NON-INDIGENOUS BRITISH BIRDS. 305 



lagoons, and low islands in deltas, the shores of lakes, 

 sandy islands, and banks. The nest is merely a slight 

 hollow scraped out in the sand, and sometimes lined with 

 a few bits of dry sea-weed and grass, but in some cases 

 the eggs are deposited in some natural hollow, without 

 any further provision or alteration. When disturbed at 

 the colony the birds rise in a fluttering crowd, become 

 very noisy, and fly to and fro in great anxiety until left 

 to themselves again. 



Range of egg colouration and measurement : 

 The eggs of the Gull-billed Tern are two or three in 

 number. They vary in ground colour from creamy-white 

 to buffish-brown, spotted with various shades of brown, 

 and with underlying markings of gray. The spots are 

 not very large — varying from the size of buck-shot 

 downwards — and usually pretty evenly distributed over 

 the surface of the ^g'g, but sometimes most numerous 

 on the major half. The gray underlying markings are 

 similar in character, and very conspicuous. Average 

 measurement, 2-0 inches in length, by \'\ inch in breadth. 

 Incubation is performed by both sexes, but the duration 

 of the period is unknown. 



Diagnostic characters : The eg^s of the Gull- 

 billed Tern are not easily confused with those of any 

 other Pal?earctic species. Small eggs similar in colour 

 might be confused with those of the Sandwich Tern, but 

 are always duller in colour. 



