The trials of life : a natural history of animal behavior

317 Pages·1993·94.77 MB·English

by  David Attenborough

-4•
Copyright ©1990 by David Attenborough Productions Ltd.
All rights reserved. No part of this book may be reproduced in any form or by
any electronic or mechanical means, including information storage
and retrieval systems, without permission in writing from the publisher,
except by a reviewer who may quote brief passages in a review.
Frontispiece: a cleaner wrasse grooms a parrot fish; the Red Sea.
ISBN 0-316-05751-7
Library of Congress Catalog Card Number 90-53592
Library of Congress Cataloging-in-Publication information is available.
Published simultaneously in Canada by
Little, Brown & Company (Canada) Limited
PRINTED IN THE UNITED STATES OF AMERICA
CONTENTS
Introduction
(cid:9)
1(cid:9) Arriving 11
(cid:9)
2(cid:9) Growing Up 36
(cid:9)
3(cid:9) Finding Food 56
(cid:9)
4(cid:9) Hunting and Escaping 78
(cid:9)
5(cid:9) Finding the Way 108
(cid:9)
6(cid:9) Home-making 134
(cid:9)
7(cid:9) Living Together 163
(cid:9)
8(cid:9) Fighting 185
(cid:9)
9(cid:9) Friends and Rivals 211
(cid:9)
10(cid:9) Talking to Strangers 229
(cid:9)
11(cid:9) Courting 252
(cid:9)
12(cid:9) Continuing the Line 286
Acknowledgments(cid:9) 310
(cid:9)
Index 314
INTRODUCTION
THIS BOOK, and the television series that was filmed at the same time as
it was being written, is the last in a trilogy of natural histories. The first
was Life on Earth. That set out to examine the vast diversity of animal life.
Why should there be such an extraordinary variety of animals all doing
somewhat similar things? Why should a whale have warm blood and
lungs, whereas a similarly-sized swimming monster, the whale shark, has
cold blood and gills? Why do indigenous Australian mammals rear their
young in a pouch whereas mammals in the northern hemisphere retain
their offspring within a womb and nourish them by means of a placenta?
The answers to such questions can only come from an understanding of
history. So Life on Earth traced the development of animal life from its
beginnings some three thousand million years ago until today and illus-
trated its great episodes by taking living animals as examples.
The second book, The Living Planet, concentrated on the other great in-
fluence that shapes the bodies of animals, the environment. Mammals that
live in deserts tend to have longer ears and legs than their equivalents in
cooler areas — bodies shaped in that way are more efficient at losing heat;
land birds, marooned on remote islands, tend to become flightless — with no
land predators present, they have no need to take to the air. Other organ-
isms with which an animal shares its environment also have their influence.
So the fur of an Arctic hare that keeps it warm in winter also turns white
when the snow comes in order that its wearer shall remain concealed from
predators. The Living Planet surveyed ecological communities throughout
the world, ranging from the baking deserts to the humid rain forest, from
the depths of the ocean to the highest layers of the atmosphere.
Thus, the first two books were concerned with the bodies of animals and
the way they have been shaped. This last book looks at the way animals use
those bodies, the way they behave.
Behaviour is perhaps the most obviously exciting aspect of natural his-
tory. It is full of action and drama — a killer whale surging up a beach to grab
a young sea-lion; an ant navigating across a Saharan sand dune by taking
repeated observations of the sun; a mother bat fighting through crowds of
begging infants on the roof of a cave in order to give her milk to her own
baby and no other. Animal behaviour might, therefore, have been the
8 Introduction
obvious choice for the first subject in this trilogy. The fact is, however, that
ten years ago when my colleagues and I began work on it, we could not
have witnessed many of the actions that I can now describe and certainly
could not have recorded pictures of them.
The reasons for this are partly technical. During the last decade there
have been major advances in both films and electronics. Now we can watch
and record events in light so dim that only recently they were beyond the
sensitivity of any photographic emulsion or even our eyes. Now, with the
aid of electronic image-intensifiers and super-sensitive film, we can record
fire-flies flashing synchronously like lavish Christmas illuminations in the
mangrove swamps of Malaysia and see them not just as featureless spots of
light but as tiny beetles engaged in elaborate courtship rituals. Now, with
fibre-optic probes developed for use in medicine, we can see for the very
first time what happens within the huge globe formed by a million army
ants bivouacked beneath a log in the rain forest of Panama.
But more important than such technical advances has been the great
increase during the past decade in the number of scientists actively in-
volved in observing animals in the wild. Almost every group of large
animals is now being studied by scientists somewhere. These researchers
have become so knowledgeable about their subjects and understand them
so intimately that they have been able to guide us to the right place at the
right time in order to see exactly that aspect of behaviour that was of
particular interest to us.
Few scientific disciplines demand greater dedication or the endurance of
such harsh physical circumstances as studying wild animals in their natural
environments. Christophe Boesch is a Swiss zoologist working with chim-
panzees that live in the thick forest of the Ivory Coast in West Africa. He
and his wife Hedwige started their project ten years ago, spending every
day for weeks on end walking quietly through the forest. For the first year
or so he counted it a good day if he got a brief glimpse of a chimpanzee. He
did not allow himself to bribe the apes with food and so lure them out in the
open towards him, believing that to do so would distort their natural
behaviour and so invalidate his findings. Only after four years of unrelent-
ing observation and tracking did the chimpanzees become sufficiently ac-
customed to their silent human shadow to have no fear of him and ignore
him.
Several more years passed before he was able to recognise with certainty
the different individuals in the group, as was necessary for his work. Today,
