EXCEPTIONAL MIGEATION PHENOMENA 121 



summer visitants. Saunders (Yarrell, British Birds, 1881) says 

 that more than thirty of these birds have been killed in Great 

 Eritain, and four in Ireland. Twenty of them were seen in one 

 day m Norfolk, and twelve were shot within the same period of 

 time at Helston in Cornwall. 



The most remarkable occurrence, however, in this connection 

 is that of the Cream-coloured Courser, a typically African sjjecies, of 

 which Harting records nineteen instances in England. Next to these 

 southern visitors to Heligoland must be considered, though within 

 a somewhat narrower compass, a few interesting natives of the Swiss 

 Alps. Thus, the Chough, and Alpine Chough (Corvus jyijrrhocorax), 

 have each occurred a few times. The Alpine Accentor I have 

 obtained three times, the bird having been observed on three other 

 occasions besides. The Snow Finch (Fringilla nivalis) has occurred 

 twice ; the Alpine Swift has once been shot, and observed on one 

 other occasion. Among these we may perhaps also count the 

 Blue Rock Thrush (Tiirdus cyanus) and the Rock Thrush (»S'. 

 saxatilis), of whom the former has been killed here once, and the 

 latter about six times. 



In regard to these species from districts much nearer to Heligo- 

 land, the south of England again completely outstrips this island. 

 Harting enumerates fourteen instances of the occurrence of the 

 Alpine Accentor, and twenty of that of the Alpine Swift in his own 

 country. Although it may not be difficult to find an explanation 

 for the frequent occurrence of this species in England, one seeks in 

 vain for reasons why natives of Central Africa, and more especially 

 of Switzerland, should so rarely extend their migrations northwards 

 to Germany and Heligoland. 



After what we have said as regards the summer excursions of 

 species from the south-east of Europe and Asia Minor, we might 

 presuppose that southern species — i.e. those resident in Spain and 

 North-west Africa — would also be met with in comparative abun- 

 dance in England, just as on the other side, the frequent occurrence 

 of these latter species north of their breeding stations proves the 

 conclusiveness of our assumption as to the causes which determine 

 the appearance of south-eastern species in a north-westerly direction : 

 like the birds from Greece and Asia Minor, which have been met 

 with in districts so far to the north-west of their homes as 

 Germany, Heligoland, and even the Shetland Islands, the numerous 

 visitors to England from Spain and Africa are also individuals that 

 have lost their pairing spouses during the earlier stages of the 

 breeding season, and which then strive to satisfy the still persis- 

 tent breeding impulse by continuing to follow the original direction 

 of their spring migi-ation, — in their case, one to the north. The 

 time of the appearance of these southern birds in England, taking 



