The Social Behavior of Older Animals

The Social Behavior of Older Animals

The SOCIAL BEHAVIOR of

OLDER ANIMALS

Anne Innis Dagg

© 2009 The Johns Hopkins University Press

All rights reserved. Published 2009

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Library of Congress Cataloging-in-Publication Data

Dagg, Anne Innis.

The social behavior of older animals / Anne Innis Dagg.

        p.    cm.

Includes bibliographical references and index.

ISBN-13: 978-0-8018-9050-5 (hardcover : alk. paper)

ISBN-10: 0-8018-9050-0 (hardcover : alk. paper)

1. Social behavior in animals. I. Title.

QL775.D34 2008

591.56—dc22        2008010643

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To my two oldest friends

Mary F. Williamson

Rosemary A. Rowe

CONTENTS

Acknowledgments

Introduction

  1    Evolutionary Matters

  2    Sociality, Media, and Variability

  3    The Wisdom of Elders

  4    Leaders

  5    Teaching and Learning

  6    Reproduction

  7    Successful Subordinates

  8    The Fall of Titans

  9    Aging of Captive Alphas

10    Happy Families

11    Mothering—Good and Not So Good

12    Grandmothers

13    Sexy Seniors

14    Their Own Person

15    Adapting and Not Adapting

16    All Passion Spent

17    The Inevitable End

Notes

References

Index

ACKNOWLEDGMENTS

I WOULD LIKE TO THANK all those who helped me in the creation of this book by reading short sections of the manuscript or by sending me information about published research or particular old animals. They include Alan Cairns, Wendy Campbell, Bernice Grant, Heidi Libesman, Bev Sawyer, Elaine Sim, and Anne Zeller. I am grateful also for the fine local libraries and librarians—the Trellis tri-university system of the University of Waterloo, Kitchener Public Library, and Waterloo Public Library. It has been difficult to collect information for this book, so my especial gratitude goes to the researchers and authors who included an index in their books with entries for old age. You are few and far between. Thank you.

For those at the Johns Hopkins University Press, my heartfelt thanks to Dr. Vincent Burke, senior editor, for his deeply appreciated encouragement and wise suggestions about organizing the book’s material; Kathleen Capels for her meticulous copyediting of each chapter and a helpful insight into the orca Eve’s behavior; Deborah Bors, for her useful advice and the oversight of the final preparation of my book; and Robin Rennison and Brendan Coyne for their efficient and pleasant communications with me.

The Social Behavior of Older Animals

Introduction

THIS BOOK IS ABOUT the social behavior of mammals and birds well past their prime who live either in the wild or in captivity where they have large areas in which to move and interact with others. It does not include data from animals kept in small cages and subject to experimentation in research facilities.

The question of who is old is fairly easily answered for people. Oldsters who take advantage of seniors’ discounts are rarely asked to produce identification to prove their age. They often have gray or white hair, and their bodies provide other physical clues.

What about other animals, where signs of aging such as wrinkles and spots are covered with fur or feathers? By definition, older animals are nearing the end of their lives, but that does not mean we can distinguish them from their companions. Indeed, most behavioral research on wild animals does not mention older individuals at all. When colleagues and I published scientific books on giraffe (Dagg and Foster 1976) and on camels (Gauthier-Pilters and Dagg 1981), using data we had collected over years in the wild and everything about these species published in the literature, we had almost nothing to report about older animals—and at the time, we never noticed this deficit.

Struhsaker (1975), in his extensive research on red colobus monkey behavior, differentiated individuals at times into young infant, infant, old infant, young juvenile, juvenile, old juvenile, subadult, approximate adult, and adult. But he had no category for old adult.

Nor have non-scientists been interested in the topic. In 2005, in a small newsletter read by 400 seniors, I asked if anyone could give me information about the behavior of older animals. Many of them had companion pets who were as gray as they were, but no one offered any anecdotes.

One problem was that, until recently, people believed that wild animals did not live to be old, dying instead from accidents or disease, or being killed and eaten by predators (Hrdy 1981). Therefore, there is little information available about aged individuals in older books and articles. The well-known naturalist Ernest Seton Thompson (who later called himself Thompson Seton), in his famous book Wild Animals I Have Known (1942), wrote that "the life of a wild animal always has a tragic end, and that no wild animal dies of old age."

