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42Evolution

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Learning to sing under water

An eighteenth century etching  showing Dutch whalers hunting Bowhead whales (Balaena mysticetus)near Jan Mayen Land in the Arctic ocean.  Bowheads are named for their unusually shaped skull, which they employ to punch through the thick sea ice in order to breathe.   They overwinter and mate in arctic waters, where the males sing to attract a mate.  
Bowheads are second only in size to the blue whale, and are very long-lived.  Stone harpoon heads, which went out of use at the turn of the 19th century, have been found lodged in the bodies of some individuals of today.  
Listen to their calls here.

An eighteenth century etching showing Dutch whalers hunting Bowhead whales (Balaena mysticetus)near Jan Mayen Land in the Arctic ocean. Bowheads are named for their unusually shaped skull, which they employ to punch through the thick sea ice in order to breathe. They overwinter and mate in arctic waters, where the males sing to attract a mate. Bowheads are second only in size to the blue whale, and are very long-lived. Stone harpoon heads, which went out of use at the turn of the 19th century, have been found lodged in the bodies of some individuals of today. Listen to their calls here.

Early whaling logs often referred to whales as ‘singers’.  All whales use sounds for communication, and most use recognisable patterns, ranging from the haunting tones of bowhead whales to the fast echolocation.  Bowheads and bottle nosed dolphins use ‘names’ to identify each other and their clan, have ‘conversations’, and copy each other’s calls.

Bowheads are second only in size to the blue whale, and are very long-lived. Stone harpoon heads, which went out of use at the turn of the 19th century, have been found lodged in the bodies of some individuals of today.  Listen to their calls here.

Whales’ land-based ancestors made sounds as we do, using the throat and mouth.  But try singing under water!  Whales call during dives; whilst holding their breath, and with their mouths closed.  Calling is essential for these highly social animals; this is evident because independently both baleen and toothed whales have evolved new ways to produce and transmit sound in the sea.

How are whale sounds made?

A humpback whale (Megaptera novaeangliae) ‘breaching’ off the coast of South Shelter Island, Juneau, Alaska.  The flexible throat pleats are visible here as a series of ridges.  Since it is unethical to perform invasive tests on live whales, it has not been proven how these intriguing animals produce sound.  Our current understanding is based on studies of the anatomy of already dead whales (Image: Wikimedia Commons). Listen to a selection of humpback calls here:  - Call at breeding ground - Call from West Indies - Yups

A humpback whale (Megaptera novaeangliae) ‘breaching’ off the coast of South Shelter Island, Juneau, Alaska. The flexible throat pleats are visible here as a series of ridges. Since it is unethical to perform invasi... moreve tests on live whales, it has not been proven how these intriguing animals produce sound. Our current understanding is based on studies of the anatomy of already dead whales (Image: Wikimedia Commons). Listen to a selection of humpback calls here:- Call at breeding ground- Call from West Indies- Yups

We produce sound in a tubular organ in our throats; the larynx.  This organ is an air valve, closing off the lungs when we swallow, and controlling the outward flow of air.  Sound is generated by vibrating paired membranes in the larynx; these ‘chop up’ the airflow into pressure waves.  This is then modified by resonating in the chambers of the chest, nose and throat before being released through the mouth.

A humpback’s larynx does not sit across the windpipe.  Instead it straddles the opening to an additional air sac located beneath the throat.  These whales make sounds by passing air between this sac and the windpipe, vibrating the vocal folds of the larynx.  These deep notes are modified and amplified by resonating in the laryngeal sac and nasal cavity, and are thought to be transmitted into the water through the sac, which vibrates the flexible throat pleats somewhat like a hi-fi speaker cone.

Recent work with trained dolphins has solved the mystery of how they generate their echolocation sounds.   During a deep dive, a small reservoir of air (around 3% of the original surface volume) remains in the nasal passages after the lungs have collapsed. Dolphins recycle the air inside this cavity, passing it through the vocal folds of the phonic lips and vibrating them in the same way that we use the larynx.  Instead of using internal resonating chambers, muscles controlling the shape of the melon modify the pitch and direction of this sound.  This enables dolphins to produce the same pitch and timbre of sounds at any depth of water, regardless of the internal air volume.  Dolphins also hear through acoustic fat deposits, this time in a cavity of the lower jaw (called the mandibular foramen).  This receives reflected sound waves and transmits them to the auditory bulla (middle ear) (Image: Wikimedia Commons)

Recent work with trained dolphins has solved the mystery of how they generate their echolocation sounds. During a deep dive, a small reservoir of air (around 3% of the original surface volume) remains in the nasal passa... moreges after the lungs have collapsed. Dolphins recycle the air inside this cavity, passing it through the vocal folds of the phonic lips and vibrating them in the same way that we use the larynx. Instead of using internal resonating chambers, muscles controlling the shape of the melon modify the pitch and direction of this sound. This enables dolphins to produce the same pitch and timbre of sounds at any depth of water, regardless of the internal air volume.  (Image: Wikimedia Commons)

Dolphins have evolved a secondary set of vocal folds inside their nasal cavities, called ‘phonic lips’.  These vibrate like our vocal chords and generating pressure waves.

