These birds also gave contact calls that were more typical of their species.
Once abnormally reared birds were exposed to normal song at about 6
months of age, they developed more normal contact calls (Brittan-Powell
et al. 1997), indicating that substantial ability for vocal learning persisted to
this age. These data suggested that social interactions were very powerful
at sculpting young birds’ calls. Adults also learned the calls of the birds with
which they interacted (Farabaugh et al. 1994; Bartlett and Slater 1999) and
formed social bonds (Hile et al. 2000), providing further evidence that vocal
learning was not limited to a sensitive phase in this species. Farabaugh
et al. (1994) showed that adult birds whose contact calls were initially distinct converged on flock mates’ calls within two months’ time, with the first
changes occurring in a week (Fig. 4.5). Mutual imitation seemed to be the
mechanism because the final contact call was composed of call elements
from different birds. The importance of social interaction was demonstrated
because birds that could hear but not interact with each other did not share
contact calls. When a single bird joined a group, that individual altered its
call to match the group (Bartlett and Slater 1999). Call convergence occurs
between males and females forming pair bonds due to males imitating their
mates’ calls (Hile et al. 2000).
Vocal learning is not limited to contact calls. Birds reared in acoustic and
social isolation developed abnormal warble songs (Farabaugh et al. 1992a),
indicating that acquisition of song was learned. In addition, males within
social groups had similar warble songs, suggesting that social modification
occurred. In support of this hypothesis, one male apparently copied syllables from a cage mate that sang abnormal songs, even though he could hear
other birds whose song was typical for budgerigars (Farabaugh et al. 1992a).
Birds whose tutor gave abnormal or heterospecific vocalizations continued
to include some species-typical characteristics in their song and calls.
This result argues that some features of vocalizations rely on underlying
genetics. On top of this genetic basis is substantial vocal flexibility and social
dependency.
3.2. Mammals
3.2.1. Bats—Greater Spear-Nosed Bat Group Signatures
Female greater spear-nosed bats (Phyllostomus hastatus) live in stable
social groups that are attended by a single male who maintains nearly
exclusive reproductive access to all females in the group (McCracken and
Bradbury 1977). Consequently, in a given year, offspring of most females
in a group are paternal half-sibs (McCracken and Bradbury 1981).
However, adult females in these groups are not close relatives (McCracken
and Bradbury 1981), a pattern that results from juvenile dispersal patterns.
All offspring disperse from their natal group during their first year. When
reproductively mature, at about two years of age, females join an existing
female social group. Females obtain several benefits from group living.
174
J.W. Boughman and C.F. Moss
Once abnormally reared birds were exposed to normal song at about 6
months of age, they developed more normal contact calls (Brittan-Powell
et al. 1997), indicating that substantial ability for vocal learning persisted to
this age. These data suggested that social interactions were very powerful
at sculpting young birds’ calls. Adults also learned the calls of the birds with
which they interacted (Farabaugh et al. 1994; Bartlett and Slater 1999) and
formed social bonds (Hile et al. 2000), providing further evidence that vocal
learning was not limited to a sensitive phase in this species. Farabaugh
et al. (1994) showed that adult birds whose contact calls were initially distinct converged on flock mates’ calls within two months’ time, with the first
changes occurring in a week (Fig. 4.5). Mutual imitation seemed to be the
mechanism because the final contact call was composed of call elements
from different birds. The importance of social interaction was demonstrated
because birds that could hear but not interact with each other did not share
contact calls. When a single bird joined a group, that individual altered its
call to match the group (Bartlett and Slater 1999). Call convergence occurs
between males and females forming pair bonds due to males imitating their
mates’ calls (Hile et al. 2000).
Vocal learning is not limited to contact calls. Birds reared in acoustic and
social isolation developed abnormal warble songs (Farabaugh et al. 1992a),
indicating that acquisition of song was learned. In addition, males within
social groups had similar warble songs, suggesting that social modification
occurred. In support of this hypothesis, one male apparently copied syllables from a cage mate that sang abnormal songs, even though he could hear
other birds whose song was typical for budgerigars (Farabaugh et al. 1992a).
Birds whose tutor gave abnormal or heterospecific vocalizations continued
to include some species-typical characteristics in their song and calls.
This result argues that some features of vocalizations rely on underlying
genetics. On top of this genetic basis is substantial vocal flexibility and social
dependency.
3.2. Mammals
3.2.1. Bats—Greater Spear-Nosed Bat Group Signatures
Female greater spear-nosed bats (Phyllostomus hastatus) live in stable
social groups that are attended by a single male who maintains nearly
exclusive reproductive access to all females in the group (McCracken and
Bradbury 1977). Consequently, in a given year, offspring of most females
in a group are paternal half-sibs (McCracken and Bradbury 1981).
However, adult females in these groups are not close relatives (McCracken
and Bradbury 1981), a pattern that results from juvenile dispersal patterns.
All offspring disperse from their natal group during their first year. When
reproductively mature, at about two years of age, females join an existing
female social group. Females obtain several benefits from group living.
174
J.W. Boughman and C.F. Moss