We now have the amazing power to collect information using Internet search engines such as Google, but searching there with the words old animals or aged animals brings up millions of items, including information on the Old World, Old English, kittens aged 3 months, and aged cheese.

Information used in this study came from a large number of books and articles on animals, the most profitable being those written by zookeepers, wildlife zoologists, and individuals or groups of people who study or simply love animals. It was not possible to merely skim the books, because words such as old age or aged animals are seldom included in the index. To ensure that I had up-to-date information, I searched article titles for pertinent data published between 2000 and mid-2007 in issues of the following academic journals: American Journal of Animal Ecology, American Journal of Human Biology, American Journal of Physical Anthropology, American Journal of Primatology, American Naturalist, Animal Behaviour, Behavioral Ecology and Sociobiology, Behaviour, Canadian Journal of Zoology, Current Biology, Ecology, Ecological Monographs, International Journal of Primatology, Journal of Mammalogy, Nature, Oecologia, Primates, Quarterly Review of Biology, and Science.

THIS INTRODUCTION FIRST CONSIDERS general knowledge about elderly animals, and then the bias inherent in collecting information on their social behavior. Throughout, I often refer to wild animals as older rather than old, to reflect the difficulty of knowing exactly how old an older animal is.

Ten Basic Facts about Aging in Animals

1. Animals in zoos tend to live longer than wild ones, because they do not have to worry about predation or lack of food or water. However, this is not true for large mammals such as orcas (killer whales) or elephants—the latter can live for 60 or 70 years in the wild, but they usually die by their forties in captivity (Gorman 2006).

2. Older animals are slower and less agile than their junior selves, and may suffer from arthritis, diabetes, cancer, heart disease, and other health problems, including mental confusion. As John Grogan (2005) stated in describing his ancient dog Marley, he and many other old animals are not only deaf and have poor vision, but their fur or hair is falling out, they are incontinent, they have arthritic hips that make it hard to get up or lie down, their teeth are broken or rotted, their confidence is eroded, and they snooze a lot. Old nonhuman animals may suffer from osteoporosis. One elderly female chimpanzee had a bone mineral density below what would indicate osteoporosis in humans; it was surmised that only her posture, locomotion, and trunk-sacral anatomy prevented her bones from fracturing (Gunji et al. 2003). Older people may suffer from these same problems, but not all of them will; women athletes in their fifties are now beating those in their twenties in long-distance running. The younger women are more physically fit, but the older ones have a mindset that involves not only physical but also emotional and spiritual energy (Kolata 2007).

3. Older mammals are often gaunt, with fur or hair that has turned gray or white. Aging leopards tend to have faded color spots (Bailey 1993), but older giraffe may have spots that are darker than those of animals in their prime (Dagg 1983). Elderly birds usually have plumage similar to that of young adults; for example, an old (at age 11) cliff swallow looked just like the other adult swallows (Brown 1998).

4. Males and females of a species may have very different average lifespans. Orca males, for example, have a longevity of about 40 years, while females often live into their fifties (Knudtson 1996).

5. Healthy female mammals are getting old if they produce fewer young than formerly (reproductive senescence), and are definitely in that category when they stop reproducing entirely. However, exceptions are possible. One Asian elephant, Tara, became pregnant in her mid-sixties, a decade after most elephants stop reproducing (Chadwick 1992). One aging lion in Nairobi National Park was assumed to be sterile because she had had no cubs for two years, but then she bore a litter (Schaller 1972a). Laboratory data on hundreds of older rhesus monkey females show that all experienced a decrease in fertility with age, but few reached a true menopausal state (meaning a permanent cessation of ovulation) comparable to that in women (Small 1984). In contrast to mammals and birds, many female fish, amphibia, and reptiles continue to grow during their lifetimes, with their increased body size allowing them to produce more young in each successive year (Clutton-Brock 1984). Females of most species reproduce until they die.

