Results

The soundscape in Best Woods during the fall season is composed of eleven dominant sound signatures:

vehicles (82.3%), squirrels (31.7%), birds (15.9%), building motor (12.2%), aircraft (11.5%), wind (8.8%), crickets (6.1%), train (3.8%), dog (3.7%), precipitation (3%), people (1.6%) (Graph).

These percentages are averages from the whole study.  Per each sampled day, twenty-four hour percentages were calculated by the AMT software that indicate percent audibility of each sound.  Percentages from all eighteen days were then averaged to attain the above values.

Sounds that are dominant and constantly in the background or that are habitually perceived are keynote sounds (Schafer, 9).  Because the Arb is a natural environment, it may be assumed that biophonic or geophonic sounds would be keynotes.  However, vehicles are audible over fifty percent more than other sounds in Best Woods and therefore are the dominant keynote.  This exemplifies the value of acoustic communication.  Without longitudinally studying the acoustic characteristics of this environment, Best Woods may be considered a natural acoustic system.  Yet, it is predominately anthropogenic.  The predominate anthropogenic sounds are from vehicles on highways 3 and 19 that flank the Arb (Map), a building motor, most likely from a turkey-processing farm located several miles away, jet and prop planes probably on flight paths from Minneapolis/St. Paul Airport, and trains located a few miles to the northeast.

Biophonic keynotes are also present though, from squirrel and bird vocalizations.  Although their audibility is less frequent than vehicle sounds, they are temporally prominent and loud and dominate other biophonic sounds.  It could be argued that the building-motor and aircraft sounds are keynotes also, but because they are less expected within this natural environment they readily stand out.  These types of sounds are called sound signals (Schafer, 10) because they are less habitually perceived and instead are consciously attended to.  As a result, of the eleven dominant sounds, the eight that are not keynotes are sound signals.

The level of activity present in and around Best Woods is reflected in its average daily circadian rhythm (Graph).  Most acoustic events occurred from 8am to 9pm, decreasing late in the evening and during early morning hours.  Such activity is indicative of the morning increase and evening decrease in number of traffic and wildlife events (Graph).  As stated, while natural sounds were evident, Best Woods is predominantly an anthropogenic acoustic system.  Human-generated noises outnumbered the total biophony and geophony, indicated by audibility percentages (Graph) and average daily rhythms (Graph).  Vehicle sounds supplied a nearly continuous amount of engine and/or tire sound during the day and frequently throughout the night.  Additionally, a building motor sound was audible at night and sporadically during the day (Graph).  These anthropogenic sounds were present in greater quantities throughout all times of the day compared to biophony and geophony.

While anthrophony was more numerous and continuous, natural sounds on average were continuous as well, however, to a much lesser extent (Graph).  The dominant audible species, birds and squirrels, were heard mostly from dawn to sunset, yet decreased to near zero over night (Graph).  At night in September and October, crickets and a lone barking dog (presumably from a house located approximately a mile away) occupied the soundscape of Best Woods (Graph).  The crickets were only audible until October 23rd (Graph).  Therefore, the only continuous audible biophonic sound at night, for the duration of the study, was the barking dog.

Rhythmic seasonal changes highlight the distinction between anthrophony, biophony, and geophony.  Natural sounds decreased in percentage time audible and average daily audibility from September to November, indicating seasonal changes as temperature decreased and daylight diminished (Graph).  In contrast, anthropogenic sounds remained constant (Graph).  The distinction between seasonal changes in biophonic and anthropogenic rhythms is represented by percent and average sound audibility (Graph 1)(Graph 2).  The decrease in biophonic sounds is emphasized by the near 14 percent decreases in both squirrel and bird vocalizations during the study period (Graph).  These results demonstrate the difference between the “animal world” and “human world.”  Animals appear to be following a seasonal cycle, indicated by the fact that at the end of the study percent and average vocalizations had declined, coinciding with shorter days.  However, the human cycle is perpetual with little alteration to changes in the seasonal patterns, indicated by consistant percent and average audibility.

In sum, average and percent calculations reveal the circadian rhythm, biological responses to seasonal change, and the interplay of human generated sound within this ecosystem.  The ascertainment of these patterns solely by sound demonstrates the communicative value of acoustics.  It is arguably impossible to determine this macro-level information using any other paradigm.  Measurements using visuals, chemical analysis, atmospheric testing, or other methods, lack the ability to relay information about the interplay between biological and mechanized entities.  Thus, sound mediates a high level of exchange between the listener and the environment.

One limitation to the study is the data represent “batch capturing” of sounds from the audio samples.  For example, during audibility analysis, every time a squirrel was heard I inputted the appropriate sound source code in AMT.  Per each sample, one or multiple squirrels may be vocalizing.  Thus, one data point indicates that the event occurred but does not reveal its extent.  To distinguish these differences, sound pressure levels need to be recorded, a feature not offered on the SM2+.  Despite this limitation, temporal representations of rhythmic sound changes are accurate, while average and percent results represent event occurrence but not necessarily intensity.  Additionally, an important distinction is that results specifically target the soundscape of Best Woods due physical limitations of sound propagation (i.e., squirrel vocalizations are audible in Best Woods but may not be in prairie regions of the Arb).  Nevertheless, broad generalizations about the entire Arb’s soundscape can be inferred from these results with this fact acknowledged.