Every pod has some unique sounds. Ford says that because the sounds of each pod are probably learned from the mother, the number of shared sounds between pods likely reveals how closely related the pods are. Ford came to the conclusion that pods with dialects 90 percent the same probably had a recent common ancestor. Pods with only 25 to 50 percent similarity are more distantly related. Dialects used by animals living in the same region are unique to orcas.
Humans are the only other species with true dialects.