Or noticed that some birds can exactly mimic specific sounds such as car alarms?
Bronchial tubes
When a bird breathes it takes in air through its bill, draws it in past its throat and into its windpipe (or trachea). The windpipe forks to carry some air to each of the lungs. These dual passages are called bronchial tubes (singular-bronchus, plural-bronchi). Air is then processed in the lungs and exhaled back along the same route. This system of air passage has become adapted for the secondary purpose of sound production (as it has in humans too).
The syrinx
At the point where the windpipe divides is situated the bird’s sound producing organ, a “voice box” called the syrinx. Humans have no syrinx but a larynx instead. The larynx is a cavity in the throat and contains our vocal chords. The avian syrinx is called a lower larynx, being differently situated at the other end of the windpipe. It is as if the human larynx were positioned in the chest.
The syrinx is double-barrelled – as if a man had twin instruments between his lips and was playing one with the outflow of one lung, and the other with air from his second lung. Theoretically, a bird with one collapsed lung would then still be able to produce sound. But if it were a species that is known to produce two different sounds simultaneously, then clearly it would not be able to offer a normal contribution to nature’s symphony.
Each half of the bird’s voice box is in the mirror-position of the other at the top of its own bronchus (so the set up is literally double-barrelled) and each consists of a pair of organs opposite each other on the wall of its bronchus. Thus if you were to slit open a bronchial tube, you would see on one side a little tympanum, a circular elastic membrane. This is the vocal chord, and opposite it would be a little bump of erectile tissue.
The stage is set
The bird is about to take its cue. It forces air along the bronchial tube, past these two organs, both of which can be adjusted. The diameter of the tympanum can be changed and the degree that it protrudes into the bronchial tube can also be varied.
As air passes, so an acoustic disturbance is set up, the tympanum vibrates and sound is created. The pitch (frequency) of that sound and the loudness (amplitude) of it can be modulated. So far as the tympanum is concerned, these two effects are usually coupled. The function of the extendable little bump is believed to be to change the loudness without having to change the pitch. Bear in mind that the bird may be playing at the same time a second tune on his other half.
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When we talk about birdsong, we cannot simply refer to a single “voice”. It is a great chorus of complex sounds, it is a real language in itself. The dry “teak” of a sparrow, the plaintive “gheck gheck gheck” of a woodpecker, the shrill “chirrip” of a lark – each sound has its own purpose and is used in very specific circumstances. For birdwatchers, learning how to ‘decode’ the secret language of birds is a great way to identify different species and to better understand their behaviour.
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Songs Change Closer to Cities
Noises, like traffic or construction, may make it harder for birds to hear each other’s songs. When the background noise increases around a population’s habitat, some birds might sing louder songs, sing for a longer amount of time, or sing at a higher pitch
to be heard above the noise [4]. Scientists are currently researching if a male’s ability to find mates in the city is affected by these changes in their songs, since those changes might come at a cost [4]. For songbirds, living near low-pitched traffic noise and needing to sing louder or at a higher pitch can be stressful [5]. This would be a little bit like using your “outside voice” all the time; your throat would end up sore! As a result of the stresses of urban life, scientists have seen that songbirds often choose to move their homes outside the city. The number of species living in urban areas with significant background noise has decreased, which could be related to their songs being drowned out by the city sounds [6].
Multiple studies have been done to test how birds change their songs in noisy places. One notable study recorded common blackbird songs in the inner city of Vienna, Austria and in the woods outside of the city [4]. The two blackbird populations were about 4 miles apart. The songs were measured early in the morning when songbirds most commonly sing. In the city, the pitch of the loudest part of the song was much higher than that of the rural birds in the woods (Figure 3). Singing in a higher pitch would be like making the sound of a flute instead of a tuba! The city birds sang fewer notes than the rural birds and sang much earlier in the morning, possibly to beat the loud car traffic. In the city, birds also sang faster—instead of pausing for a certain time between their notes, they would shorten these pauses and rush their songs [4].
* sources : https://www.bl.uk | https://www.birdlife.org/news/ | https://kids.frontiersin.org
