Blog Post Image: An Ancient Biosonar Sheds New Light on the Evolution of Echolocation in Toothed Whales

Toothed whales echolocate using ultrasonic signals — at frequencies too high for humans to hear. A new study led by WHOI postdoctoral fellow Frants Jensen found that the Ganges river dolphin produces sounds at a surprisingly low frequency compared to species of dolphins. This figure charts the energy distribution as a function of frequency for echolocation clicks used by three species of toothed whales: the Ganges river dolphin (not a member of the dolphin family, but rather the very old Platanistidae family), the Irrawaddy dolphin, a freshwater dolphin that ranges into coastal areas, and the Bottlenose dolphin, a marine dolphin. The relative sound energy has been “normalized” so the chart displays the same maximum sound energy production for each species. All three species include signal energy at low frequency, but the members of the dolphin family (the Irrawaddy and Bottlenose dolphin) include signal energy at much higher frequency as well. Graph courtesy of Frants Havmand Jensen, Woods Hole Oceanographic Institution (Click image to enlarge)

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