MIGRATION 551 
will shew that all are really affected by the same impulse, what- 
ever that may be, and that the nature of their movements at first 
sight so dissimilar is in truth almost uniform. The species which 
resort to this and to other temperate countries in winter are simply 
those which have their breeding-quarters much nearer the poles, 
and in returning to them on the approach of spring are but doing 
exactly as do those species which, having their winter abode nearer 
the equator, come to us with the spring. The Birds-of-passage 
proper, like our winter-visitants, have their breeding-quarters nearer 
the poles, but, like our summer-visitants, they seek their winter-abode 
nearer the equator, and thus perform a somewhat longer Migration. 
So far there is no difficulty and no hypothesis—the bringing to- 
gether of these three apparently different categories is the result of 
simple observation.? 
This, however, is not the only fact which is evident on the most 
cursory examination. To take the birds of the British Islands as 
an example (though exactly similar cases are presented in other 
countries), we find that while there are some species, such as the 
SwWALLow or the FIELDFARE, of which every individual disappears 
at one period of the year or another, there are other species, such 
as the Pied WacTalIL or the Woopcock, of which only the majority 
of individuals vanish—a few being always present*—and these 
species form the so-called “ Partial Migrants.” If we extend our 
view and look to birds on the continent of Europe, we find that 
many species are there notoriously migrant which are not generally 
suspected to be so in this country—such as the Song-THRUSH and 
the REDBREAST, both of which species closer observation has proved 
to be with us subject to the migratory impulse. In respect of the 
former it is known that towards the end of summer or in autumn 
our native Song-Thrushes receive a considerable accession in 
numbers from the birds which arrive from the north, though the 
immigration is by no means so well marked as it is in Belgium, 
France, or Germany, where the arrival of the strangers sets all the 
fowlers to work, and the beginning of the Chasse aux Grives or 
1 One of the first, at least in this country, to set forth the unity of the 
migratory movement seems to have been the author of a Discourse on the 
Emigration of British Birds, published anonymously at Salisbury in 1780, and 
generally attributed to ‘‘George Edwards,” though certainly not written by the 
celebrated ornithologist of that name. Mr. A. C. Smith has discovered that the 
author—a man in many respects before his time—was John Legg, hitherto un- 
known as a naturalist. But the real George Edwards also held opinions on the 
subject that are mostly sound, and his remarks gathered from various parts of 
his greater works, where they appeared ‘‘in a detached and unconnected form,” 
were republished, with a few modifications, in the third of his Essays wpon 
Natural History (London: 1770) and may yet be read to advantage. 
2 Whether these few be not migrants from another district is a point that 
would require further consideration. 
