The human larynx is fabulous at producing an extensive range of sounds, including singing, but it’s less-than-ideal in its other function, which is to act as a valve keeping food and drink from going down the windpipe. So we humans regularly aspirate food and drink, and then we cough and sputter (or worse). Other mammals have the opposite problem: their larynxes are pretty good at preventing food and drink from going to the lungs, but their larynx placement makes it impossible for most mammals to make a wide variety of sounds. Birds, by contrast, have evolved in a way that solves these problems: they have a larynx that functions as the protective valve, and they have a separate, completely different apparatus dedicated to making sound. It’s called the syrinx.

Science writer Colin Tudge has summed it up: “Mammals and birds produce sound in quite different ways—and the avian technology is superior.” In his fascinating book, The Bird: A Natural History of Who Birds Are, Where They Came From, and How They Live, Tudge explains that a syrinx “is fabulously efficient. Almost 100 percent of the energy in the air that is forced under pressure past” the syrinx membranes is turned into sound. The energy efficiency of a mammal’s larynx is only 3 percent. “If Pavarotti had had a syrinx, no opera lover would have been safe. …. the Metropolitan Opera House would surely have been shaken” all the way down to its foundations.

Could the Met in New York City be felled by a Song Sparrow?

Yes, if the sparrow was the size of a human!

The syrinx is basically a two-sided resonating chamber with highly elastic, vibrating membranes. The way it packs so much power is pretty complicated; there are specialized muscles that control the tension on the membranes, as on the surface of a kettle drum, and birds can vary both the loudness and pitch of sounds by changing the pressure of the air passing from the lungs into the syrinx.

But some birds can do even more with a syrinx! They can control the airflow through the two chambers to make two different sounds at the same time. Famed ornithologist David Sibley notes that in many songbirds “the two sides are slightly different. These species produce higher sounds with one side and lower sounds with the other. … [in] thrushes, the two sides produce entirely different sounds simultaneously, creating an incredibly rich and complex sound. In effect, the thrush can harmonize with itself.” Among Pennsylvania thrushes, the song of the Hermit Thrush is particularly pleasing to humans, and there’s a reason: they often sing in pitches that change according to mathematically simple ratios, using the same harmonic series as human music.

Pennsylvania songbirds do many other impressive things with their syrinxes. Some amaze us with their versatility. The Brown Thrasher is the recordholder for the most different variations in its songs—they sing 2,000 – 3,000 versions! The Red-eyed Vireo is believed to be the world’s most tireless singer; one ornithologist counted 22,197 separate little songs her local Red-eyed Vireo sang on a single day in May.

We should bear in mind that birdsong is hard work. Tudge explains that “singing is exhausting, and only the fit can keep it up.” Beyond the complex control of the syrinx, while it’s singing a bird also has to manage its breathing, body movements, and bill position in order to produce a song worthy of its species. Sibley suggests that we “think of a bird’s song as a kind of dance or gymnastics routine, a series of elaborate jumps, and the judges (potential mates and rivals) are looking for height and speed, along with precision and consistency.”

What do Olympic gymnasts and songbirds have in common?

This Yellow Warbler knows that it’s something profound.

They’re all virtuosos!

Male birds in springtime who are seeking a mate particularly expend a lot of energy singing; their reproductive success depends on it. They are well aware that female birds use careful, nuanced assessments of males’ singing in order to choose their mates.

There is much, much more that is intriguing and delightful about bird vocalizations, and these will be explored in future issues of Bird Beat. For now, we’d like to note how important it is that birds hear the sounds from the syrinxes of other birds:

  • Birds need consistently to hear the calls and songs of their potential mates, already-chosen mates, and babies. These communications are crucial for successful reproduction.
  • Birds need to hear subtle differences among the songs of different individuals of the same species. They pay attention to whether or not they’re hearing the song of a familiar individual (a neighbor with an established territory) versus a stranger who is seeking new territory and may pose a threat.
  • Some birds use differences in high and low pitches as indicators of how far away another bird is. They can do this because high-pitched sounds don’t travel as far through air that is obstructed by dense vegetation as low-pitched sounds do. Thus, as Tudge clarifies, in an environment such as a forest, “the greater the distance, the greater the loss of high frequencies, and the more the overall sound is biased toward the low registers. For birds staking territory, the distance between … singers is crucial.” If the song’s tenor notes stand out more than the soprano notes, the potentially rivalrous bird is farther away; if the higher notes stand out more, the other bird is nearby.

Can this Northern Mockingbird really be heard if it’s surrounded by human noise?

Clearly birds need to hear all the complexities in the vocalizations of other birds: they need to hear all that other birds’ syrinxes offer. And of course, they also need to hear all the noises that their predators and prey make. But can they, if their world is filled with noise pollution? Check out our article on that topic here.

We also have a cool article here on how bird sounds have been used in movies and TV shows.

For ideas about how to remember which songs go with which birds, check out our kids’ article here (it’s good for grown-ups, too!).

For a list of sources used in preparing this article (all are terrific books about birds!), click here.

Christine M. Du Bois, Coordinator of the Lansdowne Bird Town and editor of Bird Beat

Image Credits:

New York Metropolitan Opera House 1140788, by Ermell, licensed under CC BY-SA 4.0

Song Sparrow – Melospiza melodia -Battery Park, New Castle, Delaware, USA-singing-8, by Keith, licensed under CC BY-2.0

Simone_Biles_Rio_2016, by Fernando Frazão/Agência Brasil, licensed under CC BY-BR 3.0 BR

Yellow Warbler_(male),_singing, by Gary Leavens, licensed under CC BY-2.0

Gymnastics_brokenchopstick, by brokenchopstick, licensed under CC BY-2.0

2008-07-18 Bird on a yield sign 1, by Ildar Sagdejev, licensed under CC BY-SA 4.0