xiv MIGRATION 367 



Woodpigcons come to us in thousands, attracted by 

 our green crops or by the large supplies of acorns to 

 be found in our woods. No one who in winter sees 

 the clouds of them in the sky can doubt that our native 

 birds have been reinforced from abroad. Hertford- 

 shire in the winter of 1893 was literally invaded by 

 Woodpigcons, and the acorns almost always to be 

 found in their crops showed what the attraction had 

 been. 



It will be seen from what has been said that migra- 

 tion is far more general than is usually supposed, and 

 it is certain that even now ornithologists have not 

 succeeded in observing all the smaller movements 

 which change of season causes among our resident 

 species. 



The Nesting-places of Migrants. 



All migrants without exception nest in the coldest 

 part of their range. They pass the summer in the 

 north and the winter in the south. Birds that breed 

 in the tropics are resident there with the exception of 

 some that nest at great elevations among mountains. 

 It is quite possible that there is a migration to the 

 Antarctic regions and in this case too the breeding- 

 place is in the colder, though in the southern, part of 

 the range. 1 It has been thought that our birds on 

 reaching Africa nested a second time. When our 

 Swallows arrive at Natal, the resident birds are 

 beginning to build, for their summer is beginning. 

 But it is almost certainly untrue that the birds from 



1 See Hudson's Naturalist in La Plata, 



