Biology Reference
In-Depth Information
7.1
Introduction
Choruses, which represent the most relevant and discussed biophonic phenomena
that can be heard in nature, are the result of the contemporary vocalizations of
animals prevailing at dawn and at dusk. Choruses have attracted the attention of
bioacousticians for a long time, and ethologists and even ecologists often use
choruses to assess the abundance of populations (Pellet et al.
2007
). The contem-
porary vocalizations of different species according to a daily dynamic produce a
noisy effect that is common to all the biomes.
Choruses occur in frogs, birds, mammals, and insects, with different and distinct
strategies and effects on populations and communities. In the marine environment,
temporary choruses may be produced by the intense clicking sounds of sperm
whales.
In tropical areas, frogs and insects are the major agents, but there are birds that
dominate the sonic environment in temperate and boreal biomes.
Choruses have different temporal dynamics at a daily scale according to the
species. For instance, choruses in birds occur at dawn and at dusk, and their length
and intensity largely depend on the season and weather conditions. In temperate
regions, bird choruses reach a maximum in the middle of the reproductive season
(May-June) (Fig.
7.1
).
Choruses have also been observed as a common phenomenon in aquatic systems
(D'Spain and Batchelor
2006
). For instance, in coastal waters choruses appear
regularly after sunset and before sunrise. In the Salton Sea, California (USA),
Fish and Cummings (
1972
) have recorded nocturnal choruses around 1,000 Hz
with an increase of 50 dB resulting from the acoustic activity of the orange-mouth
corvina fish (
Cynoscion xanthulus
). In New Zealand Radford et al. (
2008
) found
that most of the acoustic energy emerging from the seabed was the result of feeding
noises of sea urchins. These animals produce initially a noise of 800-2,400 Hz that
is amplified by the ovoid calcareous skeleton, which acts as a Helmholtz resonator.
This phenomenon is important to maintain an ambient noise that can be recognized
by pelagic larvae of key reef species, such as fishes, crabs, and lobster, to locate
future territories in which to settle.
Cato (
1978
) reported choruses in tropical waters of the East Indian Ocean, in the
West Pacific Ocean, and in the Timor Sea near Australia. These choruses were
present for a few hours at a time with an energy distributed between 400 Hz and
400 kHz with spectral peaks at 800 Hz, 1.2-2 kHz, and 3 kHz, respectively. The
sonic intensity was on average 30 dB higher than the background noise. Most of the
choruses occurred at evening but some choruses were observed at various periods
of the day. The principal sources of such choruses were fish and sea urchins.
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