THE VERNAL MIGRATION 13 



Several of the above birds, it will be noticed, belong - to 

 species which are found in this country at all seasons of 

 the year. As such, they might therefore be objected to in 

 a list of migrants : but their place as above is correct. 

 Migration is infinitely more general and universal than is 

 popularly supposed. It is, of course, a matter of common 

 knowledge that birds such as the swallow, the cuckoo, and 

 the willow-wren are distinctly foreign migrants. Their 

 summer and winter haunts are far apart, separated by 

 belts of sea and land ; consequently their reappearance 

 here every April after a total absence of seven or eight 

 months is markedly conspicuous, and appeals at once to 

 eye or ear in an unmistakable manner. The annual 

 migrations of these, in short, are so patent as to be 

 obvious even to the least observant. 1 



But there are other wanderers whose movements are 

 not so conspicuous ; but which are, nevertheless, quite as 

 strictly migratory in their habits. Thus, there is the case 

 of birds whose summer and winter limits may be said to 

 overlap. Such birds are, of course, found permanently 

 within the boundaries of the overlapping zone — as shown 

 in the rough diagram annexed. The upper oblong repre- 

 sents the habitat of any given species during summer ; the 

 lower oblong is its habitat during winter. Assuming that 

 the annual range of each individual bird is approximately 

 equal, those breeding in summer at A would winter at B 

 — the two most northern points of their respective areas. 

 The intermediate birds summering at B would pass on in 



1 I leave this as it stood in the last edition : yet, after forty years' 

 experience, I fear that scarce one man in fifty knows or recognises the 

 trill of the willow-wren when first heard in every nook and corner of the 

 land from mid-April onwards. Nor yet do the great majority see any 

 difference between the sand-martin, which often comes in March, and the 

 swallow that is not due for three weeks later. 



