The Cambridge Manuals of Science and Literature THE MIGRATION OF BIRDS * * * * * CAMBRIDGE UNIVERSITY PRESS London: FETTER LANE, E.C. C. F. CLAY, MANAGER [Illustration] Edinburgh: 100 PRINCES STREET Berlin: A. ASHER AND CO. Leipzig: F. A. BROCKHAUS New York: G. P. PUTNAM'S SONS Bombay and Calcutta: MACMILLAN AND CO., LTD. _All rights reserved_ * * * * * [Illustration] THE MIGRATION OF BIRDS BY T. A. COWARD Cambridge: at the University Press New York: G. P. Putnam's Sons 1912 * * * * * _With the exception of the coat of arms at the foot, the design on the title page is a reproduction of one used by the earliest known Cambridge printer, John Siberch, 1521_ * * * * * 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.