The Trials of Life, page 1
THE TRIALS OF LIFE
A Natural History of Animal Behaviour
David Attenborough
Copyright
William Collins
An imprint of HarperCollinsPublishers
1 London Bridge Street
London SE1 9GF
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First published in Great Britain by William Collins Sons & Co Ltd and BBC Books: a division of BBC Enterprises Ltd in 1990
Fully updated and republished by William Collins in 2022
This eBook first published in Great Britain by William Collins in 2022
Copyright © David Attenborough Productions Ltd. 1990, 2022
Photographs © individual copyright holders
Cover image © Steve Woods Photography / Getty Images
Cover design by Jo Thomson
David Attenborough asserts the moral right to be identified as the author of this work in accordance with the Copyright, Designs and Patents Act 1988.
Image here: University of Washington, Freshwater and Marine Image Bank.
A catalogue record for this book is available from the British Library.
All rights reserved under International and Pan-American Copyright Conventions. By payment of the required fees, you have been granted the non-exclusive, non-transferable right to access and read the text of this e-book on-screen. No part of this text may be reproduced, transmitted, down-loaded, decompiled, reverse engineered, or stored in or introduced into any information storage and retrieval system, in any form or by any means, whether electronic or mechanical, now known or hereinafter invented, without the express written permission of HarperCollins.
Source ISBN: 9780008477837
Ebook Edition © November 2022 ISBN: 9780008477882
Version: 2022-10-28
CONTENTS
Cover
Title Page
Copyright
Introduction
1 Arriving
2 Growing Up
3 Finding Food
4 Hunting and Escaping
5 Finding the Way
6 Home-making
7 Living Together
8 Fighting
9 Friends and Rivals
10 Talking to Strangers
11 Courting
12 Continuing the Line
Picture Section
Index
Acknowledgements
About the Book
About the Author
Other Titles by David Attenborough
About the Publisher
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 illustrated its great episodes by taking living animals as examples.
The second book, Living Planet, concentrated on the other great influence 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 organisms 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. Living Planet surveyed ecological communities throughout the world, ranging from the baking deserts to the humid rainforest, 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 history. 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 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 the television series, 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 decade before this book was written, there had been major advances in both film technology and electronics. As a consequence we were just beginning to watch and record events in light so dim that only recently such events 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 rainforest of Panama.
But more important than such technical advances has been the great increase in the number of scientists actively involved 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 who worked with chimpanzees that live in the thick forest of the Ivory Coast in West Africa. He and his wife Hedwige started their project ten years before we visited them, 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 unrelenting observation and tracking did the chimpanzees become sufficiently accustomed 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. Eventually he came to know every one of the sixty or so chimpanzees in the group by sight, but he could also recognise most by their voices, even when they called from a considerable distance. Every day he followed them as they travelled through the forest, stopping when they paused to feed, running when they started to travel at speed. Only after they started making their beds in the tree tops each evening did he leave them. And in the morning, before the sun was up, he set 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 moved away to some part of the forest where they might be difficult to find. The result of all this persistent and punishing work was to reveal among many other things that forest-living chimpanzees are regular hunters and have developed techniques of working in teams to catch their prey that are more elaborate than those used by any other animal except human beings. That Christophe should have allowed us, with cameras, to accompany him and film them hunting in this way was an extraordinary privilege.
He was only one of the many scientists who helped us. A list of others who helped me personally appears at the end of this book. 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 mechanisms 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 concern 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 d
As before, I have not encumbered the text with scientific Latinised names where there is a reasonably accurate English equivalent. This inevitably 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
It is midnight on the coast of Christmas Island in the Indian Ocean, five hundred kilometres 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, twenty metres 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 eight centimetres 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 dramatically apparent. There were about forty-five 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 – up to twelve hours at a stretch, compared to only ten minutes during the dry season. 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 metres. 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. Soon the sea is fringed with a moving scarlet carpet of glinting shells, grappling legs and craning stick-like eyes. When at last the waves sluice over them, each shakes her body convulsively so that the brown eggs swill away in the water and, with a touching gesture of apparent exultation, lifts her claws above her head as if waving a salute.
