This second clip documents some extraordinary behaviour of Killer Whales in Canada. From time to time, in Johnstone Strait during the summer salmon season, Killer Whales come to an area of uniformly smooth pebbles near a beach and rub their flanks along the bottom. We filmed them underwater doing this using remotely operated cameras and recorded their calls. They expel air to reduce their buoyancy and make all sorts of strange sounds and squeaks imitating vocalisations from different dialects used by other pods. Scientists who've studied their social systems for years, like John Ford, believe it's a part of the cultural tradition of these particular groups of Killers Whales. It's amazing behaviour from one of the most fascinating animals we've ever filmed. A coproduction between the Australian Broadcasting Corporation, National Geographic and TBS Productions.