Raoul Island, a volcanically active landmass half the size of Manhattan, is not an obvious place for a whale party. But over the past decade or so, Dr. Constantine said, Department of Conservation rangers posted there had noticed humpbacks aggregating in September and October.
“Instead of just swimming in a straight line down to the feeding grounds, which is the fastest point from A to B, they will come out of their way” to spend time at the island, Dr. Constantine said.
In 2015, she and some colleagues traveled there to figure out what they were up to.
When the researchers lowered a hydrophone, or underwater microphone, into the water, they were “quite surprised at how much song we heard,” Dr. Constantine said. The singing — which the researchers could also hear through the hulls of their boats — was not quite as loud or lusty as it generally is at the breeding grounds. But at any given moment, there was almost always at least one whale performing.
Acoustic analysis of the songs told the researchers that the singing whales were from a number of different breeding grounds, a conclusion bolstered by photo identification as well as later genetic testing. They even recorded a humpback singing two different songs, perhaps in the process of learning one from another migrating whale.
Although the study’s sample size is small — only a few dozen whales were recorded — the authors have “clearly demonstrated a location where the cultural transmission of song may occur,” said Melina Rekdahl, a marine conservation scientist for the Wildlife Conservation Society, who was not involved with the research.
She added that such transmission may also occur in other places, such as feeding grounds, and that questions remain, including why certain groups from the South Pacific were not found at the island and why songs always seem to move from west to east.
But one piece of the puzzle seems to have been placed. “The great mystery for us was: Where’s the place where they share the song?” Dr. Constantine said. “And we found it!”