One possible explanation for the change is the increase in noise pollution in our oceans . In 2008, the International Fund for Animal Welfare (Ifaw) argued that ocean noise from ships and other sources was interfering with marine mammals’ ability to communicate. But McDonald argues that if whales were trying to be heard through the noise, they would sing at higher pitchers rather than lower ones.

A change in population may be another explanation. Blue whales were hunted to near extinction at the first half of the 1900s, and they’ve been recorded only since hunting stopped. “Maybe songs were higher-pitched when recording started, because the whales had to sing extra-loud in order to reach their scattered brethren,” Keim writes. “Now that there are more, they can lower their voices and their pitch.”



But even in areas where the whale population hasn’t grown significantly, the songs are still getting deeper. “The population of blue whales off the U.S. west coast hasn’t shown a dramatic upwards trend in numbers, but its pitch is declining,” Calombokidis told Wired.

Others suggest that mating and sexual selection may be a factor. Only male blue whales sing, so researchers think that maybe the “larger, ostensibly more virile whales” are producing deeper songs, which the other males are trying to copy, “just as human guys might lower their voices when trying to impress a woman,” according to Wired.