Ontogeny

 

Vocalization as a Learned Behavior


Bottlenose dolphins are capable of producing a wide range of sounds through vocalization. Bottlenose dolphins are also able to imitate new sounds accurately, referred to as mimicry. They are also capable of vocal learning, that gives them the “…ability to modify the structure of a vocal signal as a result of experience with those of other individuals(4).” Within the first few months of a young dolphins life, it will develop its own individually distinctive whistle. In a study conducted by Vincent M. Janik, he concluded that dolphins are capable of reproducing the distinctive whistle produced by another dolphin(4). This method of response is known as whistle matching. His study involved recording 176 whistle interactions of a population of Bottlenose dolphins in the Kessock Channel of the Moray Firth, Scotland. In order for two consecutive identical sounding whistles to be determined to be produced by two different individuals, the distance between the source of each whistle would have to be more than the distance that an individual dolphin could travel at its maximum speed of 7.5 m/s. Janik found that of the 176 whistle interactions he recorded, 39 were matching interactions(4).

 

Vocalization of Dolphins is Learned Through their Ability to Mimic


In a study conducted by Diana Reiss and Brenda McCowan, they concluded that the dolphins’ ability to mimic allows them to learn to produce new sounds, indicating that vocalization is a learned behavior(10). In their study, Reiss and McCowan produced a system that the dolphins could interact with and respond to in order to receive specific rewards in the form of an object or an activity. They built a keyboard which had visual forms on the keys. When the dolphin pressed one of the keys they would receive an reward either in the form of an object, such as a ball or a ring, or in the form of an activity, such as a rub. Each key had a specific reward associated with it. When the dolphin pressed a key, a computer generated whistle would also be produced. If they dolphin mimicked the whistle produced by one of the keys, they would still received the award associated with that key, even if the dolphin did not actually press the key. Figure 1 shows the image of each key (column A), and the computer generated whistle (column B) and reward (column C) associated with each key.

Figure 1: Key Image, Whistle and Reward(10)

keyboard

Reiss and McCowan found that the number of exposures required before the dolphins mimicked the computer generated whistle ranged from just 2 exposures for the ring key, to up to 19 exposures for the ball key. One interesting trend they observed was the tendency of the dolphins to mimic the second half of the whistle before the first half. Because the dolphins could accurately recreate the computer generated whistles, Reiss and McCowan concluded that the vocalization of dolphins is a learned behavior.  

Multiple studies have come to the same conclusion that the ability to mimic contributes to a dolphins learning capabilities to vocalize. In another study conducted by Janik, he showed this by demonstrating how easy it is to train dolphins to produce specific sounds(4).