146 BIRD BEHAVIOUR 



has been laid on before the shell is complete and 

 so lies deeper and looks fainter, such under-surface 

 spots being grey, lilac, or mauve in colour. 



In the eggs of Cormorants and their kin (Stegano- 

 podes), Grebes, and some of the non-parasitic 

 American Cuckoos (Crotophaga, Guira) there is a 

 chalky layer external to the real shell, which is often 

 blue, and shows here and there. In the case of the 

 Cuckoo Guira, the "White Ani," the effect is 

 exceedingly pretty, the rich blue shell being plenti- 

 fully flecked, but not obscured, by the chalky 

 secretion. Grebes' eggs, by being covered by 

 the owners with some of the sodden weed of which 

 the nest is made, soon get stained and are generally 

 seen as buff or brown objects, though the proper 

 and original colour is white ; Ducks' eggs are 

 naturally greasy on the surface. The egg of the 

 Fulmar is distinguishable by the nose, having the 

 same strong smell as characterizes every part of its 

 producer, even to one feather. 



The surface of birds' eggs generally varies a good 

 deal, from a rough one like unglazed porcelain to 

 the glazed type best shown in the Tinamous' eggs ; 

 but Kingfishers and Owls also lay very glossy eggs, 

 and Ostriches' eggs are both glossy and pitted. 

 The shell gets duller and more brittle as the eggs 

 are sat upon in the case of birds generally. 



The number of the sitting varies in a very inter- 

 esting way ; in quite a number of birds it is at the 

 minimum, the egg being single. This is the case 

 with Petrels and Albatrosses, the Gannets, the 