Because during deep dives the air volume in their nasal cavities becomes very small, their clicks, rasps and whistles do not resonate in inner cavities.  Instead, a lens of fatty material on the front of the skull known as the ‘melon’ acts as an underwater ‘speaker cone’, amplifying and transmitting these calls.

Why do whales ‘sing’?

The repetitive, phrased songs of humpback whales are a means of male display.  Whilst both genders make sounds, only the males produce song patterns.  They copy the signature calls of their clan, serenading unaccompanied females during seasonal migration  and at the winter breeding grounds.

A pod of humpback whales (Megaptera novaeangliae)  bubble net fishing; Juneau, Alaska. Humpback whales sometimes hunt in groups using a controlled release of air from their blowholes in a decreasing spiral pattern.  This forms a ‘wall’ of bubbles, with which they shoal fish together, ahead of lunge feeding.  Watch them bubble net fishing here.

A pod of humpback whales (Megaptera novaeangliae) bubble net fishing; Juneau, Alaska. Humpback whales sometimes hunt in groups using a controlled release of air from their blowholes in a decreasing spiral pattern. This ... moreforms a ‘wall’ of bubbles, with which they shoal fish together, ahead of lunge feeding. Watch them bubble net fishing here.

Their behaviour suggests that these breeding areas are a form of ‘floating lek’, where females ‘browse’ amongst available mates. Humpbacks also use other non-singing signals, e.g. when hunting together, females call to communicate with their offspring.

Bottle-nosed dolphins develop their own distinctive signature whistle in the first few months, and exchange these ‘names’ when meeting other dolphins.  Females keep their whistle throughout life, whilst males change their signature calls when they move between social groups. Like baleen whales, they also communicate during foraging dives and to maintain social ties.

What can we learn from whale song?

This unusual view of a humpback whale (Megaptera noveangelidae) off the cost of Australia shows the flexible throat pleats in a compressed position.  Clans of humpback whales modify the sound pattern of their song through each season, and evolve a completely new song form over 15 years.  However these animals are able to learn and adapt to change at a much faster rate.  A study following the arrival of a handful of male humpback whales from western Australian waters into the eastern Australian humpback population’s breeding grounds, found that the eastern males switched to the western song in only two years.  This ‘cultural revolution’ may have been driven by the mating choices of the eastern females; many female mammal species show a preference for novelty in a mate (Image: Wikimedia Commons)

This unusual view of a humpback whale (Megaptera noveangelidae) off the cost of Australia shows the flexible throat pleats in a compressed position.Clans of humpback whales modify the sound pattern of their song through... more each season, and evolve a completely new song form over 15 years. However these animals are able to learn and adapt to change at a much faster rate. A study following the arrival of a handful of male humpback whales from western Australian waters into the eastern Australian humpback population’s breeding grounds, found that the eastern males switched to the western song in only two years. This ‘cultural revolution’ may have been driven by the mating choices of the eastern females; many female mammal species show a preference for novelty in a mate (Image: Wikimedia Commons)

Biologists classify ‘song’ as following ‘a repeating, predictable acoustic pattern’.  Most songbirds mimic the calls of their peer group  as juveniles.  When they mature, this song pattern becomes ‘fixed’.  Whales are unusual; they can copy and learn new sounds throughout their lives.  Like us, they have a brain structure that continuously learns and can adapt to changes.

The diversity of signature calls and unique song patterns used by clans reveal that whales have a complex and sophisticated system of learnable language.  Studying the language and culture of whale populations can thus provide clues about how own language and social complexity may have evolved.

Text copyright © 2015 Mags Leighton. All rights reserved.

References
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Cholewiak D M (2013) ‘Humpback whale song hierarchicial structure; historical context and discussion of current classification issues’  Marine Mammal Science 29 3: E312-E332
Cranford, T.W., (2000)  "In Search of Impulse Sound Sources in Odontocetes." In Hearing by Whales and Dolphins (Springer Handbook of Auditory Research series), W.W.L. Au, A.N. Popper and R.R. Fay, Eds. Springer-Verlag, New York.
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Janik VK (2005) ‘Acoustic communication networks in marine mammals’  pp390-415 in Animal Communication Networks  McGregor PK (Ed) CUP, Cambridge
Janik VK (2009) ‘Whale song’ Current Biology  19(3)R9-R11
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Mercado E et al.  (2010) ‘Sound production by singing humpback whales’  Journal of the Acoustics Society of America  127(4) 2678-2691     ***NB  I am using the broader definition of ‘song’ as applied here by these authors.  Janik (2009) suggests that only baleen whales are singers because of their more elaborated song patterns.  However toothed whales also use patterns, even though they are clicks and whistles rather than resonating songs.
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