COMMON TERN. 305 



think as a rule, that this Tern nests so near the water 

 as the Arctic Tern, and shows more preference for 

 laying amongst or near vegetation of some kind. The 

 nest is a mere hollow, scantily lined with bits of dry 

 grass and withered marine vegetation. The behaviour 

 of this Tern at the nest is precisely similar to that of its 

 congeners. As soon as the breeding-ground is invaded 

 the birds rise in a noisy, anxious, fluttering throng, and 

 continue flying restlessly about until their haunt is left 

 in peace. 



RANGE OF EGG COLOURATION AND MEASUREMENT : 

 The eggs of the Common Tern are two or three in 

 number, and subject to some considerable amount of 

 variation. They vary from buff to grayish-brown in 

 ground colour, spotted and blotched with dark brown 

 and yellowish-brown, and with underlying markings of 

 gray. On some eggs the blotches are large, few, and 

 irregular ; on others they take the form of spots, and 

 are often distributed in a zone round the larger end ; 

 occasionally a few streaks occur, and some varieties are 

 evenly marked over most of the surface with small 

 spots. Average measurement, 17 inch in length, by 1*2 

 inch in breadth. Incubation, performed by both sexes, 

 lasts from twenty-one to twenty-three days. 



DIAGNOSTIC CHARACTERS : The eggs of this Tern 

 very closely resemble those of the Arctic Tern, but may 

 almost invariably be distinguished by their larger bulk, 

 more rotund form, and absence of any olive or green 

 tinge in the ground colour. They should, however, be 

 carefully identified wherever possible. 



