116 THE MIGRATION OF BIRDS 



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 in- 

 vestigation, and that birds are provided with 

 the means of escaping from the cold zone and cer- 

 tainly 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 hiberna- 

 tion of birds is a theory, the evidence in support 

 of which has completely broken down. The migra- 

 tion 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, 



