178 THE NESTS AND EGGS OF BRITISH BIRDS. 



ing brooding over the eggs until almost trodden upon, 

 and then often displaying various alluring antics to 

 entice an intruder from the spot. 



Range of egg colouration and measurement : 

 The eggs of the Nightjar are only two in number, elon- 

 gated and oval in shape, rounded equally at both ends. 

 They vary from pure white to white with a creamy tinge 

 in ground colour, mottled, blotched, veined, streaked, 

 clouded, and marbled with various shades of brown, and 

 with underlying markings similar in character, of violet 

 gray. Considerable variation, not only in the shade of 

 colour and style of marking, but in the amount of sur- 

 face-spots and underlying ones occurs. One variety has 

 iev^ of these gray markings, and has the surface-spots 

 numerous and large; another variety has the gray mark- 

 ings large, numerous, and conspicuous, and the surface- 

 spots ^Qw and small ; another variety is beautifully lined 

 and marbled with brown and blotched with gray ; another 

 in which the gray markings are reversed. Average 

 measurement, i'3 inch in length, by '87 inch in breadth. 

 Incubation, performed chiefly by the female, lasts from 

 fifteen to eighteen days. 



Diagnostic characters : The size, oval shape, and 

 peculiar veined character of the brown and gray mark- 

 ings, readily distinguish the eggs of the Nightjar from 

 those of any other bird breeding in the British Islands. 



