5. Acoustics and Social Behavior
261
to specific mimicry of space between signals and initiation of signals. Signal
relations are of ultimate importance in many animal communication
systems, and initial work on amplitude discrimination has been conducted
(Burdin et al. 1973; Vermin and Dubrovskii 1978) indicating discrimination
in amplitude features of signals. Preliminary recognition of sequential patterns of tones with durations or intersound intervals greater than 2 s were
not reliable (Ralston and Herman 1989).
The pattern recognition of rhythm, graded signals, sequential information, cross-modal signals, escalation in rates and intensity of signal over
time, and signal relations are needed to fully understand delphinid hearing.
New pattern recognition and neural network techniques (Murray 1997;
Deecke et al. 1999) and the possible gradation of parametric continuums
provides one of the most productive ways to analyze critical parameters. It
has even been suggested that production of sound (with increased click rate
turning into whistles) is a continuum, behaviorally and structurally. These
lines of inquiry may allow eventual comparison between behavioral states,
age, and species.
7.6 Shared Cognition-Cross-species, Eavesdropping,
and Phantom Echoes
Signals evolve by virtue of their being detected, decoded, and responded to
differentially by conspecifics and, perhaps, neighbors. Signal evolution is
influenced by interspecific audiences and their discriminative abilities, especially in sympatric species (Smuts et al. 1987; Herzing and Johnson 1997).
Shared cognitive environments take on a type of relevance for sharing
communication and negotiating. Mutual cognitive environments between
species are likely to produce pressures for interspecific communication
skills and signals. The acquisition and coopting of signals and of detection
abilities is critical in understanding the evolution of communication signals
and hearing. Sentinel species give alarm calls either to warn mixed species
aggregations of approaching predators (Munn 1986), or to effectively
deceive or divert a competitor from a desired goal, thereby involving the
coordination of different cognitive environments. Evolutionarily there
should be a high value on the interpreter needing to correctly identify
relevant cues from both conspecifics and allospecifics, and stereotypy and
redundancy are both ways to reduce demands on such cognitive challenges.
Concomitant aspects of hearing involve eavesdropping and interpretation of minimal information. Signal deciphering through eavesdropping
from conspecifics would suggest that much information is available, conspecifically, from listening and overhearing partial signals (Xitco and Roitblatt 1996). Combined with specific signature features of ensonified objects
or with phantom echoes (Au and Moore 1988), this may allow complex
discrimination of conspecific signals.
261
to specific mimicry of space between signals and initiation of signals. Signal
relations are of ultimate importance in many animal communication
systems, and initial work on amplitude discrimination has been conducted
(Burdin et al. 1973; Vermin and Dubrovskii 1978) indicating discrimination
in amplitude features of signals. Preliminary recognition of sequential patterns of tones with durations or intersound intervals greater than 2 s were
not reliable (Ralston and Herman 1989).
The pattern recognition of rhythm, graded signals, sequential information, cross-modal signals, escalation in rates and intensity of signal over
time, and signal relations are needed to fully understand delphinid hearing.
New pattern recognition and neural network techniques (Murray 1997;
Deecke et al. 1999) and the possible gradation of parametric continuums
provides one of the most productive ways to analyze critical parameters. It
has even been suggested that production of sound (with increased click rate
turning into whistles) is a continuum, behaviorally and structurally. These
lines of inquiry may allow eventual comparison between behavioral states,
age, and species.
7.6 Shared Cognition-Cross-species, Eavesdropping,
and Phantom Echoes
Signals evolve by virtue of their being detected, decoded, and responded to
differentially by conspecifics and, perhaps, neighbors. Signal evolution is
influenced by interspecific audiences and their discriminative abilities, especially in sympatric species (Smuts et al. 1987; Herzing and Johnson 1997).
Shared cognitive environments take on a type of relevance for sharing
communication and negotiating. Mutual cognitive environments between
species are likely to produce pressures for interspecific communication
skills and signals. The acquisition and coopting of signals and of detection
abilities is critical in understanding the evolution of communication signals
and hearing. Sentinel species give alarm calls either to warn mixed species
aggregations of approaching predators (Munn 1986), or to effectively
deceive or divert a competitor from a desired goal, thereby involving the
coordination of different cognitive environments. Evolutionarily there
should be a high value on the interpreter needing to correctly identify
relevant cues from both conspecifics and allospecifics, and stereotypy and
redundancy are both ways to reduce demands on such cognitive challenges.
Concomitant aspects of hearing involve eavesdropping and interpretation of minimal information. Signal deciphering through eavesdropping
from conspecifics would suggest that much information is available, conspecifically, from listening and overhearing partial signals (Xitco and Roitblatt 1996). Combined with specific signature features of ensonified objects
or with phantom echoes (Au and Moore 1988), this may allow complex
discrimination of conspecific signals.