2026年5月托福机经套卷(第4套) - Read an Academic Passage Q2

Echoes of the Deep Cetaceans—a group of mammals that includes whales, dolphins, and porpoises—use echolocation to navigate and hunt in waters too deep for sunlight to penetrate. Many cetaceans emit clicks, producing sound waves that bounce off objects and return as echoes. Echolocation techniques vary among species, depending on their environments and needs. Dolphins, for instance, produce more frequent and higher-pitched clicks than do larger cetaceans like sperm whales. Although high frequency sounds do not travel as far as low frequencies do, high frequencies with very short wavelengths help dolphins locate small objects and pick out fine detail—the higher the frequencies, the better the detail. This enables dolphins to find and track small, agile fish that make up their diet. Sperm whales, on the other hand, dive deep to hunt prey such as giant squid and use lower-frequency clicks that travel farther in the deep ocean. Noise pollution can interfere with the echolocation signals used by cetaceans. Human-made sounds—such as those from sonar and ship engines—can make it difficult for whales and dolphins to locate prey, orient themselves, or communicate with others. The disruption can cause stress and disorientation, increasing the risk of collisions and strandings, and it can also induce changes in behavior or habitat.