4. Comparative Vocal Learning
191
1997). Even so, the effective migration rate between ocean basins is estimated to be between 0.5 (Baker et al. 1993) and 10 (Palumbi and Baker
1994) whales per generation.
Each ocean basin contains several populations, and movement of individuals is primarily within ocean basins (Fig. 4.11). In the North Pacific
Ocean, one population migrates between Alaska and Hawaii, a second
between California and Mexico, and a third winters near Japan and has
unknown feeding grounds. Infrequent movement of individuals between
these populations occurs (Perry et al. 1990; Calambokidis et al. 1996).
Isolation of California–Mexico and Alaska–Hawaii populations is indicated
by differences in mtDNA haplotypes (Palumbi and Baker 1994) and
nuclear DNA allele frequencies (Baker et al. 1998). However, occasional
interbreeding between California and Hawaii whales must have occurred
because they share some nuclear DNA alleles (Palumbi and Baker 1994).
MtDNA data suggest that other California whales breed with humpbacks
that feed in the South Pacific (Baker et al. 1990; Stone et al. 1990; MedranoGonzalez et al. 1995).
North Atlantic humpbacks may also segregate into several subpopulations (Fig. 4.11), one migrating between the West Indies and the Western
North Atlantic, the other between the Cape Verde Islands and the Eastern
North Atlantic (Mattila et al. 1989, 1994; Katona and Beard 1990; Palsboll
et al. 1995; Larsen et al. 1996). MtDNA variation indicates that these
populations form two distinct matrilineal aggregations (Palsboll et al. 1995;
Larsen et al. 1996). However, some gene flow occurs because no differences
were found in allele frequencies at six microsatellite loci (Larsen et al.
1996).
Genetic data support the hypothesis that males move more often
between populations than females (Palumbi and Baker 1994; Baker et al.
1998). However, one study found that males were more likely to be
resighted on the breeding grounds than females (Craig and Herman 1997),
so whether migration is sex-biased remains unclear.
Male humpback whales sing long, complex, stereotyped songs (Payne and
McVay 1971). Humpback song consists of repetitive elements ranging in
frequency from 30 to 4,000 Hz combined into “themes.” Themes are combinations of elements given in set patterns. A number of themes are combined in apparently fixed order to produce a single song (Payne and McVay
1971). Variation occurs in the number of repetitions of elements in a theme,
the presence of themes in a song, and song duration, but not in the order
of themes (Payne and McVay 1971; Payne and Payne 1985). Males sing
primarily on the breeding ground, and other adult males move away from
singing whales (Tyack 1981) and from song playback (Tyack 1983), suggesting that song serves to space individuals.
There are two lines of observational evidence for social modification and
perhaps learned acquisition of humpback songs: shared temporal changes
and dialects. Themes are shared by most of the males in a population during
191
1997). Even so, the effective migration rate between ocean basins is estimated to be between 0.5 (Baker et al. 1993) and 10 (Palumbi and Baker
1994) whales per generation.
Each ocean basin contains several populations, and movement of individuals is primarily within ocean basins (Fig. 4.11). In the North Pacific
Ocean, one population migrates between Alaska and Hawaii, a second
between California and Mexico, and a third winters near Japan and has
unknown feeding grounds. Infrequent movement of individuals between
these populations occurs (Perry et al. 1990; Calambokidis et al. 1996).
Isolation of California–Mexico and Alaska–Hawaii populations is indicated
by differences in mtDNA haplotypes (Palumbi and Baker 1994) and
nuclear DNA allele frequencies (Baker et al. 1998). However, occasional
interbreeding between California and Hawaii whales must have occurred
because they share some nuclear DNA alleles (Palumbi and Baker 1994).
MtDNA data suggest that other California whales breed with humpbacks
that feed in the South Pacific (Baker et al. 1990; Stone et al. 1990; MedranoGonzalez et al. 1995).
North Atlantic humpbacks may also segregate into several subpopulations (Fig. 4.11), one migrating between the West Indies and the Western
North Atlantic, the other between the Cape Verde Islands and the Eastern
North Atlantic (Mattila et al. 1989, 1994; Katona and Beard 1990; Palsboll
et al. 1995; Larsen et al. 1996). MtDNA variation indicates that these
populations form two distinct matrilineal aggregations (Palsboll et al. 1995;
Larsen et al. 1996). However, some gene flow occurs because no differences
were found in allele frequencies at six microsatellite loci (Larsen et al.
1996).
Genetic data support the hypothesis that males move more often
between populations than females (Palumbi and Baker 1994; Baker et al.
1998). However, one study found that males were more likely to be
resighted on the breeding grounds than females (Craig and Herman 1997),
so whether migration is sex-biased remains unclear.
Male humpback whales sing long, complex, stereotyped songs (Payne and
McVay 1971). Humpback song consists of repetitive elements ranging in
frequency from 30 to 4,000 Hz combined into “themes.” Themes are combinations of elements given in set patterns. A number of themes are combined in apparently fixed order to produce a single song (Payne and McVay
1971). Variation occurs in the number of repetitions of elements in a theme,
the presence of themes in a song, and song duration, but not in the order
of themes (Payne and McVay 1971; Payne and Payne 1985). Males sing
primarily on the breeding ground, and other adult males move away from
singing whales (Tyack 1981) and from song playback (Tyack 1983), suggesting that song serves to space individuals.
There are two lines of observational evidence for social modification and
perhaps learned acquisition of humpback songs: shared temporal changes
and dialects. Themes are shared by most of the males in a population during