Vocalizations of the three killer whale ecotypes, the fish-eating (resident) killer whale, the mammal-eating (transient) killer whale, and the offshore killer whale (genetically similar to resident type, but ecologically not well understood) are difficult to distinguish by the untrained ear. However, for the researcher studying killer whale vocalizations they are almost as distinct as photographic images of the whales. The vocalizations not only tell the researcher whether the calling killer whale is a resident, a transient or an offshore, but also reveal to which resident or transient population or sub-population the caller belongs. If the caller is a resident, it furthermore shows who his closest relatives are.
Both residents and transients use discrete calls, whistles, and clicks. Calls and whistles are used only in social communication, while clicks are predominantly used in echolocation. A clicking killer whale produces high-frequency sounds and uses the echoes of those sounds to form images of the areas around him or her. In much the same way that humans use sonar to investigate the seafloor, the ultra-structure of certain materials, or medical views of the inside of our bodies, whales use echolocation to orient and find food in an environment where lighting conditions are poor. Based on differences in usage of calls, whistles, and clicks, researchers can tell whether the whales are foraging, resting, or socializing.