Sperm Whales: Social Evolution in the Ocean

by Hal Whitehead

Overview

Famed in story as "the great leviathans," sperm whales are truly creatures of extremes. Giants among all whales, they also have the largest brains of any creature on Earth. Males can reach a length of sixty-two feet and can weigh upwards of fifty tons.

With this book, Hal Whitehead gives us a clearer picture of the ecology and social life of sperm whales than we have ever had before. Based on almost two decades of field research, Whitehead describes their biology, behavior, and habitat; how they organize their societies; and how their complex lifestyles may have evolved in this unique environment. Among the many fascinating topics he explores is the crucial role that culture plays in the life of the sperm whale, and he traces the consequences of this argument for both evolution and conservation. Finally, drawing on these findings, Whitehead builds a general model of how the ocean environment influences social behavior and cultural evolution among mammals as well as other animals.

The definitive portrait of a provocative creature, Sperm Whales will interest animal behaviorists, conservationists, ecologists, and evolutionary biologists as well as marine mammalogists.

Product Details

ISBN-13:	9780226895185
Publisher:	University of Chicago Press
Publication date:	08/15/2003
Edition description:	1
Pages:	456
Product dimensions:	6.00(w) x 9.00(h) x 1.30(d)
Age Range:	3 Months

About the Author

Hal Whitehead is the Killam Professor in the Department of Biology at Dalhousie University in Canada. He is the author of Voyage to the Whales and coeditor of Cetacean Societies: Field Studies of Dolphins and Whales, the latter published by the University of Chicago Press.

Read an Excerpt

SPERM WHALES
Social Evolution in the Ocean

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By Hal Whitehead
THE UNIVERSITY OF CHICAGO PRESS
Copyright © 2003 The University of Chicago
All right reserved.
ISBN: 978-0-226-89518-5

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Chapter One
The Sperm Whale: An Animal of Extremes

1.1 Social Complexity in the Ocean

The open sea is an environment where technical knowledge can bring little benefit and thus complex societies-and high intelligence-are contraindicated (dolphins and whales provide, maybe, a remarkable and unexplained exception). -Humphrey 1976

Nicholas Humphrey's essay "The social function of intellect," from which this quote is taken, sparked the "Machiavellian intelligence" hypothesis, which proposes that sophisticated animal intelligence evolved as selection favored those animals that effectively exploited social complexity (Byrne and Whiten 1988). This hypothesis is now widely accepted, but the "remarkable and unexplained exception" of the cetaceans (dolphins and whales) has received little attention in writings about the evolution of intelligence and social complexity, except from a few cetologists (e.g., Connor et al. 1998) and open-minded primatologists (e.g., Whiten and Ham 1992).

This situation is changing, and cetacean science is gradually adding to our knowledge of the fabric of nonhuman social systems and cognitive abilities. However, of the eighty-five or so extant species of whales and dolphins, four have received almost all of the attention (Mann 1999): the killer whale (Orcinus orca), bottlenose dolphin (Tursiops spp.), humpback whale (Megaptera novaeangliae), and sperm whale (Physeter macrocephalus). These are the species whose behavior has been studied in greatest detail. A variety of factors draw science toward particular organisms. For the sperm whale, these factors include the largest brain on Earth, its commercial significance, and its highly social lifestyle.

As the observations in the prologue illustrate, sperm whales interact with one another conspicuously, both during their daily routine and at the critical junctures of birth, predation, and death. Some of their social behavior is unusual, and perhaps unexpected, when considered from the perspective of terrestrial mammalian socioecology. In this book, I will describe the social life of the sperm whale as quantitatively and rigorously as current data allow and relate it to the sperm whale's ecological role in the deep and open ocean, an environment structured very differently from the habitats of our terrestrial model organisms (Steele 1991). The structure and scale (see Levin 1992) of the physical, biotic, and social environments of the sperm whale and the importance of culture will be recurring issues throughout the book. First, though, in this chapter, I will summarize some other elements of the biology of the sperm whale that bear on their ecology and behavior, and I will explain my approach to the study of sperm whale society and culture. The subsequent chapters will consider the sperm whale's habitat (chapter 2), how the whales move through it (chapter 3), behave (chapter 5), and organize their societies (chapter 6), and what we know of their culture (chapter 7). At the end of each of these chapters, I will summarize those results that seem to have significant bearing on social and cultural evolution.

