Chapter I: Preface

Any attempt to elucidate the problems connected with the
Migration of Birds must, in the present state of knowledge, contain
some theory and speculation, but the diligent observations of an
army of careful workers yearly add facts, which though they may
appear insignificant when considered alone, tend in the aggregate
to confirm or repudiate the conclusions of past workers. I have
endeavoured to bring together some of the more important theories,
and to give prominence to ascertained facts; I have also striven
to check desire on my own part to wander into realms of pure
speculation, though conscious that I have not always evidence to
support my suggestions.

The numbers in brackets ( ) in the text refer to the books or
papers mentioned in the list at the end of the volume, which is in
no ways an attempt at a full bibliography. I have quoted freely
from the works of past and living ornithologists. To these I offer
apologies if I have misconstrued their arguments, and acknowledge
my indebtedness to those whose observations or writing have given
me light. In particular I tender thanks to Mr Wells W. Cooke for
his permission to reproduce the maps facing pp. 76, 78, 80. I have
found his writings and those of Herr Otto Herman and Mr W. Eagle
Clarke especially valuable. Mr Eagle Clarke's long looked-for book
on Migration is, as I write, still in the press; had mine been more
than a manual I should have hesitated to publish until his had
appeared.

T. A. COWARD.

BOWDON, CHESHIRE,
_4 November 1911_.

CONTENTS

CHAP. PAGE

I. MIGRATION OF BIRDS 1

Definition--Variation of migration.

II. CAUSE AND ORIGIN OF MIGRATION 13

Direction of passage--The potentiality of flight--Habit
of wandering--Memory--Extension of range--Influence
of Temperature--Desire for Light--Glacial Epoch--Food
Basis--Sexual Impulses--Competition.

III. ROUTES 33

Route or Broad
Front--Coasting--Fly-lines--Isepipteses
--Land-bridges--Coast Lights.

IV. THE HEIGHT AND SPEED OF MIGRATION FLIGHT 47

Altitude of Normal Migration--Variation in
Speed--Effect of Wind.

V. ORIENTATION AND ROUTE FINDING 56

Route Finding--Use of Memory--Eyesight--Errors--Guidance
of Young--Beam Winds--Homing of Terns.

VI. THE DISTANCES TRAVELLED BY BIRDS 65

The Swallow--Variation in Distances--Marking
Birds--Results--Routes of the Golden Plover--Evolution
of the Routes.

VII. MIGRATION AND WEATHER 83

Knowledge of Approaching Weather--Favourable and
Unfavourable Conditions--Importance of Winds--Cyclonic
and Anticyclonic Winds--Continental Migration.

VIII. THE PERILS OF MIGRATION 104

Contrary Winds--Lighthouses and Lightships--Leeward
Drift--Catastrophes.

IX. EARLY IDEAS OF MIGRATION 114

Literature--Hibernation--Carriage of Small by Large
Birds.

X. SUGGESTIONS AND GUESSES 119

Trans-Atlantic Migration--Ship-borne Wanderers
--Storm-blown Birds--Casual Wanderers--Swimming and
Walking.

XI. SUMMARY 126

BIBLIOGRAPHY 131

INDEX 135

LIST OF MAPS

FACING PAGE

Map showing the range of the American Golden Plover,
with its known migration route 76

(From _The National Geographic Magazine_.)

Map showing the evolution of the migration route of the
American Golden Plover 78

(From _The National Geographic Magazine_.)

Map showing the evolution of the migration route of the
Eastern or Pacific Golden Plover 80

(From _The National Geographic Magazine_.)

Map to show that a bird leaving Norway, near Aalsund,
might be carried round the British Islands in twenty-four
hours. The arrows indicate the actual directions
and force of wind at the times marked during a
slow-travelling circular storm in autumn 1901.
Speed of bird about twenty-five miles per hour 98

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THE MIGRATION OF BIRDS