1. Overview
25
associated with widely separated populations that do not normally mix.
Dialect is best reserved for sound emission differences on a local scale
among neighboring populations that can potentially intermix (Grimes
1974). Geographic variations are generally considered to result from
acoustic adaptations to different environments, or a functionless by-product
of isolation and genetic divergence caused by isolation (Ford 1991). The
functional significance of dialects is controversial, with some maintaining
that dialects are epiphenomena of song learning and social adaptation,
whereas others believe that they playa role in assorted mating and are of
evolutionary significance (Ford 1991). Dialects are known to occur in many
species of birds (Nottebohm 1969) but appear to be very rare in mammals.
4.4.4.1 Killer Whale
The dialects of resident killer whales (0. orca) in the coastal waters of
British Columbia and Washington State have been studied over a prolonged
period by Ford and his colleagues (Ford and Fisher 1983; Ford 1984,1991).
They used photographic identification techniques, keying on unique natural
markings on the whales to identify 16 pods or stable kin groups of 232
resident killer whales. Differences in acoustic behavior formed a system
of related pod-specific dialects within the call tradition of each clan. Ford
(1991) has proposed that each clan is comprised of related pods that have
descended from a common ancestral group and pod-specific repertoires
probably serve to enhance the efficiency of acoustic communications within
the group and act as behavioral indicators of pod affiliation.
Killer whale calls are typically made up of rapidly emitted pulses, which
to the human ear have a tonal quality (Ford 1991). Many calls have several
abrupt shifts in pulse repetition rate allowing them to be divided into different segments or parts. Although all pods belonging to a clan share a
number of calls, these calls were often rendered in consistently different
form by different pods. Also, certain pods produced calls that were not used
by the rest of the clan. Such variations produced a set of related groupspecific dialects within the call tradition of each clan. Spectrograms of call
types N7 and N8 are shown in Fig. 1.11. In this example, we can see that
different pods produce similar but different versions of call type N7 and
N8. Pods AI, A4, and A5 produced two versions of call type N7 and pods
Band 11 produced two versions of call type N8. All of the spectrograms
have two parts except for call type N7ii, which had three parts.
Ford (1991) contended that pod-specific repertoires can be retained for
periods in excess of 25 years. Discrete calls generally serve as signals for
maintaining contact within the pod and the use of repertoire of podspecific calls enhances this function by conveying group identity and affiliation (Ford 1991). Killer whales, like most other small dolphins, are able to
learn and mimic a wide variety of sounds. Even from a young age, killer
whale infants can selectively learn specific calls, especially the calls of their
mothers. Bowles et al. (1988) studied the development of calls of a captive-
25
associated with widely separated populations that do not normally mix.
Dialect is best reserved for sound emission differences on a local scale
among neighboring populations that can potentially intermix (Grimes
1974). Geographic variations are generally considered to result from
acoustic adaptations to different environments, or a functionless by-product
of isolation and genetic divergence caused by isolation (Ford 1991). The
functional significance of dialects is controversial, with some maintaining
that dialects are epiphenomena of song learning and social adaptation,
whereas others believe that they playa role in assorted mating and are of
evolutionary significance (Ford 1991). Dialects are known to occur in many
species of birds (Nottebohm 1969) but appear to be very rare in mammals.
4.4.4.1 Killer Whale
The dialects of resident killer whales (0. orca) in the coastal waters of
British Columbia and Washington State have been studied over a prolonged
period by Ford and his colleagues (Ford and Fisher 1983; Ford 1984,1991).
They used photographic identification techniques, keying on unique natural
markings on the whales to identify 16 pods or stable kin groups of 232
resident killer whales. Differences in acoustic behavior formed a system
of related pod-specific dialects within the call tradition of each clan. Ford
(1991) has proposed that each clan is comprised of related pods that have
descended from a common ancestral group and pod-specific repertoires
probably serve to enhance the efficiency of acoustic communications within
the group and act as behavioral indicators of pod affiliation.
Killer whale calls are typically made up of rapidly emitted pulses, which
to the human ear have a tonal quality (Ford 1991). Many calls have several
abrupt shifts in pulse repetition rate allowing them to be divided into different segments or parts. Although all pods belonging to a clan share a
number of calls, these calls were often rendered in consistently different
form by different pods. Also, certain pods produced calls that were not used
by the rest of the clan. Such variations produced a set of related groupspecific dialects within the call tradition of each clan. Spectrograms of call
types N7 and N8 are shown in Fig. 1.11. In this example, we can see that
different pods produce similar but different versions of call type N7 and
N8. Pods AI, A4, and A5 produced two versions of call type N7 and pods
Band 11 produced two versions of call type N8. All of the spectrograms
have two parts except for call type N7ii, which had three parts.
Ford (1991) contended that pod-specific repertoires can be retained for
periods in excess of 25 years. Discrete calls generally serve as signals for
maintaining contact within the pod and the use of repertoire of podspecific calls enhances this function by conveying group identity and affiliation (Ford 1991). Killer whales, like most other small dolphins, are able to
learn and mimic a wide variety of sounds. Even from a young age, killer
whale infants can selectively learn specific calls, especially the calls of their
mothers. Bowles et al. (1988) studied the development of calls of a captive-