Masking – Are we louder than dolphins?

With human activity increasing both in coastal and deep ocean, the world’s ocean has become quite a noisy environment. Concerned researchers have investigated how this may be impacting marine life, including marine mammals.

One study has investigated the potential effects of pile driving on the dynamics of bottlenose dolphin populations.

Importance of Sound to Bottlenose Dolphins

Bottlenose dolphins use sound to:

  • investigate and understand their environment
  • find and capture prey
  • transmit information to other members or conspecifics

Depending on the surrounding contexts, dolphins will utilize different sound types and project the soundwave at varying frequencies and sound levels (Table 1). Approximately, unmodulated whistles within 3.5-10 kHz have an effective range of 14-25 km. However, when the whistle frequency increases to 12 kHz, the effective range decrease to 1.5-4 km. Pulsed sounds, such as clicks, rarely travel further than a few kilometers.

Table 1.

Sound TypeFrequency Range (kHz)Dominant Frequencies (kHz)Source Level (dB re μPa at 1m)

Sound Generated by Pile Driving

On average, an individual pile driving pulse generates a sound source level of 151 dB re 1 μPa. Dr. Mciwem (2006) summarized potential masking of dolphin call types (i.e., whistles, clicks) in the figure below.

The figure depicts how 3 different frequencies (9, 50, 115 kHz), commonly used by dolphins, dissipates as the sound travels further from the source. Sounds that lie under the lines of the pile driving hammers (i.e., diesel, drop) potentially mask dolphins sounds.

At 9kHz (top panel), the drop hammer could mask vocalizations at a radius of 1.3 km; while the diesel hammer potentially masks vocals over 40 km away.

At 50 kHz, the diesel hammer could mask echolocation clicks up to 6 km away, and the drop hammer up to 0.2 km.

At 115 kHz, the diesel hammer could mask echolocation clicks up to 1.2 km away, and the drop hammer 0 km.

What does this mean?

Here, we see that depending on the loudness of a sound received by and call type – dolphin vocalizations have the potential to be masked or go unheard by a conspecific. Masking may cause dolphins to change the frequency range, loudness or even how often they emit signals. This can cause additional excursion of energy, or possibly change vocal composition of specific social groups. Masking could also influence missed opportunities to mate or receiving vital information from another individual because signals were not heard.

It is important to keep in mind that this information comes a single review study and only goes over potential sound interference from pile driving. However, there are multiple sounds, both natural and human-made, occurring all at once. Therefore, the influence of masking may be underestimated. Scientists continue to do work on understanding the full spectra of masking.

Who’s Saying What? Answers from New Tech

While researchers have studied dolphin communication for decades, science has only been able to generalize what signals are used during behaviors. This is because technology has not been available to localize or tell us which individual is talking and what signals they are emitting.

When researchers record communication and behaviors, typically a hydrophone and separate video recording device is used. Acoustic and visual recordings are synced, and while some researchers are able to associate physical behaviors to concurrent acoustic signals – neither video nor acoustic recording give an indication on who spoke the signal. So, it has been difficult to say what animals and signals are meant to act as a back-and-forth conversation. However, slowly but surely technology has advanced, and scientists are one step closer to localizing the ‘whistler‘.

Dr. Herzing from the Wild Dolphin Project began preliminary work using a new localizing device. This custom underwater device uses three hydrophones and camera to simultaneously record audio and video. The recordings are interpreted by a specialized software that will identify a whistle in real time. When watching the recording, the software will mark a ‘whistler’ with either: a yellow star if it emits a whistle, or a red square if it emits a click.

Watch this device in action and learn about Dr. Herzing’s work in the Bahamas.

Scientists have also developed novel technology capable of tracking the strength and projection of a dolphin’s echolocation. Dr. Amundin and colleagues have been working on the ELVIS project.

The ELVIS system includes an array of hydrophones and specialized software that visually tracks a dolphin’s echolocation beam. A dolphin is given the opportunity to choose a symbol on a screen – each symbol representing a food reward. Upon approach, a dolphin can point via their echolocation and ELVIS will follow the beam, showing both the strength of the signals and indicating the choice.

It is truly incredible the advances we have made in our technology and all the new questions we can work to answer!


What is a soundscape? Let’s say you step outside your house, a plane flies over head, 5 o’clock traffic is happening down the road, a nice breeze sweeps by and rustles the trees, and your neighbor’s kids are playing with the sprinkler in their front yard — all these sounds coming in and hitting your ear create a “soundscape”.

The combined sounds, that vary in loudness, duration and pitch compose the soundscape for that area. If we were to take the above scenario and put it underwater, all the sounds you hear would be louder, and you perhaps would even hear additional sounds. Sound travels 4.5x faster and travels much further underwater than in air! So, while you may have missed the whispering neighbors at the far end of your street above water, you may now be hearing the gossip below water.

