Cetaceans with dialects: the killer whale and the sperm whale

Last week, the press was full of news about a recent article that highlight that sperm whales in the Eastern Pacific have distinct dialects. For this reason, the post of this week will explain what a dialect is (in cetaceans), which cetaceans have dialects in addition to sperm whales and which is the explanation to this. 

INTRODUCTION

The first question to be answered is “What is a dialect?”. This question is not simple because sometimes this concept is confused with another one: geographic variation. While dialects are song differences between neighbouring populations of potentially interbreeding individuals, geographic variations refer to differences in song over long distances and between populations which normally do not come together. In the case of dialects, the explanation of their presence is social learning, while in geographic variations the reason can be found in their genes. The function of dialects is to be an acoustical signature that help maintain cohesion and integrity of groups and as an inbreeding avoidance mechanism.

CETACEANS WITH DIALECTS

To date, dialects have been described in two cetacean species: killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus). These two species have several features in common:

• They live in matrilineal groups, that are highly stable groups of individuals linked by maternal descent that protect themselves against predators and other dangers.
• They live in multilevel societies, that consist of hierarchically nested social levels. From the upper to the lowest level, there are three levels: vocal clans, social units and individuals. This kind of societies are also present in human and other primates and in African elephants.

KILLER WHALE DIALECTS

Dialects have been found in resident killer whales from the northeastern Pacific, Norway and Kamchatka. In this species, these dialects consists on repertories of several call types that are different among pods. Each pod have distinctive features in the call repertories and, therefore, each pod has a particular dialect. Pods that share part of the repertories constitute acoustic clans. So, each clan is acoustically different. Pods from different clans can overlap and interact and new pods can be formed by fission of other pods, which turn out in divergence of dialects.

Killer whales (Orcinus orca) are one of the cetacean species with dialects (Picture: Oceanwide Science Institute).

SPERM WHALE DIALECTS 

Sperm whales have repertories that varied in the proportional usage of different coda types and classes. Sperm whale codas are stereotyped sequences of 3-40 broad-band clicks usually lasting less than 3 seconds in total, which functions are to help maintain group cohesion, reinforce bonds, aid negotiations and collective decision-making. These groups with distinct dialects also interact. To give a particular example, in the South Pacific and the Caribbean, there are six sympatric acoustic clans based on coda sharing, which simultaneously differ in movement and habitat use patterns and in feeding success.

Dialects have been described in sperm whales (Physeter macrocephalus) (Picture: CBC News).

ORIGIN OF DIALECTS IN CETACEANS

A recently published article in the magazine Nature suggests a mechanism that may explain the origin of multilevel societies in sperm whales. As we have seen, it is in these societies where dialects are present in cetaceans. So, here we will explain the origin of multilevel societies in sperm whales as an example.

In sperm whales, the upper level of the multilevel society are clans of individuals that communicate between them using similar codas. These clans are originated from cultural transmission via biased social learning of codas, when they learn the most common codas (conformism) from behaviourally similar individuals (homophily). Thus, the result are groups with increasingly homogeneous behaviour with a strong integration. The cultural transmission plays a key role in the partitioning of sperm whales into sympatric clans (clans that live together but without interbreeding). So, it is in these clans where distinctive behavioural patters may appear, like dialects. The lower level, social units, are originated from ecological, cognitive and time constraints and benefits.

Multilevel societies. Individuals (stars and filled circles) are the lowest level and in association (black lines) with other individuals they constitute social units (empty black circles). Socials units with acoustic similarity (orange lines) form vocal clans (blue and green). It is in vocal clans where dialects can emerge (Picture: Marc Arenas Camps).

HUMPBACK WHALES: A DIFFERENT CASE

The differences in the songs of humpback whales (Megaptera novaengliae) cannot be considered dialects since they happen between geographically isolated populations. Due to a geographic and reproductive isolation, these differences have appeared as a result of genetic distinctions among populations.

REFERENCES

• Cantor, M; Shoemaker, LG; Cabral, RB; Flores, CO, Varga, M & Whitehead, H (2015). Multilevel animal societies can emerge from cultural transmission. Nature Communications. 6:8091. DOI: 10.1038/ncomms9091
• Conner, DA (1982). Dialects versus geographic variation in mammalian vocalizations. Animal Behaviour. 30, 297-298
• Dudzinski, KM; Thomas, JA & Gregg, JD (2009). Communication in Marine Mammals. In Perrin W, Würsig B & Thewissen JGM (edit.). Encyclopedia of Marine Mammals. Academic Press (2 ed).
• Ford, JKB (2009). Dialects. In Perrin W, Würsig B & Thewissen JGM (edit.). Encyclopedia of Marine Mammals. Academic Press (2 ed).

