BLACK-HEADED GULL. 299 



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

 They vary in ground colour from rich brown through 

 ev^ery 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 t^^. 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 i"5 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. 



