Vibration Communication in Vertebrates
141
3.7 Scaphiopus spp.- the Spadefoot Toad and Others
Seismic cues may be used to signal environmental changes that are critical for an
organism's reproductive behavior. For example, the emergence of burrowing
species of spadefoot toads (Scaphiopus) in response to rain has been shown to be
triggered by the seismic vibrations produced by the rain drops (Dimmit and Ruibal
1980). It is likely that other burrowing amphibian species respond to seismic
vibrations of rainfall in a similar fashion. Likely candidates for this behavior are
individuals of the relatively unknown genus Breviceps. These are entirely
terrestrial and fossorial frogs endemic to sub-Sarahan Africa, that occupy a wide
range of habitats including forest, montane grassland, open and closed woodland,
and vegetated coastal dunes (Minter 1998).
For example, during the breeding season in Pietersburg, Republic of South
Africa, the response to rain by populations of Breviceps adspersus pentheri
(Microhylidae) is very rapid; the first calls were heard 15-30 min after rain began
to fall (Minter 1998). Although it is possible that water seeping down to the buried
frogs signaled the onset of the breeding season, the rapid response times suggest
that other cues, perhaps vibrational, in fact trigger the emergence of these
interesting animals. Future field experiments will undoubtedly be designed to
distinguish between these (and other) possibilities.
3.8 Dipodomys spectabilis - the Banner-Tailed Kangaroo Rat
It has long been known that banner-tailed kangaroo rats, Dipodomys spectabilis,
engage in foot-drumming behavior as a territorial signal (Randall 1984). In
addition, there is some evidence that they may recognize foot-drum patterns and
use them to distinguish neighbors from strangers (Randall 1984). The question of
whether the airborne component or the seismic component is important in
signaling territoriality and individual recognition was experimentally tested in an
ingenious experiment in which an artificial thumper was used to simulate the footdrumming pattern; the timing of the responses of individual kangaroo rats was
then compared to the stimulus (Randall and Lewis 1997). In one set of
experiments, kangaroo rats in their burrows were given a choice of two stimuli:
(I) simultaneous seismic foot-drums from the mechanical thumper buried in the
ground plus high-level broadband noise broadcast through a loudspeaker to mask
any airborne sound generated by the buried thumper, or (2) simultaneous airborne
foot-drumming sounds lacking any seismic components plus high-level broadband
noise.
When the number of foot-drumming sequences initiated during the 7 s of
seismic playback stimuli with airborne masking noise was compared to the
number initiated in the 7 s before and after the playback, it was shown that the
kangaroo rats initiated significantly fewer drumming sequences (suggesting they
detected the seismic stimulus) during the seismic playback than either before or
141
3.7 Scaphiopus spp.- the Spadefoot Toad and Others
Seismic cues may be used to signal environmental changes that are critical for an
organism's reproductive behavior. For example, the emergence of burrowing
species of spadefoot toads (Scaphiopus) in response to rain has been shown to be
triggered by the seismic vibrations produced by the rain drops (Dimmit and Ruibal
1980). It is likely that other burrowing amphibian species respond to seismic
vibrations of rainfall in a similar fashion. Likely candidates for this behavior are
individuals of the relatively unknown genus Breviceps. These are entirely
terrestrial and fossorial frogs endemic to sub-Sarahan Africa, that occupy a wide
range of habitats including forest, montane grassland, open and closed woodland,
and vegetated coastal dunes (Minter 1998).
For example, during the breeding season in Pietersburg, Republic of South
Africa, the response to rain by populations of Breviceps adspersus pentheri
(Microhylidae) is very rapid; the first calls were heard 15-30 min after rain began
to fall (Minter 1998). Although it is possible that water seeping down to the buried
frogs signaled the onset of the breeding season, the rapid response times suggest
that other cues, perhaps vibrational, in fact trigger the emergence of these
interesting animals. Future field experiments will undoubtedly be designed to
distinguish between these (and other) possibilities.
3.8 Dipodomys spectabilis - the Banner-Tailed Kangaroo Rat
It has long been known that banner-tailed kangaroo rats, Dipodomys spectabilis,
engage in foot-drumming behavior as a territorial signal (Randall 1984). In
addition, there is some evidence that they may recognize foot-drum patterns and
use them to distinguish neighbors from strangers (Randall 1984). The question of
whether the airborne component or the seismic component is important in
signaling territoriality and individual recognition was experimentally tested in an
ingenious experiment in which an artificial thumper was used to simulate the footdrumming pattern; the timing of the responses of individual kangaroo rats was
then compared to the stimulus (Randall and Lewis 1997). In one set of
experiments, kangaroo rats in their burrows were given a choice of two stimuli:
(I) simultaneous seismic foot-drums from the mechanical thumper buried in the
ground plus high-level broadband noise broadcast through a loudspeaker to mask
any airborne sound generated by the buried thumper, or (2) simultaneous airborne
foot-drumming sounds lacking any seismic components plus high-level broadband
noise.
When the number of foot-drumming sequences initiated during the 7 s of
seismic playback stimuli with airborne masking noise was compared to the
number initiated in the 7 s before and after the playback, it was shown that the
kangaroo rats initiated significantly fewer drumming sequences (suggesting they
detected the seismic stimulus) during the seismic playback than either before or