Hearing to Survive
The term “anthropogenic” is often used by scientists to refer to environmental change caused or influenced by people, be it directly or indirectly. Anthropogenic noise basically means sounds produced by human activities that usually associate with urbanisation, economic development, or transportation networks etc. Anthropogenic sounds have now penetrated even the quietest places on Earth (Buxton, 2017). According to scientific studies in the US, over 60% of US protected lands experience noise levels that double up the background noise regardless of their distance from major metropolitan areas.
“Hearing” to survive
This has led to a concern whereby anthropogenic noise may impact the living environment of animals. One of the major impacts that noise has caused on wildlife is that anthropogenic noise may mask off acoustic signals used by animals greatly, which affects the inter- and intraspecific communication among them. To overcome this, some animals had to change their vocal behaviour to cover the signal-masking effects of the noisy environments. Animals can do this by changing the amplitude and frequency of their vocal output, or by changing its temporal structure (Berger-Tal, Wong, Candolin, & Barber, 2019).
It has been found that the consequences of noise in natural landscapes have multifaceted, thus impacting the activities of vertebrates like mating, movement, the dynamics of prey-predator, and physiology (Graeme Shannon, 2015). However, most research mainly focused on the impacts of pressure waves on vertebrates, leaving the impact of anthropogenic sounds on invertebrates unstudied, hence lesser understandings on the acoustic modalities that invertebrates rely on.
But that was only the case back in 2016, where only 4% of the research on the impact of anthropogenic sound on animals had been about invertebrates, even though invertebrates occupy 97% of the species on Earth (Graeme Shannon, 2015).
In 1881, Charles Darwin published a book entitled “The Formation of Vegetable Mould Through the Action of Worms”. His publication became one of the earliest recognitions of an inaudible invertebrate acoustic world. In his words, he reported that, “…if the ground is beaten or otherwise made to tremble, worms believe that they are pursued by a mole and leave their burrows” (Darwin, 1881). This had then become one of the popular techniques for collecting earthworms, called “Worm charming”. Like many other invertebrates, earthworms rely on substrate-borne vibrations to avoid the attack from predators.
Being the prey, invertebrates need to use sound to identify, avoid and deter predators and harm. On the other hand, as predators, invertebrates also need sound to distinguish, localise and lure their prey. Communication is also crucial for invertebrates to transmit information about reproductive status, quality and location among the species. They rely heavily on sound to attract and find mates. Not just that, invertebrates have high reliance on sound for its ability to carry general environmental information. This is because environmental processes like wind, rain, fire, water (river, streams etc) all produce different sounds with their specific acoustic properties recognisable by the invertebrates.
Relationship between anthropogenic sound and invertebrates
Since the first decade of the twenty-first century when the idea of anthropogenic sound took hold, scientists started their action: establishing acoustic monitoring programs, creating sound libraries, documenting acoustics of ecosystems. For example, there was an attempt in 2015 in the Grand Teton National Park, WY, to create awareness of noise pollution. This attempt had noise meters installed along the Park roadsides, penetrating the quiet of each vehicles’ interior with a visualisation (green-yellow-red) of airborne pressure wave drivers introduced into the ecosystem.
Anthropogenic noise, or noise from human activities is dominated by frequencies less than 2000 Hz. This range corresponds with the frequency sensitivities of most of the terrestrial and marine invertebrates. As the sound radiates from the source, it may encounter with various invertebrates hence intruding into their acoustic environments causing interference (Raboin, 2021).
Therefore, it is important to understand that noise pollution not only affects human beings, but the anthropogenic sounds that we human beings make, will also strongly impact the wildlife.
Berger-Tal, O., Wong, B. B., Candolin, U., & Barber, J. (2019). What evidence exists on the effects of anthropogenic noise on acoustic communication in animals? A systematic map protocol. Environmental Evidence 8. doi:https://doi.org/10.1186/s13750-019-0165-3
Buxton, R. M. (2017). Noise pollution is pervasive in U.S. protected areas. Science 356, 531-533. doi:https://doi.org/10.1177/1757913914566549
Darwin, C. (1881). The Formation of Vegetable Mould Through the Action of Worms with Observations on Their Habits. London, UK: John Murray.
Graeme Shannon, M. F. (2015). A synthesis of two decades of research documenting the effects of noise on wildlife. Biological Reviews 91(4). doi:https://doi.org/10.1111/brv.12207
Raboin, M. (2021). Inaudible Noise Pollution of the Invertebrate World. Acoustics Today, 17(2), 32-39. doi:https://doi.org/10.1121/AT.2021.17.2.32
Written by Khei Yinn Seow
Posted on June 21, 2021