Acoustic Observations in Agricultural Landscapes - The Ecology of Agricultural Landscapes - page 362

Soundscape

Biological Geophysical Anthropogenic

Intentional Incidental Mechanical Verbal

Stationary Temporal

Figure 14.1 . An acoustic taxonomic schema of biological, geophysical, and anthropogenic
sounds. Anthropogenic verbal communication can also be considered biological, although
here they have been categorized separately for clarity.

information but are not dispatched for the explicit purpose of communication.
Similarly, human-induced sounds can be verbal or mechanical . Verbal signals are
those produced by the human voice (e.g., talking, shouting, or singing). Conversely,
mechanical signals are produced by machinery and technology. Mechanical sig-
nals can be stationary or temporal . Stationary sounds are those that impose them-
selves on the ambient soundscape indefinitely (e.g., turbulence from ventilation
fans), while temporal sounds include noises that impinge on the soundscape for a
limited period (e.g., occasional automobile or train traffic). Each of these compo-
nents occurs at a range of frequencies that can be used to quantify the soundscape.
Importantly, this schema differentiates between sounds produced by vocalizing ani-
mals and those produced by machines.

Soundscape Analysis

Acoustic diversity metrics attempt to measure and quantify the number and type
of signal sources in the soundscape (Slabbekoorn and Peet 2003, Katti and Warren
2004, Warren et al. 2006). Organisms make selective use of acoustic frequencies
when attempting to communicate information such as mating potential, territory size,
and the presence of predators (Narins 1995, Catchpole and Slater 1995). Essentially,
each vocalizing species can develop a dynamic niche by modulating the temporal
periodicity and frequency of its respective signals to unused portions of the sound-
scape in order to avoid competition for spectral or temporal resources (Narins 1995).
This suggests that soundscape diversity might be a sensitive index for identifying
ecological change. Dale and Beyeler (2001) identified the value and characteristics
of ecological indices, among which by their criteria would include environmental
acoustics. Derived metrics from the soundscape are potentially valuable as ecologi-
cal indices because they can provide predictable measures of ecosystem stress that
can be used to interpret and measure both ecological and anthropogenic disturbances.