong can communicate identity. “They can recognize individuals just the way you and I can recognize each other by our voices,” said Mike Webster, director of the Macaulay Library at the Cornell Lab of Ornithology.

When birds from a certain area hear a familiar bird singing, he explained, it’s no big deal. But if the same bird moves to a new area, the birds there “go bananas” in a territorial uproar. In this sense, singing is like a way for birds to identify themselves — but there may be more to it than that.

Why do birds sing?

While scientists have studied birdsong for decades, they know little about why and how birds select specific tunes and what counts as deliberate communication versus meaningless song.

Through brain-imaging studies, neuroscientists have found that the human brain responds to music most strongly along a particular neural circuit that is activated when a person listens to a song perceived as pleasant. Studies have shown that birdsong elicits the same response in female birds, possibly as an evolutionary mechanism for mate attraction. But scientists still wonder whether birds sing for entertainment in addition to mating.

“What’s going on in the bird’s head when it’s singing? Is it happy?” Dr. Webster said. Humans often sing when they are emotional — happy and heartbroken alike — but scientists do not know if birds have such an emotional range.

Dr. Webster, who studies bird behavior and communication, added another unknown: If birdsong’s main purpose in some species is for males to attract females, then why do some females also sing? “Female song actually arose very early in songbird evolution,” he said. “In species where females don’t sing, it’s because they’ve lost the ability to sing rather than it being gained.” This indicates that it may have once been evolutionarily beneficial for females to sing — and scientists can’t say why.

There are other mysteries. Ornithologists have observed “bird chatter” in parrots, when two birds appear to be whispering to each other. There are also nonvocal sounds, Dr. Webster said: Some birds snap their wings, some drum on trees and others rub their feathers together as if playing the violin. The purpose of these sounds — whether communicative, musical or both — sits on the next frontier of ornithology research.

“We’ve just scratched the surface,” Dr. Webster said. “Birds are constantly making sound, and I think most of the time we don’t really know why, and we don’t really know what they’re saying to each other.”