Call diversity in the North Pacific killer whale populations: implications for dialect evolution and population history

► We investigated variation in calls among four North Pacific killer whale populations. ► Diversity was higher in monophonic than in biphonic calls for all populations. ► Monophonic calls were more diverse and biphonic less diverse in larger populations. ► There was no correlation between call repertoire similarity and geographical distance. ► Call evolution is caused by interaction between stochastic processes and selection.