Many bird species are more often heard than they are seen through their unique bird calls. Most birds have some sort of ability to make sounds, which they use for several different reasons, including attracting potential mates, claiming and signaling territories, making alarm calls and deterring nearby predators.

Birds are capable of generating sounds from structures called syrinxes, which are situated at the junction of two air passages called bronchi within their respiratory tracts. Syrinxes are controlled by muscle pairs, and generally, species of birds that have more muscle pairs are able to create more complex bird calls.

Birds that are classified as songbirds, which are known as passerines from the order Passeriformes, have four to nine pairs of muscles, and are able to create the most elaborate and longest bird calls.

A species that has one of the most unique bird calls in the world is the northern cardinal, which has been named the official bird of seven states in the country. Cardinals are social birds that live together in flocks. They are active songbirds that are able to sing a variety of melodies.

There is also the lyre bird, which has the unique ability to copy the calls of other birds, along with specific items such as camera shutter and chainsaws.

It is through a bird call that scientists were able to discover an entire new species in central China. Now called the Sichuan bush warbler, the new bird species which looked similar to the russet bush warbler has a lower-pitched song with more drawn-out notes compared to the already known bird species. Comparing the sonograms of the songs of the two bird species also shows a huge difference.

"I first heard this species together with my friend Urban Olsson when we visited the sacred Emei mountain in Sichuan province, central China in May 1992", said Swedish University of Agricultural Sciences professor of evolution and systematics Per Alström.

However, it was not until almost 20 years later that Alström was able to return to China and assemble a team that was able to capture the first Sichuan bush warbler.

As more of the birds were discovered, captured and studied, along with the species' DNA and song recordings, the Sichuan bush warbler was confirmed as a new species. All of this was made possible through the unique bird call of the Sichuan bush warbler.

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