British, and many Continental observers too, saw when birds had come and in autumn that they had gone. Early swallows and martins were always met with near water, and were watched dropping to roost in the reed beds, as they always do in autumn before departure. Next morning none was visible. Certainly then they had vanished to hibernate in the water. The discovery of masses of torpid swallows, dead or dying, by no means an unknown thing when birds are overtaken by sudden falls in temperature in autumn or by a severe setback in the spring, was to these puzzled men confirmation of their theory of hibernation. Other details of the many stories of swallow hibernation are due to exaggeration or to misconception. In the second half of the eighteenth century a fierce discussion waged for and against hibernation, and many, including Geoffroy St Hilaire and Montagu, sat on the fence, admitting that it might be possible with some species and probably was with swallows. Later some Americans produced "evidence" in favour of avian hibernation, and even Mr Charles Dixon, in his earlier book at any rate, did not think it impossible (25). The only argument in favour of hibernation is that it is a habit resorted to by other vertebrates to escape the consequence of exposure to severe temperatures. The arguments against it are that not a single instance of avian hibernation will stand the light of reason and investigation, and that birds are provided with the means of escaping from the cold zone and certainly use these means. There are flightless birds, but they all live in climates in which they can exist at all seasons. As Seebohm puts it--"The hibernation of birds is a theory, the evidence in support of which has completely broken down. The migration of birds is a fact, as completely authenticated as the fact of their existence."
Dr Derham's "Physico-Theology" appeared in 1737 (24), and contained some sound reasoning about migration, though he was a little puzzled with the many hibernation stories. In 1780 an anonymous pamphlet--"A Discourse on the Emigration of British Birds," flouted the theory of winter sleep in no measured terms (33). This pamphlet was, at first, attributed to George Edwards, and the 1811 edition has his name on the title, but Mr A. C. Smith shows that the real writer was a comparatively unknown man, John Legg. Legg must be looked upon as one of our first real students of migration. It is Legg who refers to a pamphlet which appeared in 1740 in which it was seriously argued that swallows migrated annually to the moon.