"How do marine mammals use sound when feeding?" (continued)
Toothed whales and baleen whales produce other sounds to increase their chances of success during feeding. Humpback whales have developed a feeding technique called bubble feeding. Bubble feeding involves one or a few whales blowing air from their blowhole while underwater. This produces sound as the bubbles form a cloud, curtain, or column that rises toward the surface. The bubbles trap the prey between the surface and the whales mouth. A bubble net is formed when the bubbles emitted by the whales form a ring and concentrate the prey inside. Both the sound and the bubbles work to concentrate prey so the humpback can capture more food per mouthful.
Aerial photograph of bubble net produced by a humpback whale. A humpback whale dives down, beneath its prey, then blows bubbles as it slowly spirals towards the surface. The bubbles form a circular curtain that concentrates the prey in the center. The whale then swims up through the bubble net with its mouth open, gulping up the trapped prey. Photo by J. Olson, NMFS.
Bottlenose dolphins also make use of sound and bubbles. Dolphins foraging in seagrass beds in Australia and Florida use a technique called kerplunking to drive fishes from the protection of the sea grasses. A dolphin will lift its tail and lower body out of the water and crash it down on the water surface. This causes a loud splash and creates a trail of bubbles under the water. This startles the fishes hiding in the seagrass and flushes them from their hiding places, making it easier for the dolphin to detect them.
Sequence of above-surface movements during a typical kerplunk. Dolphin lifts flukes out of water and pivots about 90 degrees before bringing flukes down to impact water surface. Initial small splash is directed at a 45 degree angle behind flukes, followed 0.25 second later by a much larger splash that may reach several meters in height (from Connor, R.C., Heithaus, M.R., Berggren, P., Miksis, J.L. 2000. "Kerplunking": Surface fluke-splashes during shallow-water bottom foraging by bottlenose dolphins. Marine Mammal Science 16(3): 646-653).
The spectrogram below is an example of a kerplunk from a foraging dolphin in Australia. Listen to the sound while watching the spectrogram. You first hear a series of echolocation clicks that sound like a buzz. The kerplunk happens at about 2.5 seconds and sounds like a deep splash. This is then followed by more echolocation as the dolphin scans for fishes driven from the seagrass.
Click either choice below to hear a kerplunk:
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Courtesy of Connor, Heithaus, Berggren and Miksis
Lastly, there is the simple mechanism of listening for sound produced by prey items. Some marine mammal species may use this technique to find prey. Fishes make a variety of sounds that cetaceans and pinnipeds may detect. Transient killer whales sit and quietly listen for sounds of other marine mammals in the area before they make their attack. In this instance, it benefits the killer whale to be as quiet as possible while listening so it doesn't scare away its prey. Listening for prey sounds is a mechanism that is also used by seals and sea lions. Once the seal or sea lion detects a fish by sounds, it waits for it to get close enough to use its sensitive whiskers to track the path of the fish as it tries to escape.
References
Baird, R.W. 2000. The killer whale - foraging specializations and group hunting. In Cetacean Societies: Field Studies of Dolphins and Whales. Edited by Mann, J., Connor, R.C., Tyack, P.L. and Whitehead, H. University of Chicago Press.
Connor, R.C., Heithaus, M.R., Berggren, P. and Miksis, J.L. 2000. "Kerplunking": Surface fluke-splashes during shallow-water bottom foraging by bottlenose dolphins. Marine Mammal Science 16(3):646-653.
Tyack, P.L. 1999. Communication and Cognition. Pages 287-323 in Reynolds, J.E. III and Rommel, S.A. (eds.). Biology of Marine Mammals. Smithsonian Institution Press, Washington D.C.
Wells, R.S., Boness, D.J. and Rathbun, G.B. 1999. Behavior. Pages 324-422 in Reynolds, J.E. III and Rommel, S.A. (eds.). Biology of Marine Mammals. Smithsonian Institution Press, Washington D.C.
