We are therefore talking about a genuine acoustic imprinting, necessary for the development of this ability.
Then there is a physiological aspect, linked to the vocal organ. That is, the syrinx.
Have you ever wondered whether birds have vocal cords like mammals? The intuitive answer is no.
They do, however, have an organ called the syrinx, located where the trachea branches into the bronchi. It is the syrinx that allows birds to produce the complex sounds we hear in nature. They can even produce two simultaneous sounds – more or less the equivalent of what in humans is diplophonia – thanks to two vibrating membranes controlled by specialised muscles.
It is precisely this prodigious physiological complexity, evidently acquired through evolution, that enables them to sing complex and even harmonised melodies.
Finally, there is a properly neurological aspect. In birds’ brains there are complex neural circuits, with specialised nuclei that regulate and coordinate these functions. It goes without saying that in the most vocal species (or the most songful, if you prefer) these circuits are even more developed.
But what is the meaning and purpose of birdsong?
From an ethological point of view, song is nothing other than a complex communicative behaviour, with precise functions linked to survival and reproduction.
First of all, there is the defence of territory. Song serves to mark and protect an individual’s living space from intruders, especially other males of the same species.
The acoustic warning reduces physical conflict, signalling the presence and strength of the territory’s owner.
Then there is the aspect of males winning over females. Males use song to show their vitality, health and genetic quality.
According to ethologists, complexity, variety and skill in singing are indicators of sexual fitness, which in turn is linked to a greater probability of reproductive success.
The aspect of social communication is no less important in birdsong. Song helps to maintain social bonds within groups or flocks, to coordinate collective activities, and to warn of imminent dangers, above all the presence of predators.
Birdsong is by no means a fixed phenomenon, unvarying in its patterns. On the contrary, it adapts to the surrounding acoustic environment and the characteristics of the habitat, first of all in order to maximise sound transmission.
Species that live in dense forests tend to produce simpler, low-frequency sounds, whereas in open environments songs can be more complex and high-frequency in order to cover greater distances.
There is another characteristic that will surprise many. Birdsong has genuine ‘regional variations’. In other words, dialects.
Within a single species, in fact, song can vary geographically, giving rise to what scholars actually call different ‘dialects’. These are sub-languages that are learned socially and can significantly influence sexual selection and social structure.
The ‘curiosities’ about birdsong (which are actually ethological aspects of great importance) are countless. Here are just a few:
- A thousand-year-old singing tradition: Some birds, such as American swamp sparrows (Melospiza georgiana), learn, copy and pass on their song practically unaltered for over 1,000 years, creating genuine singing traditions that are stable over time. It is a phenomenon called ‘conformist bias’, similar to that found in humans.
- The role of hormones and seasonality: The frequency and intensity of song are influenced by hormones such as testosterone, which vary with the season, explaining why many birds sing mainly during the breeding season.
- Female and social song: It is not only males that sing; in many species females sing too, sometimes duetting with their partner or singing in groups. Female song is subject to complex evolutionary pressures linked to migration, latitude and nesting habits.
- Effects of inbreeding: Mating between related individuals can make birdsong ‘out of tune’, negatively affecting the quality of the song and therefore the chances of reproductive success.
Finally, perhaps the most incredible and wonderful ‘curiosity’. It is possible for birds to sing for pleasure.
Although scholars are not entirely unanimous on this, many ornithologists believe that in certain cases birds may sing ‘quietly’ simply because they appreciate the beauty of the song itself and the pleasure of producing it, especially when there are no obvious territorial or courtship urgencies.
So song would also have for them an emotional component and a source of personal gratification, entirely similar to the pleasure that singing gives human beings.
In these cases, birds would ‘perform’ even in the presence of other responsive birds, as a form of social interaction based on the enjoyment of natural music.