In a range of characteristics as diverse as brain size, nasal complexity, sexual dimorphism, ecological success, social complexity, and diving ability, sperm whales have evolved unusual or extreme states. The evolutionary and ecological links between these extremes and the animals' social ecology will be explored toward the end of the book (chapter 8). In several places I will compare sperm whales with other marine and terrestrial animals, using the comparative method informally to examine the processes of social and cultural evolution in the ocean.

1.2 Evolutionary History of the Sperm Whale

The sperm whale has had a distinct, interesting, and controversial evolutionary history, but all agree that it is of the order Cetacea, the whales and dolphins. The cetaceans evolved from ungulate-like creatures that made their way back into the oceans perhaps 60 Ma (million years ago). About 25-35 Ma, the mysticetes, or baleen whales, separated from the odontocetes, or toothed whales (Berta and Sumich 1999, 59), and here the controversy begins.

Milinkovitch et al. (1993) used results from molecular studies to make the radical suggestion that sperm whales were more closely related to the baleen whales (Mysticeti) than to the toothed whales (Odontoceti). This conclusion seemed odd, as sperm whales, unlike baleen whales but like odontocetes, have substantial teeth and a single, rather than double, blowhole. More recent morphological and molecular analyses, especially those of Heyning (1997) and Nikaido et al. (2001), have come down strongly in favor of the traditional arrangement, with the sperm whale as an odontocete. Milinkovitch et al.'s conclusion may have resulted, at least partially, from the problem of rooting the cetacean phylogenetic tree. The morphological evidence and some recent molecular analyses (e.g., Nikaido et al. 2001) strongly indicate that the split between the mysticetes and all other extant cetaceans is the oldest division in the tree. Other molecular data are less well founded and more equivocal, with some analyses agreeing with the evidence from morphology and others supporting Milinkovitch et al.'s primacy of the division of the sperms and mysticetes from all other odontocetes (Heyning 1997).

In any case, not too long after the odontocete-mysticete division, sperm whales started to go their own way. Species possessing characteristic sperm whale features-the family Physeteridae-are found from about 25 Ma onward (Berta and Sumich 1999, 73), and soon evolved some highly specialized features (Mchedlidze 2002). The sperm whales had radiated into a number of different species by about 15 Ma (Rice 1998, 82; Kazar 2002), but only three survive today: the sperm whale itself(Physeter macrocephalus) and the pygmy sperm whale (Kogia breviceps) and dwarf sperm whale (Kogia simus), which at 2-4 m long are much smaller. The kogiids seem to have separated from the lineage that led to the sperm whale at least 8 Ma (Berta and Sumich 1999, 73), making the sperm whale the most phylogenetically distinct of all the seventy-five-odd species of living odontocetes.

1.3 Morphology: What Does the Sperm Whale Look Like?

A sperm whale is to my fancy the most uncomely shaped animal that I can think of. -Ellsworth 1990, 49

The cetaceans include some lovely creatures. The finback whale (Balaenoptera physalus) and right whale dolphins (Lissodelphis spp.) are as well-proportioned, beautifully colored, and graceful as anything in the animal kingdom. But the right whale (Eubalaena spp.) is a fat, lumpy animal, and Baird's beaked whale(Berardius bairdii) seems a misshapen spindle. And then there is the sperm whale. From just about any angle, it looks very strange.

During its final moments, if in daylight and not too deep, a doomed cephalopod might see the sperm whale advancing formidably on a broad front from the gloom of the ocean (fig. 1.1). Coming directly toward it is the long and narrow, but powerful, lower jaw, outlined in white, which will soon open to display two rows of large conical teeth and the white lining of the folds of the mouth and tongue (the teeth in the upper jaw rarely emerge). Above, or perhaps below (the sperm whale may feed upside down), the jaw is the mass of the spermaceti organ, expanding from the narrow jaw to the "high and mighty god-like dignity inherent in the brow" (Melville 1851, 454). The front of the spermaceti organ is often scarred from encounters with past prey, other sperm whales, or other hazards of the ocean. Protruding on either side of the head are the eyes, and behind them the rest of the body fades into the murk of the ocean. Such is the vision of this devastating predator as seen by its prey.

