Ecoacoustics, The Scaled Acoustic Biodiversity
Ecoacoustics is an emerging cross discipline combining bioacoustics and ecology as a method for monitoring and managing the environment. The Centro Interdisciplinare di Bioacustica e Ricerche Ambientali (CIBRA) at Università degli Studi di Pavia has been a key player in the development and progression of Ecoacoustics research. In Professor Gianni Pavan's paper, "Bioacoustics and Ecoacoustics Applied to Environmental Monitoring and Management," Ecoacoustics attempts to, "describe the acoustic environment in terms of quality, quietness, richness, complexity and diversity".
GOAL: Using Ecoacoustics to Assess Anthropogenic and Climate Change Impacts
CIBRA's goal is to describe the acoustic environment, sometimes called a soundscape, of natural habitats, and correlate the quality of the soundscape with different levels of protection and human presence. One of Gianni's many projects is collaboration with the Scaled Acoustic Biodiversity project (SABIOD) managed by the University of Toulon and granted by the French CNRS MASTODONS Project on Big Data acquisition, analysis and processing.
SABIOD's goal for Gianni's project is to collect sound data to assess the short and long term changes in the soundscape structure, in particular those connected with anthropogenic impacts and climate changes.
The Role of Song Meter Recorders
To capture the soundscape and record sounds for months, the SABIOD team selected Wildlife Acoustics Song Meter recorders. Dr. Pavan explains, "I started using the Song Meter SM1 for other projects many years ago. Then I used several Song Meter SM2s because they were the first instruments for doing long term scheduled field recordings. Then the Song Meter SM3 appeared as a great improvement in overall quality and reliability. The SM3 clearly stands up over all the other similar equipment. Of course they can be further improved! I'm looking forward to the SM4. In particular I'm interested in the lower self-noise that will enable me to collect more sounds. In particular, more "high quality" sounds can be used for listening and producing high quality audio materials for education, for training and also for sound exhibitions (in museums and visitor centers)."
Since there are no standard protocols yet for soundscape recording, for the SABIOD project, Gianni's typical deployment cycle for a Song Meter is 2 months, recording in stereo 10 minutes every 30 minutes at 48 kHz sample rate. The Song Meters are serviced regularly and the deployment cycles repeat to achieve 12 months of recordings. During the winter months three SM3 have been deployed using powerful external batteries and Gianni is waiting retrieve and verify the data after the long cold period.
"I deploy and maintain the SM3s with the support of agents of the Italian Forestry Police who bring me into the very wild and highly protected areas they manage. Two units are in a wild forest (RNI Sassofratino, the first Italian integral nature reserve created in 1959) where even access is prohibited. There are no trails and each unit requires some hours of hard walking, always escorted by the agents. The remaining two units are on the boundaries of the forest in other protected areas."
Once the Song Meters are deployed, the absence of human operators allows for recording real habitat conditions with minimal disturbance. This unattended recording permits greater reliability in the data analysis and a greater chance to record shy and elusive species.
Results to Date
The highly protected area where Gianni works is very rich in terms of the diversity of biological sounds. The only anthropic noise is from airplanes passing over as there are no roads in the area. Fig. 1 is a packed spectrogram of one day stereo recording in Sassofratino (day 20140609), 10 min every half-hour (48 frames/day). The spectrogram shows sharp transitions at dawn and dusk and a high density of biological acoustic activity in between. Airplanes produce the traces on the x axis. (x-axis 24h, y-axis 24 kHz).
Figure 1: Spectrogram of one day stereo recording in Sassofratino, 10 min every half-hour (48 frames/day). There are sharp transitions at dawn and dusk.
Advice for Deploying Song Meters and Analyzing Data
It's always best to think about how data will be analyzed and against what baseline when conceptualizing your study. The first year of the project has been dedicated to building a reference database of high quality recordings of natural habitats, primarily Integral Nature Reserves and Nature 2000 sites. The analysis of the recordings produced a reference library for species identification to be used for building classifiers. In literature, there are no publications about the noise level and acoustic structure of Gianni's sites. Gianni explains that Ecoacoustics, "is opening new and very interesting analysis perspectives and we are now working with mathematicians to improve our ability to analyze the data and provide informative "summaries" and "indices", other than spectacular spectrograms at different time scales (24h, 1h, 10min, down to high res spectrograms showing 3-4 second in detail)." Indices of quality, quietness, bioacoustics richness, bioacoustics complexity and bioacoustics diversity are all being measured. By analyzing the noise of a very quiet place, the RNI Sassofratino, a reference noise model will be developed for comparing and scoring habitats affected by anthropogenic noise and assessing the impact on animal communities (e.g. communication masking).
Figure 2: Spectrogram of 10 minutes. In the beginning the low frequency wind is evident and the leaves produce the wideband noise.
From a scientific point of view Gianni wants year round continuous monitoring of several locations in the same area. If he can get grant funding, he is interested in expanding the monitoring effort to a larger number of sites with different degrees of environmental protection. Gianni would also like to start projects utilizing ultrasonic monitoring (with smart triggering) to study poorly known forest and mountain bats with equipment such as Wildlife Acoustics SM4BAT recorder.
*Thanks to Gianni Pavan and his collaboration for this case study as well as his paper, "BIOACOUSTICS AND ECOACOUSTICS APPLIED TO ENVIRONMENTAL MONITORING AND MANAGEMENT", Rivista Italiana di Acustica Vol. 39, N. 2, p. 74 which provide the majority of this content.