convergence between mothers and offspring or among adult group mates
results from subtle acoustic changes to a single call type (e.g., sonar signal,
isolation call, or contact call). This convergence may arise through mutual
imitation of acoustic characteristics or selective attrition from a more variable acoustic space. In dolphins, several studies have inferred mimicry in
both juveniles and adults, suggesting open-ended learned acquisition. This
is certainly possible, yet the size and turnover of juvenile repertoires suggest
that individuals may choose matching whistles from a large repertoire.
Experimental tests of these two mechanisms are lacking and would be
fruitful.
5.2.5.3. The Importance of Social Interaction for Mammals
Experimental evidence of the relative importance of social interaction is
also lacking. Much of the data on vocal learning in mammals are observations and experiments showing convergence among social partners. The
apparent advantage of vocal learning is to modify the degree of acoustic
similarity to enhance social function. All of this points to an important role
for social factors. Individuals who serve as models for imitation are those
who are the focus of other social interactions.
Recent research is just beginning to outline patterns for the importance
of sensorimotor input, call matching, and social interaction in mammalian
call learning. As yet, we have little data on the actual processes that underlie these patterns and cannot yet evaluate how closely call learning in
mammals matches song learning in birds. Research is likely to progress most
rapidly with small-bodied mammals, such as bats, because of the greater
ease with which they can be housed. We hope that methods will be developed to study processes in cetaceans as well. Interest in comparing the
process of call learning in both birds and mammals to song learning is high
and should lead to further work on the underlying processes. This area
promises rich rewards.
5.3. Future Directions
5.3.1. Studying Vocal Learning in a Phylogenetic Context
We are close to the point where we can consider comparative tests for
hypotheses about the mechanisms, function, and evolution of vocal learning in a phylogenetic framework. Many fundamental questions regarding
vocal learning would be possible within this framework, such as: How often
has vocal learning evolved? Do learned acquisition and social modification
represent distinct processes, or are they different outcomes of the same
process? A comparative approach opens up the possibility to test specific
hypotheses about the motor, sensory, and physiological underpinnings of
learned vocalizations. Which mechanisms, if any, are common to the taxa
4. Comparative Vocal Learning
207
results from subtle acoustic changes to a single call type (e.g., sonar signal,
isolation call, or contact call). This convergence may arise through mutual
imitation of acoustic characteristics or selective attrition from a more variable acoustic space. In dolphins, several studies have inferred mimicry in
both juveniles and adults, suggesting open-ended learned acquisition. This
is certainly possible, yet the size and turnover of juvenile repertoires suggest
that individuals may choose matching whistles from a large repertoire.
Experimental tests of these two mechanisms are lacking and would be
fruitful.
5.2.5.3. The Importance of Social Interaction for Mammals
Experimental evidence of the relative importance of social interaction is
also lacking. Much of the data on vocal learning in mammals are observations and experiments showing convergence among social partners. The
apparent advantage of vocal learning is to modify the degree of acoustic
similarity to enhance social function. All of this points to an important role
for social factors. Individuals who serve as models for imitation are those
who are the focus of other social interactions.
Recent research is just beginning to outline patterns for the importance
of sensorimotor input, call matching, and social interaction in mammalian
call learning. As yet, we have little data on the actual processes that underlie these patterns and cannot yet evaluate how closely call learning in
mammals matches song learning in birds. Research is likely to progress most
rapidly with small-bodied mammals, such as bats, because of the greater
ease with which they can be housed. We hope that methods will be developed to study processes in cetaceans as well. Interest in comparing the
process of call learning in both birds and mammals to song learning is high
and should lead to further work on the underlying processes. This area
promises rich rewards.
5.3. Future Directions
5.3.1. Studying Vocal Learning in a Phylogenetic Context
We are close to the point where we can consider comparative tests for
hypotheses about the mechanisms, function, and evolution of vocal learning in a phylogenetic framework. Many fundamental questions regarding
vocal learning would be possible within this framework, such as: How often
has vocal learning evolved? Do learned acquisition and social modification
represent distinct processes, or are they different outcomes of the same
process? A comparative approach opens up the possibility to test specific
hypotheses about the motor, sensory, and physiological underpinnings of
learned vocalizations. Which mechanisms, if any, are common to the taxa
4. Comparative Vocal Learning
207