People from all over the world are fascinated by whales and dolphins. Is it because of their grace and elegance or their similarities to humans? Nobody will give you one answer, because people are drawn to these marine mammals for many different reasons. As a research assistant at the Marine Mammal Research Lab at the Hawaii Institute of Marine Biology I was drawn to the mystery and obvious intelligence of dolphins. One question I, and many others, have is how dolphins do “talk” to each other underwater.
Hawaiian Spinner Dolphins (Stenella longirostris) have the ability to coordinate movement between other specific members in their pod while hunting, but the most amazing part about it is that they do it in complete darkness. Hawaiian Spinner Dolphins feed on squid that rise from the depths only at night. Scientists have been able to tag animals with acoustic recorders and observe how they hunt together as a whole pod. One question is how these animals can discern the direction of an incoming whistle from another pod member. Sound travels five times faster in water than in air, and humans lose the ability to discern direction of a sound underwater. In air the human brain determines the direction of a sound by the time difference heard in each ear, but underwater the sound is traveling too fast for the brain to recognize a difference in time of arrival at each ear.
Therefore how can dolphins do this? Currently there are two hypotheses; one is that the shape of the head of the dolphin actually creates a shaded region of sound on the opposite side of the incoming sound, much like a rain shadow caused by mountains. The other hypothesis is that the physical properties of the whistle, such as intensity and number of harmonics, provide information that the animal uses to determine the direction and movement of the dolphin that produced that whistle.
I had the opportunity to present some of this research at the Society of Marine Mammology Biannual Conference in Dundein, New Zealand this past month. The conference answered many questions, but it also created more questions. It is obvious to me that these animals are vastly more intelligent than humans. With the recent news of illegal killing and inhuman captivity of dolphins we are all now aware that something needs to be done.
“Never depend upon governments to do anything. All social change comes from the passion of individuals.” Margret Mead
-by Taylor Shedd
Lammers, M., Au, W. (2003) Directionality in the Whistles of Hawaiian Spinner Dolphins (Stenella longirostris): A Signal Feature to Cue Direction of Movenment?, Society of Marine Mammology, Marine Mammal Science v.19 p.249-264
Miller, P (2002) Mixed-directionality of killer whale stereotyped calls: a direction of movement cue?, Behavioral Ecological Sociobiology v.52 p.262-270
Mooney, A., Nachtigall, P., Castelloteb, M., Taylor, K., Pacinia, A., Esteban JA. (2008) Hearing pathways and directional sensitivity of the Beluga Whale, (Delphinapterus leucas). Journal of Experimental Marine Biology and Ecology v.362 p.108-116