Background: The point of this study was to measure the effect that noise pollution, primarily automobile generated, affected wildlife populations close to the sources of noise. While there is much documentation about direct effects of noise pollution on wildlife species that have auditory senses, especially birds and mammals, this study was designed to look at the cascading effects of noise pollution on ecosystems and food webs as a whole. Additionally, the study wanted to see if the effects of noise pollution would reach communities in quiet ecosystems separated from the noise pollution that were adjacent to the area with the exposure. The hypothesis was that noise pollution has greater systematic and cascading effects on wildlife than previously widely known.

Methods: The study measured both forest and grassland ecosystems. Six treatment sites were chosen for each ecosystem, along with six control sites for each ecosystem. All of these sites were roadless, wild sites in their respective ecosystem that had negligible noise pollution. In treatment sites, artificial recorded traffic noises were played from stationary points, and the treatment zones were split into near and far groups at the 150 meter mark from the noise source. This point was chosen because that is the distance at which the decibels of the traffic noise were registered as the same as the constant decibels of the noiseless control sites. The decibels were also measured and that data provided to confirm the treatment zones were appropriate. After a period of time, species richness and abundance data was collected in each zone for birds, grasshoppers, which represented insects capable of hearing, and odonates, which cannot hear. 

Results: The results show that a statistically significant lower amount of bird richness and abundance was recorded at the sites close to the noise, but only in forest sites. Grasshoppers and odonates showed statistically significant lower amounts of richness and abundance at the sites farther away from the noise source. The study believes that this is proof of the cascading effect of noise pollution, and claims that the results support their hypothesis. The study claims the change in bird population is responsible for the change in insect populations, and therefore the claim of cascading effects of noise pollution is proven. 

Criticisms: The study looked at result categories in a very general sense. The results contained species richness and abundance for “songbirds” as a category. I think it may be more informative to, if possible, collect more specific species data to get a sense on if these noise conditions affect all songbirds equally. While the study is focused on communities as a whole and the cascading interactions between niches, I still think more specified species information could provide a clearer picture. It’s also not clear if species abundance and richness was measured in each site beforehand, or if only theorized. If it was measured, a figure with that data does not appear to be included. I would have liked to see this experiment done with a focus on change in richness and abundance before and after treatment, rather than raw numbers on richness and abundance, as that would more clearly indicated if the treatment had an effect on the animals, rather than some other effect, or preexisting conditions of the site. I also do not know if this study is truly enough to prove that noise pollution has cascading effects. Proof of changing results for insect populations can certainly be correlated with changing results for bird populations, but I don’t know if causality can be proven. How do we know the noise itself isn’t also responsible for insect population changes?

Citation: Sensaki, Mazayuki., Kadoya, Taku., and Francis, Clinton. Direct and indirect effects of noise pollution alter biological communities in and near noise-exposed environments. NIH National Library of Medicine. 2020 Mar 25. https://pubmed.ncbi.nlm.nih.gov/32183626/