Sperm whales usually see one another from a different perspective, in profile from the side (fig. 1.2). From this angle, the spermaceti organ and jaw are also prominent, particularly the spermaceti organ, which overhangs the jaw and extends the whole vertical profile of the animal, giving the head a boxlike appearance. The spermaceti organ is smooth and rounded, but appears to consist of two barrels stacked on top of each other, rather like a double-barreled shotgun. If seen from the left, the asymmetric S-shaped blowhole is apparent at the tip of the spermaceti organ, capping a remarkable nose. The nose is remarkable in both shape and size, for it does not end until a quarter to a third (in large males) of the body has passed. And then, at about the position of the eye, the smooth case of the spermaceti organ gives way to a deep dimpling that covers almost all of the rest of the body. At the transition between nose and trunk there is often a crease along the top of the head. This crease is particularly apparent in the largest males, whose spermaceti organs appear swollen. Behind the eye, and normally tucked in close to the body, is a small, paddle-shaped flipper. The following portion of the back is usually quite straight until we reach the dorsal fin, which is low and rounded, and is followed by a series of "knuckles" as the trunk narrows to the peduncle leading to the flukes. If the whale rotates slightly, the belly becomes visible. Just behind the jaw are a few ventral grooves (see fig. 1.1), which presumably add flexibility to the throat, allowing the whale to suck in its prey. Farther back may be large patches of white pigmentation, especially around the genital slits. There are three slits in females-the mammaries on either side of the urogenital opening-and a single long slit in males, from which the penis sometime protrudes, with the anus behind. Farther back, perhaps hidden in the murk of the ocean, is the profile of the large tail, or flukes, of the whale.

We humans viewing whales from above the surface usually see very little of this. From our perspective, the sperm whale is just a long, loglike back stretching between the offset bulge of the blowhole and the curve of the dorsal fin (fig. 1.3), perhaps indented toward its middle by the crease at the end of the spermaceti organ. But we do see, and may hear, the blow-a rather low, bushy blow for such a large whale, pointed forward and to the left (fig. 1.4). We also can get a good view of the dorsal fin, and may note a white, or whitish, callus on the top (fig. 1.5). This callus is a secondary sexual character that indicates a mature female, although not all mature females possess calluses and some immature males do (Kasuya and Ohsumi 1966; Clarke and Paliza 1994). Other parts of the sperm whale are seen only briefly from our above-water perspective (see fig. 5.4): the spermaceti organ during a spy-hop, the flippers and belly during a roll, and most spectacularly and briefly, almost the entire body during a breach, or leap from the water. More frequently, during lobtails, sideflukes, or fluke-ups, only the flukes of the sperm whale emerge. When compared with those of other cetaceans, the tail of the sperm whale is one of its least unusual external features, but the morphology of the triangular flukes is especially important for our research. On the trailing edge of the flukes is a pattern of marks and scars that can be reliably photographed as the whale raises its flukes to dive (see fig. 5.13) and used to identify individuals (see appendix, section A.3).

From snout to flukes a mature female stretches about 11 m, and she may weigh about 15 t. A mature male is very much larger, often surpassing 15 m and 45 t. Thus the sperm whale is the largest of the toothed whales, being surpassed among extant animals only by the largest baleen whales, and is the most sexually dimorphic of all cetaceans.

1.4 The Peculiar Anatomy of the Sperm Whale: The Spermaceti Organ

Beneath its thick skin, the sperm whale is a mixture of the standard cetacean anatomy and physiology (see Berta and Sumich 1999; Elsner 1999; Pabst et al. 1999 for summaries) and some unusual features specific to sperm whales (described by Berzin 1972 and Rice 1989). One of these features is the largest brain on Earth (see section 8.3), but by far the most prominent and unusual is the spermaceti organ. It takes up 25-33% of the animal's body, dominates the head, and affects the surrounding organs, including the skull, jaw, and nasal passages.

