data on gene flow required to test these alternative mechanisms are lacking,
although the work on cetaceans, particularly humpback whales, has made
great strides in this direction (Baker et al. 1990, 1993, 1998; Palumbi and
Baker 1994; Larsen et al. 1996; Valsecchi et al. 1997).
Comparisons of geographic variation in genetic similarity and dialect
boundaries can illuminate the extent to which dialects may result from
vocal learning. In species with sharp dialect boundaries, a lack of congruence between dialect boundaries and the extent of sharing in molecular
genetic markers (usually mtDNA haplotypes or microsatellite alleles) supports a strong role for vocal learning. Unfortunately, few study systems have
such data available. We present case studies where vocal learning has been
implicated and also briefly describe other birds (Table 4.1) and mammals
(Table 4.2) for which vocal learning of dialects has been studied. Because
population structure is important in testing alternative hypotheses, we
describe this evidence when available, along with evidence consistent with
vocal learning.
4.1. Birds
4.1.1. Parrots—Yellow-Naped Amazon Parrot Contact Call Dialects
Yellow-naped amazon parrots, Amazona auropalliata, are monogamous, yet
gregarious birds (Wright 1997). Pair bonds are long-lasting, and pairs jointly
defend nest sites against conspecifics. Pairs spend most of their days feeding
and socializing with other pairs and at night congregate with others at large
traditional roosts (Wright 1996) primarily for protection against predators.
Dispersal patterns of juveniles are unknown. The species is resident
throughout its range in semiarid woodland scrub and savannahs along the
Pacific coast from southern Mexico to northern Costa Rica, Honduras, and
several Bay Islands in the Caribbean (Juniper and Parr 1998).
Yellow-naped Amazons have a repertoire of calls that serve a variety of
social functions (Wright 1997). The most ubiquitous call is the contact
call, a multiharmonic, frequency-modulated call (Fig. 4.9). Both males and
females give this call often near their nesting site and at communal roosts
(Wright 1996). In other parrot species, contact calls function to maintain
proximity between members of a flock or mated pairs (Farabaugh and
Dooling 1996) and to recognize mates and other social companions, including siblings (Wanker et al. 1998). The function in A. auropalliata is not
known, but is suspected to be similar to that of these other psittacines. Pairs
also duet near nesting sites, and these duets are thought to function in territorial defense (Wright 1997).
Evidence for vocal learning in this species includes observational work
describing dialects in the contact call (Wright 1996) and other calls (Wright
1997), and genetic analyses (Wright and Wilkinson 2001). Disjunct acoustic
and geographic boundaries separate three dialect groups in Costa Rica: the
southern, northern, and Nicaraguan. Dialects are characterized by different
4. Comparative Vocal Learning
185
although the work on cetaceans, particularly humpback whales, has made
great strides in this direction (Baker et al. 1990, 1993, 1998; Palumbi and
Baker 1994; Larsen et al. 1996; Valsecchi et al. 1997).
Comparisons of geographic variation in genetic similarity and dialect
boundaries can illuminate the extent to which dialects may result from
vocal learning. In species with sharp dialect boundaries, a lack of congruence between dialect boundaries and the extent of sharing in molecular
genetic markers (usually mtDNA haplotypes or microsatellite alleles) supports a strong role for vocal learning. Unfortunately, few study systems have
such data available. We present case studies where vocal learning has been
implicated and also briefly describe other birds (Table 4.1) and mammals
(Table 4.2) for which vocal learning of dialects has been studied. Because
population structure is important in testing alternative hypotheses, we
describe this evidence when available, along with evidence consistent with
vocal learning.
4.1. Birds
4.1.1. Parrots—Yellow-Naped Amazon Parrot Contact Call Dialects
Yellow-naped amazon parrots, Amazona auropalliata, are monogamous, yet
gregarious birds (Wright 1997). Pair bonds are long-lasting, and pairs jointly
defend nest sites against conspecifics. Pairs spend most of their days feeding
and socializing with other pairs and at night congregate with others at large
traditional roosts (Wright 1996) primarily for protection against predators.
Dispersal patterns of juveniles are unknown. The species is resident
throughout its range in semiarid woodland scrub and savannahs along the
Pacific coast from southern Mexico to northern Costa Rica, Honduras, and
several Bay Islands in the Caribbean (Juniper and Parr 1998).
Yellow-naped Amazons have a repertoire of calls that serve a variety of
social functions (Wright 1997). The most ubiquitous call is the contact
call, a multiharmonic, frequency-modulated call (Fig. 4.9). Both males and
females give this call often near their nesting site and at communal roosts
(Wright 1996). In other parrot species, contact calls function to maintain
proximity between members of a flock or mated pairs (Farabaugh and
Dooling 1996) and to recognize mates and other social companions, including siblings (Wanker et al. 1998). The function in A. auropalliata is not
known, but is suspected to be similar to that of these other psittacines. Pairs
also duet near nesting sites, and these duets are thought to function in territorial defense (Wright 1997).
Evidence for vocal learning in this species includes observational work
describing dialects in the contact call (Wright 1996) and other calls (Wright
1997), and genetic analyses (Wright and Wilkinson 2001). Disjunct acoustic
and geographic boundaries separate three dialect groups in Costa Rica: the
southern, northern, and Nicaraguan. Dialects are characterized by different
4. Comparative Vocal Learning
185