Biology Reference
In-Depth Information
8.3 Seismic Signals from Mammals
Considering that the subterranean environment is not favorable to the diffusion of
airborne sounds, seismic communication has been proved in blind subterranean and
fossorial mammals (Mason and Narins
2001
), as in the case of
Spalax ehrenbergi
(Nevo et al.
1991
). This superspecies has a somatosensorship independent from the
auditory system for long-distance communication. Head thumping along the
excavated tunnel represents the vibration-borne mechanism for long-distance
communication.
Seismic vibrations have been found in the mole rat (
Georychus capensis
) and in
the spalacine mole rat
Nannospalax
. Recently the golden mole (
Eremitalpa granti
namibiensis
) has also been hypothesized to use seismic vibrations to locate food.
Utilization of the seismic waves produced by clumps of grasses scattered among
the sand dunes of the Namib desert have been shown to be used by the Namib
golden mole (
Eremitalpa granti namibensis
). The grasses under a light wind emit
low-amplitude vibrations that are used by this mole to orient itself toward such
clumps of plants, rich in invertebrates, when it is searching for food by sand-
swimming a few centimeters below the surface of the sand (Narins et al.
2006
).
Soil percussion seems an important system for communication in many animals
from insects to large mammals such as elephants. Vibrational signaling can be
produced by foot drumming, as in kangaroo rats (genus
Dipodomys
). In the banner-
tailed kangaroo rat (
Dipodoomys spectabilis
), foot drumming is produced during
courtship or when encountering a snake. Ehrenberg's mole rat (
Spalax ehrenbergi
)
thumps the head to signal but also to receive back the seismic echo to localize
obstacles.
The Asian elephant (
Elaphus maximum
) has been shown to use signals
associated with rumbles and foot stomps. The acoustic signal travels at 309 m/s
and the seismic signals at 248-264 m/s. Both signals have a predominant frequency
of 20 Hz. The seismic waveforms can be detected at a distance of 16 km. If the
elephants are able to detect such waves the communication between the different
familiar groups could be maintained also at long distance (O'Connell-Rodwell
et al.
2000
).
As in marine mammals, the elephant's foot cushion can be used to facilitate the
impedance between soil and the elephant's body. For a review about the communi-
cation tools adopted by elephants, see O'Connell-Rodwell et al. (
2000
) and
O'Connell-Rodwell (
2007
).
Seismic sensors have been applied to detect elephants and other large mammals.
Using a buried geophone, Wood et al. (
2005
) have demonstrated it is possible to use
this technique to estimate the energy produced by passing elephants (Fig.
8.2
) and
to discriminate species using the spectral content of their footfall with an accuracy
of 82 %. This technique has been recommended to estimate species and number of
individuals of large African mammals.
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