call types (Fig. 4.9). Several birds at roosts near the border between the
southern and northern dialects are “bilingual”; that is, they produce some
calls similar to each dialect. In addition to dialect variation, birds from
roosts within a dialect differ in frequency and temporal characteristics of
their shared call type. The amount of differentiation correlates with geographic distance, at least within the southern dialect (Wright 1996). Wright
(1996) also reports slight differences among individuals within a roost.
Several other calls in the repertoire, including short contact calls, growls,
and pair duets, show dialect variation (Wright 1997). One call class, squeals
and gurgles, does not show a dialect pattern but is highly variable within
individuals. Pairs respond strongly to playback of roost mates’ pair duets
near their nest site but not to playback of calls from outside the dialect
region (Wright and Dorin 2001), indicating that parrots perceive these
dialect differences, that they are functionally relevant, and that local birds
are attended to and thus more likely to be copied.
Genetic analyses indicate substantial gene flow across dialect boundaries
(Wright and Wilkinson 2001). Thus, dialects are not a result of population
genetic structure. The parsimonious interpretation is that birds copy the
local dialect after dispersal, indicating strong social pressure to conform to
the local dialect.
4.1.2. Trochilids—Hummingbird Song Dialects
Several studies have been conducted on dialect variation in hummingbird
song using the little hermit, Phaethornis longuemareus (Snow 1968; Wiley
1971), Anna’s hummingbird, Calypte anna (Baptista and Schuchmann
1990), the sparkling violet-ear, Colibri coruscans, and the green violet-ear,
Colibri thalassinus (Gaunt et al. 1994). Unfortunately, no single species has
been studied intensively, and the hermits are not closely related to the other
hummingbirds (Bleiweiss 1998).
Hummingbirds are surprisingly long-lived birds for their size and metabolic rate, living 6–10 years in captivity (Skutch 1972). Most tropical species
are rather sedentary, although species that breed in North America migrate
to the tropics to overwinter. We know little of population structure in any
of these species where vocal learning has been studied. Males of many tropical genera, including Phaethornis and Colibri, congregate and sing at traditional sites in dispersed leks. Several North American species perform
complex aerial courtship displays and are less likely to lek, although Calypte
anna males do sing within hearing distance of one another.
Snow (1968) first discovered dialects of little hermits, P. longuemareus, in
Trinidad, and this discovery was further investigated by Wiley (1971). Males
sing songs that are very similar to those of their nearest neighbors, yet
several song groups occur on a single lek (Snow 1968; Wiley 1971). Within
an individual, songs vary in the number of introductory notes and the structure of the song’s terminal part (Wiley 1971). Spectral variation has not
4. Comparative Vocal Learning
187
southern and northern dialects are “bilingual”; that is, they produce some
calls similar to each dialect. In addition to dialect variation, birds from
roosts within a dialect differ in frequency and temporal characteristics of
their shared call type. The amount of differentiation correlates with geographic distance, at least within the southern dialect (Wright 1996). Wright
(1996) also reports slight differences among individuals within a roost.
Several other calls in the repertoire, including short contact calls, growls,
and pair duets, show dialect variation (Wright 1997). One call class, squeals
and gurgles, does not show a dialect pattern but is highly variable within
individuals. Pairs respond strongly to playback of roost mates’ pair duets
near their nest site but not to playback of calls from outside the dialect
region (Wright and Dorin 2001), indicating that parrots perceive these
dialect differences, that they are functionally relevant, and that local birds
are attended to and thus more likely to be copied.
Genetic analyses indicate substantial gene flow across dialect boundaries
(Wright and Wilkinson 2001). Thus, dialects are not a result of population
genetic structure. The parsimonious interpretation is that birds copy the
local dialect after dispersal, indicating strong social pressure to conform to
the local dialect.
4.1.2. Trochilids—Hummingbird Song Dialects
Several studies have been conducted on dialect variation in hummingbird
song using the little hermit, Phaethornis longuemareus (Snow 1968; Wiley
1971), Anna’s hummingbird, Calypte anna (Baptista and Schuchmann
1990), the sparkling violet-ear, Colibri coruscans, and the green violet-ear,
Colibri thalassinus (Gaunt et al. 1994). Unfortunately, no single species has
been studied intensively, and the hermits are not closely related to the other
hummingbirds (Bleiweiss 1998).
Hummingbirds are surprisingly long-lived birds for their size and metabolic rate, living 6–10 years in captivity (Skutch 1972). Most tropical species
are rather sedentary, although species that breed in North America migrate
to the tropics to overwinter. We know little of population structure in any
of these species where vocal learning has been studied. Males of many tropical genera, including Phaethornis and Colibri, congregate and sing at traditional sites in dispersed leks. Several North American species perform
complex aerial courtship displays and are less likely to lek, although Calypte
anna males do sing within hearing distance of one another.
Snow (1968) first discovered dialects of little hermits, P. longuemareus, in
Trinidad, and this discovery was further investigated by Wiley (1971). Males
sing songs that are very similar to those of their nearest neighbors, yet
several song groups occur on a single lek (Snow 1968; Wiley 1971). Within
an individual, songs vary in the number of introductory notes and the structure of the song’s terminal part (Wiley 1971). Spectral variation has not
4. Comparative Vocal Learning
187