The loud, moaning calls of large, baleen whales—such as fin, right, gray, and blue whales—can travel hundreds of kilometers through the sea as the cetaceans reach out to contact others of their kind. Many of the whales’ calls are in the same low-frequency range as those produced by human activities, including military exercises, commercial shipping, and energy exploration. That overlap has led marine biologists to worry that the human cacophony may be harming the whales. (All baleen whale species are endangered, except the gray whale.) Yet it’s been difficult to devise regulations governing this noise, because scientists have not fully understood how sounds reach the baleen whales’ ear bones. Now, researchers report today in PLOS ONE that they’ve solved the mystery by means of a 3D computer model of a fin whale’s (Balaenoptera physalus) skull. They based their model on the skull of a young fin whale (seen in the photo above) that died in 2003 on a southern California beach. By simulating sound waves traveling through the computerized skull, the scientists discovered that the whales use an unusual mechanism for hearing: bone conduction. The fin whale’s skull bones (and likely those of other baleen whales) vibrate and amplify the low-frequency sounds, directing them to the ear bones. The discovery may help lawmakers set limits on the amount of noise humans can make in the deep sea.