6. Healthy males may stop reproducing when they grow old. One ancient wolf in the wild had small testes that were no longer producing sperm (Mech 1996). Jan Smuts, a long-lived male giraffe at the Taronga Zoo in Sydney, Australia—who looked ancient with a gaunt neck and face and almost black spots—no longer mated with the females around him, so a younger male, Oygle, had taken over this function (Dagg 1970).

7. Small animals in general have a far shorter lifespan than large animals, and longevity is correlated to some extent with metabolism. An elephant who lives for perhaps 65 years has a normal heart rate of less than 25 beats per minute, while a masked shrew who lives only a year or two has a rate of about 1300 beats per minute (Gunderson 1976). Insectivorous bats also have a fast heart rate while active, but their lifespan is about 10 times as long as that of shrews, because they spend much of their existence in hibernation (Barclay and Harder 2003).

8. Longevity is an adaptive trait, positively correlated with unique attributes such as flying ability (sometimes), possession of armor (in turtles and armadillos), and life underground (for moles and mole rats) (Carey 2003). Parrots may live for 50 years, while tortoises can survive to about age 175—the tortoise Harriet from the Galápagos Islands, who died recently, was apparently taken to England by Charles Darwin and later sent to Australia, where the climate was more suitable (Rook 2006; Discovery Channel 2006). The echidna, an egg-laying mammal, is primitive but also very long lived, surviving sometimes for 50 years (Crandall 1966). Human beings have an exceptionally long lifespan for their size, much longer than that of other primates.

9. In dogs, larger species such as Great Danes and collies have a short lifespan of 8 to 10 years, while small dogs live much longer on average. Among dogs weighing 9 kg (20 lb), cairn terriers have a typical lifespan of 13 to 14 years, a miniature poodle 15 to 16 years, and a Cavalier King Charles spaniel only 11 or 12 years (Coren 1994).

10. Researchers in different areas may have varying standards for old age. In Gombe, Tanzania, Jane Goodall (1986) defined old chimpanzees as those who were at least 33, while at the nearby Mahale Mountains research area, old age was considered to be 41 or older (Huffman 1990).

For this book, I have sometimes had to use my own judgment, case by case, to decide who was old. In general, I assume animals are old if the author who writes about them says they are. (This resembles Darwin’s sensible definition of a species: a species is a species if an expert on the group defines it as such. When I first heard this maxim I was horrified at the lack of rigor it seemed to imply, but now I realize that it is eminently practical. Who better to decide than a person studying the animals?)

Of course, very elderly animals near death are usually easily recognized as being old. Often their teeth are broken or gone, so they cannot eat properly; indeed, this factor often causes their death. Such animals tend to be loners. They either cannot keep up with their group as it forages (elephants), or they have been driven out of the group because of their age (hyenas). For an intra-species comparison, measurements have been taken of over 600 rhesus monkeys of all ages, showing age-related changes in their vision, muscles, and bones (DeRousseau et al. 1986).

Biased Information about Social Behavior

HUMANS KILLING OLDER ANIMALS

Joyce Poole has written a fascinating book, Coming of Age with Elephants (1996), about growing up in Africa and beginning research on elephants in Kenya when she was only 19 years old. She spent thousands of days driving around the Amboseli National Park, observing wild elephants, especially males, and writing down what they were doing. Within a few years, by using individual photographs and computer cards, she and Cynthia Moss, her mentor, could individually identify all the elephants in the park—164 adult males and 451 adult females and calves—by such characteristics as size, tusk shape, and ear descriptions (involving their size, notches, tears, and holes). Altogether, Poole spent 14 years in a tented camp in the park, studying male elephants both for her graduate work and as part of the Amboseli Elephant Project. By 1995, she had increased her male count to 450 animals.

Wow! I thought. This will be a gold mine of information on the behavior of old elephants. Poole and Moss must have observed scores of them over the years. I turned to my copy of Poole’s book with enthusiasm. Alas, my excitement was misplaced. When Poole began her research in 1975, poaching in Amboseli Park was extensive, with the largest and oldest animals being slaughtered for the ivory of their huge tusks. As she checked through the photographs of 68 known males, she realized that such behemoths were no longer around. Although the lifespan of adult elephants in the wild is about 65 years, no elephant in the park even began to approach this age. Of the 68 males, only eight remained who were over 30 years old, and only one, Iain (M13), was over 40. By 1995, only six of this original group were still alive.

