An Ecoacoustic Snapshot of a Subarctic Coastal Wilderness: Aialik Bay, Alaska 2019

Abstract

I recorded the ambient sounds at three locations in the wilderness of Aialik Bay in Kenai Fjords National Park, Alaska between 25 June and 21 September 2019. My aim was to capture an ecoacoustic snapshot of the coastal soundscape to provide a comparable baseline for evaluating wilderness characteristics defined by the Wilderness Act of 1964. I visually and empirically characterized the Aialik Bay wilderness soundscape using the acoustic metrics of soundscape power (normalized watts/kHz) and Normalized Difference Soundscape Index (NDSI) from 5373 five-minute recordings, combined with visual and aural spectral examination of 4386 recordings. Soundscape power exhibited similar patterns across frequency intervals with sound sources primarily occurring in the low-frequency (1–2 kHz) and mid-frequency (2–5 kHz) intervals. Significant differences within frequency intervals between sites suggested the presence of distinct sonotopes. Low-frequency sounds were dominant across all three sites with peak soundscape power values across study days and 24 h timeframes attributed to wind and occasional periods of technophony emitted from commercial tour boats and private boating activities. Low-frequency geophony from wave action was ever present. Technophony exhibited some predictable patterns consistent with the timing of sightseeing boat tours. Peak values of soundscape power at mid-frequencies were attributed to the geophony of rain. Although biophonies were less common than geophonies, the choruses of songbirds were prevalent in July and promptly occurred daily between 0300 and 0600. Biophonies generally declined over the course of the day. All sites displayed negative NDSI values over most study days and consistently negative values over 24 h time frames, indicating a soundscape primarily influenced by low-frequency geophony and periods of technophony. However, NDSI values showed patterns and peaks similar to biophonies at mid-frequency intervals indicating biophony was still a notable contribution to this geophony-dominant soundscape. Despite the acoustic footprint of motorboat noise detected at all sample sites, the soundscape of the Aialik Bay wilderness was dominated by the natural sounds of geophony, biophony, and occasional periods of natural quiet indicative of a wilderness only partially impacted by technophony.

Sonotope patterns within a mountain beech forest of Northern Italy: a methodological and empirical approach

“…Concurrently, sonic events were more dissimilar among astronomical periods in May-June than July-August which may be explained by the fact that this region commonly experiences more wind in May and early June with daily wind events throughout a 24-h period than it does in July and August (https://beach-weather.com/Southern-Europe/Italy/ Tuscany/averages/#windinfo). Despite this being a managed and recovering Mediterranean forest, the type of geophonically dominated soundscape is more commonly documented in subarctic environments and winter (Mullet et al, 2016;Mullet, 2020) and is not suggestive of a healthy forest for songbirds and stridulating insects. Perhaps what is also unusual is that breeding birds in this region are more sonically active between May and June, not July and August (Farina, 1997).…”

“…In order to better understanding the role of geophonies and of biophononies in the composition and dynamics of sonotopes, we have adopted a threshold of 2000 Hz to discriminate geophonies (≤2000 Hz) from biophonies (>2000) (Gage and Axel, 2014;Mullet et al, 2016;Mullet, 2020).…”

Perspectives on the Ecological Role of Geophysical Sounds

“…Similarly, geophonies express temporal variation too, depending on its source (e.g., river sounds compared to rain showers), geographic region, time of day, and season. Some good examples of spatial and temporal differences in geophony are evident in the seasonal patterns of rainfall constituting the Amazon's wet and dry season (Sombroek, 2001) compared to the more extreme seasonal differences in geophony of south-central Alaska's boreal forests with rainy summers and actively flowing streams (Mullet, 2020) to winters with prolonged periods of ambient geophony interspersed with intense wind events over frozen lakes, rivers, and tundra (Mullet et al, 2016). The Amazon's wet season comes with increased geophony from rain but also marks the height of the breeding period for many songbirds that coincides with food availability (Stouffer et al, 2013).…”

“…The Amazon's wet season comes with increased geophony from rain but also marks the height of the breeding period for many songbirds that coincides with food availability (Stouffer et al, 2013). Similarly, the biophony of south-central Alaska increases considerably in summer months as the geophony of rushing water and rain dominate the soundscape (Mullet, 2020) while most soniferous species migrate or become dormant over winter (Mullet et al, 2016). These geophonically-related ecological processes are not only a product of geography, geomorphology, and vegetation, but their seasonality is also a result of the Earth's planetary tilt toward the Sun.…”

“…This method enables a researcher to standardize their sample rate and recording intervals while allowing the recording device to run unattended for long-periods of time, generating a broad temporal sample of geophonic events. The temporal sampling period is dependent on the research question (see Buxton et al, 2016;Krause and Farina, 2016;Mullet et al, 2016Mullet et al, , 2017bMullet, 2020 for examples), but we recommend 1min as a sufficient recording interval. Sonic data collected by ARS are often generated as a digital waveform (wav) file which can be processed into a metric or index using the computation of an algorithm suitable to answer the focused research question.…”