he not only knows every one of the sixty or so chimpanzees in the group by
sight, but he can also recognise most by their voices, even when they are
Introduction 9
calling from a considerable distance. Every day he follows them as they
travel through the forest, stopping when they pause to feed, running when
they start to travel at speed. Only after they have started making their beds
in the tree tops each evening does he leave them. And in the morning,
before the sun is up, he sets off from his house in the forest to rejoin them, if
necessary running for an hour or so to make contact with them again before
they move away to some part of the forest where they might be difficult to
find. The result of all this persistent and punishing work has been to reveal
among many other things that forest-living chimpanzees are regular hun-
ters and have developed techniques of working in teams to catch their prey
that are more elaborate than those used by any other animal except man.
That Christophe should have allowed us, with cameras, to accompany him
and film them hunting in this way was an extraordinary privilege.
He is only one of the many scientists who have helped us. A list of others
who helped me personally appears on page 310. In addition to these, a great
number more most generously gave advice and practical guidance to the
directors and cameramen working on the television series and so made it
possible for us all to share sights that they themselves had only been able to
witness after years of intensive and patient study. Our debt to them all is
unpayable.
The science of animal behaviour, which such researchers serve, is known
as ethology. I have not attempted in this book to describe the body of theory
that it has developed any more than I examined theories about the mechan-
isms of evolution in Life on Earth. The reader who wants a full exposition of
such subjects as selfish genes, game theory, altruism or the relationship
between learning and instinct, must look to more technical texts. My con-
cern here is to describe the happenings, rather than the psychological and
evolutionary mechanisms that produce them. That, I now realise even more
vividly than when I started on this project, is a big enough task.
It is not always possible to disentangle behaviour from anatomy, and to
that extent there is inevitably some overlap between what I have written in
this book and its two predecessors. On a few occasions a species has been
described for a second time because its behaviour is unique and so extra-
ordinary that this survey would have been inexcusably incomplete without
it. But the variety of animal life is so vast that for the most part it has been
possible to find different examples to make my points and if this has meant
neglecting more famous and obvious instances, then that perhaps is to be
welcomed.
As before, I have not encumbered the text with scientific Latinised names
where there is a reasonably accurate English equivalent. This inevitably
10 Introduction
leads to some loss of precision, but those readers who wish to know exactly
which animal I am describing can discover by looking up the English name
in the index, where its genus if not its species will be found in italics.
All organisms are ultimately concerned to pass on their genes to the next
generation. That, it would seem to a dispassionate and clinical observer, is
the prime objective of their existence. In the course of achieving it, they
must face a whole succession of problems as they go through their lives.
These problems are fundamentally the same whether the animals are
spiders or squirrels, mice or monkeys, llamas or lobsters. The solutions
developed by different species are hugely varied and often astounding. But
they are all the more comprehensible and engaging for they are the trials
that we also face ourselves.
ONE
ARRIVING
TT IS midnight on the coast of Christmas Island in the Indian Ocean, two
'hundred miles south of Java. The November moon is in its third quarter
and the tide is coming in. Behind the narrow sandy beach stands a sheer
cliff of coral rock, seventy feet high. On its vertical face, clinging beneath
overhangs, jammed three or four deep into cracks, are a million scarlet
crabs. In places, they are so crowded that their bodies touch and the cliff
seems to have been painted crimson. These crabs are found nowhere else in
the world. They are large animals with glossy rounded shells five inches
across. All are females, each with a huge mass of brown eggs bulging
beneath the semi-circular flap on her underside. They are about to spawn.
A month ago they, together with the males, left the burrows on the floor
of the forest inland where they had spent most of the year and began a long
march to the coast. Then the vast size of their population became dramati-
cally apparent. There were about one hundred and twenty million of them.
They moved mostly in the early morning or the evening, for they dry out
easily and cannot withstand the full tropical sun. But when the sun went
behind clouds, and particularly after a rain shower when the undergrowth
was moist, they travelled during much of the day. Nothing deterred them.
In places their traditional routes cross roads made by the people who now
live on Christmas Island. Thousands of the marchers were inevitably
crushed beneath the wheels of the traffic but still, day after day for two
weeks or so, they kept coming. When they reached the coast, the males
excavated burrows and there mated with the females. The males then
returned inland, but the females had to wait in the burrows for a further
two weeks while their fertilised eggs matured.
And now the moment to release the eggs has arrived. The crabs have
climbed down the cliffs, for their eggs must be deposited directly into the
sea if they are to hatch. But this is not without hazard. Although the crabs'
distant ancestors came from the sea, these are land crabs. They breathe air
and they cannot swim. If they lose their hold on the rock or are swept away
by the waves, they will assuredly drown.
As the tide reaches its height, the width of the beach is reduced to a few
yards. The females move down from the cliffs, across the shingle to the
breakers, scrambling over one another in their anxiety to get to the water.
Overleaf: female land crabs descending to the sea to spawn, Christmas Island