Tag Archives: bioacoustics

The complexities of underwater acoustics

The ecological importance of natural soundscapes is increasingly recognized, as their degradation may lead to biodiversity loss and disruptions in ecosystem functioning. The disappearance of these soundscapes poses a serious concern, underscoring the need for their preservation. Soundscape studies offer valuable insights into ecological change, enabling researchers to identify affected ecosystems and attribute shifts to factors such as anthropogenic noise. A wide array of methodologies supports this research–from auditory observation and spectrographic visualization to the computation of acoustic indices and sophisticated statistical modeling. Passive acoustic monitoring has emerged as a vital ecological tool, facilitating research, environmental surveillance, and conservation management across both terrestrial and aquatic soundscapes.

A geoacoustic imaging project studying underwater acoustic networks for services in support of the discovery of new underwater cultural heritage (UCH) sites.

In the context of aquatic environments, acoustic recording presents distinct challenges due to the complex nature of sound propagation. Unlike in air, sound does not travel in straight-line paths underwater; instead, it undergoes reflection, refraction, and diffraction. Acoustic energy interacts with uneven surfaces such as the sea surface and seafloor, as well as with suspended objects in bodies of water–including gas bubbles, fish swim bladders, and particulate matter–leading to scattering. Furthermore, some sound waves may penetrate the seafloor and eventually dissipate as heat. Misunderstandings about underwater acoustics are common, including the beliefs that (1) low-frequency sound cannot propagate in shallow water, (2) hard seafloors cause complete reflection with cylindrical spreading, and (3) soft seafloors produce spherical spreading. These oversimplifications overlook the nuanced physics of underwater sound transmission.

Water-column analysis in the Bay of Biscay using broadband acoustic technology.

Understanding sound propagation across diverse environments requires a critical evaluation of commonly used acoustic models and their limitations. Dispelling prevalent misconceptions involves recognizing the nuanced behavior of sound and the assumptions underlying sound propagation equations. To address this, sonar equations have been created for various scenarios, ranging from animal acoustic communication and noise-induced communication masking to the acoustic surveying of marine fauna. Central to these analyses is the “layered ocean” concept, which examines how variations in temperature, salinity, and depth influence sound speed, ultimately affecting propagation pathways and signal fidelity.

This according to “Introduction to sound propagation under water” by Christine Erbe, Alec Duncan, and Kathleen Vigness-Raposa, Exploring animal behavior through sound. I: Methods, ed. by Christine Erbe and Jeanette A. Thomas (Cham: Springer Nature Switzerland, 2022, 185–216; RILM Abstracts of Music Literature, 2022-27424).

July 18 is World Listening Day.

Photo credit for the first image: Douglas Klug.

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Filed under Acoustics, Animals, Geography, Sound, Space

Ecoacoustics and birdsong recording

Advancements in technology have facilitated diverse research strategies in ecoacoustics (or acoustic ecology), algorithmic sound recognition, and aesthetic approaches, with significant scientific and technological applications. These developments have opened new avenues for studying the relationship between humans and their environment through sound. Portable ambisonic recorders, capable of capturing sound trajectories in a 360° sphere, have proven valuable for surround sound systems, as they accurately reproduce the acoustic environment’s spatial characteristics. This technology allows for faithful representation of the sound emitter’s unique qualities, movement patterns, and the reverberant properties of the environment. As a result, soundscape research intersects with multiple disciplines, including robotic listening, census strategies, acoustics, and algorithmic classification of fauna. Moreover, soundscape studies have increasingly contributed to environmental conservation efforts by informing strategies to mitigate the impact of human activities on natural ecosystems.

Ambisonic microphones

These technological advancements have facilitated the development of diverse strategies and mechanisms, ranging from traditional audio capture techniques to interactive systems that enable communication between humans and other species through sound. In all cases, soundscape studies provide valuable insights into how human activities impact the environment. This includes analyzing the effects of land and air traffic, power lines that generate electromagnetic fields, and other anthropogenic factors. By interpreting such interactions, soundscape research deepens our understanding of ecological disruptions and contributes to the development of strategies for minimizing human-induced environmental disturbances.

Algorithmic recognition plays a crucial role in identifying and classifying bird vocalizations. In ornithology, specialists undergo extensive training to recognize bird species and their songs based on region or mating season–a process that is time-consuming and requires significant expertise. To streamline this task, applications capable of recognizing and categorizing birdsong have been developed, enhancing efficiency and accuracy. The study of soundscapes has further contributed to refining algorithmic recognition strategies for cataloging wildlife within specific environments. A notable example is the Raven software, developed by Cornell University’s Center for Conservation Bioacoustics, which can analyze audio recordings to identify and classify numerous bird species. This technology has proven invaluable for tracking and documenting avian populations across different regions. As these systems continue to evolve, there is significant potential for further advancements, making automated bioacoustic analysis an increasingly powerful tool in ecological research and conservation.

This according to “Paisaje sonoro: Creatividad interdisciplinaria y tecnologías aplicadas para el registro del canto de las aves” [Soundscape: Interdisciplinary creativity and applied technologies for the recording of birdsong] by Pablo Rubio Vargas and Jorge Rodrigo Sigal Sefchovich (ANTEC: Revista peruana de investigación musical 8/2 [2024] 170–183; RILM Abstracts of Music Literature, 2024-13931).

Click the link below to watch a video titled Empowering bioacoustics research in Southeast Asia, which explains efforts at the Center for Conservation Bioacoustics to create biacoustic networks across the region.

https://www.birds.cornell.edu/ccb/empowering-bioacoustics-research-in-southeast-asia/

Related Bibliolore posts:

https://bibliolore.org/2018/05/21/angelic-bird-musicians/

https://bibliolore.org/2014/11/13/afghan-perceptions-of-birdsong/

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Filed under Acoustics, Science, Sound

Courtship dance step sounds of the blue-capped cordon-bleu

While vocalizations have been elucidated in various songbird studies, non-vocal sounds have received less attention. In the blue-capped cordon-bleu (Uraeginthus cyanocephalus), both sexes perform courtship displays that are accompanied by singing and distinct body movements (i.e., dance). A previous study revealed that cordon-bleu courtship bobbing includes multiple rapid steps. This behavior is quite similar to human tap dancing, because it can function simultaneously as a visual and acoustic signal.

In many cases, the acoustic signal value of such steps (along with the high-speed step movements) produce non-vocal sounds that have amplitudes similar to vocal sounds. In this sense, step behavior strongly affects step sound amplitude. Additionally, the dancing step sounds were substantially louder than feet movement sounds in a non-courtship context, and the amplitude range overlapped with that of song notes. These observations support the notion that, in addition to song, cordon-bleus produce acoustic signals with their feet.

Read more in “Songbird tap dancing produces non-vocal sounds” by Nao Ota, Manfred Gahr, and Masayo Soma (Bioacoustics: The international journal of animal sound and its recording 26.2 [2017], 161–168). Find it in RILM Abstracts of Music Literature.

Below is the step-dancing performed by male and female Uraeginthus cyanocephalus (blue-capped cordon-bleu) captured on a research video by the authors.

Related Bibliolore posts:

https://bibliolore.org/2018/05/21/angelic-bird-musicians/
https://bibliolore.org/2014/11/13/afghan-perceptions-of-birdsong/

Comments Off on Courtship dance step sounds of the blue-capped cordon-bleu

Filed under Animals, Curiosities, Dance, Nature, Science