How Bottlenose Dolphins (Tursiops truncatus) Produce Sounds?
Bottlenose dolphins are renowned for their playful and intelligent nature, capturing people’s attention with their acrobatic displays and social behaviours. One of the most fascinating aspects of these animals is their ability to produce sounds, from simple clicks and whistles to complex vocalizations. Here we will delve into the intricacies of how bottlenose dolphins generate these sounds and explore the significance of their acoustic communication.
Anatomy of Sound
Anatomy of Sound Production
The primary mechanism by which dolphins produce sounds is through their blowhole and respiratory cavities. Unlike humans, dolphins lack vocal chords, so they rely on a specialized structure known as the phonic lips to create sounds. The dolphin’s larynx, situated at the base of the blowhole, controls the passage of air through the nasal sacs, modulating the sounds produced. Dolphins also have a mass of fat tissue in their heads called the melon, that helps to amplify the sounds.
Anatomy of Sound Reception
To perceive the sounds, dolphins have specialized structures in their lower jaw called the lower jaw fat bodies that receive and transmit the sounds to the middle and inner ear and then to the brain. Similar to humans, dolphins have a structure in their inner ear called the cochlea that helps them hear and process sounds underwater. The cochlea is responsible for converting sound vibrations into electrical signals that the brain can interpret as sounds.
The cochlea contains specialized hair cells that react to different frequencies of sound. Each hair can sense a particular sound wave, amplify the signal, and transmit it later to the brain. These hair cells are small in dolphins compared to other mammals because they are adapted to hear high-frequency sounds. These hairs are crucial for dolphins’ communication, echolocation and survival in their natural habitat.
Bottlenose Dolphins’ Vocalisations
Clicks for Echolocation
Dolphins can create high-frequency sound waves, called clicks that travel through the water and spread out. When these sounds waves hit an object, they bounce back as echoes. These echoes give the dolphins information about the object, its shape, size, and distance. This way, they are able to identify what’s around them, even in dark or murky waters. This ability is known as echolocation.
Clicks
Dolphins can also produce other sounds known as ”gunshots”. This sound is an intense focused click that can disorient or stun the prey. This stun effect is a precise and well-tailored use of echolocation to manipulate the sensory perception of the prey and making it easier to hunt.
Gunshot
Whistles for Communication
Bottlenose dolphins use whistles as a form of communication within their social groups. Each dolphin has a unique whistle, often referred to as a “signature whistle,” which acts as a vocal fingerprint. Each dolphin developed their individual whistle by learning from the sounds present in their environment during the first few months of life. Dolphins use these signature whistles to identify themselves and built social bonds with other individuals.
Dolphins can also produce a variety of other whistles with different frequencies and patterns to send specific messages. These whistles serve purposes such as coordinating group activities, signalling distress, or expressing excitement. The complexity and diversity of dolphin whistles highlight the sophistication of their communication system.
Clicks and whistles
Collection of dolphin vocalisations
Social Significance of Sounds
Signature whistles
Signature whistles are like personal names. They play a crucial role in the mother-calf relationship among bottlenose dolphins. As the calf grows, it develops its own unique signature whistle, which is believed to be influenced by the vocalizations of its mother. The calf’s signature whistle becomes a distinctive vocal pattern that allows the mother to locate and identify her calf in a group of dolphins. The mother’s ability to recognize and respond to her calf’s signature whistle is crucial for maintaining close contact and ensuring the calf’s safety.
The ability to produce a wide range of sounds plays a crucial role in the social structure and cohesion of bottlenose dolphin communities. Communication through clicks and whistles allows dolphins to coordinate activities, establish and maintain social bonds, and navigate their dynamic environment effectively.
Whether engaging in playful interactions, hunting for food, or navigating through the open ocean, the dolphins’ acoustic communication is a key component of their success as a highly social species.
Threats
Our oceans and seas are very noisy places and these noise levels continue to increase annually. This has negative implications for dolphin who live in an acoustic world. Anthropogenic noise can disturb dolphins and mask important dolphin vocalisations, such as mother-calf calls. Noises can also damage dolphins’ hearing. The hairs located in their inner ear are very sensitive to sound vibrations and strong sounds like the ones produced by some boats, wind turbines, drilling or sonar technologies can damage these hairs permanently, making dolphins deaf to certain sounds.
How Scientists Study Dolphin Sounds?
Scientist use a range of acoustic methods to study dolphin’s sounds. Since 2001, we have used static underwater microphones called hydrophones and click detectors (PODs) in key locations throughout the estuary to gain a much better understanding of how dolphin use the Shannon estuary.
We have accumulated over 10,000 days of acoustic monitoring data from at least 12 different sites. This has shown that the Shannon dolphins regularly travel up river to feed, mostly off Foynes and Aughinish, Co Limerick and even up to Shannon Airport. These datasets provide us with useful information such as asses the effects of tidal cycles and phases on their behaviour and the variations between day and night.