166 THE WONDER OF LIFE 



Referring to the general occurrence of migration, Professor 

 Newton said 



' I cannot point out any species which I believe to be, as a 

 species, entirely non-migratory. No doubt many persons 

 would at first be inclined to name half a dozen or more which 

 are unquestionably resident with us during the whole year, 

 and even inhabit the same very limited spot. But I think 

 that more careful observation of the birds which are about 

 us, to say nothing of an examination of the writings of 

 foreign observers, will show that none of them are entirely 

 free from the migratory impulse.' 



He instanced the Hedge Sparrow which seems so station- 

 ary on Britain, and yet is well known as a migrant on the 

 Continent. 



Our knowledge of bird-movements in the Southern 

 Hemisphere is very scanty, and must be left out of account 

 at present ; but for the Northern Hemisphere it is a very 

 familiar fact that the birds of any country can be classified, 

 from the migration point of view, into five sets : 



(1) There are the summer- visitors, such as swallow, 

 swift, cuckoo, nightingale, and so on through the long list 

 (mostly insectivorous, one should note), who arrive from 

 the South in Spring, nest and breed within our bounds, 

 and return in late summer or autumn * to warmer lands 

 and coasts that keep the sun '. 



(2) Against these we have to place the winter- visitors, 

 such as fieldfare and redwing, both first cousins of the 

 thrush, the snow bunting, and many of the northern ducks 

 and divers, who nest in the far North, but come South in 

 winter. 



(3) In a set by themselves we may rank the birds- 

 of-passage in the stricter sense, like some of the sand- 



