From carolling magpies to the lullaby of fairywrens, the nature and purpose of birdsong is more varied than you might think

Birdsong seems to be always around us, but have you ever wondered why they sing? For more than 10 years, I have been studying birds and am constantly fascinated by them and their song. I want to share with you some amazing facts I learned.

Songbirds belong to the order Passeriformes, making up more than half of all bird species in the world. That's nearly 5,700 species! These are among the most abundant birds found on nearly every terrestrial location on Earth. Their song is one of the most complex signals in the animal world and has always fascinated humans.

As female songbirds in Europe and America don't sing, this led to the assumption all female birds don't sing. Male songbirds such as the European blackbird will sing in the early morning to mark their territory, letting others know he is still present. If he hasn't secured a mate, he will also sing to attract a female. For a listening female, male song can be viewed as honest signals - conveying useful information about the singer's physical health.

Research on songbirds in Australia has shown female birds also have a lot to say for themselves. Just like male song, female song can be used to mark territory and deter competing females from moving in on their territory and mating with their partner. In superb fairywrens, female song is thought to be used to stop other females from mating with their male. This is a real threat as neighbouring females will visit other territories looking for males to mate with.

Songbirds start to learn their parents' songs and calls while they are still in the egg. Female fairywrens will sing to their eggs to teach a specific call that the young produce once they hatch. The reason for teaching a specific call is to help protect the brood from cuckoos. As cuckoo eggs are generally incubated for a short time before they hatch, the embryo doesn't have time to learn the call. In this way, the female teaches her young a password that helps identify them in a dome-shaped nest with poor visibility.

Songbirds are vocal learners, meaning they need to learn their song from an adult tutor, usually a parent. They do this through a process remarkably similar to how we learn to speak. Just as human infants learn to talk, young songbirds listen, learn and practice the songs and calls of their parents. If a young songbird is raised in isolation without hearing song, it won't be able to sing or call accurately.

Just like the growing brain of human teenagers, sleep is necessary when learning. When a young songbird is learning its song, some research has found the regions of their brains dedicated to song are active as they sleep, leading the researchers to characterise the sleeping song movements of zebra finches in particular as "much like a dream". The following day the bird sings a better-quality song, similar to its parent song. As the young bird reaches adulthood it continues to dream of song and when deprived of sleep, song output will suffer.

All songbirds need to practise their song to help remember and sing it better. The warble song of an Australian magpie is a form of vocal practice that is sung when alone, at low volume and varies from version to version. The warbling song allows the magpie to develop their vocal skills so it can perform in the group carolling song. The carolling song is sung with others at high volume to mark territory and group cohesion, so quality matters.

When a songbird is listening to another's song, it identifies the singer by its spectral and temporal envelope, its pitch, rhythm, tempo and volume/amplitude. Being able to identify the individual who is calling helps birds such as noisy miners to decide to help specific individuals such as a mate or a sibling while ignoring unknown or untrusted birds. The noisy miner's "chur" call is used to warn others about a perceived threat and recruit others to start mobbing a predator. While we might hear this chur call as monotone, miners use its spectral properties to identity the caller.

As songbirds are vocal learners, we can learn about our own language development by studying their brain. Our very own zebra finch is used as a model to study the human brain and language development. Zebra finches have brought us closer to understanding what happens in the brain of people with speech and neurological disorders, from dyslexia to Alzheimer's disease.