One of the most remarkable features associated with my winged friends is their ability to sing. We all have heard their melodious voices and we also use them as a measure of sweetness like “Sings like a koel” or “Sweet as a Nightingale”. But behind this ability to sing is a larger reason and the fact that existence of majority of birds in the world depends on this.
All birds can make a sound from within their body using their Lungs and a special part called “SYRINX” or the voice box. There are some birds that make sound using wings and beaks but these are not called Songs. They can be called as “Calls”…
This brings us to one more issue to be clarified at the onset, what is a call and what is a song?
Technically speaking when a bird uses Multiple –notes, with frequent repetition, Consistent and Conspicuous, then it is said to be singing.
If the bird uses Single note or a few notes and as a principal means of communication (in birds that do not sing) or as means of erratic communication (in case of singing birds ) then it is called as a “Call”.
So for simpler understanding if the sound is frequent and at multiple note levels then it’s a song.
How do birds create sound for a song or call?
The bird anatomy that plays important part in this process consist of windpipe, air sacs, SYRINX and Lungs (BRONCHUS). The windpipe (TRACHEA) gets divided under an organ called SYRINX. The TRACHEA divides itself into BRONCHI near the lungs. The SYRINX is composed of complex muscles and the BRONCHI with cartilaginous rings. They are further divided into two independent units on top of each BRONCHUS, forming two independent Voice box ( as compared to one in Humans). Each of these voice boxes are connected to brain with their own nerve .This dual voice box control gives the birds a choice of producing multiple sounds at same time and each voice box can be controlled independently. This means that a bird with such system can sing its own duet. Imagine Kishore Kumar and Latha Mangeshkar singing from the same body ….that is the ability of these winged wonders.
As the air is forced out of SYRINX, the muscles there undergo subtle changes in tension creating a variety of sounds. And to keep the sound going for some time a lot of air is needed, this is where the “Air sacs” come handy and provides the extra air to keep the sound on for long time.
( Diagram from Beat About the Bush -Birds , by Trevor Carnaby)
Now for the most amazing adaptation, each sound box is supplied with its own nerve that is connected to a part of brain called Cell groups or “Sound Centres”. This area is responsible for both hearing and producing sound. This helps the birds in various ways
- Register different voices and Mimic them
- Listen to their own voices and correct their notes
- Create their own song to attract mates.
These “sound centres” are large in male birds esp. the Song birds. They shrink during the non-breeding season and as the Breeding seasons approaches the hormones in the males get generated and the Male bird develops the reproductive organ “Testes” and the “Sound Centre” enlarges to provide more songs at higher pitch. This contraction and expansion is requisite for the birds to reduce their weight and put less pressure esp. in migration time.
Types of “Song Birds” :
The “Song Birds” are called Passerines. A passerine is any bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds, they are distinguished from other orders of birds by the arrangement of their toes ,three pointing forward and one back, which facilitates perching. ( To understand the feet structure of birds better pls. visit http://ogaclicks.com/wordpress/foot-structures-of-birds/).
With more than 110 families and some 5,100 identified species, Passeriformes is the largest order of birds and among the most diverse orders of terrestrial.
They are divided into two groups
- The Genetically and Physiologically advanced PASSERI or OSCINES
- The primitive TYRANNI or Sub-OSCINES
The OSCINES are considered better song producers basis the human perception while each group has its own speciality.
These are usually birds that hatch their own brood and take care of their own chicks. So the ability of singing depends on the chicks learning their species song from their parents and other relatives. The “Song Centre” in chicks registers these voices of Adults in the nest and this they practice regularly as they grow. The sounds created by these chicks in their learning stages are called a SUB-SONG. The hearing and “Song centre” are close by in the brain because the bird has to listen to its own voice and correct the notes regularly in the learning stages. The OSCINES are great mimics and hence all the sounds that they hear in the surrounding are stored in the “Song Centre”. This is practiced regularly as per need of the bird and used in various scenarios.
The OSCINES also have a limitation that if the chick is separated from its parents or groups and reared in captivity, it has no idea what its species song is and will start mimics all sounds in its surroundings.
The few brood parasites that fall under this group like the Indigo bird or Whydahs do not learn their species song and as a result of many centuries of evolution they lack a species specific Song. They also remember the song of the hosts they grew in. This helps them to locate the nests of the hosts when they are ready to lay eggs
Singing Bush lark….
