juvenile males immigrate (Piper et al. 1995) and then learn their new
group’s call repertoire (Price 1998b). For the occasional immigrants to
be able to match the calls of a new social group, call repertoires cannot
be hardwired. Learning vocalizations allows both the incorporation of
unrelated individuals into groups (which is a way for pairs to increase group
size) and sex-specific transmission of calls.
1.1. Detecting Vocal Learning—What Constitutes
Good Evidence?
Vocal learning has a fairly clear function in the example above, yet what
exactly is vocal learning? Vocal learning refers to changes in vocalizations
influenced by social interaction. Here, we focus on vocalizations given by
species that live in social groups and organize our discussion around the
function these vocalizations serve.This functional focus rests on the premise
that vocal learning has evolved to facilitate the social function of some calls.
Learning is likely to occur for a specific subset of the vocalizations in a
species’ repertoire whose function is enhanced by the degree of acoustic
similarity to social partners who may or may not be related (e.g., members
of a social group, territorial neighbors, competitors, and kin). We discuss
the evidence for learning of calls that serve a variety of functions, including affiliative vocalizations, contact calls, food vocalizations, vocalizations
used in defending a group or individual territory, and vocalizations that
convey individual or group identity. We present evidence for several families of birds and mammals. The taxonomic distribution of various forms of
vocal learning supports the hypothesis that it has evolved independently in
several taxa. Our review is intended to help develop hypotheses about
the social and ecological factors that favor its evolution and to stimulate
additional research to test the hypotheses we present.
We distinguish two types of vocal learning: learned acquisition and
social modification. These may differ in the learning process involved, and
each type may be the outcome of different forms of selection and rely on
different neural mechanisms. However, both are true vocal learning.
Learned acquisition is the adding of new vocalizations to an individual’s
repertoire. Acquisition is frequently, but not always, age-dependent, and
changes are influenced by social interactions. Typically, juveniles require
auditory experience to produce adult-form vocalizations. Social interactions
are often essential and can be important in identifying who serves as
the tutor in this developmental process. Subtle forms of interaction can
reinforce the acquisition and retention of specific vocalizations during
development (e.g., West and King 1988). The production of abnormal vocalizations in acoustically or socially isolated individuals has long been considered strong evidence for vocal learning. In contrast, vocalizations
that are produced normally by deafened, or acoustically or socially isolated
individuals are good evidence against learned acquisition. They do not;
4. Comparative Vocal Learning
139
group’s call repertoire (Price 1998b). For the occasional immigrants to
be able to match the calls of a new social group, call repertoires cannot
be hardwired. Learning vocalizations allows both the incorporation of
unrelated individuals into groups (which is a way for pairs to increase group
size) and sex-specific transmission of calls.
1.1. Detecting Vocal Learning—What Constitutes
Good Evidence?
Vocal learning has a fairly clear function in the example above, yet what
exactly is vocal learning? Vocal learning refers to changes in vocalizations
influenced by social interaction. Here, we focus on vocalizations given by
species that live in social groups and organize our discussion around the
function these vocalizations serve.This functional focus rests on the premise
that vocal learning has evolved to facilitate the social function of some calls.
Learning is likely to occur for a specific subset of the vocalizations in a
species’ repertoire whose function is enhanced by the degree of acoustic
similarity to social partners who may or may not be related (e.g., members
of a social group, territorial neighbors, competitors, and kin). We discuss
the evidence for learning of calls that serve a variety of functions, including affiliative vocalizations, contact calls, food vocalizations, vocalizations
used in defending a group or individual territory, and vocalizations that
convey individual or group identity. We present evidence for several families of birds and mammals. The taxonomic distribution of various forms of
vocal learning supports the hypothesis that it has evolved independently in
several taxa. Our review is intended to help develop hypotheses about
the social and ecological factors that favor its evolution and to stimulate
additional research to test the hypotheses we present.
We distinguish two types of vocal learning: learned acquisition and
social modification. These may differ in the learning process involved, and
each type may be the outcome of different forms of selection and rely on
different neural mechanisms. However, both are true vocal learning.
Learned acquisition is the adding of new vocalizations to an individual’s
repertoire. Acquisition is frequently, but not always, age-dependent, and
changes are influenced by social interactions. Typically, juveniles require
auditory experience to produce adult-form vocalizations. Social interactions
are often essential and can be important in identifying who serves as
the tutor in this developmental process. Subtle forms of interaction can
reinforce the acquisition and retention of specific vocalizations during
development (e.g., West and King 1988). The production of abnormal vocalizations in acoustically or socially isolated individuals has long been considered strong evidence for vocal learning. In contrast, vocalizations
that are produced normally by deafened, or acoustically or socially isolated
individuals are good evidence against learned acquisition. They do not;
4. Comparative Vocal Learning
139