Why do birds sing?

The hills are alive with the sound of... birds.

While writing this post - I can hear two birds outside. One is our resident garden robin, and the other, a woodpigeon. This soundscape is pretty normal for a residential area in Scotland. But once you start to think about it, bird song can become really complicated.

Firstly, are the birds singing or are they calling? Technically only songbirds can sing. Songbirds are classified as birds in the suborder Passeri, which includes 50% of all living bird species. Despite this, many other birds make noises too, which are usually called calls. Bird song is classed as bird sound which is complicated, with multiple notes whereas calls are simpler.

Listen to this robin song.

Its a complicated sound, with many different notes. Put together they make a high pitched twittering, but robins can perform many different songs at different frequencies. For example, when they make a warning call, it is sharp and designed to alert other birds nearby about a potential predator (or a person just walking past a bush).

Now listen to this crow call:

Its very different from the robins complicated song. Though the pitch is different between individual birds, the core sound is the same repeated over and over. This defines it as a call.

Bird calls have many different purposes, but they can mostly be conveyed in simple terms like ‘go-away’ or ‘I’m over here’. True bird song is almost always territorial - as is the case with robins who have to sing all year round to hold their permeant territory. But both forms of sound can be used for attracting mates. In ducks, calls are usually to locate each other as they aren’t territorial but do get very confused in a crowd, whether on the ground or in the sky.

So what they are basically saying here is ‘where are you?” - “I’m over here!”.

Birds make noise through a tiny pea sized structure in their throat - the syrinx. It is similar to our larynx which is a collection of muscles and air sacs which we use to make sound. But singing birds have their syrinx much lower down than our larynx, closer to the lungs, so they are able to make sound much more efficiently, using nearly all the air in their lungs to sing. With our structure, we only manage to use around 2%. Different birds have different modifications to their syrinx to allow different species to make unique sounds. Each species has a distinctive song (except for a few exceptions where two species sound so alike they can’t tell each other apart - not very useful when you are trying to find a mate!). We as humans can tell the difference with practice, but the difference is clearly defined for birds. It is important that they know who to listen to. There isn’t much point in a crow being able to listen in to a conversation between robins. Some birds like the Great Tit have calls that are easily recognisable to us because of their well defined structure. Listening to their song, you can tell that they tend to alternate between two notes - with many noting their calls sound like ‘teacher-teacher’.

Others like the wren can be more difficult to identify because of the sheer variety of songs they produce.

It was once believed that only male birds could sing, but it has since been discovered that many female birds sing too. This was clear in the tropics, but it has become more well known in the northern hemisphere too. When birdsong first began to be studied, it was mainly be men and so the possibility of female birdsong was discounted. We now know that females sing in many species for the same reasons as males - territoriality and to attract mates. But clearly more female orientated research is needed in this area if we are to truly understand the functionality of bird song.

Another yet unsolved question is - why do birds sing at dawn? While there are many theories there has never been a definitive answer. It is thought that they do it to begin the day with a ‘roll call’ of territory, so that everyone knows who is about, and who is defending what. Dawn is a good time for this because of its acoustic properties. Songs travel 20x more effectively first thing in the morning than at noon because there is reduced background noise and air flow. Singing at dawn could also be helpful in attracting mates, as females are most fertile at dawn and usually lay their eggs in the morning. But not all birds sing or call in the morning. There is no point in owls calling first thing when they are just about to go to bed, and so their calls, like this of the tawny owl, have become a symbol of night-time.

But the big question has always been - do they choose to do it or do they do it by instinct. And as yet, no one can really know. Some have suggested that birds actually enjoy singing as it sets off regions in their brain that show pleasure but no one can agree on the meaning of this. Some wonder if people are just projecting their humanity onto the birds. Bird calls seem to be instinctual but bird song is at least partially learnt. Birds raised away from their parents have an incomplete song while birds raised in the nest develop a song that has a ‘regional’ dialect to the area in which they were raised.

But whatever the answers to these questions are, the impact of birdsong upon our lives is clear. It defines our mornings and our evenings, it provides comfort or, occasionally, fear. It is the background noise to sunny spring mornings and dark winter nights. Hearing birdsong makes us happier and brings back memories. So as we go into winter, listen to the robins beautifully twittering away and remember that really they are screaming ‘Get out of my patch!”