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but this change is insufficient to modify the signal-to-noise ratio. In conclusion,
Parris et al. (
2009
) underline the risk of local extinction also for populations
exposed to traffic noise in suitable habitats.
How to protect frogs from traffic noise is a real challenge. The adoption of solid
barriers may seem a first choice but such barriers increase the isolation of managed
areas. A ultimate solution could be the adoption of a dense vegetation barrier that is
cheaper and more environmentally compatible.
In common marmosets (
Callithrix jacchus
), a New World monkey, the effect of
increased noise produced an increase in the sound level of their spontaneous calls,
but no noise-induced increase in the number of syllables per call series was
observed. This finding suggested that an increased serial redundancy of vocal
signals is not utilized by this species when the environment becomes noisy.
Marmosets increased the duration of their call syllables when environmental
noise increased, demonstrating a vocal plasticity in the communication system
(Brumm et al.
2004
).
The effect of traffic on grassland birds and the unexpectedly great reactions of
birds to the presence of road traffic is well documented in a study conducted by
Reijnen et al. (
1996
) in Dutch agricultural grasslands. Using transect counts these
authors have found that of 12 species considered, 7 showed reduced density close to
roads. Species showed great variability in the distance from roads, from 20 to
1,700 m for a road with 500 cars a day, and from 65 to 3,530 m from a road with
50,000 cars a day. In the first case the decrease of density ranged from 12 to 56 %
within 100 m. For roads with 50,000 cars a day, the decrease of density was 12 to
52 % within 500 m. Figure
6.12
presents the loss of population (%) of the most
common open range birds.
Rheindt (
2003
), investigating the effect of highways on birds, has found a
decrease in richness and diversity of birds living close to a German motorway.
He found a significant relationship between dominant frequency and the decline in
abundance of species toward the motorway. Birds that produce a high-frequency
pitch are less susceptible to noise pollution and express a greater abundance in the
proximity of the roads.
Noise from anthropogenic origin seems to produce permanent changes in the
structure of song in red-winged blackbirds (
Agelaius phoeniceus
). In fact, popula-
tion living in quiet marshes far from traffic noise, when exposed to traffic noise
playback reacted with an increase of signal tonality, demonstrating high acoustic
plasticity (Hanna et al.
2011
). But in marshes located at the side of traffic-heavy
roads, red-winged blackbirds maintain higher tonalities when the area is temporar-
ily not exposed to traffic noise. This last fact demonstrates that anthropogenic noise
influences the structure of their song, at least in this species.
In passive noise, for listeners such as the greater mouse-eared bat (
Myotis
myotis
) anthropogenic noise could represent a strong limitation to foraging sites.
Experiments conducted on this species by Schaub et al. (
2008
) on caged bats have
demonstrated how greater mouse-eared bat avoided entering an area in which noise
was produced. Submitted to three types of noise, this species reacted at increasing
rate from a noise produced by traffic, noise produced by vegetation movement, and
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