CONTENTS 



PAGE 



I. MIGRATION OF BIRDS:— 



1. Course of Migration generally in Heligoland, 3 



II. Direction of the Migration Flight, . . 24 



III. 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 



VIII. What Guides Birds during tiieik 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 