What about the behavior of older males? Are they patriarchs? Are they important in elephant society? Unfortunately, we do not have enough data to answer such questions; largely because of culling and poaching for ivory, many African countries no longer have any older males and, therefore, no natural populations of elephants. Even if poaching and culling are curtailed, wherever elephant herds roam near agricultural lands there are continuing problems (and killings), largely attributable to older elephants, who are the most experienced and boldest in foraging and trampling agricultural crops.

In Zaire, killing elephants for their ivory was banned in 1977, but it has been replaced by killing elephants because they are raiding crops, even in areas where there are no crops. A recent inventory found ivory from 6500 animals, with older elephants as the preferred target, because of their large tusks (Chadwick 1992).

In the Central African Republic, elephants have been killed for their ivory for years, the oldest—and therefore largest individuals, of course—first. A 1986 inventory of thousands of tusks, obtained from elephants who had been shot for allegedly raiding crops, turned up none from animals older than 35. Since older, experienced elephants are the most notorious crop raiders, it seems as though the entire country has few or no elephants beyond middle age.

The same problem of excessive harvesting exists for whales. Before commercial whaling began, large whales lived into their sixties and seventies, while smaller bowhead and sperm whales may have survived much longer than this (Whitehead 2003). Since then, as killing technologies have improved, whalers have been slaughtering their prey more and more effectively, by the thousands and even millions. They only largely ceased doing so in 1986, with the worldwide moratorium on commercial whaling. Wherever possible, the targeted whales were the largest, most lucrative animals, so that even today, whale populations remain skewed toward younger individuals. (Some nations, especially Japan and Norway, continue to slaughter whales despite international agreements not to do so, claiming that this is necessary for scientific research [Glavin 2006].) The behavior of current whale groups almost certainly has been affected because of this harvesting, but we do not know how. The natural behavior of many of these large mammals will probably never be fully known, given our human insistence in meddling with their populations.

TEN PROBLEMS WITH RESOURCES

There are many other reasons why information about the social behavior of older animals has been biased, as well as little observed, reported, or understood.

1. Few methods have been developed to determine the age of animals that have no economic, scientific, or recreational interest for people. Veterinary books dealing with livestock do not include information pertinent only to older animals, because virtually no stock individual lives out its full lifespan. Animals raised for food are killed in early adulthood, and racehorses are not allowed to race in North America beyond their fifteenth birthday (Delean 2007).

2. Most animal species have not been studied by field ethologists, so we have little or no idea about their behavior in general, let alone that of their oldest members.

3. Any animal population tends to have only a few old individuals. For example, among the chimpanzees studied by Jane Goodall, roughly 12 percent were considered old at any one time, and during 30 years of research, only three females and six males appeared ancient looking (Engel 2002).

4. Virtually nothing is known about the social behavior of members of non-social species, even those that have been studied, because many individuals within these species seldom interact.

5. For some species, old age correlates in part with an individual’s usually unknown reproductive history. For the willow tit, females who breed every year grow old and die sooner than those who skip breeding early in their lifetimes (Orell and Belda 2002). Similarly, female red-billed choughs who lay small clutches and fledge few offspring early on have longer lives than females who are more productive when they first mature (Reid et al. 2003).

6. Few small mammals in the wild live to an old age, and their behavior is almost impossible to observe (for example, for white-footed mice, see Havelka and Millar 2004). Yet laboratory experiments indicate that there are behavioral changes with age. For example, old rats in captivity have decreased motor activity compared to young rats, and also differ from them in their emotional and social behavior (Boguszewski and Zagrodzka 2002). Unlike mammals, birds can be aged when they are banded or ringed as nestlings, and later captured in a mist net (see chapter 2). About 200 million birds have been banded worldwide, although few such marked individuals are subsequently recaptured (Berthold 1996).

