Perspectives on the Ecological Role of Geophysical Sounds

Humans categorize unwanted sounds in the environment as noise. Consequently, noise is associated with negative human and ecological values, especially when it is derived from an anthropogenic source. Although evidence confirms that many machine-generated anthropogenic sounds have negative impacts on animal behavior and communication, natural sources of non-biological sound, such as wind, rain, running water, and sea waves (geophonies) have also been categorized as noise and are frequently dismissed or mischaracterized in acoustic studies as an outside factor of acoustic habitats rather than an integrated sonic component of ecological processes and species adaptations. While the proliferation of machine-generated sound in the Biosphere has become an intrusive phenomenon in recent history, geophony has shaped the Earth’s sonic landscapes for billions of years. Therefore, geophonies have very important sonic implications to the evolution and adaptation of soniferous species, forming essential ecological and semiotical relationships. This creates a need to distinguish geophonies from machine-generated sounds and how species respond to each accordingly, especially given their acoustic similarities in the frequency spectrum. Here, we introduce concepts and terminology that address these differences in the context of ecoacoustics. We also discuss how Acoustic Complexity Indices (ACIs) can offer new possibilities to quantifiably evaluate geophony in relation to their sonic contest.

Soundscapes and protected area conservation: Are noises in nature making people complacent?

This study explores how existing connections to natural places may affect PA visitors’ experiences and perceptions within the PA. Specifically, outside-the-PA soundscape perceptions are examined to better understand how their experiences outside the PA may affect perceptions of PA soundscapes and visitors’ ability to effectively contribute to conservation monitoring. Survey research (n=389) of recent urban visitors to the Chilean Coyhaique National Reserve (CNR) in Patagonia unpacked perceptions of the acoustic environments within the places where participants felt most connected to nature, including landscape features, favorite and prevalent sounds, and acceptability of particular anthrophonic sounds. Favorite and prevalent sounds were open-coded, and anthrophonic sounds were rated for prevalence and acceptability. The mountain landscape features and sounds (‘wind’, ‘running water’,‘ birds’) participants described as prominent within the places where they felt most connected to nature aligned well with CNR characteristics. Participants who ‘sometimes’‘/often’ heard certain anthropogenic sounds (vehicles, aircraft, machines, city sounds), within the places where they felt most connected to nature, rated those sounds as more acceptable than participants who reported ‘never’ hearing them, raising concerns about complacency toward anthrophony in natural settings. Continued research efforts are warranted to better understand visitors’ frames of reference, their influence on the reliability of social norm data for PA soundscape monitoring, and their influence on PA managers’ ability to protect conservation values.

Boat noise interferes with Lusitanian toadfish acoustic communication

ABSTRACT Anthropogenic noise is considered a major underwater pollutant as increasing ocean background noise due to human activities is impacting aquatic organisms. One of the most prevalent anthropogenic sounds is boat noise. Although motorboat traffic has increased in the past few decades, its impact on the communication of fish is still poorly known. The highly vocal Lusitanian toadfish (Halobatrachus didactylus) is an excellent model to test the impact of this anthropogenic stressor as it relies on acoustic communication to attract mates. Here, we performed two experiments to test the impact of boat noise on the acoustic communication of the Lusitanian toadfish. Using the auditory evoked potential (AEP) technique, we first compared the maximum distance a fish can perceive a boatwhistle (BW), the mate attraction acoustic signal, before and after embedding it in boat noise. Noises from a small motorboat and from a ferryboat reduced the active space from a control value of 6.4–10.4 m to 1.7–2.5 m and 6.3–6.7 m, respectively. In the second experiment we monitored the acoustic behaviour of breeding males exposed to boat noise playbacks and we observed an increase in the inter-onset interval of BWs and a disruption of the usual vocal interactions between singing males. These results demonstrate that boat noise can severely reduce the acoustic active space and affect the chorusing behaviour in this species, which may have consequences in breeding success for individuals and could thus affect fitness.

Toward Crowd-sourced Soundscape Monitoring in Protected Areas: Integrating Sound Dominance and Triggers to Facilitate Proactive Management

This research expanded on prior use of visitor perception data to inform potential social indicators of soundscape quality, by integrating existing urban-context soundscapes work, and the emerging use of triggers to help managers identify concerns before they reach the threshold level. Along with existing measures of sound appeal and acceptability, sound dominance helped provide a sense of how the extent of particular sounds influenced visitor experiences and a desire to visit more. Geospatial data collection for 899 visitors and eight sites within the Coyhaique National Reserve (CNR) in southern Chile during the summer high visitation season of 2019, allowed researchers to examine perceptual similarities and differences, facilitating an evaluation of new perceptual variables for soundscape monitoring. Correlation analyses identified informative relationships between the dominance (sound duration and foreground/background placement) of natural and anthropogenic sounds, and overall soundscape ratings. The duration of natural sounds was positively correlated with soundscape-level ratings, while the duration of anthropogenic sounds was negatively correlated with these ratings. Unique trends and relationships were identified across specific sites, demonstrating the value of adding measures of perceived sound dominance to soundscape monitoring processes. Observed Protected Area (PA) visitor enthusiasm for sounds and soundscapes suggests potential for crowd-sourced citizen science-based methods that could be done voluntarily and regularly using simple and accessible applications and technologies.

Fin whale singing decreases with increased swimming speed

The attributes of male acoustic advertisement displays are often related to a performer's age, breeding condition and motivation, but these relationships are particularly difficult to study in free-ranging marine mammals. For fin whale singers, we examined the relationships between a singer's swimming speed, song duration and amount of singing. We used a unique set of fin whale singing and swimming data collected in support of the US Navy's marine mammal monitoring programme associated with the Navy's Integrated Undersea Surveillance System. A goal of the programme is to improve understanding of the potential effects of anthropogenic sound sources on baleen whale behaviours and populations. We found that as whales swam faster, some continued to sing, while others did not. If swimming speed is an indication of male stamina, then singing while swimming faster could be a display by which females and/or other males assess a singer's physical fitness and potential reproductive quality. Results have implications for interpreting fin whale singing behaviour and the possible influences of anthropogenic sounds on fin whale mating strategies and breeding success.

Perspectives in ecoacoustics: A contribution to defining a discipline

Ecoacoustics is a new discipline that investigates the ecological role of sounds. Ecoacoustics is a relevant field of research related to long-term monitoring, habitat health, biodiversity assessment, soundscape conservation and ecosystem management. Several life traits of the species, populations, communities, and landscapes/waterscapes may be described by ecoacoustics. Non-invasive programmable recording devices with on-board ecoacoustic metric calculations are efficient and powerful tools to investigate ecological systems. A set of processes in four [adaptive, behavioural, geographical, ecosemiotic] domains supports and guides the development of ecoacoustics. The first domain includes evolutionary mechanisms that join sound typology with the physical and biological characteristics of the environment and create frequency partitioning among species to reduce competition. The second domain addresses interspecific signals associated with geophysical and anthropogenic sounds that operate to shape temporary acoustic communities and orient species to select suitable acoustic habitats. The third domain pertains to the geography of sound, an entity composed of three subordinate acoustic objects: sonotopes, soundtopes, and sonotones, which are operationally delimited in a geographical and temporal space by the distribution of the ecoacoustic events. The ecoacoustic events allow the classification of complex configurations of acoustic signals and represent the grain of a soundscape mosaic. The fourth domain operates by ecosemiotic mechanisms within the species level according to a function-specific perception of the acoustic information facilitated by encoding processes.