gesting that these differences were perceived by the animals and contributed to call function.
Morphological and genetic data suggest that the subspecies of S. fuscicollis are independent and isolated from one another (Cheverud et al.
1993), and even populations of the same species are isolated by geographic
barriers (Peres et al. 1996). Combined with the data on call structure of
hybrids, this suggests that vocal differences between subspecies (Hodun et
al. 1981) are likely to be influenced heavily by genetic differences. It appears
that some call features are more strictly under genetic control than others.
This finding for S. fuscicollis raises the distinct possibility that dialects in
S. labiatus (Maeda and Masataka 1987) are also influenced by genetic differences among populations. Indeed, under an additive model of genetic
variation, intermediacy in acoustic structure is predicted and was found.
Further study comparing genetic and acoustic variation for populations
within species and between subspecies would help to reveal the extent of
genetic control and whether vocal learning is possible.
5. Conclusions
5.1. Comparing Patterns
Call learning in mammals and birds is less well-understood than song learning in birds; nonetheless, progress has been made. Patterns are beginning
to emerge in the preponderance of both forms of vocal learning—learned
acquisition and social modification—and we have gained insight into what
factors favor vocal learning. We discuss these patterns and insights here.
5.1.1. Patterns of Learned Acquisition Compared
Birds from all three families studied—oscines, psittacines, and trocholids—
acquire vocalizations through learning, but the evidence for mammals is
scant, inconclusive, and limited to cetaceans. Abnormal development of
vocalizations in acoustically isolated or deafened birds indicates that chickadees, budgerigars, and Anna’s hummingbirds acquire some aspects of calls
or song through learning. Other features are apparently innate and still
others socially modified. The B and C notes in chickadee calls, but not the
A note, require acoustic and social input to develop normally. Tonal features of budgerigar contact calls are acquired through learning, but bandwidth, maximum and minimum frequency, and duration appear to be innate.
Some features of budgerigar warble song require acoustic input for normal
development. Several frequency and temporal features of Anna hummingbird song are abnormal in isolated birds, although other frequency characteristics develop normally. All members of stripe-backed wren family
groups share a sex-specific repertoire. The occasional unrelated male shares
its group’s repertoire, implicating learned acquisition (Table 4.1). The one
4. Comparative Vocal Learning
197
Morphological and genetic data suggest that the subspecies of S. fuscicollis are independent and isolated from one another (Cheverud et al.
1993), and even populations of the same species are isolated by geographic
barriers (Peres et al. 1996). Combined with the data on call structure of
hybrids, this suggests that vocal differences between subspecies (Hodun et
al. 1981) are likely to be influenced heavily by genetic differences. It appears
that some call features are more strictly under genetic control than others.
This finding for S. fuscicollis raises the distinct possibility that dialects in
S. labiatus (Maeda and Masataka 1987) are also influenced by genetic differences among populations. Indeed, under an additive model of genetic
variation, intermediacy in acoustic structure is predicted and was found.
Further study comparing genetic and acoustic variation for populations
within species and between subspecies would help to reveal the extent of
genetic control and whether vocal learning is possible.
5. Conclusions
5.1. Comparing Patterns
Call learning in mammals and birds is less well-understood than song learning in birds; nonetheless, progress has been made. Patterns are beginning
to emerge in the preponderance of both forms of vocal learning—learned
acquisition and social modification—and we have gained insight into what
factors favor vocal learning. We discuss these patterns and insights here.
5.1.1. Patterns of Learned Acquisition Compared
Birds from all three families studied—oscines, psittacines, and trocholids—
acquire vocalizations through learning, but the evidence for mammals is
scant, inconclusive, and limited to cetaceans. Abnormal development of
vocalizations in acoustically isolated or deafened birds indicates that chickadees, budgerigars, and Anna’s hummingbirds acquire some aspects of calls
or song through learning. Other features are apparently innate and still
others socially modified. The B and C notes in chickadee calls, but not the
A note, require acoustic and social input to develop normally. Tonal features of budgerigar contact calls are acquired through learning, but bandwidth, maximum and minimum frequency, and duration appear to be innate.
Some features of budgerigar warble song require acoustic input for normal
development. Several frequency and temporal features of Anna hummingbird song are abnormal in isolated birds, although other frequency characteristics develop normally. All members of stripe-backed wren family
groups share a sex-specific repertoire. The occasional unrelated male shares
its group’s repertoire, implicating learned acquisition (Table 4.1). The one
4. Comparative Vocal Learning
197