Courses:PHYS341/2021/Project 17 Humpback Whale Song
Introduction
Anatomy
The humpback whale is a mysticetes[1], which unlike odotocetes (toothed whales) use only the larynx for sound production. Inside the larynx is a thick u-fold (similar to the vocal folds of other mammals) that is adjacent to the laryngeal sac (large inflatable pouch). The humpback whale contracts the throat and chest muscles, cause the air to flow between the lungs and the laryngeal sac. By alternating the expansion and contraction of the lungs and laryngeal sac, the air is pushed across the u-fold causing vibrations and the production of sound. These vibrations can then propagate through the ventral throat pleats and into the surrounding water as sound waves. The changes in the laryngeal sac shape (width of the u shape) alter the frequency and/or amplitude of the sounds. There is also an indication that the patterns in the harmonics and in broadband sounds (similar to a cry) reflect on the different resonating air chambers contributing the humpback whales’ sound production. As the anatomy of a humpback whale is much larger than a human’s (ranging from 12-16 meters in length) the sound is much lower, with low frequency sound pulses being produced.
Humpback whales also produce percussive sound by slapping different parts of their body (tail or fluke) against the surface of the water, with its tail producing a broadband of 30-12,000Hz.
Whale Song and Communication
Communication
Because of the larger scale (one of the largest aquatic mammals in the ocean) of humpback whales, as well as the speed of sound through water (around 1500 m/s, as opposed to air which is around 343m/s), they produce long wavelength frequencies ranging from 8Hz-8kHz. Their songs are at a high source level of around 175-188dB (one femto Pascal (fPa, 10^-15) at one-meter distance) and a low frequency range. The combination of these factors allows for the whales to communicate from hundreds of kilometres away.
Song and Acoustics
The structure of humpback whale songs are the most complex vocals emitted by aquatic mammals, with a single whale having the ability to sing continuously for hours on end. The song is composed of three to nine ‘themes’, taking between 8-15 minutes (though sometimes going for up to 30 minutes) to return to the initial theme. Each theme is composed of phrases that repeat several times, with each phrase being made up of different tonal notes that last several seconds. Humpback whales also have the ability of learning new phrases, themes and patterns, with the pattern of a song changing frequently
Figure 1 depicts a short segment of a whale song (1 minute and 4 seconds in length), and shows several different phrases, with a couple of low tonal repeating phrases, as well as some higher register phrases. The lower register phrases are generally louder and have a larger amplitude, with the higher register phrases and notes usually being quieter and having a smaller amplitude (though in this case some of them are louder than the low register phrases).
| Low Tonal Phrases | High Tonal Phrases | Low to High | Gurgle |
|---|---|---|---|
| 0.10 - 0.30 seconds
8:50 - 10:50 seconds 15.50 - 17:00 seconds 21.50 - 24:00 seconds 28:00 - 30:00 seconds |
4:00 - 7:00 seconds
11.50 - 14.50 seconds 18.50 - 20:00 seconds 25:00 - 26.50 seconds |
31.50 - 32.50 seconds
37:00 - 38:00 seconds 48:00 - 48.50 seconds 55.75 - 56.50 seconds |
42.50 - 47:00 seconds
58.50 - 1:20 seconds 1:30 - 1.40 seconds |
As is seen in this table, the first section of the whale song goes back and forth between low and high phrases, and then transitions into a back and forth of the fast low to high phrases and the longer gurgles (two low to high phrases, then a gurgle, and a repetition of that with an additional short gurgle on the end). This shows the complexity of the humpback whale's song, as well as the ways in which they can repeat different patterns of phrases within a song.
Although this example shows the patterns of the whale song, it doesn't accurately capture the full amplitude nor volume of the whale song, as the recording used was taken far away, and from a single device. The use of vertical line arrays have been incredibly useful in determining the acoustic properties of singing humpback whales, as it gives precise source levels as opposed to other recordings. There is a variance of over 20dB between the least and most intense phrases, with the lower broadband sounds (lasting around 2 seconds) being louder, and the tonal sounds usually being quieter (similar to how we can usually shout louder than we can sing).
References:
Au, Whitlow, et al. “Acoustic Properties of Humpback Whale Song.” Research Gate, vol. 120, no. 2, Sept. 2006, pp. 1103–10, doi:http://dx.doi.org/10.1121/1.2211547.
Bilal, Muhammad, et al. “Bionic Morse Coding Mimicking Humpback Whale Song for Covert Underwater Communication.” MDPI, vol. 10, no. 1, Dec. 2019, p. 186, doi:https://doi.org/10.3390/app10010186.
“How Do Marine Mammals Produce Sound?” Discovery of Sound in the Sea, 2002,
https://dosits.org/animals/sound-production/how-do-marine-mammals-produce-sounds/.
Mercado, Eduardo 3rd et al. “Sound production by singing humpback whales.” The Journal of
the Acoustical Society of America, vol. 127,4 (2010): 2678-91. doi:10.1121/1.3309453
https://pubmed.ncbi.nlm.nih.gov/20370048/
“Sounds Recorded in Glacier Bay.” National Park Service, 20 Nov. 2020, https://www.nps.gov/glba/learn/nature/soundclips.htm.
[1]A large cetacean, usually larger than 9.1m (30ft) long. Instead of teeth, they have a series of horny plates called baleen (made from the same material as human hair and fingernails). The baleen plates hang from the gums of the upper jaw and filter small pieces of food from the water. Baleen whales have symmetrical skulls, and have two (or connected) blowholes.
[2]Sound signal that includes the acoustics energy across a wide range of frequencies (doesn’t have a largely distinguishable tonal sound).