Dolphins with Tasers

In the video The Hunt, Attenborough describes how dolphins work together to concentrate fish together so that they can catch and feed on the fish more easily while preventing the fish from escaping the area. The video shows that dolphins not only use sonar to communicate with each other, but that they also use loud sonar clicks to gather the school of fish together and stun their prey.

Dolphins are capable of hunting together because their groups are usually concentrated at sites such as straits or entrances of channels. They stay within 100m of the shore in groups as large as 20-40 members and disperse into smaller 2-5 member groups to hunt [1]. In addition to the use of sonar clicks to locate their prey, dolphins use sonar to signal pre-captures and communicate successful hunts to other dolphins [2]. After dolphins make a click, the echo bounces back from an object and to the very agile body of the dolphin. The body then takes in and sends all the information to the brain, which evolved over 10 million years ago in water [3].

Using sonar, dolphins are capable of locating the sounds precisely. For example, Bottlenose dolphins have millimeter-scale controlling over the sound generation site because they have bilaterally asymmetrical phonic lips, which are the “vocal cords” in a dolphin’s nasal pathway. Bottlenose dolphins are also capable of slightly altering the exact site of sound generation, thereby adjusting the relative path length for pulses, and controlling the precise time the sounds take to reach any destination [4].

Throughout the hunting process, dolphins use sonar clicks separated into three phases, each with unique representative sonar clicks to signal each distinct event. Before the capture, each sonar click lasts about 0.4s to indicate the searching of the fish. Once the location of the fish is found, the clicks speed up to form a terminal buzz noise. Lastly, once the prey is captured, the buzz transforms into an emotional squeal that lasts between 0.2 to 20s. The squeals resemble bursts of pulses that have varying duration, peak frequency, and amplitude. They may reflect the dopamine-triggered emotions that follow a successful hunt [2].

Inspired by dolphin’s echolocation ability, humans have developed radar systems to detect explosives and buried catastrophe victims (3). However, there are still many more aspects of the echolocation system of dolphins for scientists to explore and uncover.

by Iris Mao, Gloria Wan, Linda Wu, Leo Chen and Vince Wu

The Hunt, Season 1, Episode 4, starting at 17:25

References

1. Fernando F. 1994. Ecology of the coastal bottlenose dolphin Tursiops Truncatus in the Gulf of Guayaquil, Ecuador. Investigations on Cetacea 15: 235-256.
2. Ridgway S, Dibble D, Van Alstyne K and D Price. 2015. On doing two things at once: dolphin brain and nose coordinate sonar clicks, buzzes and emotional squeals with social sounds during fish capture. Journal of Experimental Biology 218: 3987-3995.
3. Leighton T and P White. 2015. Dolphin-inspired target detection for sonar and radar. Archives of Acoustics 39: 319–332.
4. Cranford TW, Elsberry WR, Van Bonn GW, Jeffress JA, Chaplin MS, Blackwood DJ, Carder DA, Kamolnick T, Todd MA, and SH Ridgway. 2011. Observation and analysis of sonar signal generation in the Bottlenose Dolphin (Tursiops Truncatus): evidence for two sonar sources. Journal of Experimental Marine Biology and Ecology 407: 81–96.