174
P.L. Tyack and c.w. Clark
signature whistles have been documented in wild dolphins (Sayigh et al.
1990).
2.6.2 Advertisements
Among baleen whales, there is little evidence for bonds other than the
mother-infant bond on the breeding and calving grounds (Taber and
Thomas 1982; Thomas and Taber 1984). Baleen whales on the feeding
grounds may aggregate around patches of prey, but are seldom thought
to form stable social groups, although there is some evidence for preferential association between individuals humpbacks on the feeding grounds
(D'Vincent et al. 1985; Weinrich 1991; Baker et al. 1992). The setting where
we know the most about social functions of whale vocalizations involves
the calving and breeding grounds for coastal species such as the humpback
and right whales. For humpbacks, Megaptera novaeangliae, social interactions involving mate choice and male-male competition on the breeding
ground appear to be little influenced by stable grouping patterns, but rather
are mediated by complex male advertisement displays (Tyack 1981). These
interactions may be more influenced by acoustic properties of the display
than by associating the display with a particular individual or group (Tyack
1986). In right whales, Eubalena glacialis, social interactions involving
mate choice are often accompanied by vocal displays that are believed to
be produced by an estrous female (Kraus 1991).
Charles Darwin (1871) coined the term "sexual selection" to describe
the evolutionary pressures selecting for traits that increase mating success.
There are two ways sexual selection can work. It can increase the ability of
an animal to compete with a conspecific of the same sex for fertilization of
a member of the opposite sex (intrasexual selection) or it can increase the
likelihood that an animal will be chosen by a potential mate (intersexual
selection). In most animal species, it is the male sex that produces courtship
displays and the female sex that selects a male for mating. The basic
question for the evolution of displays by intersexual selection is: How and
why are females choosing particular features of the male display? In most
cetacean species, there is little evidence that males provide direct benefits
to a female, such as parental care or a resource-rich territory. Three factors
that may influence female choice in the absence of direct benefits are association between a feature of the display and the quality of the male, sensory
bias of the female, and positive feedback between a female preference and
a male display.
One commonly reported association between a display and indicators of
male quality concerns the association between the fundamental frequency
of a display and the size of the male. Body size is an important feature of
quality in males, and females of many species tend to select larger males as
mates (e.g., Schmale 1981 for bicolor damselfish). In some species, the
frequency of a male's display may correlate with body size. The basic
P.L. Tyack and c.w. Clark
signature whistles have been documented in wild dolphins (Sayigh et al.
1990).
2.6.2 Advertisements
Among baleen whales, there is little evidence for bonds other than the
mother-infant bond on the breeding and calving grounds (Taber and
Thomas 1982; Thomas and Taber 1984). Baleen whales on the feeding
grounds may aggregate around patches of prey, but are seldom thought
to form stable social groups, although there is some evidence for preferential association between individuals humpbacks on the feeding grounds
(D'Vincent et al. 1985; Weinrich 1991; Baker et al. 1992). The setting where
we know the most about social functions of whale vocalizations involves
the calving and breeding grounds for coastal species such as the humpback
and right whales. For humpbacks, Megaptera novaeangliae, social interactions involving mate choice and male-male competition on the breeding
ground appear to be little influenced by stable grouping patterns, but rather
are mediated by complex male advertisement displays (Tyack 1981). These
interactions may be more influenced by acoustic properties of the display
than by associating the display with a particular individual or group (Tyack
1986). In right whales, Eubalena glacialis, social interactions involving
mate choice are often accompanied by vocal displays that are believed to
be produced by an estrous female (Kraus 1991).
Charles Darwin (1871) coined the term "sexual selection" to describe
the evolutionary pressures selecting for traits that increase mating success.
There are two ways sexual selection can work. It can increase the ability of
an animal to compete with a conspecific of the same sex for fertilization of
a member of the opposite sex (intrasexual selection) or it can increase the
likelihood that an animal will be chosen by a potential mate (intersexual
selection). In most animal species, it is the male sex that produces courtship
displays and the female sex that selects a male for mating. The basic
question for the evolution of displays by intersexual selection is: How and
why are females choosing particular features of the male display? In most
cetacean species, there is little evidence that males provide direct benefits
to a female, such as parental care or a resource-rich territory. Three factors
that may influence female choice in the absence of direct benefits are association between a feature of the display and the quality of the male, sensory
bias of the female, and positive feedback between a female preference and
a male display.
One commonly reported association between a display and indicators of
male quality concerns the association between the fundamental frequency
of a display and the size of the male. Body size is an important feature of
quality in males, and females of many species tend to select larger males as
mates (e.g., Schmale 1981 for bicolor damselfish). In some species, the
frequency of a male's display may correlate with body size. The basic