How do whales communicate with each other?

The post of this week talks about baleen whale communication, it is, cetaceans that feed thanks to the presence of baleen plates in the mouth. In concrete, we will focus on the acoustic communication in baleen whales and, in specific, in the humpback whale case.

INTRODUCTION

Bradbury and Vehrencamp defined the term communication like the process in which an information is given through a signal from a speaker to a receiver and this receiver uses this information to decide how to respond or if the receiver responds to the signal.

There are several types of communication among marine mammals, either chemical, visual, tactile or acoustic. Due to solar light has a delimited capability to penetrate into the water, whales and other marine mammals have difficulties on visual communication with each other from a certain distance, so they use sound. In addition, chemical communication is not efficient in the aquatic environment.

COMMUNICATION PROCES IN BALEEN WHALES

Production and reception of sound

While anatomical structures related with the production and transmission of sound have been found in odotocetes (cetaceans with teeth), they have not been found in the case of baleen whales (mysticetes). Baleen whales, despite they present larynx, don’t have vocal chords. However, it is accepted that cranial sinuses, empty spaces in the skull, are involved in phonation, but its role is unclear.

The big whales are by far the most resounding marine mammals. Humpback whales (Megaptera novaeangliae) produce songs that last some hours and can be heard long distances (some kilometres). Blue whales (Balaenoptera musculus) and fin whales (Balaenoptera physalis) don’t fall behind: they produce low frequency sounds that travel more than 3,200 km of distance. In fact, blue whales produce sounds around 190 decibels, the loudest sound produced for an animal.

Blue whales (Balaenoptera musculus) can produce sounds of 190 decibels  (Picture: iTravel Cabo).

Some behavioural studies have demonstrated that all cetaceans, but specially odontocetes, have a good hearing.

Function

While some experts defend the idea that this sounds are used to communicate each other at long distances, other suggest that are used to detect the underwater relief to orientate (echolocation). Anyway, it is more accepted that they have a communicative function, including behaviours like exhibition and the establishment of the territory, among others.

THE CASE OF HUMPBACK WHALES

Humpback whales (Megaptera novaeangliae) produce complex sounds that can be heard to long distances. They are one of the most resounding baleen whales. During winter, in the breeding grounds, these whales produce long and complex songs at the same zone. These songs are different in the different zones. These songs (you can hear one of them here) lasts 10-15 minutes, but they can sing them for hours, and are composed by themes, phrases and subphrases. Each subphrase lasts some seconds and are composed by low frequency sounds (normally under 1,500 Hz).

Structure of a humpback whale song (Megaptera novaeangliae) (Picture: Hawai’s Marine Mammal Consortium).

But the complexity doesn’t end here. The structure of this musical pieces changes along winter. Not only they change the frequency and duration of the phrases and themes, but also some of them are changed by new compositions. Moreover, they also modified the composition and sequence of these themes.

Anyway, all the whales at the same area sing the same song and all of them modify it at the same rate to other mates. So, they learn from other mates.

Some studies highlighted that adult males are the only that produce this songs. So, it indicates that this songs play a role in reproduction, similar to bird songs. Therefore, these songs indicate to females the sex, the species, the position and that he is ready to compete with other males and he is ready for mating.

In addition, according to Mobley y Herman (1985) the fact that males sing at the same time stimulates the synchronization of the ovulation of the females.

The fact that males sings at the same time produce the synchronization of the ovultion of females of humpback whale (Picture: Yellowmagpie).

REFERENCES

• Berta A, Sumich J & Kovacs KM (2006). Marine mammlas. Evolutionary biology. Ed. Academic Press (2 ed)
• Day (2008). Guía para observar ballenas, delfines y marsopas en su hábitat. Ed. Blume
• Perrin WF, Würsig B & Thewissen JGM (2009). Ed. Academic Press (2 ed)
• Reeves RR, Stewart BS, Clapham PJ & Powell JA (2005). Guía de los mamíferos marinos del mundo. Ed. Omega