266 



with the dead bodies of the Hooded Crow. When countries are over-crowded 

 with birds some appear (like human beings in similar circumstances) to migrate 

 for good and all into distant lands. The curious irruptions of the Sand Grouse 

 into England in 1863, and again in the present summer, appear to be migrations of 

 this nature (12). 



Migration, then, among British birds may be considered as of three kinds. 

 First the regular stream of birds which comes here in spring to breed and which 

 leaves us again in autumn, and again that similar stream which appears in October 

 and leaves in February or March ; next, the continuous migration of our common 

 birds. Blackbirds, Jays, &c. ; and thirdly, exceptional immigrations, such as that of 

 the Sand Grouse just named. 



As for the continuous migration of common birds, it may be noticed that 

 this movement has only been discovered of late years, and that the reports from 

 the different lighthouses show constant examples of it. Thus a migration of the 

 same kind of birds frequently occurs, but in opposite directions, across the North 

 Sea. Crows, Rooks, Jackdaws, Starlings, Larks, Sparrows, Buntings, and 

 Finches, have been noticed there crossing each other. Indeed Professor Newton 

 says : " Hence we are led to the conclusion that every bird of the Northern 

 Hemisphere is to a greater or less degree migratory in some part or other of its 

 range." Mr. Cordeaux takes Blackbirds as an example of this tendency, and 

 says : " In the autumn, during September, the young of the year leave their 

 summer quarters, and their place is shortly taken by others, likewise young birds, 

 coming in October and November from districts which lie directly east or south- 

 east of Great Britain. Should an English winter prove severe, or even partially 

 so, our old birds will also leave, and in their place we have an influx of old 

 Blackbirds from the Continent, pushed forward by similar causes. In the Spring 

 the Continental visitors disappear, and our so-called resident Blackbirds come 

 back to their nesting quarters. As far as our knowledge extends the normal 

 conditions of locality and climate over the whole area are such as do not 

 necessitate a regular interchange of the members of their respective avi-faunas. 

 There is apparently no reason why our Rooks, Starlings, Skylarks, and Black- 

 birds should not be able to winter in England just as well as abroad ;" and he 

 adds : " Such are the ordinary phenomena of migration ; a movement which is as 

 regular and persistent as the flow and ebb of the tide " (13). And once more : 

 ' ' Practically such birds as the Lark and the Starling are migrating all the year 

 round " (14). The Robin, too, seems almost always moving from woods to the 

 vicinity of houses and back again, and even to far distant countries such as Africa. 



With regard to the third kind of bird migration — that which is local, 

 occasional, and exceptional — it must be remembered that it is only so because we 

 do not as yet see the full purpose which thus stirs so many birds at once. Doubt- 

 less, want of food is one great cause, or abundance of food in an unusual locality. 

 Thus in 1885 the abundance of Arctic ice brought down mollusca, entomostraca, 



(12). Seebohm's " .Siberia in Asia," p. 193 — 206. 

 (13). " Migration Report," 1884, p. 69, 70. 

 {14). Report, 18S0. 



