E DUARDO M ERCADO III 1 & L. N EIL F RAZER 2 1 Department of Psychology, University at Buffalo, SUNY 2 School of Ocean and Earth Sciences, University of Hawaii Why Whales Sing

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

Which whales sing?

Humpback whales are the most studied species of singing whale

Singers appear to all be males

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

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.

Where do whales sing?

Whales sing all over the worlds’ oceans Caribbean Australia Hawaii

Whales often sing in shallow coastal waters

Where whales sing determines how well songs travel through the ocean

Mathematical models of underwater sound propagation can predict how whale songs attenuate with distance

Sandy bottoms are better

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

How do whales sing?

What are whale songs like? Like human songs? Like bird songs?

Whale song is not like bird song

Sounds within songs can be LOUD A loud bird song may travel 100s of meters A loud whale song may travel 100s of KILOmeters

Whale song is not like bird song START FINISH

Whale song is not like bird song Three seconds

Whale songs are like acoustic carousels

Sections of songs can be monotonous

Mathematical models of humpback song signals can reveal their temporal and spectral features

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

Biologist’s answer: Whales sing to increase their opportunities to reproduce their genes. Psychologist’s answer: Whales sing to be heard. Why do whales sing? Who is hearing the songs, what are they hearing, and what do they do when they hear songs?

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

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

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. The evidence How might singing increase a male humpback whale’s chances?

Step one in mating: Find a female. Singing males that are alone haven’t 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. Finding females

Songs could attract females Songs could encourage females to make sounds Songs could discourage other males from sticking around Songs could reveal females’ locations 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 How might whale songs help males to find a female?

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

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

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. Do songs attract or inspire females?

Singers locate and approach silent whales

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 Against the sonar hypothesis

What is sonar like?

Some components of whale songs are suitable for use as long-range sonar

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. The evolution of song Whales that are scanning the environment for other whales “sing”

Produce Classify Receive Classify Produce OCEAN CHANNEL y 2 (t,r) y 1 (t,r) x 2 (t,r) x 1 (t,r) G(t,r) Can singers hear echoes?

Produce Classify Receive Classify Reflect OCEAN CHANNEL y 2 (t,r) y 1 (t,r) x 2 (t,r) x 1 (t,r) G(t,r)

Produce Classify Receive Classify Produce OCEAN CHANNEL y 2 (t,r) y 1 (t,r) x 2 (t,r) x 1 (t,r) G(t,r)

Cochlea Humpback whale cochleagram Mammalian auditory system Mathematical models of humpback auditory perception can clarify whether long-range sonar is feasible

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. Findings to date

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. For the sonar hypothesis

Testing the sonar hypothesis

They don’t. Humpback whales produce structured sonar signals primarily to actively perceive what is happening in the world around them. Why do humpback whales sing? 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.