CONTENTS 



PAGE 



I. MIGRATION OF BIRDS: 



i. COURSE OF MIGRATION GENERALLY IN HELIGOLAND, 3 



n. DIRECTION OF THE MIGRATION FLIGHT, . . 24 



in. ALTITUDE OF THE MIGRATION FLIGHT, . . 46 



iv. VELOCITY OF THE MIGRATION FLIGHT, . . 63 



v. METEOROLOGICAL CONDITIONS WHICH INFLUENCE 



MIGRATION, . . . . .74 



vi. ORDER OF MIGRATION ACCORDING TO AGE AND SEX, 100 



vii. EXCEPTIONAL MIGRATION PHENOMENA, . . 114 



vni. WHAT GUIDES BIRDS DURING THEIR MIGRATIONS? . 131 



ix. THE CAUSE OF THE MIGRATORY MOVEMENT, . 143 



II. CHANGES IN THE COLOUR OF THE PLUMAGE OF 



BIRDS WITHOUT MOULTING, . . .149 



III. ACCOUNT OF THE BIRDS OBSERVED IN HELIGO- 



LAND, . .165 



