Sonic Patterns I: The Noise - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 147

In social animals, anthropogenic noise can create serious difficulties in
maintaining social aggregation or can reduce the exchange of strategic information
such as the location of areas with abundant food.
Background noise and bird acoustic patterns seem strictly related. In fact, as
emphasized by Slabbekoorn ( 2004 ), many animals use acoustic signals, and a low
level of background noise is essential to attract mates, to defend territories, and to
collect other information to track the necessary resources to maintain individual
fitness
Many functions are connected to the active sonic ambience such as choruses and
long-distance signals to inform individuals about the reciprocal presence or to
signal special events such as water sources. The entire animal communication is
based on the signal-to-noise ratio, and this largely depends on the amount of
background noise that is present in an environment at a specific time of day or
season, which interferes with the efficient of the signal emitted.
Rabin et al. ( 2003 ) has conducted research on the effect of highway noise on
California ground squirrel vocalizations. The California ground squirrel
( Spermophilus beecheyi ) is a common vocal mammal that also lives in human-
modified grassland landscapes under a different level of noise masking. This
species has a broad repertoire of chatters, whistles, and single-note repetitive
calls. Its vocalizations change according to the predator that is approaching. Chatter
and repetitive call are emitted in presence of mammalian predators; whistles are
emitted when a raptor appears. Variations in the structure of chatter calls are
statistically different according to the presence of snakes, badgers, other mamma-
lian predators, raptors, and conspecific competitors. These authors have observed
that the California ground squirrel has the capacity to shift acoustic energy into
those harmonics that do not overlap with highway noise. They argued that this is a
case similar to the human Lombard effect that consists in change in amplitude to
avoid the masking effect of noise. This species seems to have a high acoustic
plasticity and online adjustment, demonstrated by a capacity to change the type of
vocalization according to the type of menace.
6.9 Masking Effect on Animal Life
We know quite well the effect of a large dose of noise on psychology and in general
on the health of exposed people, but little is known about the effects of noise on
wild animals.
Vocal species produce sounds, and according to the acoustic niche hypothesis
every species tries to accommodate itself in a way to reduce acoustic interspecific
overlap.
Evaluating noise effects on an animal is a complicated issue because the effects
vary between species and individuals, with time of the year, and by day.
In soundscape ecology noise is not simply an unwanted sound but a sound that
reduces, by masking, the quality of every other acoustic signal. To reduce the