THE AUTUMN MIGRATION OF BIRDS. 



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Another equally interesting fact concerning 

 Autumn Migration is, that all the more northern 

 birds that appear earliest at their breeding-grounds 

 in spring, as a rule, linger the longest at them in 

 autumn, probably because they are the hardiest and 

 most robust of migrants. The Wheatear {Saxicola 

 cenantke) and the ChiffchafF {Phijlloscopus rufus), 

 for instance, arrive amongst the earliest of birds 

 throughout their summer area of distribution, 

 reaching the British Islands during the last week in 

 March; they linger in the autumn until most 

 others have departed, being amongst the last to go. 

 On the other hand, the Swift {Cijpselus a/jus) and 

 the Red-backed Shrike {Lanius collurio) arrive very 

 late in spring (in the British Islands not before 

 May), and are amongst the earliest to retire south 

 in autumn. Probably these very early autumn 

 migrants would be the first to relinquish a northern 

 journey in the event of the summers becoming 

 shorter than they are now, just as the hardy late 

 autumn migrants would continue to visit the 

 northern zones as long as any summer remained at 

 all ; or, in the event of warmer climatal conditions 

 rendering the present winters shorter and milder, 

 they would be the first to forego migration alto- 

 gether. This is another deeply interesting instance 

 of how some of the grandest changes our Planet 

 has undergone are indelibly stamped upon Avian 

 Migration, or are correlated with such a compara- 

 tively insignificant phenomenon as the Season Flight 

 of Birds. 



