58 



— it follows, therefore, that we are forced to the conclusion 

 that the prevalence of warm weather with light south-easterly 

 winds near the surface of the earth is also abnormal. And again, 

 as he also does not recognise such a fact as retarded or deflected 

 migration (page 75), then the constant prevalence of such condi- 

 tions of the weather before described, at some height or other, 

 becomes an absolute necessity to the performance of migration. 



Let us just consider whether light south-east winds with 

 warm weather at the periods of migration can be fairly considered 

 abnormal. Herr Giitke himself has many remarks to show that 

 at one period during his long experience such meteorological 

 conditions were for many years the rule rather than the exception, 

 and he also gives us tables showing that these conditions prevailed 

 for long periods over immense tracts of land in Asia. Another 

 important point, too, must not be overlooked. There is absolutely 

 no evidence to prove that these same conditions do not prevail up 

 to great heights in the atmosphere at the same time as they 

 obtain near the surface of the earth. If such is the case, as seems 

 very probable, one naturally wonders why do birds perform their 

 migratory flights near the earth's surface, when there is nothing 

 to prevent their accomplishing their flight in the — according to 

 Herr Gatke — normal manner, or at the immense heights before 

 stated ? As this is not their custom, under these conditions it 

 seems reasonable to infer that they really prefer to migrate at 

 lower elevations. It will, perhaps, be readily admitted that 

 migration in the earlier stages of its development was conducted 

 at low elevations and in short stages, such as described by Herr 

 Gatke on page 46. Taking into consideration this fact as well as 

 the foregoing evidence, and also bearing in mind the wonderful 

 records of visible migrations presented to our notice by the author, 

 would it not be more reasonable to look upon the migration, 

 which is said to take place at such vast heights, as the abnormal 

 rather than the normal ? 



It is difficult to understand how Herr Gatke postulates a 

 migration on a large scale at heights far beyond our vision. 

 His notes on certain birds rising to great heights on setting out, 

 refer to highly specialised species given to soaring at all times of 

 the year. To the writer he seems to base his theory on the 



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