DOI: 10.5061/dryad.sxksn038p
title: The impact of vehicular noise on the effectiveness of acoustic indices

description: Passive acoustic monitoring (PAM) is a sampling technique that has gained
 increasing popularity in the field of wildlife monitoring and research.
 The technique involves the deployment of programmable autonomous recording
 units, allowing for non-invasive and cost-effective collection of acoustic
 information across a breadth of temporal and spatial scales. Retrieving
 biological information from PAM recordings can often involve
 time-consuming sound annotation methodologies, but the advent of acoustic
 indices has allowed for biodiversity metrics to be estimated quickly and
 with reasonable accuracy. While correlations between acoustic indices and
 species richness have been observed in a variety of ecological contexts,
 these relationships tend to faulter in environments with increased
 vehicular noise. In turn, many researchers will avoid areas with vehicular
 traffic for PAM with intent on using acoustic indices. Here, we assessed
 the direct impact of vehicular noise on nine acoustic indices through
 controlled manipulation of vehicular noise within computer-generated
 soundscapes. Acoustic index values derived from these soundscapes were
 then used to fit a suite of linear mixed-effects models from which
 indicator variable coefficients were derived. These coefficients were used
 to determine the impact of respective vehicular noise levels on acoustic
 index values. Our results demonstrate that recording distance from
 roadsides and number of passing cars per minute have notable and
 persistent impacts on acoustic index values, but the magnitude of the
 effect varies across indices. Four acoustic indices demonstrated greater
 resilience to vehicular noise interference and may therefore be better
 suited for PAM in developed areas: Bioacoustic Index
 (BI), Acoustic Complexity Index (ACI), Acoustic Diversity Index
 (ADI), and Acoustic Evenness Index (AEI). By contributing to the
 collective understanding of acoustic index behaviors under anthropogenic
 noise pollution, we hope to better inform their ecological application
 within future PAM efforts in human-developed contexts.
description: # THE IMPACT OF VEHICULAR NOISE ON THE EFFECTIVENESS OF ACOUSTIC
 INDICES ### [Rebecca L.
 Ducay](https://scholar.google.com/citations?hl=en\&pli=1\&user=JjNPMdwAAAAJ) & [Brent S. Pease](https://peaselab.com) #### Please contact the first author for questions about the code or data: Rebecca L. Ducay () --- ## Repository Directory ### [RCode](./RCode): Contains code for cleaning, processing, and analyzing experimental and supplemental data * 101 - Bird Assemblages - EBD_list.R - script used to retrieve a random list of bird species from an eBird checklist. Data used from eBird is not compatible with the CC0 license waiver required by Dryad and thus cannot be posted. The EBD was used in Feb 2023 to retrieve checklists from Illinois from May - July 2022. The EBD data can be downloaded using the following link with a valid eBird log-in: [https://science.ebird.org/en/use-ebird-data/download-ebird-data-products. ](https://science.ebird.org/en/use-ebird-data/download-ebird-data-products.) * 201 - Acoustic indices - Acoustic Index Loop.R - script used for calculating all acoustic indices except AR from .wav files. * 202 - Acoustic indices - AR Code.R - script used for calculating AR from .wav files. * 301 - Analysis - Species Effect Code.R - script used for generating Figure 2, depicting the interactive effects of distance and cars at each level of species richness. * 302 - Analysis - Vehicular Effect Code.R - script used for generating Figure 3, depicting the interactive effects of distance and cars with 4 vocalizing bird species. Also used to retrieve p-values for all mixed- effects model coefficients * 303 - Analysis - Species Equivalence Code.R - script used for generating Figure 4, depicting the added species equivalence of each acoustic index at low, mid, and high traffic levels. * 401 - Supplemental - Appendix Figure Code.R - script used for generating Figure A1, depicting the control acoustic index values as predicted by the number of added bird species. ### [Data](./Data): Contains raw data used in scripts * all_species_indices.csv - acoustic index values for all soundscapes containing 2, 8, and 12 species, as well as all soundscapes derived from the first 4 assemblages containing 4 bird species. Variables are as follows: * assemblage - the index number indicating the randomized bird assemblage used to develop the soundscape, in which soundscapes with the same assemblage contain the same bird species. * Cars - the number of car drive-by sound clips added to the soundscape. * Distance - designates which car drive-by sound clips were added to the recording in order to simulate the effort of a deployment configuration at specific distances from the roadside. * Species - the number of vocalizing bird species added to the soundscape. * BI - Bioacoustic Index first described in Boelman et al. (2007). * H - Acoustic Entropy Index first described in Suer et al. (2008). * ACI - Acoustic Complexity Index first described in Pieretti et al. (2011). * ADI - Acoustic Diversity Index first described in Villanueva-Rivera et al. (2011). * AEI - Acoustic Evenness Index first described in Villanueva-Rivera et al. (2011). * M - Amplitude Index first described in Depraetere et al. (2012). * NDSI - Normalized Difference Soundscape Index first described in Kasten et al. (2012). * NP - Number of Frequency Peaks first described Gasc et al. (2013). * AR - Acoustic Richness Index first described in Depraetere et al. (2012). * four_species_indices.csv - acoustic index values for all soundscapes containing 4 bird species. Variables are the same as described above. ### [Audio\_Files](./Audio_Files): contains original and modified car driveby soundclips, as well as .wav files for all generated soundscapes * Car driveby.wav - original drive-by sound clip retrieved from the Youtube Audio Library * Car_50m.wav - drive-by sound clip edited to reflect the frequency and amplitude at 50 meters from the roadside * Car_150m.wav - drive-by sound clip edited to reflect the frequency and amplitude at 150 meters from the roadside * Car_250m.wav - drive-by sound clip edited to reflect the frequency and amplitude at 150 meters from the roadside * All other audio files are generated soundscapes. File names provide the assemblage index number, the number of added car drive-by sound clips, and the distance that the added car drive-by clips reflect (e.g., assemblage23_5c_250m.wav). Control soundscapes only contain bird vocalizations and pink noise with no added car sounds.