The Rain quail…. Starts its song as the rain starts drizzling
This is perhaps the most mind blowing adaptation about sound in birds. These birds have their species song encoded in their DNA. This means that irrespective of where they hatch and grow they can start singing their species song from day one. They do not need practice and corrections as in OSCINES. Examples of Sub-OSCINE are Pitta and Broad bill.
The limitation of Sub-OSCINES is that they cannot Mimic other sounds and hence lack the sound centre as in OSCINES.
The Sub-Oscine : Long-tailed Broadbill
The Sub-Oscine : Indian Pitta
The Non-passerines are not good at singing and are usually very bad at mimicry. They have genetically encoded songs like the Sub-Oscines and use other means like dance, flight, colours etc. to attract mate. The Non-Passerines like the doves and pigeons which are reared in captivity can make their species sound from day one.
Parrots and Hummingbirds are the only Non-passerines with ability to mimic various other sounds. The parrots can do this due to their brain having special ability to keep growing with respect to their body (similar to humans)
Why do birds sing?
There are many reasons why a bird sings as detailed below.
To attract mates the birds will sing aloud. When the mate responds to the song a continuous exchange of songs happen and this is called “Duet”. Usually the Male members sing the most. The pitch and clarity of sound indicates the gene pool. Some of the Song bird males will also learn the songs of some other birds and use it in their own songs to create a “Special effect” for the females to judge them. The females will pick the males with the best song and pitch to mate.
The males who are monogamous will become quite after mating and will stop singing. The males who have not been paired will continue singing at higher pitch in desperation to mate.
The striated Grass bird calling for its mate
But in case of Polygamous birds the male will continue singing to attract more mates.
In some cases the females also sing to attract mates. This happen in Polyandrous species. And in some non-passerine birds like the raptors the female makes all the sounds to defend her territory.
( To know more about the various types of breeding system in birds pls. visit http://ogaclicks.com/wordpress/mating-in-birds-part-i-different-type/)
The female Bronzed winged Jacana is Polyandrous and calling out for mates.
It is found that the songs of the male will also cause rush of hormones in the female body and they will launch into a “pre-copulatory display” with tail up or wagged to their sides.
So much happens with a song ……..
Many passerines are not very social and hence they will not encourage other birds of their species or competition into their territory. They declare their presence with loud songs and the louder and more varied the song is it shows how superior the bird is. This can lead to confrontations and fight for territory but males being males will always declare their territory. This is because a good territory with lot of food and protection from predators is ideal for building a nest and attracting many females.
This is behaviour exhibited in the non-passerines as well like the Saras Cranes.
The Saras Crane Pair calling out to declare their territory
The songs are also a form of communication amongst the same species or species that live together about danger, availability of food and time to go forging. The communication is usually a duet between many males and sometimes feels like a cacophony.
Some birds like Drongos are excellent mimics. They will use the songs/sounds of larger animals to scare off smaller animals from a carcass. They also use this technique to steal food from other birds that in a hurry to escape the predator would drop the food they have caught.
The master of Mimicry : Drongo
When do the birds sing?
The birds sing throughout the day for various purposes as listed above but their songs are the loudest in the morning. There are birds that start singing as soon as the first light hits the horizon. There are a few reasons why they sing so much in the morning.
The morning air is dense and cool which helps the sound travel far. This is one reason that we hear a lot of bird voices in the morning.
Each night is an adventure for most birds as there are enough predators lurking around. So in the morning they declare to their mates, groups and competitors that they are alive. The birds keenly listen also in the morning. Any territory that doesn’t have a call is a potential territory to be taken over. In many species the family members roost in different places and in some social groups the call is necessary to gather all in one place and synchronise their daily activities like migration or forging.
A well-rested bird is filled with energy and restless in the morning. The heavy air, dew on feathers etc. don’t allow them to fly so early. So they express this energy in form of melodious songs.
Adaptations related to Songs in birds:
Some birds like the Hornbill have a small bony structure on their beaks. Its called a casque. It is hollow and is used to amplify the song of the hornbill. The sound resonates inside the casque and is amplified so that it can be heard in a distance.
The Great Hornbill with its Casque
Now that you know the secret behind the melodious songs of the bird please take some time out in the morning and listen to their songs and enjoy them while wondering about their wonderful abilities.
Text Source : Wikipedia, Beat About the bush -Birds by Trevor Carnaby
Pictures : Saravanan Janakarajan