THE AUTUMN MIGRATION OF BIRDS. 225 



Great Spotted Cuckoo is controlled by the smaller 

 geographical limits of the species selected to hatch 

 its young and bring them to maturity. The 

 Blackcap {Sijlvia atricapilla)^ again, with its com- 

 paratively short fly- line, reaching from lat. 60° in 

 Scandinavia down principally to North Africa, and 

 more rarely towards the Equator, is a late migrant, 

 passing Heligoland in October and November. 

 The rule appears to be that the further north a 

 bird breeds^ the more anxious it is to get south in 

 autumn^ and the longer its fly-line the earlier it is 

 to start. We have already alluded to the fact that 

 some species reverse their routes almost entirely in 

 autumn, and travel south by quite a different fly- 

 line from that they followed north in spring ; we 

 have seen that the time in some species is reversed, 

 and night instead of day is selected for Flight. 

 Migration in autumn is also slow and leisurely in 

 comparison with the wild mad rush of spring ; 

 birds take their time in moving south, dallying 

 here and there for a few days wherever food is 

 plentiful ; taking it easy, as it were ; enjoying a 

 well-earned hohday after all the bustle and excite- 

 ment of summer. 



The Autumn Migration of birds in the Northern 

 Hemisphere practically lasts about four months, 

 beginning, we will say, during the latter half of 

 July, and continuing until the first half of November. 

 Some few species wander south later than this, but 

 these must be regarded as Nomadic rather than 

 Regular migrants. Autumn Migration is at its 



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