ROSEATE-TERN 95 



Apparently they are crowded out by their neighbours, the common- 

 terns, but why they should not be able to hold their ground is not 

 clear. Possibly the protection now extended to the Terns may be the 

 indirect cause ; for the common-tern is an earlier nester than the 

 roseate, and on the rocky islets, where both species breed, the space 

 available for nesting-sites is limited. As the colonies of common- 

 terns respond readily to protection and tend to increase rapidly in 

 numbers, it may be that the roseate-terns are gradually driven away 

 by finding their breeding-sites occupied already. Against their 

 natural enemies the habit of breeding in large colonies is a great 

 protection. Even the larger gulls, bold robbers though they are, 

 would hesitate to provoke the attacks of some hundreds of terns, 

 intent on delivering their needle-like thrust with the closed bill from 

 above. But the unfortunate wanderers, thus driven out, and pre- 

 vented from nesting under the protection of their neighbours, if they 

 breed at all, must found new colonies, where they are at the mercy of 

 the first prowling gull which passes by. 



The fecundity of this species is also less than that of its congeners. 

 The normal clutch of the common-tern is three eggs, while two are 

 much less usual. Among the Arctic-terns, it is true, clutches of 

 two are more general and three are less usual, but with the roseate- 

 tern the clutch ranges from one to two, while out of a large number 

 of nests examined in situ by the writer, not a single one contained 

 three eggs. It is of course quite possible that clutches of three occur 

 occasionally : some instances have been recorded, but they must be 

 regarded as quite exceptional. Mr. H. Noble, who has had consider- 

 able experience of this species, is inclined to consider one as 

 being the normal clutch, sometimes two, and he also has never seen 

 three (British Birds, iii. p. 90). My own experience leads me to regard 

 two as the normal clutch in an ordinary season in the British Isles. 

 In the colony of roseate-terns discovered by M. Blanc in Tunisia, the 

 clutch consisted invariably of a single egg. 



Another point which may possibly have some bearing on the 



