D note. Social experience appears to be a powerful determinant of call
development because birds who were socially but not acoustically isolated
produced B and C notes that were at least as aberrant as those of totally
isolated birds.
Social modification also occurs and produces convergence within flocks
(Fig. 4.4B; Nowicki 1989). Birds who had no prior contact with one another
gave calls that initially differed in several parameters of the D note (week
0). Calls converged rapidly. This is shown by the reduction in variation and
increased similarity in means by week 1. No single bird appeared to serve
as the model; instead, calls converged on the mean spectral characteristics
of the flock. Convergence was observed in several frequency measures,
including the bandwidth, maximum frequency, and difference between the
minimum frequencies produced by each side of the syrinx. No convergence
was observed in temporal measures or proportions of note types in calls.
Calls began changing within a week, and by four weeks substantial convergence occurred. Both juveniles and adults changed calls, indicating that
social modification is not limited to a sensitive phase in this species. Both
types of vocal learning occur in P. atricapillus calls. This oscine species is a
good counterpoint to studies of song learning in other oscines because it
challenges some of our notions about the distinction between song and calls,
and the importance of vocal learning to these two kinds of vocal signals.
3.1.2. Parrots—Budgerigar Flock Signatures
Budgerigars (Melopsittacus undulatus) are a highly social, nomadic parrot
from inland Australia. Budgerigars live in flocks of 20–30 birds that associate seasonally with other flocks in very large assemblages. Both sexes
provide parental care, and mated pairs may remain together over several
breeding attempts. The arid environment has highly variable productivity
both spatially and temporally, and budgerigars are opportunistic feeders
that will move great distances to find productive areas. Flock living is
thought to provide several benefits in food finding and predator protection
(Farabaugh and Dooling 1996). Budgerigars are opportunistic breeders
as well, initiating breeding when ecological conditions are favorable
(Brockway 1964; Wyndham 1980a). Little is known of the composition of
budgerigar flocks in regards to relatedness or stability. However, much is
known of their vocal behavior.
Budgerigars give several types of calls, and complex, variably structured
song. Most work on vocal learning has examined the most frequently used
call, the contact call (Fig. 4.5), but all calls and song are thought to be learned.
Contact calls seem to function to maintain social cohesion.Adults give them
in flight and when separated from mates or other individuals in the flock
(Wyndham 1980a). Contact calls also facilitate reunions between parents
and their fledged offspring. Once fledged, offspring live in a creche. Parents
visit the creche to feed their fledglings until they reach full independence
4. Comparative Vocal Learning
171
development because birds who were socially but not acoustically isolated
produced B and C notes that were at least as aberrant as those of totally
isolated birds.
Social modification also occurs and produces convergence within flocks
(Fig. 4.4B; Nowicki 1989). Birds who had no prior contact with one another
gave calls that initially differed in several parameters of the D note (week
0). Calls converged rapidly. This is shown by the reduction in variation and
increased similarity in means by week 1. No single bird appeared to serve
as the model; instead, calls converged on the mean spectral characteristics
of the flock. Convergence was observed in several frequency measures,
including the bandwidth, maximum frequency, and difference between the
minimum frequencies produced by each side of the syrinx. No convergence
was observed in temporal measures or proportions of note types in calls.
Calls began changing within a week, and by four weeks substantial convergence occurred. Both juveniles and adults changed calls, indicating that
social modification is not limited to a sensitive phase in this species. Both
types of vocal learning occur in P. atricapillus calls. This oscine species is a
good counterpoint to studies of song learning in other oscines because it
challenges some of our notions about the distinction between song and calls,
and the importance of vocal learning to these two kinds of vocal signals.
3.1.2. Parrots—Budgerigar Flock Signatures
Budgerigars (Melopsittacus undulatus) are a highly social, nomadic parrot
from inland Australia. Budgerigars live in flocks of 20–30 birds that associate seasonally with other flocks in very large assemblages. Both sexes
provide parental care, and mated pairs may remain together over several
breeding attempts. The arid environment has highly variable productivity
both spatially and temporally, and budgerigars are opportunistic feeders
that will move great distances to find productive areas. Flock living is
thought to provide several benefits in food finding and predator protection
(Farabaugh and Dooling 1996). Budgerigars are opportunistic breeders
as well, initiating breeding when ecological conditions are favorable
(Brockway 1964; Wyndham 1980a). Little is known of the composition of
budgerigar flocks in regards to relatedness or stability. However, much is
known of their vocal behavior.
Budgerigars give several types of calls, and complex, variably structured
song. Most work on vocal learning has examined the most frequently used
call, the contact call (Fig. 4.5), but all calls and song are thought to be learned.
Contact calls seem to function to maintain social cohesion.Adults give them
in flight and when separated from mates or other individuals in the flock
(Wyndham 1980a). Contact calls also facilitate reunions between parents
and their fledged offspring. Once fledged, offspring live in a creche. Parents
visit the creche to feed their fledglings until they reach full independence
4. Comparative Vocal Learning
171