Is any environment more secluded from our imagination than the seas surrounding Antarctica? Icebergs grind above a seabed dotted with salps, sea squirts, sponges, and other barely animate organisms. The sun scarcely rises for half the year. Under the elemental conditions at these latitudes, Antarctic blue whales exist in a world defined by bioacoustics. Blue whales, Earth’s largest animals, call to others of their kind, though exactly what these cries communicate remains a mystery. Whether to attract a mate, to repel a rival, or for some other social purpose, the sounds blue whales make are less song, more drone—a tectonic rumble on the furthest edge of human hearing. That the sounds of blue whales seem simple might suggest they are unchanging across generations. But these atonal sounds have begun evolving. Since at least the 1960s, their pitch has downshifted the equivalent of three white keys on a piano. Scientists have theories as to why—some worrisome, some hopeful, all involving humans.
The deepening of Antarctic blue whales’ sounds is not unique to the subspecies. Groups of pygmy blue whales found near Madagascar, Sri Lanka, and Australia, as well as fin whales, which live in seas around the world, have also dropped their pitch. (Even before this change, fin whales emitted sounds so low as to be nearly imperceptible to humans; the wavelengths of their calls were often longer than the bodies of the whales themselves.) In a study last year that analyzed more than 1 million individual recordings of whale calls, scale shifts were found across species, and among populations that don’t necessarily interact with one another. Which is to say, whatever has triggered the change doesn’t seem to have a specific geographic origin.