406 NATATORES. 



a specimen sometimes straggles into the east of England, near 

 Yarmouth, opposite to which the sea is narrow, and birds' 

 food plentiful over the fishing banks, which the water both 

 forms and disturbs by its currents. 



In the summer plumage, the head and feathers on the 

 upper part of the neck, which are produced, and long and 

 silky, are deep black ; the upper part is ash colour, and the 

 under part white. But neither its breeding place nor its 

 breeding plumage is very well understood, nor strictly falls 

 within the scope of a popular account of British birds. With 

 us, birds from that quarter of the world in which the 

 Caspian tern is at home, may be looked for principally in the 

 winter, even though their situation on the continent should 

 at that season happen to be several degrees to the southward 

 of ours. The cold not only sets in earlier in these longitudes, 

 but it sets in much more severely ; and as it is towards the 

 heat that most birds migrate in autumn, and not upon the 

 direction of the equator, which of course influences them 

 only in so far as it heats them, we may reasonably conclude 

 that there is a tendency in those eastern birds towards the 

 Atlantic and its unfrozen divisions during the winter months ; 

 and when the birds come as far westward as the sources of 

 the Danube, it is fully more natural that they should descend 

 the valley of the Rhine, than that they should pass the moun- 

 tains and forests of the north-east of France, in order to 

 reach the western plains and valleys of that country, which, 

 from their characters, are not the best adapted for birds of 

 this genus. In its winter plumage, in which we know it a 

 little better, the forehead and part of the head are white, 

 the rest of the head, the neck, and upper part, bluish ash ; 

 the coverts brownish ash, barred with black arid white ; and 

 the tail pale ash. The quills, and all the under parts pure 

 white. The bill is bright vermilion red ; the feet black. 

 The male and female birds do not differ in their plumage, 