So, what does the ocean sound like? Below gives us a snapshot of different sounds that occur:

Abiotic and biotic sounds are heard throughout the ocean. Weather, such as rain, wind and lightning can create loud or consistent sounds. Earthquakes create noise that can be heard from miles away. Human noise from boats or seismic devices has grown exponentially and can be heard daily. Marine life from corals, fish to large marine mammals emit their own sounds too. Imagine all these sounds being heard at once! This makes for a noisy environment.

Marine mammals use acoustic sounds to communicate with one another. As the background noise of the ocean has drastically increased over the years, scientists have become concerned about potential “masking” of marine mammal acoustic communication.

Examples of soundscape data presentations using an 11-month dataset recorded 20 m off the seabed in 1,280 m of water off Newfoundland, Canada. B: Long term spectral average of the complete dataset. Orange dashed ellipses, presence of seismic survey signals; black solid ellipses, fin whales; solid blue circles, a distant dynamic positioning (DP) vessel signature.

The above figure demonstrates examples of soundscape data taken offshore at Newfoundland, Canada. The figure (B) shows the loudness of different frequencies recorded in the area. Circled are the frequency and timescale ranges for of 3 different sources: dynamic positioning vessel, seismic survey, and fin whale songs. Notice that the noise of the seismic surveys overlaps with fin whale songs.

Not only do some anthropogenic (human-made) sounds fall in the same frequency ranges these animals communicate at, but they are also very loud. Imagine being at a rock concert and trying to talk with your friend. You probably have to shout or get really close; you may even choose to say fewer words because communicating with your voice is not efficient. Your friend may not even understand the words you are saying and ask you to repeat. You may just switch to hand signals or just choose not to communicate until the music stops. Scientists believe marine mammals may be facing similar decisions when trying to communicate to their group members during noisy events.

Marine mammals have been reported to change the frequency and/or duration of their calls – sometimes ceasing all communication – when they are in the presence of loud anthropogenic noise. This can lead to serious impacts:

  • exerting extra energy to try and send audible calls
  • missing important calls that may indicate food or a mate
  • temporary or permanent shifts in behavior
  • temporary or permanent avoidance or relocation

It is important for scientists, decision-makers, boaters and even recreational swimmers to continue to work together to reduce the noise we impart into the ocean. Remember it is louder and travels much further than you may think, so we must keep in mind the animal’s perspective and allow them to live out their natural behaviors as best as possible.

For additional information on soundscapes and research click here.

“I did it!” – Dolphins cheer for themselves

Dolphins may call success and squeal in victory when completing a task correctly or catching prey.

Dolphins emit different types of vocalizations to transmit information about food, location and emotional state. One type of vocalization is called a “burst pulse”. Burst pulse signals are considered rapid click trains and have been observed when dolphins are foraging, as well as socializing.

Victory squeal with a simultaneous whistle. (Ridgway et al., 2015)
Victory squeal. (Ridgway et al., 2014)

Dr. Ridgway and colleagues conducted a unique study that combined simultaneous video and acoustic recordings to investigate what behaviors and vocals dolphins used when attempting to capture prey.

Researchers and trainers used a natural sea pen where a dolphin and trainer stayed at one end of the enclosure, while a fish was baited at the opposite end. Once the trainer cued the dolphin, it would swim across the enclosure in search of the fish.

A unique device was utilized in order to visually record the animal’s physical and acoustic behaviors at the same time. The device was temporarily placed on the melon (i.e., the top of the dolphin’s head) along with an additional hydrophone near the baited fish.

Customized device that simultaneously documented visual and audio recordings.

The researchers found a unique, 3-part vocal pattern during prey capture:

  1. Echolocation clicks were used to search out the fish,
  2. Clicks became closer together as the dolphin neared the fish
  3. A victory squeal (VS) (i.e., burst pulse signal) was emitted at (or just before) the time of capture
(A) As the dolphin eats the fish, head jerks are recorded on the forehead camera microphone. (B) Beginning of approach, echolocation clicks are found; the inter-click-interval became smaller when closing in on fish; at capture, victory squeal was emitted (C) Left to right: (a) view from forehead camera of fish (white arrow) in the distance (b) closing in on fish, TB (c) view of fish in dolphin’s mouth and simultaneous victory squeal (d) view of dolphin rostrum as the animal moves away clicking. (D) spectrogram of vocal pattern emitted during prey capture (from approach to just after capture).

Researchers coined the term “Victory Squeal” to represent the context of when it occurs (when a dolphin knows it has/or is about to succeed in a task), and the vocal being reminiscent of a child-like squeal.

This study was the first of its kind – connecting video and audio at the same time. Researchers were able to confirm dolphins using head jerking behavior when they are consuming a fish. They also presented a particular vocal sequence used when successfully capturing prey. They even extended their research and found that dolphins used a VS when doing a request from their trainer correctly!

Research in the future could potentially use this vocal pattern to assume successful behaviors in managed care or in the wild when people are unable to visualize what the dolphins are doing.

Dive into their study here and find out more about their investigation.