Acoustics and Biodiversity

By Jonathan Spoelhof

Scientists measure biodiversity in many ways, each of which reveals critical information about the state of biological communities. Regular censuses of plant and animal communities monitor populations of rare or endangered species, and may signal the arrival of introduced species or shifts in species’ habitat preferences over time. Collecting genetic information is just as important, because it reveals otherwise invisible patterns of diversity. In fact, many cryptic species were only discovered after their genetic differences were revealed through DNA or RNA sequencing. Genetic data can also alert conservationists to dangerous losses of diversity within a species or identify the geographic origin (or origins) of introduced species.

PC Robin Singer

Another way of measuring biodiversity is through sound, a practice that falls under the field of Bioacoustics. While this field certainly isn’t new (the sounds of birds, frogs, mammals, and insects have long been important to scientists and laypeople alike), scientists are currently developing and utilizing new bioacoustic tools to study biodiversity.

For instance, when scientists take an audio recording of an ecosystem, they could listen for the calls or sounds of each species and perform an acoustic census by checking the recorded sounds against reference recordings. This is a time-consuming task, especially for long or repeated recordings. One alternative is to use software that automatically detects and identifies the various species in an acoustic recording. This approach saves time and may identify biological sounds that a human listener would miss. Still, this type of software is typically limited to a certain group of organisms, and may not be useful for broader-scale measurements of biodiversity in a given ecosystem[1]. That’s why scientists have developed acoustic indices to serve as proxy measures of biodiversity. Acoustic indices, such as the widely used Acoustic Complexity Index (ACI)[2], are mathematical characterizations of sound recorded from a given ecosystem. Although they are not direct measures of biodiversity, acoustic indices can be powerful, objective predictors of biological diversity that allow scientists to process large amounts of data, which is important for long-term monitoring or studies that cover broad geographic areas.

The usefulness of these tools underscores the need to catalog the sounds of life. The species recognition software described above would not work without adequate reference recordings, and understanding how organisms use sound to interact with their environment is a crucial to our knowledge of their life history. As museums, universities and other organizations move to digitize their biological collections, they are also beginning to consolidate digitized audio recordings into large, publicly accessible databases. The University of Florida has participated extensively in this effort. The Florida Museum’s Bird Sound Collection contains recordings of over 3,000 species of birds and comprises one of the largest avian bioacoustic databases in the world[3]. IdigBio (Integrated Digitized Biocollections), a national collection of digitized collection of biological specimens and media based at the University of Florida, has also initiated a project[4] to digitize over 100,000 hours of (primarily acoustic) communication signal recordings from insects, birds, frogs, toads, and fish from 11 different institutions. This collection will be hosted by the Macaulay Library at the Cornell Lab of Ornithology, which already maintains the world’s largest collection of biological audio and video recordings.


  1. Obrist, M. K., Pavan, G., Sueur, J., Riede, K., Llusia, D., & Márquez, R. (2010). Bioacoustics approaches in biodiversity inventories. Abc Taxa 8: 68-99.

  1. Pieretti, N., Farina, A., & Morri, D. (2011). A new methodology to infer the singing activity of an avian community: the Acoustic Complexity Index (ACI). Ecological Indicators 11: 868-873.