Have you ever wondered whether animals (other than us) in nature also have their own kind of language? Can they understand each other? do their signals "mean" something? or are their signals just random noise?
Animals do communicate, and not only using sound, but any kind of signal that can be captured by their senses (e.g., chemical signals, or visual cues). It is an extensive topic of research in animal behavior that I will not cover entirely here.
However, I would like to introduce and summarize here the story of my research on acoustic communication in dolphins, in particular, on their whistles.
Dolphins produce different types of vocalizations, from which whistles are just one example. Whistles are continuous frequency-modulated sounds with a frequency range within 2-24 kHz. They occur within the human hearing range. Thus, they are sounds that we can directly listen with our ears. Whistles are mainly used for communication, while other signals, like clicks, for instance, are used for echolocation: this is, to perceive their environment during navigation, and to detect preys and potential predators, when foraging (similar to bats!).
Would you like to listen to dolphins? Let's see if you can identify whistles and clicks from the recording below. The example is quite long, so feel free to forward/rewind the recording as you like.
Did some of the vocalizations sound familiar or funny to you?
In this study, which was part of my Bachelor thesis, I wanted to investigate whether whistles could be associated to specific behavioral context. This is, whether whistles had communicational value for the dolphins. Since whistles are frequency-modulated sounds, we could identify different shapes when analyzing the sonograms on the computer (see figure 1 below). Other features to describe the whistles were also considered, but I will not explain them here.
Figure 1. Sonograms of different types of whistles: A: ascendent, D: descendent, C: constant, M: multiple.
The subject of my study was the bottlenose dolphin (figure 2). This species is very well known worldwide, and has even been a star in movies (e.g., flipper).
Figure 2. The bottlenose dolphin.
I conducted my research study at the coast of Aragua state (Venezuela). The landscape is characterized by a chain of mountains facing the see, where one can find few settlements located close to rivers. These settlements have a very interesting history since they were established by people that escaped slavery during colonization time. Fishing and cacao plantations are their main economical activities nowadays. Something that I can recommend very much is to do hiking from one side of the mountain (facing the city of Maracay) to the other until the beach. It is beautiful and amazing! And of course! do not forget to carry with you your mask and snorkel! If you are lucky, you can find sea turtles and more!
From my research I found that dolphins avoid whistling when traveling together in close proximity. Instead, they perceive their environment and search for prey using clicks. When they travel scattered, they generally emit simple whistles and, some rare times, the complex ones, so the group can still keep acoustic contact and the same traveling orientation. Complex whistles, especially those reaching low frequencies, may facilitate the communication among distant dolphins. Underwater light attenuates faster than it would do in air, and sometimes the concentration of sediments is too high, that vision is limited to short distance (meters). Whistles would be the dolphin version of wireless phone communication.
On the other hand, when they engage in social activities and interactions, they emit many types of whistles and use more often the complex ones (figure 4). Complex whistles can potentially carry more information, which could be useful during courtship, for instance.
Figure 4. Types of whistles per behavior. The arrows indicate whether the association was stronger / weaker for those types of whistles with the corresponding behavior.
An interesting observation is that dolphins seem not to emit whistles when they happen to be alone. this reinforces the communicational value of these signals. According to my work, whistles differ in relation to the dominant behavior of the group (whether traveling or socializing, figure 4). In addition, evidence also suggests that whistles differ among groups of dolphins, as if they would speak different dialects. Probably, they are culturally passed on to the next generations (i.e., probably they are learned).
Could we someday be able to decipher the code of dolphin whistles?
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If you liked the information and want to use it (or part of it), please cite as:
Romero-Mujalli D, Tárano Z, Cobarrubia S, Barreto G (2014) Characterization of the whistles of Tursiops truncatus (Cetacea: Delphinidae) and their association with surface behavior. Argent J Behav Sci 6:15–29 DOI: http://dx.doi.org/10.30882/1852.4206.v6.n1.6362
Technical details of the hydrophone used for my research:
Recordings were made using an omnidirectional hydrophone SQ26-08 (frequency range 0.03-30kHz) connected to a solid-state digital recorder M-Audio Microtrack II. This hydrophone was acquired from Cetacean Research Technology (I highly recommend this site for the acquisition of underwater sound recording technology).
Funding
This work was funded by Cetacean Society International and the Simon Bolivar University of Venezuela.
Recordings were made using an omnidirectional hydrophone SQ26-08 (frequency range 0.03-30kHz) connected to a solid-state digital recorder M-Audio Microtrack II. This hydrophone was acquired from Cetacean Research Technology (I highly recommend this site for the acquisition of underwater sound recording technology).
Funding
This work was funded by Cetacean Society International and the Simon Bolivar University of Venezuela.
