One Planet News: The secrets of bird song

Unlocking the secret code within bird sounds

By Annette J Beveridge

Have you ever wondered about the many bird sounds and wondered why they occur and what they represent?

You are not alone if so as a new study endeavoured to find distinctive patterns within bird sounds.

During the spring months, bird song is louder and more frequent. Birds fight for territories and for mates. Birds also sing for the sheer pleasure of doing so.

In the study, more than 100,000 audio recordings of bird sounds from around the world were researched. The recordings were used by researchers at the University of Wisconsin, Madison, and focussed on factors that influence bird sounds. The study revealed insightful patterns for why birds make certain noises and the frequency of sounds.

Although bird sound hypotheses were in place, H.S. Sathya Chandra Sagar, a University of Wisconsin, Madison doctoral student working with Professor Zuzana Buřivalová in the Department of Forest and Wildlife Ecology and the Nelson Institute for Environmental Studies, wanted to see if these existing hypotheses held up on a global scale.

Sagar analysed the audio recordings and submitted them to a repository known as xeno-canto [a website dedicated to sharing wildlife sounds from around the world] and this represented 77% of known bird species.

The following information was confirmed:

• Habitat influences the frequency of sound made in unexpected ways. Where rushing water sounds are present, researchers found that birds often make higher frequency calls so the sound is not drowned out.

• Birds that live at the same latitude will make similar sounds. This is an important part of the evolutionary story of bird sounds.

• The shape of the bird’s beak or body mass was also deemed important. Smaller birds generally create sounds on a higher frequency while larger birds create sounds that are at a lower frequency. This matches the hypothesis but also added information about beak shape and body mass with sound.

The study found that smaller birds have a wider range of frequencies used as a protection mechanism. Higher frequencies enabled them to communicate with birds of the same species, lower frequencies could be used as camouflage and to trick any predator into thinking that they were larger than they actually are.

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Soundscapes are typically used in conservation studies.

Sagar said: “There’s very little that we know about the forces that govern soundscapes. In the tropics and all over the world, larger birds tend to be hunted for meat, and larger birds tend to call at a low frequency. If we don’t find any sound in the lower frequency, we could conclude there may be more hunting in this landscape.”

It is hoped that this new research forms a foundation for future studies and will develop new ways to monitor the health of specific ecosystems via soundscapes.

The next step is to use the 24-hour soundscape recordings to determine if birds modify the timing of their song as well as their frequencies to communicate with birds of the same species. This would also require bird watchers and citizen scientists to play a role in discovering new insights into bird songs and into the natural world.

The data was published recently in the Proceedings of the Royal Society B journal.