Off the Mediterranean coast, sperm whales are divided into two distinct groups. Their point of divergence? Their way of communicating. Researchers have discovered that these populations use different dialects, a rare fact among non-human animals.
Sperm whales emit series of clicks called codas to communicate with each other. These sound patterns act as group signatures: a clan recognizes itself by its particular rhythm. In the Mediterranean, all sperm whales were thought to share the same dialect, a pattern of three clicks followed by a pause and then a final click. But recent recordings show something else.
These two populations have been isolated for about 20,000 years between the eastern and western Mediterranean, after the initial entry of sperm whales through the Strait of Gibraltar. These animals almost never leave their territory in the inland sea, not even the males, which are otherwise migratory. This isolation has favored the emergence of unique acoustic features, but also an unexpected divergence between east and west.
The western sperm whales, near the Balearic Islands, remain faithful to the traditional slow dialect. Those in the east, around the Hellenic Trench off the coast of Greece, produce a faster version of the same pattern. In some recordings, the eastern animals occasionally use the slow dialect, as if remembering their origins.
Researchers compare this phenomenon to the emergence of slang among young humans: groups distinguish themselves by creating new sounds. One linguist believes that Mediterranean sperm whales, spreading from west to east, gradually modified their language.
This process is very slow, on the scale of hundreds or thousands of years. Sperm whales live up to 70 years, so the 19 years of study represent only a snapshot. This eastern dialect probably began to emerge while Greek and Roman civilizations flourished around the Mediterranean. If given another 10,000 years, the dialects might become completely separate.