BLACK-HEADED GULL. 299 



considerably in colour, style of markings, shape, and size. 

 They vary in ground colour from rich brown through 

 every shade to pale bluish-green, spotted, blotched, 

 and sometimes blurred or streaked with dark brown, 

 and with underlying markings of violet-gray. On 

 many varieties the markings are mostly distributed in 

 an irregular zone round the larger end of the egg. Very 

 eccentric-looking eggs may sometimes be found with 

 the colouring matter in a circular patch on the larger 

 end, gradually tinting off and fading into the ground 

 colour round the margin ; others may be seen with one 

 or two large blotches or clouds of colour here and there, 

 and the remainder of the shell free from markings. 

 Average measurement, 2-2 inches in length, by 15 inch 

 in breadth. Incubation, performed by both sexes, lasts 

 from twenty-two to twenty-four days. This Gull will 

 continue to lay clutch after clutch of eggs as they are 

 removed ; in many places the eggs are gathered for 

 food, the poor birds patiently submitting to regular and 

 systematic pillage every year, and yet continuing to 

 haunt the old colony with a persistence that deserves a 

 better reward. 



Diagnostic characters : The small size and 

 characteristic Larine colouration distinguish the eggs of 

 this Gull from those of all other allied species breeding 

 in our islands. 



