Usually, there’s no more than 10 meters of visibility underwater, and sounds run 3 times faster trough the water than in the air. That kind of events made cetaceans to developed ear sense more than the others to survive in this environment.
Whales and dolphins have been adapted in order to use the sounds in the aquatic environmental
Differences in sound production and sound reception between whales and dolphins.
Dolphins
Whales
Skull
Asymmetric
Symmetric
Aerial sack
Yes
No
Melon
Yes
No
Panbone
Fatty region (fat)
No fatty region
Emission and reception of sound
Produced by monkey lips/aerial sacks and larynx. Directed by melon and received by Panbone (jaw)
Unknown. Jaw bones do not participate in the process.
Sounds
High frequencies (short distances)
Low frequencies (long distances)
More research has been done about dolphin’s sound production than whales’, so we describe some of the odontocetes’ structures related in the emission and reception of sound.
Sounds emission and reception structures
Blow whole: End of the nasal system. Located in the frontal part of the head, used for gas exchanges.
Aerial sacks: Structure that fill out of air before produce sounds.
Monkey lips: Specific place where the sound is produced, located behind the melon.
Melon: Fatty tissue where the sound is directed to the front.
Ear: Isolated from the skull, receive vibrations from the panbone and send it to the cranium.
Panbone: Hollow structure with fatty tissue, it receive sound (vibrations) from the environment and then send it to the ear.
Functionality
Sound and feeding
Echolocation is a skill developed by odontocetes whales that allow them to get information through sounds and echoes from the environment. Some benefits obtained out of this system are:
Detect predators
Detect preys
Navigate and explore physical environment
Echolocation is composed of three different processes:
Sound production
Sound reception
Signal procesing
Clicks are broad band sounds. Clicks can travel just short distances since they are high frequency pulses. The intensity and intervals in between clicks may vary depending on the echolocation target, sound’s reflection and environmental factors.
Sound and reproduction
Research about whale’s songs has shown the variety and complexity about them. They have different styles, depending on the species and family group. Frequency of songs increases on the reproductive season.
Some exclusive characteristics showed by humpback whale males are their elaborated songs that can last for several minutes, and travel several kilometers. These songs are composed by repeated phrases followed by new phrases. All males sing the same song during the breeding season when they share the same reproductive area. The song can change year to year. Songs are used by males to compete with other males, but the main purpose could imply attracting females.
Sound and communication
Whistles are another kind of vocalization produced by some cetaceans. These are tonal sounds transmitted as continuum not as pulses (clicks). Whistles are used by different species of dolphins to communicate. We can not assume they communicate like human do, but researches have observed behavioral changes associated to certain vocalizations. Apparently, whistles are abundant when dolphins socialize, and those might be used in order to:
Keep the group together
Hunt in a collective way
Transmit alarm signs
Keep bonds between mother and calf
General Socialization
Sound specificity
There are several vocalization types depending on the cetacean species, which work as particular features of the species we are listening, dolphin or whale. The hearing range varies depending on the species too.
Some species like the bottlenose dolphin show very specific acoustic characteristics. An individual could be identified by other members of the group, since it produces certain individual-specific vocalizations called signature whistles.
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