i897. THE MIGRATION OF BRITISH BIRDS. 249 



Of equal interest with the discussion of the routes taken is the 

 section devoted to " Seasonal " migration. 



The difference between the behaviour of the birds on their 

 autumn and spring passages is very marked. At the close of the 

 summer the great business of the year — procreation — is over, food is 

 still abundant, and the birds pass leisurely along, their numbers 

 swelled by the broods of young ones ; but in spring the conditions are 

 quite different, they hurry on to their breeding-grounds, and the 

 opportunities for observation are far more limited. 



Commencing with the Autumn Immigration, it is remarked that, 

 notwithstanding the month of July being the height of the Arctic 

 summer, certain birds, such as the whimbrel and knot — and a few 

 others less frequently — are recorded as arriving in that month. In 

 explanation of this fact, Mr, Clarke remarks that the majority of 

 these early arrivals are probably non-breeding birds which have not, 

 perhaps, passed far beyond the limits of Britain on their spring 

 journey northward ; and in support of this conclusion he points out 

 that these migratory pioneers, so far as reported, are all adults. In 

 August the return movement of twenty-six species of birds, whose 

 summer haunts lie entirely beyond the British area, is recorded ; 

 and, in addition to these, the northern representatives of several 

 species which are summer visitors to Britain also put in an 

 appearance. In September a marked increase takes place in the 

 number of immigrants, both as to species and individuals ; over forty 

 species which do not summer in Britain, including those already 

 recorded for August, are enumerated. In October the return-current 

 reaches its maximum, and it is in this month chiefly that the great 

 " rushes " of migrants arrive on our shores ; these rushes, as will be 

 explained, are entirely due to meteorological conditions. Forty-seven 

 species of regular birds of passage are recorded in this month, besides 

 many other birds which breed in both Northern Europe and Britain. 

 It is noticed, however, that signs of slackening are apparent in some 

 respects, for certain species have already ceased to occur, and a few 

 others appear less numerously. The migratory movements in 

 November are on a much reduced scale. A few northern summer 

 birds which do not breed in Britain, such as the redwing and field- 

 fare, still arrive early in the month, often in considerable numbers, 

 also a few northern species, which we are accustomed to regard as 

 hard-weather birds, become more numerous ; but Mr. Clarke found 

 that " after the middle of the month the immigration of such birds as 

 spend the summer in the north entirely ceases, with the exception of 

 certain marine species (ducks, gulls, grebes, swans), whose late move- 

 ments to the south are dependent upon severe weather conditions. 

 This is entirely contrary to the views hitherto propounded regarding 

 the limits of these movements, but it is, nevertheless, a fact well 

 sustained by the enquiry." 



Besides those derived from the north, there are certain Autumn 



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