To compare the sounds of technology and whale calls, listen to this online exclusive feature. 

Up north in the Pacific Ocean near Washington, the orcas are changing their calls. Twenty degrees south near Baja California, gray whales have drifted from the lagoon that served as their nursery for millennia. On the shores of the Canary Islands off the northwestern coast of Africa, an area teeming with marine life and ferryboats, sperm whales are turning up dead, their jaws smashed and backbones splintered by collisions with ships.

In three distinct areas of two different oceans, these animals are plagued by a raucous cacophony of unnatural noise. The orcas struggle to be heard over the persistent buzz of whale-watching ships. The grays flee not only the briny discharge of the Guerrero Negro salt factory, but also the constant thrumming of its diesel pumps. The sperm whales may have gone deaf to approaching vessels: When French biologist and engineer Michel André examined two that had collided with a cargo ship, he found their sensitive hearing mechanisms severely damaged—perhaps, he hypothesized, from constant exposure to the thwack of propellers.

As the mainstream media have reported, marine biologists know that high-powered military sonar has immediate and lethal consequences for marine life. Whales and dolphins have stranded and died following Navy experiments with mid- and low-frequency sonar all over the globe, spurring hard-fought court battles to limit sonar exercises in sensitive ocean habitat.

What is not widely known is that researchers also worry about constant background noise in the sea: sound that causes little in the way of instant injury, and whose effects are harder to prove, but may have a long-term, chronic impact on marine mammals. “It may be preventing them from doing things that they need to do,” says John Hildebrand, a professor at the Scripps Institution of Oceanography in La Jolla, California, “like detect signals from other animals of their own species and detect signals that would help them find food.”