Calls beyond the ocean

During the cold war, the U.S. navy had set up a network of underwater listening stations in the Pacific and Atlantic to keep an eye out for the Soviet submarinse. Their Sound Surveillance System, or SOSUS network, picked up a flood of sea noises. Several of them seemed as if they were not of military origin. Some were more perplexing. One particularly intriguing sound had a frequency of 20 Hz, which is an octave lower than the lowest note on a typical piano. It was monotonous, repetitive and low in pitch. People started questioning if an animal could be producing such a loud hum. Was it a result of tectonic activity beneath the sea or did it originate from faraway shoreline waves? Navy scientists began tracking the noises to their origins and discovered a fin whale at the end, making the assumption true. Fin whales are the second largest species after blue whales that produce incredibly low-pitched cries that are audible over entire oceans. The typical human hearing threshold (lower end) is 20 Hz and sound below this frequency mark is infrasound, which is only audible to us at very high volumes. The frequency produced by a body is inversely proportional to its size. A large body (like whales) produces low frequency- big wavelength sounds. In contrast, smaller bodies (like a bee) produce high frequency sounds with very short wavelengths.

via CK12-Foundation

It is this infrasound that is produced by fin whales. Their calls are capable of travelling 13,000 miles. NO OCEAN is THAT wide. When you watch them travel, it appears as though these animals have an audio map of the oceans. It is also believed that over the course of their long lives (fin whales have an average lifespan of 90 years), these animals create such maps by amassing sound-based memories that linger in their minds' ears.

If you wanted to design a signal that could be used to communicate across oceans, you’d come up with something similar to a blue whale’s song. The largest animals on land may use infrasound in a similar manner. While researching African elephants in Kenya's Amboseli National Park, Joyce Poole and Cynthia Moss discovered that even when elephant families were separated by several miles, they frequently moved in the same directions for weeks at a time as an act of coordination to meet each other. They travel across savannah by employing infrasound for communication. The waves travel via air across great distances. The largest animals on land might use infrasound in the same way. Joyce Poole and Cynthia Moss, who had been studying African elephants in Kenya’s Amboseli National Park noticed that elephant families would often move in the same directions for weeks at a time to meet, even though they were separated by several miles. Infrasound can travel long distances even in air, but with slightly lower efficiency than in water. In 1986,an extended research by the same team showed that African elephants use infrasound just like their Asian counterparts —and in every conceivable context. There are contact rumbles that help individuals find each other. There are greeting rumbles that they make when reuniting after a separation. These infrasonic rumbles are airborne sounds. The low-frequency parts of the rumbles range between 14 and 35 Hz —about the same as a large whale’s. We still don’t know how far these animals are listening to each other, or what they’re listening for. The same applies to whales, but those calls don’t carry as far in the air as underwater. Much of what has been theorised is still speculative, based on little snapshots of whale behavior and educated guesses about what they should be capable of. When it comes to the largest animals that live or have ever lived, actual data are hard to come by, and experiments are close to impossible. Smaller animals can be kept in captivity and studied ethically, but it can be really hard to house an animal as big has 3 buses and that takes deep dives in the ocean. Scientists like Darlene Ketten have estimated what these giants hear by analysing their ears with medical scanners. Her work strongly suggests that they hear the same infrasonic frequencies that are found in their calls. What they do with that sense is another matter. There are still holes in these ideas. Like in blue whales,only male blue whales seem to sing, so if they’re really navigating or communicating with their calls, then what are females doing?