Orcas possess sophisticated underwater sonar that enables them to perceive their surroundings ten times more effectively than our most advanced equipment. Initially, the Orca's nasal passages produce a stream of several hundred high frequency sounds lasting just milliseconds. Objects partially reflect this energy back to the whale as echoes, which it receives in its lower jaw and translates into information about the object's distance, speed, shape, texture and composition. Orcas are even able to 'zoom in' on objects by varying the sonar pitch, speed and duration and then use this information to locate and chase prey.
Echolocation is so sophisticated that transients will often hunt silently using 'passive sonar'. They remain silent to stay undetected by their prey, but translate energy waves bounced at them from other sources.
Orcas also produce other vocal signals which sound like bursts of shrill whistles, squeaks and high pitched screams. These calls distinguish the whale's identity, activity and location and help them stay in contact even when separated by miles of ocean. Orca calls are not made in sequence as in human language, but are 'contagious', that is, they are repeated back to the sender before responding.
Certain calls are given more frequently in association with certain activities. Generally, as an orca's activity level increases, so does its vocalization. An increase in pitch and duration of calls is also linked to an increase in the whale's excitement. Transients vocalize far less frequently than residents, presumably to remain undetected by their mammalian prey, and are far more likely to vocalize after an attack.
Researchers can identify as many as 62 different vocal variations, some of which share a distinctive structure. These are called 'discrete calls'. A collection of discrete calls forms a dialect, which is shared by all members of a pod and remains unchanged over time. Researchers use dialect as a tool for identifying whales when visual markers are unclear. In fact this is the primary method of identifying transients, which all use the same dialect. Whereas residents will remain with the same whales for their whole lives, transients will shift groups, making it essential to share a common language. Dialects have also been used to identify orcas of uncertain origin in captivity, although captive whales can be trained to learn other dialects.
Resident pods in British Columbia exhibit a complex system of related dialects that have been linked to their evolution. In fact researchers have been able to establish an evolutionary tree of resident pods in these communities from dialect similarities. No calls are shared by resident and transient orcas, reflecting their divergent evolution.
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