Why do birds sing? How do birds make their songs heard over background noises? Do female birds sing?

by GrrlScientist for SciLogs.com (now defunct)| @GrrlScientist

Birdsong Dawn Chorus England 26th May 2013. (Video by ESL and Popular Culture.)

The early morning sky blushed pink as it was greeted with songs produced by a flirtatious ensemble of starlings on the power lines overhead. A robinโ€™s cheery carol and the intricate whistle of a wren drifted lightly through this concert. As in countless ages past, the dawn chorus had begun.

An American robin (Turdus migratorius), sings.

โ€œBirdsong serves the two main functions of advertising a territory and attracting femalesโ€ says Eliot Brenowitz, a professor of both Psychology and Zoology who studies birdsong at the University of Washington.

Interestingly, some scientists think birds also sing for the pure pleasure of hearing their own voice.

Not all birds can sing. The passerines, or songbirds, comprise about half of the worldโ€™s 10,000 avian species. They are characterized by their special muscular voice box, the syrinx, which consists of one set of vocal cords located at the top of each lung. Each set of vocal cords is controlled separately, which allows birds to sing two different notes at the same time. Surprisingly, birds can also sing with their beaks closed or while they are eating.

Song-learning pathway in birds (based on Nottebohm, 2005)

Specific brain regions, known as โ€œsong control nucleiโ€, play unique roles in both song learning and production, and their size apparently limits the number of songs that a bird can learn. The number of songs that birds learn varies by species: some bird species, such as red-eyed vireos, have many different songs in their collection, or repertoire, while other species, such as white-crowned sparrows, sing only one or two song types.

โ€œIt is speculated that singing a number of different songs provides a more ambitious message than singing just one songโ€, explains Brenowitz. However, it might be more favorable to produce only one song when it is important to get the message across to potential receivers. Further, it is thought that birds produce songs that travel farthest in the particular environment where they live. In forests, sound is reflected off tree trunks and is absorbed by the leaves, so a constant, brief signal works best there: If intended recipients miss hearing the song the first time, they will surely hear it again.

Savannah sparrow singing. (Video by Scott Carpenter)

Birds of the forest floor use low-pitched calls that will not be bounced off and distorted by the ground. Out in the plains species like the Savannah Sparrow favor the buzz. The buzz is a compressed message which carries over great distances in open areas, such as savanna and grassland.

Wild New Zealand blue ducks, or Whio, have a high-pitched call. (video by Darron Gedge.)

Running water produces a lot of interfering background noise that makes hearing any other sounds quite difficult. The high frequency calls of New Zealand blue ducks cut through the bubbling and rushing sound of the water.

Nightingale singing. (Video by BIA birdimagency)

In the open, sound travels best a meter or so above the vegetation. Many small birds therefore sing on elevated perches high in the vegetation to minimise interference from the ground and foliage. The nightingale sings its beautiful, melodious song from a branch on a tree, from where its song carries a long way.

Blue-black grassquit jumps whilst singing. (Video by Osvaldo Scalabrini)

Another performance ploy is to transmit the signal from above the vegetation by leaping up and calling from mid-air. The blue-black grassquit, a tropical grassland bird of South America, leaps clear of the grass during displays.

Skylark singing. (video by neuberga)

In Europe, the skylark has solved the problem of few high vantage points in its habitat of open grassland. It soars high into the air to deliver its glorious warbling song, hovers then plummets down almost vertically.

Skylarks actually uses song as a form of defence against predator birds such as merlins or peregrines. By singing, the skylark signals to the merlin that it is in good condition and will be a hard job to catch. Only a fit skylark can afford to sing whilst being chased by a predator.

โ€œIn some species, like red-winged blackbirds and canaries, the number of songs an individual produces increases with ageโ€, explains Brenowitz. โ€œThe number of songs may therefore provide information about a maleโ€™s relative age โ€” which may correlate with male quality โ€” to females seeking matesโ€. Choosy females may then pass their matesโ€™ desirable genes to their offspring.

Why do females sing in some, but not all, species?

โ€œSome form of female song is probably much more common among bird species than we tend to think. Actually, cases in which females have no song may prove to be the exception rather than the ruleโ€, explains Brenowitz.

However, it has been shown that males sing more often and their song is more elaborate than female song for most species that have been well studied. โ€œThis is thought to be the outcome of sexual selection in which males compete for access to females and the resources required for reproductionโ€, Brenowitz continues.

Birdsong has many similarities to human speech. Nestlings learn songs just as children learn language; by listening to adults. When practicing their songs, young birds go through a โ€œbabblingโ€ stage, just as humans do. Further, to develop normal song or language, both birds and kids must hear their own utterances as they practice. Moreover, both birdsong and human language are characterised by regional dialects.

It is these common features that make birds the best model to understand the role of the brain in learned vocal communication. Even though research is still ongoing, it appears that the general organization of brain pathways that integrate auditory input and vocal production share some similarities between birds and humans. Thus, birds can reveal how we evolved our own remarkable language capacities.

โ€œI find birdsong to be endlessly fascinatingโ€, says Brenowitz. โ€œUnderstanding why and how birds sing is like trying to understand a cryptic (to us) language. And is there a more beautiful sound than a wood thrush singing his melodic songs in a forest at dawn?โ€

Wood thrush singing. (Video by Lang Elliott)

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NOTE: this piece was researched, written and published in the Biology Department newsletter when I was a zoology grad student at the University of Washington. At the time, I had my own column with a definite word limit. The target audience was biology undergrads, specifically, those enrolled in the BIO200 series. Although I was a grad student a few years ago, many things have changed since then: I am a neither an employed scientist, nor am I a respected science writer, and even my home department, Zoology, has ceased to exist.


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Originally published online at www.scilogs.com.

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Evolutionary ecologist & ornithologist, science journalist. Writes about science for Forbes. Formerly: The Guardian. Always: Ravenclaw. Will write for food.