Blue whales are the largest animals on Earth, and they also make one of the longest migrational journeys each year, totaling up to 4,000 miles. Now, researchers have found a pattern in the songs of these great beasts that serve as a prelude to their epic travels to warmer waters every fall.
Tiny Instrument, Big Data
Eighteen miles off the coast of California at a depth of 3,000 feet, a palm-sized underwater microphone known as a hydrophone has been monitoring the sounds of the sea since 2015. It frequently picks up the sonic emissions from blue whales, which the researchers from Stanford and the Monterey Bay Aquarium Research Institute (MBARI) were interested in examining.
“Sound is a vital mode of communication in the ocean environment, especially over long distances,” said William Oestreich, a graduate student in biology at Stanford University’s Hopkins Marine Station. “Light, or any sort of visual cue, is often not as effective in the ocean as it is on land. So many marine organisms use sound for a variety of purposes, including communicating and targeting food through echolocation.”
When the researchers combined the data from the hydrophone with data obtained from accelerometer tags on the whales, they realized that when blue whales switch their singing from nighttime to daytime, they are getting ready to migrate towards warmer waters. That switch happened in October and November over the five years of data analyzed, and that was when the songs were also the loudest.
Whistling While They Work
“We decided to compare daytime and nighttime song patterns from month to month, and there, in the divergence and convergence of two lines, was this beautiful signal that neither of us really expected,” said John Ryan, a biological oceanographer at the Monterey Bay Aquarium Research Institute and senior author of the paper. “As soon as that image popped up on the screen, Will and I were both like, ‘Hello, behavior.'”
The researchers believe the shift has to do with feeding patterns. In the summer, whales eat during the days to pack on weight for their eventual migration odyssey, so they saved the evenings for singing. However, the whales seem to have no problem whistling while they work towards their winter homes, so the songs shift back to the day when their journey begins.
Oestreich also wonders if the song pattern that he and the other researchers picked up on might be used by other whales to communicate departure times.
“Blue whales exist at incredibly low densities with enormous distances between them but, clearly, are sharing information in some way,” he said. “Trying to understand that information sharing is one motivation, but also potentially using that signaling as a means to study them, is another exciting possibility.”
One other application of the findings could be to develop a kind of forecast to warn large vessels in major shipping lanes when the migration is about to begin to avoid dangerous and tragic collisions.
The research has been published in the peer-reviewed journal, Current Biology.