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ing migration, there are certain species of very regular appearance 

 on Heligoland which Herr Gatke tells us always, or only on the 

 smallest number of occasions, perform their migrations at very 

 low elevations, viz., the Hooded Crow, Starling, and Skylark, 

 and in the opinion of the writer, the Lapwing, Fieldfare, and 

 Eedwing might have been added to these. Are we to assume 

 that these species are devoid of that special sense of approaching 

 changes of the weather supposed to be possessed by the majority 

 of species, or is it more perfected in them, so that they are always 

 able to choose a favourable time for their journeys? The 

 evidence presented by the author rather points to the former 

 conclusion, for we read of Hooded Crows meeting with adverse 

 winds and Skylarks being overtaken by thunderstorms. 



If there is one fact calculated to strike the reader in perusing 

 Herr Gatke's work more than another, it is the marvellous 

 number of birds actually seen or heard passing his observatory, 

 To the writer this fact alone is enough to make one pause before 

 admitting that visible migration is the abnormal and invisible the 

 normal. Those, however, who are also ready to agree with the 

 author in his theory of a broad migration front corresponding to 

 the breeding area, have to face in addition the incredible but 

 necessary myriads of birds which must exist to enable the latter 

 theory to be granted as even reasonably probable. 



That certain species, such as Cranes and Hawks, fly at times 

 to great heights, is undoubtedly a fact, and it may readily be seen 

 that it is an advantage to the smallest birds to ascend to a good 

 height before crossing wide seas. For it must often happen that 

 they encounter sudden changes of weather which may materially 

 retard their progress. Nansen in crossing Greenland experi- 

 enced this a't a height of over 8,000 feet — a gale which had 

 been raging for two days suddenly blowing with only a pause of 

 a few minutes from the opposite quarter. It is very evident that 

 the further a bird has to fall, as its strength gra.dually fails, the 

 greater chance it will have of eventually reaching the land, of 

 course providing forward progression is not altogether impossible. 

 But to the writer the effort put forward to attain a vertical height 

 of four miles or more would, by the consumption of energy at the 

 outset, more than counteract the benefit before mentioned. 