The spermaceti organ, or "case," as the whalers called it-the upper barrel of the shotgun-is long and has a shape somewhere between a barrel and a cone (fig. 1.6; see also fig. 8.1). It is covered by a muscular sheath and contains spongy tissue soaked in spermaceti oil. Before, behind, and beneath it are other strange structures. At the wide posterior (rear) of the spermaceti organ, the skull forms a huge semicircular basin. The two are separated by an air-filled cushion, supplied by the right nasal passage. This passage also runs beneath the spermaceti organ and above another large mass of tissue, also saturated with oil, which the whalers called the "junk"-the lower barrel of the shotgun. At the narrow anterior (front) end of the spermaceti organ, the right nasal passage reaches another air sac. Air enters this distal air sac through a valvelike clapper system, the museau du singe (or "monkey's muzzle"). Meanwhile, the left nasal passage runs more directly to the blowhole, through which the whale breathes.

As might be expected, the huge and strange spermaceti organ has attracted its share of scientific attention. Why should an animal carry around an enormous barrel of oil? Why is it partially abutted by air sacs? What is the junk? There have been a number of theories about the function of the spermaceti organ, ranging from the battering ram of Melville (1851, 443) and Carrier et al. (Carrier et al. 2002) to the buoyancy regulator of M. R. Clarke (1970, 1978). Most can be largely dismissed (see box 8.1). Instead, modern science has focused attention on the acoustic theory of Norris and Harvey (1972). It now seems that the spermaceti organ is involved in the production of echolocation clicks, but the exact mechanism by which clicks are produced is not quite clear.

The most informed speculation as to how the spermaceti organ functions is that of Cranford (1999) and Madsen (2002). Like Norris and Harvey (1972), they suggest that a pulse of sound is initially produced by air being forced through the museau du singe. The pulse then passes through the spermaceti organ until it is reflected off the air-filled cushion at its far end. The reflected pulse is partially redirected into the junk, from where it is broadcast into the ocean through a series of acoustic lenses present in the junk. However, part of the pulse makes an additional transit back and forth along the spermaceti organ, leading to a secondary pulse entering the junk, and then the environment, a little later. Some clicks contain three or more pulses (fig. 1.7). In fact, as several authors have pointed out, the inter-pulse interval is proportional to the size of the spermaceti organ and is thus a function of the length of the whale, giving rise to the possibility of acoustic measurement (Norris and Harvey 1972; Adler-Fenchel 1980; Gordon 1991a; Goold 1996). Although the multiple-pulse structure of the sperm whale click is characteristic of the species, multiple pulses are generally heard only off the axis of this highly directionalized sound (Møhl 2001). This model of sperm whale sound production has recently been supported by an experiment in which sounds were played into the head of a recently dead whale and recorded (Møhl 2001): when the sound was made in front of the museau du singe or junk, a multipulse structure with an inter-pulse interval corresponding to the predictions of Gordon (1991a) was recorded, but when the sound was made above the head, no pulse structure was recorded.

(Continues...)

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Table of Contents

Acknowledgments
Conventions
Symbols and Abbreviations

Prologue: Observations of Sperm Whale Societies

1 The Sperm Whale: An Animal of Extremes
1.1 Social Complexity in the Ocean
1.2 Evolutionary History of the Sperm Whale
1.3 Morphology: What Does the Sperm Whale Look Like?
1.4 The Peculiar Anatomy of the Sperm Whale: The Spermaceti Organ
1.5 The Lives and Populations of Sperm Whales
1.6 Sperm Whales and Humans
Box 1.1 The Sperm Whale in Print
1.7 What Is Social Structure, and How Is It Studied in Sperm Whales?
1.8 What Is Culture, and How Is It Studied in Sperm Whales?
1.9 What Do We Know and What Don't We Know about Sperm Whale Societies?
1.10 Summary

