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Abstract

In killer whales or orcas (Orcinus orca) vocal matching appears to be an important aspect of within-group communication, but fish-eating “resident” orcas frequently associate with whales that share little or none of their repertoire. The production of calls belonging to another group's repertoire would allow vocal matching in such contexts and has been observed in captive and free-living orcas. However, reports were largely descriptive and neither structure nor usage of such “resemblance calls” have been investigated in detail. We analyzed resemblance calls in free-living orcas when groups known to produce the respective call types were absent. In this context, they made up only 0.2% of the recorded calls. Time and frequency parameters of resemblance calls differed significantly from the “original” calls, and the accuracy of the resemblance calls ranged from rough renditions of a call type to the resemblance of call subtypes. Our results show that call sharing across vocal clans occurs in orcas but is rare and that shared calls are structurally distinguishable from original call types in the absence of the groups originally producing the calls. We discuss whether this call sharing represents cases of vocal imitation as suggested by previous, qualitative reports.