7. From necessity, much of the information in this book is anecdotal. Yet observations about one old individual do not necessarily apply to other individuals of the same species. Each group has a history, as well. One can watch what individual baboons do, and assume that this represents baboon social behavior, but one must also know what has gone on in the troop’s past, even the remote past, which is still reflected in the actions of present-day animals (Sapolsky 2001).

8. Numerous toxic chemicals from human pollution have accumulated in the bodies of predators, especially those who are older. Three orcas dying in the Puget Sound area off the west coast of North America had PCB levels of 250, 370, and 661 parts per million; the U.S. FDA standard for PCBs in fish for human consumption is 2 parts per million (Lord 2004). Many endocrine-disrupting chemicals now present in the environment are known to cause bizarre behaviors in wild animals (Clotfelter et al. 2004).

9. Depending on the species, aging methods are not always accurate, and may reflect such things as diet (which affects wear on teeth) or extreme weather conditions. Female waterbuck in Uganda seldom live more than 12 years, but one female with exceptionally strong teeth survived until age 18 (Spinage 1982). In contrast, the elderly chimpanzee Flo’s teeth were worn down to her gums eight years before her death (Goodall 1986).

10. It is usually impossible to tell how old adult animals are in the wild, unless some method to age them, such as tagging youngsters or counting the annual rings on teeth or horns, has been devised by wildlife experts. In the baboon troop observed by Barbara Smuts (1985), it was impossible to tell an animal’s age from his or her physical appearance, especially for males. In 1977, Boz had been an adult male for one year, while Alexander and Sherlock were both subadults (about 8 years old), nearing full size. Six years later, Boz looked much the same as he had earlier, still about 24 kg (53 lb) in weight, with a rich mantle of hair over his neck and shoulders; by contrast, the other two seemed old, with slow and labored movements, drooping lower jaws, and scarred faces. Both had badly worn or broken canine teeth. (Boz and Alexander would become good buddies, as described in chapter 10.)

Most important of all, we must remember that zoologists studying animal behavior are usually trying to correlate the production of young with evolutionary concerns. Who has the most healthy young? Great. Are more young produced by some individuals with one type of characteristic rather than another? Wonderful. What about animals who no longer reproduce? Forget them.

But let us not forget them.

Scientists studying the behavior of animals now largely agree that they have feelings and emotions, just as people do. As Marc Bekoff (2006) stated: There are pleasure-seeking iguanas, amorous whales, elephants who suffer from post-traumatic stress disorder, pissed off baboons who beat the stuffing out of others, sentient fish and a sighted dog who serves as a Seeing Eye dog for his canine buddy. This is why, of course, we cannot assume that the behavior of one animal is representative of its entire species. Ethically, it also means we should think of animals as the sentient beings that they are, and it helps if we use the names of individual animals when these are known. If possible, in the text I refer to individuals as he or she rather than it, and use who or whom to denote them.

CHAPTER 1

Evolutionary Matters

BEHAVIORAL ZOOLOGISTS ANALYZE the behavior and adaptations of animals to determine why and how these characteristics developed over time. The reason they evolved was to improve the species’ potential to reproduce. The more offspring individuals produce compared to their peers, the more likely they are to have their genes survive. Yet for most mammals and birds, older individuals are either no longer reproducing, or reproducing at a slower rate than younger adults. Given that reproduction is the bedrock of evolutionary theory, can the lives of social animals who have reached an advanced age be important in evolution? Surely, from an evolutionary perspective, the wiser course would be death rather than an old age where consumption seems to exceed contribution. But since animals do live to be old, there must be an evolutionary reason for this.

Older social animals are vital to their group for two main reasons: (1) they have a good genetic inheritance that they pass on to their descendants, and (2) they have extensive experience with their environment and their species’ culture, both of which they share with the younger members of their group. These aspects of their existence, inextricably intertwined, are considered under four headings in this chapter. First, to have survived to old age, senior animals must have good genes in general, including genes involved with a successful personality; as it is in human beings, personality in wild animals is likely to be most fully developed in adults and elders. Older animals also have a vast store of knowledge to impart to younger group members, which is vital in helping their whole group survive and thrive during hard times. Second, some species have females who