At either end of the beach, where the sea beats directly on the face of the cliffs, the crabs have a harder time of it. So great is the traffic between those striving to clamber down to the sea and those who, having spawned, are attempting to get back again, that many cannot reach the water. They are thus compelled to release their eggs while they are still high on the rock and a brown rain of spawn falls sporadically from as high as six metres. In the confusion, many crabs lose their foothold, tumble into the water and are swept away.
Each one of these females sheds about a hundred thousand eggs. The waves and the water beyond have become a thick brown soup. As the sky lightens in the east, the crabs leave the water’s edge and are on their way back to the forest. Only a few stragglers remain on the shore. Here and there, limp bodies float in the shallows and great expanses of the beach are covered with a layer of brown grains that are not sand but eggs. The extraordinary laying is over for another year and the crabs’ progeny, abandoned, must now look after themselves.
Huge numbers of the hatchlings are immediately eaten by the fish that swim in shoals around the reefs. Moray eels squirm right to the water’s edge and greedily gulp down the feast. As the survivors are swept out to sea, so the larger fish, trawling with open jaws, sieve them from the water. They are helpless, drifting wherever the currents and tides take them. They feed by collecting tiny particles from the water. Periodically, they moult their thin transparent skins, changing shape as they do so. But they cannot assume their final adult form and breed unless they reach land. The vast majority of them never do so. They die unmated and without progeny. Most years the entire spawning is lost. But then, about one year in six, some fortunate swirl in the currents brings them back to the island where they first fell into the water a month earlier and at a high tide in December, a horde of tiny crablets no bigger than ants suddenly emerges from the waves and marches valiantly up the beach and on inland to restock the forest. Even then, their ordeal is not over – invasive ants, inadvertently introduced to the island in the 1930s, have eaten tens of millions of crabs in the intervening years.
The land-crabs’ breeding strategy is extravagant and wasteful but successful. The multitudinous hazards that face their young – the predatory fish, the vagaries of the currents, the absence of islands over vast areas of the surrounding ocean – are met and ultimately defeated by sheer numbers. But the cost is stupendous. The average female lives for about ten years and produces in all about a million eggs. Almost all the hatchlings will die within a few weeks. But if only two of this million reach adulthood, one for each parent, then the land-crab population of Christmas Island will be maintained.
This profligate recipe for survival is used by many animals of many kinds. A single female cod can produce six million eggs in one spawning. On land, insects use the same strategy. A female fruit fly, simply because of her tiny size, can hardly be expected to produce eggs in numbers to rival a cod, but even so, she can lay two thousand in a season in batches of a hundred at a time. The really big egg-producers, however, are some of the simpler animals that live in the sea, such as corals, jellyfish, sea-urchins and molluscs. And champion of them all, whether on land or in the sea, is almost certainly the giant clam. That can produce five hundred million eggs in one gargantuan splurge. And it may perform this stupendous reproductive feat annually for up to a century.
There is, however, an alternative to this extravagance. A female, instead of manufacturing the maximum number of eggs that can be created from her bodily reserves, may produce rather fewer but give each one a better chance of survival by supplying it with food in some way, so that it is sustained during its first difficult days. Some animals place this food within the egg as yolk. In simpler creatures, granules of it are distributed evenly throughout the egg – in a frog’s egg, it is concentrated at one end – and in a bird’s egg it initially fills the greater part of the shell. So generous is this bequest by birds to their young that a chick needs no additional food from which to build the flesh and bones and feathers of its infant body, and it still has enough energy left over to break its way out of the shell.
Insect eggs, however, contain very little yolk. Instead, the females may help their young by placing their eggs where the minute hatchlings will find food just as soon as their heads emerge from the egg capsule. A butterfly sticks them on the leaves of the particular plant that her caterpillars eat; a blowfly on the dead flesh that her maggots will relish; and some wasps, for the sake of their young, become body-snatchers.
