The largest animals on the earth manage to be covered by a great shroud of mystery. In the 1960s scientists studied the whale's behavior by analyzing recordings of their underwater songs. Over the years it has been noticed that the blue whales are not singing the same way they used to. According to the data, it appears as if these massive creatures are singing in deeper voices each year. This puzzling abnormality was initially realized when marine biologists off the coast of California needed to continuously recalibrate their automated song detectors used to track the whales. These detectors are triggered by songs matching a specific waveform. As of late, these detectors have to be reset every year.
The results have been published in Endangered Species Research, and show song data gathered from thousands of blue whale populations since the 1960s from the North Atlantic, to the South Pacific, to the East Indian Ocean. In all regions, results indicate that the songs' tonal frequency is falling by a few fractions of a hertz every year. There are some theories floating around which attempt to explain this mystery, including shifting population dynamics, new mating strategies, or increased ocean noise pollution. Another theory involved the recovery of blue whale populations, which were almost extinct in the first half of the last century. Since only male blue whales sing, the answer might involve sexual selection.