Whale VocalizationsWhales adapted to the utilization of acoustics during their evolution quite intensively. This is very sensful since many other forms of energy like light, electromagnetic and thermal energy are attenuated fast in water but sound waves are not. Sound travels 4.5times faster in water than in air. Some low frequecy sounds produced by baleen whales can be heard over thousands of kilometers and thus cover whole ocean basins. Sound transmission in water depends on many factors such as water temperature, salinity, depth, ice cover, ambient noise, topography of the sea bottom and water stratification. The variety of calls produced by cetaceans (whales, dolphins and porpoises) is big and different species often produce different kinds of vocalizations. Some baleen whales for example are well known for their very low frequency sounds called moans which are used for communication. Many toothed whales produce whistles which are used for communication as well but the most interesting sounds of toothed whales are probably their clicks since they help the whales to find their prey and to investigate their environment. That means the whale produces a click and waits for its echo. The time between the production of the sound and the arrival of the echo tells the whale about the distance between itself and whatever has caused the echo. That can be the sea floor, a rock, a boat or another animal. This method is called echolocation.
Acoustic signals produced by whales can be directional which is the case for clicks, or undirectional like different communication sounds. That makes sense since communication siganls usually are to be heard by many animals which are placed in different directions to the whale which produces the call. Echolocation signals however are supposed to give information about the position of prey or of an obstacle and should therefore travel to one direction only. The frequency of the sound can either stay the same during the call or can be modulated. That means the frequency can e.g. increase during the call which is called an upsweep or decreases which is called a downsweep. But frequency modulations can also be much more complicated within a single call. Whistles for example are characterized by rapid changes in frequency. Every sound wave has a certain pressure which can be realized by the loudness of the sound. The higher the sound pressure the louder the call is. Not only single calls are produced by whales. Some species, like humpback whales, are known to sing long songs which consist of many different sound types and can therefore be very complicated.
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