Fourth International Orca Symposium and Workshop - CEBC - CNRS

within the lineage. The actual process of dialect change is poorly known. Recent studies
have described fine changes in the structure of call types shared by two matrilines of northern
residents in British Columbia. Each matriline had parallel changes, as if one matriline had
copied changes from the other. This apparent synchrony of calling behaviour over time has
implications of defining a “cultural clock”, or the rate of dialect change within clans. Dialect
change may also occur in a punctuated manner, corresponding to sudden social or
demographic changes within a lineage.
Whistles in resident killer whales are strongly associated with socializing contexts, as
are variable pulsed calls. These sounds appear to be used as close-range communication
signals, often occurring together with physical interactions and visual displays. Whistles may
also occur repetitively with levels of stereotypy approaching those of discrete calls.
Mammal-hunting transient killer whales from Southeastern Alaska, British Columbia
and California share a related call repertoire. The lack of kin-group-specific dialects in
transients is no doubt related to their social system, which is more fluid and dynamic than that
of resident killer whales. Nonetheless, there appear to be some regional variations in call
repertoires within the west coast transient community.
Studies of killer whales in regions other than the Northeastern Pacific have revealed
similar patterns of acoustic behaviour, with signals being dominated by repetitive, stereotyped
pulsed calls. Regions where discrete call types have been identified include Norway, Iceland,
the Kamchatkan area of eastern Russia, Argentina, and Antarctica.
Structure and Function of Echolocation Signals
Echolocation has been relatively little studied in killer whales compared to the social
signals of the species. Early captive studies demonstrated that, as with most odontocetes,
killer whales are able to orient in their environment and detect objects through the use of
series (or ‘trains’) of echolocation clicks. Field studies in British Columbia and Alaska have
described major differences in the echolocation behaviour of resident and transient killer
whales, apparently associated with the different hunting specializations of theses two
ecotypes. Fish-feeding residents frequently emit echolocation click trains while foraging, but
transients do not. Instead, transients forage either in silence, or sporadically produce isolated
clicks. Suppressed echolocation activity in transients appears to be a tactic for hunting
mammalian prey, which have excellent hearing abilities and would be alerted to the predators’
approach if they detected echolocations signals.
Recent field studies have focused on describing echolocation signal structure in killer
whales through the use of wide-band recording systems and arrays of hydrophones. Such
studies in Norway and British Columbia have found that killer whale clicks are similar to
those of other delphinids, though they tend to have lower frequency emphases than do the
clicks of smaller dolphins. Further research is needed to describe the function of killer whale
echolocation in better detail.
Acoustics as a Tool
Underwater acoustics not only provides a means of interpreting killer whale behaviour
and social structure, it can also be used as a tool for other purposes. Fixed shore-based
hydrophone installations at strategic coastal sites can provide a means of remotely monitoring
FOURTH INTERNATIONAL ORCA SYMPOSIUM AND WORKSHOPS
SEPTEMBER 23-28 2002, CEBC-CNRS, France
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