Sonic Patterns I: The Noise - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 160

Fig. 6.11 Common outdoor A-weighted levels in different environments (From Miller 2003 )
Transportation noise is highly impacting in every developed country. Miller
( 2003 ) has presented a detailed report about this problem across the USA
(Fig. 6.11 ). Noise produced by vehicles can travel up to 4 km in distance according
to the type and volume of traffic.
The acoustic effect of traffic is well known, and species seem to react to noise
masking produced by traffic by modifying acoustic traits and by population shifting.
These effects have been proven by Parris and Schneider ( 2009 ) on two species of
Australian birds: the grey shrike-thrush ( Colluricincla harmonica ) and the grey
fantail ( Rhipidura fuliginosa ). The grey shrike-thrush sings at a higher frequency in
the presence of traffic noise. The other species, which normally sings at a higher
frequency than the first species, seems to not change its acoustic pattern but to appear
less frequently in areas with high traffic noise. These different effects on these two
species demonstrate two different strategies to cope with traffic noise: the first can
raise the frequency to avoid the masking of the lower frequency of traffic noise, and
the second species, which already has a song emitted at high frequency and cannot
further accommodate the frequency, reacts by avoiding louder conditions. Birds have
been shown to sing at a higher pitch, sing louder (Lombard effect), and change the
time of day for singing to reduce the masking effect of traffic.
In other animals, research in this field is not as common. For instance, in frogs it
has been found that motorcycle noise changes their chorusing behavior and that
noise can reduce the diversity of species and abundance.