84 THE MIGRATION OF BIRDS 



added more to our knowledge of the connection, 

 in what we may term British migration, than Mr 

 Eagle Clarke, but it must not for a moment be 

 imagined that his conclusions and the data from 

 which he arrived at them are purely insular. The 

 British Islands are merely the field of observation, 

 the centre of the field, of the movements of Holarctic 

 birds which travel regularly or occasionally through 

 Britain. Mr Clarke points out repeatedly that in 

 studying the phenomena it is the conditions at the 

 point of departure not at the point of arrival gener- 

 ally the point of observation which are important. 

 The oft-repeated assertion that birds'can foretell 

 the nature of approaching weather that they are 

 living barometers is not supported by any satis- 

 factory evidence, but it is certain that on many 

 occasions the weather into which they have passed 

 in moving from one zone to another has not only 

 retarded, checked, or exhausted them, but has 

 proved fatally disastrous. During the westward 

 rushes in winter, when exceptionally severe weather 

 has cut off the food-supply of ground-feeding birds, 

 observers who have seen the birds moving in front 

 of the storm have maintained that they had felt 

 its approach and retreated in time. The truth 

 seems to be that the birds start so soon as the supply 

 is cut off but in many cases speedily outstrip the 

 storm. When these exceptional winter migrations 



