264 



SEA-BIRDS 



joy ^ 



Fig. 47 

 Breeding distribution of the 

 black tern, Chlidonias nigra. 

 Black lines embrace prob- 

 able extent of breeding- 

 range; black dots represent 

 some known breeding places 



hat off, and draw blood with the sharp pointed bill. Sometimes 

 two or more join forces, hurling themselves repeatedly at an enemy, 

 screaming and striking. Yet this behaviour is not always successful: 

 skunks ignore it and kill terns freely. Short-eared owls will pounce 

 on and carry off both adult and young terns. But dogs, rabbits, rats, 

 sheep, lambs and other birds are effectively driven away. 



Gulls especially seem to draw the anger of terns and are successfully 

 driven away from tern eggs and chicks. The common tern has been 

 known to kill young ring-billed gulls, driving them to the water and 

 stabbing their heads — the old gulls offering no resistance. Herons, 

 which if permitted would no doubt do a great deal of damage by 

 devouring chicks, are violently attacked and driven away. 



