Whales, dolphins, and porpoise occupy a wide variety of habitats. They range from the small harbor porpoise found in shallow coastal waters to massive sperm whales diving below 1000 meters to catch the perfect squid! The underwater world can be like a labyrinth, and at times can have limited visibility-, especially below 200m, in the dark and murky waters. And so, how does a hungry dolphin locate a nearby school of fish? The answer: Echolocation!
Seeing with sound
Echolocation is the process of using reflected sound to obtain information about a nearby object. It could be food, another dolphin, or even an approaching iceberg perhaps. Sound can travel for many miles underwater, much farther than it travels in the air. The greater distance an object is from a dolphin, the longer it will take their returning echo to reach them. Then, the dolphins process these returning echos to determine the object’s size, shape, and speed.
Whales and dolphins are not the only creatures to use this fascinating tool. In fact, echolocation exists throughout the whole animal kingdom. Bats are perhaps the most well-known and well-studied animals that use echolocation. However, other animals that use echolocation include; shrimp, fish, shrews, and bird species. Interestingly, the technique is now adapted and used by some humans themselves.
The nitty gritty – how it works
Echolocation in dolphins works this way; dolphins and whales produce high-pitches whistles and clicks to communicate with each other. They produce clicks as they pass air through their tightly puckered “phonic lips” (also called monkey lips), found below the dolphin’s blowhole (see below). After that, the clicks are projected forward through the fatty melon (the soft area on a dolphin’s forehead) and into the water towards their target. This produces a sharp directional beam of sound.
This sound beam will bounce off the chosen target, returning to the dolphin, like a boomerang! The dolphin receives this sound through “acoustic windows” in its lower jaw (see below). Equivalent to the human outer ear, the lower jaw directs sound into the middle ear for processing.
Eavesdropping on dolphins
Passive acoustic monitoring (PAM) uses technology to detect, monitor, or even track whales and dolphins. Scientists use hydrophones or, in other words, microphones to record and listen to sound underwater. It’s like eavesdropping on the dolphins! We can sort different species according to the frequencies of their echolocation clicks. Frequencies can range from 10-20 Hz with sperm whales, to high-frequency echolocation signals of harbor porpoises (up to 180 Hz). For some dolphins species, such as the bottlenose dolphin, we can recognize and track individuals in a population by their unique signature whistles!
We have many tools for PAM in the marine environment. Most platforms are fixed or mobile and deployed in one location for a set period of time (ranging from days to months). This is also called static acoustic monitoring and is very popular for long-term monitoring projects. Mobile platforms record sound for short periods while in motion, often a towed hydrophone from a boat or a drifting platform.
Monitoring our protected species
We use PAM set-ups across the globe to monitor most species of whales and dolphins. It has been critical in measuring marine mammal responses to human-made noise, such as shipping traffic or seismic surveys. PAM is vitally important for the long-term monitoring of ‘hot-spots’ such as breeding or feeding grounds to detect behavioral patterns and changes over the years.
PAM has also been useful in endangered species management and monitoring. Moreover, it has been key in efforts to save the critically endangered vaquita. The vaquita is the world’s smallest and most endangered cetacean. Intensive acoustic monitoring in the Gulf of California has allowed researchers to closely monitor the vaquita population’s declines to protect the species from extinction. Unfortunately, the latest surveys indicate that less than twenty vaquitas remain.
BUZZ! It’s dinnertime
Passive acoustic monitoring records a series of echolocation clicks in what we call a click train. Scientists study click trains to identify behavioral patterns of the animals. One of the main behaviors commonly identified is foraging behavior, or in other words, prey hunting. Interestingly, the patterns of clicks used in foraging behavior in dolphins are similar to prey hunting behavior seen in echolocating bats!
When chasing prey, the time interval between clicks decreases, helping us to identify three distinct phases in dolphin click trains; search, approach, and prey capture.
- The search phase: dolphins search for their prey by scanning their head and constantly click before they detect their prey.
- The approach phase: once they detect their prey, clicking increases rapidly- the dolphin is homing in on their target.
- Prey capture attempt: At 1 m distance, the dolphin goes into the terminal “buzz,” indicating prey capture. We can see this by a very high rate of successive clicks sounding like a high pitch buzz. The time interval between clicks can decrease to as low as 1 millisecond. This is 0.001 of a second!!!
Feeding buzzes can be recorded for many dolphins and whales, including narwhals, dolphins, and beaked whales. An amazing example is Blainville’s beaked whales, which can produce as many as 300 buzz clicks in the last 3 m of approaching their prey.
Humans can learn echolocation too
Did you know humans can do it too? Human echolocation is a new technique. It’s all about developing your perception skills! Certainly, it is beneficial to help blind people orientate themselves with their surroundings.
In fact, Daniel Kish, the real-life ‘bat-man,’ is fully blind but he can use sound to “see” as well as anyone else! Why not be a dolphin for a day? You can learn it too! Daniel Kish demonstrates human echolocation, Link: https://youtu.be/-kB1-P-hZzg
Check out these links to learn more on echolocation in dolphins
- Check out my talk ‘Eavesdropping on dolphins’ for FameLab Ireland! https://youtu.be/BztKKTQ9ie8
- If you want to know the basics: https://dosits.org/
- Save the Vaquita!
- Can dolphins advance medicine? https://www.medimaging.net/ultrasound/articles/294773777/dolphin-echolocation-could-advance-medical-ultrasound.html
- How sound affects echolocation in dolphins and whales
Nicole is a PhD student at University College Cork. Her research focuses on the use of passive acoustic monitoring to detect patterns in occurrence and foraging behaviour for harbour porpoise. Research interests are marine mammal bioacoustics, disturbance ecology, and conservation.