EDUARDO MERCADO III1

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Why Whales Sing

• EDUARDO MERCADO III1 L. NEIL FRAZER2
• 1Department of Psychology, University at Buffalo,
  SUNY
• 2School of Ocean and Earth Sciences, University
  of Hawaii

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Overview

• Which whales sing?
• When do whales sing?
• Where do whales sing?
• How do whales sing?
• Why do whales sing?

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Which whales sing?
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Humpback whales are the most studied species of
singing whale
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Singers appear to all be males
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Which whales sing?

• Only a few species of baleen whales sing, of
  which humpbacks are the most soniferous
• Adult, male humpback whales are the main singers

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When do whales sing?
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When do whales sing?

• When they are not eating
• When they are old enough
• Prototypical singers sing during the breeding
  season, in shallow coastal waters, when they are
  alone and stationary.

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Where do whales sing?
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Whales sing all over the worlds oceans
Hawaii
Caribbean
Australia
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Whales often sing in shallow coastal waters
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Where whales sing determines how well songs
travel through the ocean

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Mathematical models of underwater sound
propagation can predict how whale songs attenuate
with distance
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Sandy bottoms are better
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Where do whales sing?

• Everywhere
• Sing most in tropical shallow water environments
• Singers congregate in predictable locations, but
  whales seldom sing in the same place twice
• Sing in areas with flat sandy bottoms, where
  temperature is constant, 15 m below the surface

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How do whales sing?
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What are whale songs like?
Like human songs?
Like bird songs?
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Whale song is not like bird song
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Sounds within songs can be LOUD

• A loud bird song may travel 100s of meters
• A loud whale song may travel 100s of KILOmeters

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Whale song is not like bird song
START
FINISH
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Whale song is not like bird song
Three seconds
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Whale songs are like acoustic carousels
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Sections of songs can be monotonous
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Mathematical models of humpback song signals can
reveal their temporal and spectral features
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How do whales sing?

• Humpback whales produce long, structured
  sequences of broadband sounds
• Individual whales change the sounds and patterns
  of sounds produced within these sequences
  throughout their lives
• Changes are made progressively in such a way that
  whales within a particular region produce similar
  sequences

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Why do whales sing?

• Biologists answer Whales sing to increase their
  opportunities to reproduce their genes.
• Psychologists answer Whales sing to be heard.

Who is hearing the songs, what are they hearing,
and what do they do when they hear songs?
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Motivations for listening to songs

• Other male humpbacks
• may maintain spacing between males
• may establish male dominance hierarchies
• may maintain contact during migration
• Female humpbacks
• may play a role in courtship and bonding
• may enable them to locate or identify potential
  mates
• may facilitate ovulation
• The singers themselves
• may provide information about the environment and
  other whales activities

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OR
Humpback Whale
Song

• Whales could potentially use songs to communicate
  or to echolocate, two abilities that are often
  assumed to require radically different auditory
  processing.

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The evidence

• Lone males sing during the breeding season, which
  strongly suggests singing plays some role in
  mating.
• Singing males are interested in mating, and are
  presumably singing to increase their chances of
  mating.

How might singing increase a male humpback
whales chances?
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Finding females

• Step one in mating Find a female.
• Singing males that are alone havent achieved
  this first step.
• Given that lone males sing for hours on end, it
  seems likely that singing increases the chances
  that the singer will find a potential mate.

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How might whale songs help males to find a female?

• Songs could attract females
• Songs could encourage females to make sounds
• Songs could discourage other males from sticking
  around
• Songs could reveal females locations

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How might whale songs help males to find a female?

• Songs could attract females
• Songs could encourage females to make sounds
• Songs could discourage other males from sticking
  around
• Songs could reveal females locations

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Motivations for listening to songs

• Other male humpbacks
• may maintain spacing between males (possibly
  hierarchical)
• Female humpbacks
• may enable them to locate and choose males
  through approach or vocal invitation
• The singers themselves
• may provide information about the environment,
  especially the activities and locations of other
  whales

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Why do whales sing?

• Other male humpbacks
• may maintain spacing between males (possibly
  hierarchical)
• Song hypothesis
• females locate and choose singers through
  approach or vocal invitation
• Sonar hypothesis
• singers use their songs to monitor the activities
  and locations of other whales

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Do songs attract or inspire females?

• Observational and playback studies have found
  that whales are more likely to avoid than
  approach singers
• Males are much more likely to approach singers
  than are females.
• Females only rarely make sounds during the
  breeding season
• There are no reports of males approaching
  vocalizing females.

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Singers locate and approach silent whales
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Against the sonar hypothesis

• Humpback whale song is not suitable for use as a
  sonar signal.
• Seasonal, male-only, song-like echolocation does
  not fit within current ecological and
  evolutionary frameworks.
• Singers cannot hear any echoes from whales
  produced by songs because
• songs are not loud enough (echoes are too quiet
  and ambient noise is too loud)
• there are no such echoes

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What is sonar like?
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Some components of whale songs are suitable for
use as long-range sonar

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The evolution of song

• Song hypothesis Songs evolved as a secondary
  mating strategy through processes of runaway
  sexual selection.
• Sonar hypothesis Whales evolved echolocation
  abilities as an adaptation to the sensory
  constraints of underwater environments.

Whales that are scanning the environment for
other whales sing
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Can singers hear echoes?
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Mathematical models of humpback auditory
perception can clarify whether long-range sonar
is feasible
Auditory Cortex
Cochlea
Humpback whale cochleagram
Mammalian auditory system
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Findings to date

• Mathematical models indicate that whales exposed
  to songs should generate echoes.
• These models also show that the echoes generated
  will be much more complex and variable than the
  original songs.
• Preliminary models of humpback auditory
  processing suggest that echoes from some sounds
  within songs should be detectable at long ranges,
  but echoes from other sounds would be impossible
  to detect.

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For the sonar hypothesis

• Singing humpback whales localize and approach
  silent whales.
• Components of humpback song are well-suited for
  detection of whale-sized targets at long
  distances.
• Humpback whale ears are more highly innervated
  than those of all other mammals (including bats),
  with the exception of a small number of toothed
  whales.

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Testing the sonar hypothesis
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Why do humpback whales sing?

• They dont. Humpback whales produce structured
  sonar signals primarily to actively perceive what
  is happening in the world around them.

Acknowledgements Alexandra Tolstoy and Ruth
Keenan contributed to the development of the
mathematical models that provide the foundation
for the sonar model of humpback song.