THE BIRDS OF HELIGOLAND 231 



viduals. There are two ways in which this phenomenon may be 

 explained. It is possible that this species may occasionally, in 

 European and Asiatic Russia, advance north as far as the latitude 

 of Heligoland, and breed in this region, a portion of the young, 

 like many other species residing in districts far to the east of this 

 island, do not in such cases follow the normal course of the autumn 

 migration of their species, but turn to the west, and in this manner 

 reach Heligoland. According to the other explanation, we are here 

 dealing with one of those cases of frequent occurrence, where birds 

 which have advanced to Scotland have bred in that country, the 

 birds observed in Heligoland being the broods of such individuals 

 engaged on their passage to Persia or India. An attempt at 

 nesting of this kind is mentioned by Gray (Birds of the West of 

 Scotland, p. 161). 



The above-mentioned migration beyond the normal limits of 

 the spring migration of south-eastern species which breed in Greece, 

 Asia Minor, or Syria, and whose winter stations range from southern 

 Persia through the whole of India, must not be regarded as a mere 

 roving about without plan or purpose, but as has been discussed 

 in detail in the section on Migration under ' unusual phenomena,' 

 is doubtless caused by the fact that one member of the breeding 

 pair, mostly the laying or breeding female, has perished during the 

 first stages of the breeding process, while the surviving member of 

 the pair seeks to satisfy the still active breeding instinct by con- 

 tinuing the spring migration in the direction peculiar to its species. 

 This, in the case of the Rose-coloured Starling, proceeds in a 

 westerly direction, and conveys the bird across Germany to 

 England, Scotland, and the islands north of that country. 



However adventurous such an attempt may appear, the above- 

 cited observation of Gray's proves that it may, nevertheless, be 

 successful. From the Reports of the Marquis Antinori in the 

 Naunmnnia, for 1856, we learn in what unprecedented quantities 

 these birds are destroyed by predatory animals in their breeding 

 colonies, which are located on the ground amongst the rubble. 



This bird occurs as a breeding species from Asia Minor to 

 southern Russia, in the Caucasus and Turkestan, extending east- 

 ward within the same parallels of latitude into Central Asia. 



Thrushes Turdince. This genus comprises about two hundred 

 species, if we include therein the great White's Thrush, the 

 Rock Thrush, and the American Mocking Thrushes, all of which 

 are here, following the older system of classification, noted as 

 Thrushes. About twenty-one of these have hitherto been met 

 with in Europe, of which, however, only eight can be regarded as 



