250 NATURAL SCIENCE. April, 



immigrants that reach our shores by a westerly movement along the 

 east and west route. These birds cross the narrow passage of the 

 North Sea, and land on the south-eastern shores of England, per- 

 forming the journey by daylight. The chief arrivals are in September 

 and October, ordinarily ceasing in the middle of November ; but in 

 exceptionally severe weather they are again renewed, the birds at 

 that time chiefly passing westward to the warmer portions of the 

 kingdom. The latter movements, however, are exceptional, and due 

 to meteorological causes. 



The Autumn Emigration begins in July, and is probably led off 

 at the end of that month by the adult cuckoos and swifts. Towards 

 the close of the month also there are occasional records of movements 

 of small birds, such as wheatears, redbreasts, warblers, pipits, 

 swallows, etc. ; but Mr. Clarke adds a caution that many of this latter 

 class are " outcasts," whose parents are engaged with second broods, 

 and they may, in their wanderings, reach the coast where their 

 appearance would be duly recognised. During August, however, the 

 retreat sets in in earnest, and a large number of migratory birds 

 take their departure ; with them are probably some species which are 

 mere birds of passage on their way south from more northerly 

 breeding-stations. September witnesses the " height and close " of 

 the emigration of the bulk of the smaller British summer visitors ; 

 most of these are absent from the records of October, which month 

 witnesses the departure of the laggards. The partial migrants are, 

 however, niuch on the move in October, their numbers doubtless 

 being largely recruited by arrivals of the same species from the north ; 

 but the first half of November brings the movement to a close, and 

 the ordinary southward retreat, both of birds of passage and of 

 British emigrants, ceases. 



The first indications of the Spring Immigration sometimes occur 

 as early as February, but these are almost entirely confined to partial 

 migrants within the British area, such as pied wagtails and lapwings ; 

 especially mild weather may, however, bring us an occasional wheat- 

 ear, or even a solitary swallow. March witnesses the return of many 

 species which had quitted our shores in consequence of the severity 

 of v/inter, and generally a few of our regular summer visitors, such as the 

 whinchat, wheatear, willow wren, chiffchaflF, and even an early sand 

 martin or cuckoo; but we must wait till- April for the first pronounced 

 influx of the summer migrants. In this month the arrival of thirty- 

 seven species is recorded in the chronicles ; the birds of passage, 

 which only visit us on their way to their northern breeding-stations, 

 also begin to put in an appearance at this time. Early in May the 

 spring immigration reaches its full force, and before the close of the 

 month comes practically to an end. The number of passing migrants 

 is also greatly increased, and by the middle of June the bulk of the 

 Polar breeding birds have passed, although some few which go very far 

 north, such as the knot and the grey plover, may linger a little longer. 



