BRITAIN^S BIRDS AND THEIR NESTS. 49 



Fames to the Orkneys both are found, the Arctic Tern 



becoming the more abundant of the two north of the 



Moray Firth. Only the Arctic Tern is found in the 



Shetland Isles. Both species are found along the western 



sea-board of Great Britain, from the Scilly Isles to the 



Outer Hebrides ; but the Common Tern predominates as far 



as Skye, and the Arctic Tern has only a very few haunts 



much south of this. Both birds are found nesting all 



round Ireland, the Arctic Tern everywhere predominating. 



The actual sites of the colonies also differ. The Arctic 



Tern shows a distinct preference for low islands, and the 



more sheltered dune-lands are not typical haunts. In 



Great Britain, lake and river haunts, too, are left almost 



entirely to the Common Tern; but in Ireland there are 



many large colonies on inland waters. When colonies of 



both species are found side by side, the Arctic Terns are 



usually nearer the sea; the species keep more or less 



apart, but are said to shift ground to some extent in 



various localities. 



In habits the two species are much alike, but the 

 Arctic Tern is the bolder in the defence of its eggs 

 and young. Any large bird straying too near the colony 

 is mobbed to death or driven off with great fury, and 

 even the human intruder is met by threatening swoops. 



The Arctic Tern seems much more inclined to dispense 

 with a lining for its 'scrape,' and two eggs appear to 

 form the normal clutch. The difference between the eggs 

 themselves is a question of some difficulty, but we may 

 safely steer a middle course. We may reject the state- 

 ment that there is no difference, and we may also reject 

 as unsafe the various methods suggested for identifying 

 individual eggs of 'unknown antecedents.' But generalis- 

 ing we find that there are differences. To begin with, 

 the Arctic Tern's eggs run perceptibly smaller on an 



G 