2 The Oceanic Habitat of the Sperm Whale
2.1 Spatio-Temporal Structure of the Ocean
2.2 Oceanographic Habitat of the Sperm Whale
2.3 The Diet of the Sperm Whale: The Walnut, the Pea, and the Half-Pound Steak
Box 2.1 An Alternative View of the Sperm Whale Diet: The Picky Eater
2.4 The Sperm Whale and Its Competitors
2.5 The Ecological Role of the Sperm Whale
2.6 Feeding Success of the Sperm Whale
2.7 Intraspecific Competition
2.8 Natural Enemies
2.9 Attack, Defense, and Escape in the Ocean
2.10 Summary

3 The Sperm Whale: On the Move through an Ocean
3.1 Why Movement Is Crucial
3.2 Vertical Movements: The Sperm Whale's Dive
3.3 Costs and Benefits of Vertical Movement
3.4 Horizontal Movements of Females and Immatures
3.5 Movements of Males
3.6 Movements of Other Oceanic and Terrestrial Animals
3.7 Costs and Benefits of Horizontal Movement
Box 3.1 How Fast Should a Sperm Whale Swim?
3.8 Summary

4 Sperm Whale Populations
4.1 Geographic Structure
4.2 The Sizes of Sperm Whale Populations
Box 4.1 Methods of Assessing Sperm Whale Populations
4.3 Population Parameters
4.4 Population Dynamics
Box 4.2 Changes in Sperm Whale Populations off the Galápagos Islands, 1985-2002
4.5 Summary

5 Sperm Whale Behavior and Vocalizations
5.1 Measuring Behavior
5.2 Vocalizations
Box 5.1 Are Sperm Whale Clicks Echolocation?
Box 5.2 Measures of Sperm Whale Behavior
5.3 Modes of Behavior
5.4 Foraging
5.5 Socializing
5.6 Aerial Behavior (and Other Peculiar Activities)
5.7 Birthing
5.8 Behavior of the Calf
5.9 Defense against Predators
Box 5.3 Interactions between Sperm Whales and Killer Whales
5.10 Stranding
5.11 Summary

6 Sperm Whale Societies
6.1 Social Scales
6.2 Concentrations
6.3 Aggregations
6.4 Groups
Box 6.1 The Problems of Estimating Group Size
6.5 Social Units
Box 6.2 Delineating Social Units
6.6 Genetic Structure of Groups and Units
6.7 The Functions of Groups and Units
Box 6.3 A Week in the Life of a Sperm Whale Group
6.8 The Cluster
6.9 Care of the Calf
6.10 The Social Male?
6.11 Mating Systems
Box 6.4 An Observation of Two Male Sperm Whales Fighting
6.12 Summary

7 Sperm Whale Cultures
7.1 The Quest for Sperm Whale Culture
7.2 Coda Dialects of Units and Clans
Box 7.1 Describing and Comparing Coda Repertoires
Box 7.2 Sperm Whale Clans of the South Pacific
7.3 Nonvocal Cultural Traits of Sperm Whales
7.4 Low Mitochondrial DNA Diversity and Culture: Cultural Hitchhiking
7.5 Summary

8 Social and Cultural Evolution in the Ocean
8.1 Evolution to Extremes
8.2 The Function and Evolution of a Big Nose
Box 8.1 The Spermaceti Organ: A Buoyancy Control Device or a Battering Ram?
8.3 The Function and Evolution of a Large Brain
8.4 Sperm Whales and Other Deep Divers
8.5 The Colossal Convergence: Sperm Whales and Elephants
8.6 K-Selection, Sociality, and Ecological Success
8.7 Social Evolution of Female Sperm Whales: Facing the Predators
8.8 The Lives of Males
8.9 Sexual Segregation
8.10 Social Evolution in the Open Ocean
8.11 Cultural Evolution in the Ocean
8.12 Summary

9 Sperm Whales and the Future
9.1 Ghosts of Past Whaling
9.2 The New Threats to Sperm Whales
9.3 Studying Sperm Whales in the Future
9.4 The Nature and Future of the Sperm Whale
9.5 Summary

Appendix: How We Study the Sperm Whale
A.1 Examining Carcasses
A.2 Studying Living Animals
A.3 Photoidentification and Photographic Measurement: The Key to Individuals
A.4 Quantifying Sounds
A.5 Unraveling Genes
References
Index