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 bi'eeding-quarters nearer 

 the poles, but, like our summer-visitants, they seek their Avinter-abode 

 nearer the equator, and thus perform a somewhat longer i\Iigration. 

 So far thex-e 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 

 Swallow or the Fieldfare, of which every individual disappears 

 at one period of the year or another, there are other species, such 

 as the Pied Wagtail or the Woodcock, 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 Avhich 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 (.mo:. Grives or 



^ One of the first, at least in this country, to set fo*th the unity of the 

 migratory movement seems to have been the author of a Discourse cni 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 tliird of his Essays tipon 

 Natural History (London : 1770) and may yet be read to advantage. 



^ Whether these few be not migrants from another district is a point that 

 would require further consideration. 



