INCUBATION AND MOULT, 43 



colour of the eggs to their natural surroundings for the purpose of concealment. 

 Similarity of eggs in a natural group of birds is observable in "Warblers and 

 Buntings. Dissimilar eggs in closely allied species are seen in the Missel Thrush, 

 Song Thrush and Blackbird; Black Kedstart and Common Eedstart; Eed, Spotted, 

 and Eed-breasted Fly-Catchers ; the Book and the Cape Crow. 



Though the greater number of species of birds lay eggs, all of which are of 

 tolerably uniform character, varying only within narrow limits, there are some 

 cases in which the eggs of different individuals of one species present a remark- 

 able diversity. Similarity in all the eggs of one species is seen in the Water-hen 

 ((?. chloropus). Dissimilarity in the eggs of one species is to be observed in the 

 Tree Pipit, Tree Sparrow, Fantailed "Warbler, Guillemot. 



INCUBATION 



is performed by the females of nearly all birds, but with most of the Passeres, 

 and many others, the male seems to share the duties. Among the Ratitce the 

 male takes that office wholly on himself. Most of the smaller Passeres of 

 Europe hatch their young in about thirteen days, and in a few species the time is 

 believed to be shortened to ten or eleven days, while in the largest of the order 

 (the Eaven) it is lengthened to twenty-one. This is the ordinary time taken by 

 the Barndoor Fowl, but the Pheasant takes twenty-eight. Most water birds seem 

 to require as long a time, but in the Swan incubation is protracted to six weeks, 

 the same period as for an ostrich. 



MOULT 



This is the shedding of the old and often weather-beaten feathers, to be in turn 

 replaced by an entirely new suit. As a general rule all birds are subject to an 

 annual moult, which begins at the close of the breeding season. Such renovation 

 is required in birds which nearly all have to depend upon their quills for the 

 means of locomotion and hence of livelihood. Feathers do not last for ever, and 

 they are liable to accidental breakage. The remiges, or quill feathers, are always 

 shed in pairs, and the power of flight is only slightly deteriorated thereby. In 

 the young of most species the original quills are not shed during the first year, 

 but in the typical Gallinm, which are able to fly at a very early age, often before 

 they are one-third grown, the original quills are shed before the bird has attained 

 its full size and are succeeded by others that serve it when it has reached 

 maturity. In the Duck tribe, however, we have a very singular exception. 

 Most of these birds shed their quill feathers all at once, and thus become 

 absolutely incapable of flight for a season, and it is further to be particularly 

 remarked that the males of most of two sections of the family (Anatince and 

 FuUguUnce) at the same period " go into eclipse," and put on for several weeks 

 the garb of the female (Kandahar in 1879, p. 249), resuming their full-coloured 

 plumage under an additional moult, when their new quills are grown and fit for 

 flight. In the Ptarmigan [L. mutus), both sexes of which not only moult after 

 the breeding season into a grey suit, but again as autumn passes away have an 

 additional moult into their snowy winter clothing, and yet again in spring put on 



