NON-INDIGENOUS BRITISH BIRDS. 301 



have been recorded. Probably it mates for life, as it 

 uses the same localities year by year. One of the most 

 remarkable breeding places of this Tern is situated on 

 the island of Ascension, and consists of two small colonies 

 and one very large one. Here the eggs are so thick 

 upon the ground that it is a difficult matter to walk 

 amongst them without treading on them. The nest is 

 merely a hollow in the ground. I have seen photographs 

 of this curious and interesting colony, which resembles 

 the usual breeding places of sea-birds, say at the Fame 

 Islands or Scoulton Mere ; that is to say, the ground 

 covered with nests (the Terns all sitting head to wind), 

 and the air clouded with birds. Vast numbers of eggs 

 are taken in Ascension for food — three thousand being 

 picked up in a single morning — and the laying season 

 is abnormally prolonged, as at the Fame Islands, as the 

 poor deluded birds are induced to replace their losses. 



Range of egg colouration and measurement : 

 The eggs of the Sooty Tern are normally three in num- 

 ber. (Conf. Ibis, 1 89 1, p. 145.) They are smooth in 

 texture, and vary in ground colour from white, through 

 cream to pale buff, spotted with reddish-brown, and 

 with underh'ing markings of pale brown and gray. The 

 spots are not very large, but are irregular in shape, and 

 somewhat evenly distributed over most of the surface of 

 the egg, occasionally forming an irregular zone round 

 the major half Average measurement, 20 inches in 

 length, by i -5 inch in breadth. The duration of the period 

 of incubation is unknown, as is also the sex which 

 performs the duty. 



Diagnostic characters : The eggs of the Sooty 

 Tern somewhat closely resemble certain types of those 

 of the Sandwich Tern, but the spots are never so dark 

 in colour. From eggs of the Nodd}^ Tern they are at 

 once distin:ruished bv their smooth shell. 



