exposure only to each other’s song shared many song characteristics, including the structure of individual syllables and temporal pattern of song.
The group isolates’ songs differed from those of wild males in cadence and
minimum frequency. One group isolate was initially raised in the nest and
may have heard an adult male singing, so this group’s experience differed
in two ways from the single isolate, confounding tests of the relative importance of social and acoustic isolation. Both single and group isolates
used a chitter that was not heard in the songs of wild males. Baptista and
Schuchmann (1990) noted that the single isolate’s song resembled the island
songs of Mirsky’s study and suggested that the initial founder of the island
population may have been a young bird who had not completed song learning. Their study, although small, suggested that both learned acquisition and
social modification might be involved and mirrors the patterns described in
observational studies, lending credence to the vocal learning interpretation.
Additional experimental tests are necessary before firm conclusions can be
drawn.
4.2. Mammals
4.2.1. Cetaceans—Humpback Song
Humpback whales (Megaptera novaeangliae) migrate from summer feeding
grounds in northern latitudes of the Pacific and Atlantic oceans to equatorial breeding grounds in each ocean basin. They are also found in the southern hemisphere, where they feed off Antarctica and winter in the South
Pacific near Australia, New Zealand, and Tonga. Although highly social,
they have few long-term associations except for mother–calf pairs. On the
breeding grounds, mature females and their calves are often accompanied
by an escort. Escorts are likely to be males, and these escorts compete for
access to mature females (Tyack and Whitehead 1983), but females show
no fidelity to individual males (Clapham and Palsboll 1997). In some cases,
individuals feeding on locally abundant schooling fish will associate repeatedly (Perry et al. 1990), and a few recurring associations among adults
are known (Weinrich 1991), but large, loosely structured aggregations are
common when humpbacks feed on krill, and individuals often feed and
travel alone.
Information on population structure greatly facilitates evaluation of
the potential influence of cultural transmission and genetic factors on song
sharing. Even though few physical barriers exist, both resighting and genetic
data indicate that humpback populations are structured. Numerous genetic
analyses provide detailed information on population structure, an enviable
position compared with the dearth of genetic data for other species in which
dialects have been described. Analyses of both mitochondrial (mtDNA)
and nuclear DNA (microsatellite and intron sequence) variation indicate
that ocean basins are largely isolated from one another (Valsecchi et al.
190
J.W. Boughman and C.F. Moss
The group isolates’ songs differed from those of wild males in cadence and
minimum frequency. One group isolate was initially raised in the nest and
may have heard an adult male singing, so this group’s experience differed
in two ways from the single isolate, confounding tests of the relative importance of social and acoustic isolation. Both single and group isolates
used a chitter that was not heard in the songs of wild males. Baptista and
Schuchmann (1990) noted that the single isolate’s song resembled the island
songs of Mirsky’s study and suggested that the initial founder of the island
population may have been a young bird who had not completed song learning. Their study, although small, suggested that both learned acquisition and
social modification might be involved and mirrors the patterns described in
observational studies, lending credence to the vocal learning interpretation.
Additional experimental tests are necessary before firm conclusions can be
drawn.
4.2. Mammals
4.2.1. Cetaceans—Humpback Song
Humpback whales (Megaptera novaeangliae) migrate from summer feeding
grounds in northern latitudes of the Pacific and Atlantic oceans to equatorial breeding grounds in each ocean basin. They are also found in the southern hemisphere, where they feed off Antarctica and winter in the South
Pacific near Australia, New Zealand, and Tonga. Although highly social,
they have few long-term associations except for mother–calf pairs. On the
breeding grounds, mature females and their calves are often accompanied
by an escort. Escorts are likely to be males, and these escorts compete for
access to mature females (Tyack and Whitehead 1983), but females show
no fidelity to individual males (Clapham and Palsboll 1997). In some cases,
individuals feeding on locally abundant schooling fish will associate repeatedly (Perry et al. 1990), and a few recurring associations among adults
are known (Weinrich 1991), but large, loosely structured aggregations are
common when humpbacks feed on krill, and individuals often feed and
travel alone.
Information on population structure greatly facilitates evaluation of
the potential influence of cultural transmission and genetic factors on song
sharing. Even though few physical barriers exist, both resighting and genetic
data indicate that humpback populations are structured. Numerous genetic
analyses provide detailed information on population structure, an enviable
position compared with the dearth of genetic data for other species in which
dialects have been described. Analyses of both mitochondrial (mtDNA)
and nuclear DNA (microsatellite and intron sequence) variation indicate
that ocean basins are largely isolated from one another (Valsecchi et al.
190
J.W. Boughman and C.F. Moss