6 Introduction 



actual colouring matter, if indeed it occurs at aU, must 

 be most exceptional. Gloss and iridescence are due to 

 the structure of the feathers, which may be polished or 

 shew little ridges under the microscope. 



Newly hatched birds often run from the sheU, and 

 are therefore called "nidifugous" or "nest-deserting," 

 but the majority are "nidicolous" or "nest-inhabiting," 

 and fly only when fully fledged ; some again of those 

 which run from the shell can only move to short 

 distances for a considerable time. These habits are 

 naturally related to the position of the nest. 



With the exceptions already mentioned, and ex- 

 cluding the time of moult, birds have extraordinary 

 powers of flight, though these powers are in constant 

 use only in the case of certain forms, and in others 

 are put forth periodically; speed, endurance, and like 

 factors here come to be considered, while the style of 

 movement, including the amount of wing-action or 

 oarage, and tail-action or steerage power, varies to 

 an enormous extent. The greatest example of un- 

 tiring flight is that of an Albatros, which will follow a 

 ship for days together ; but the same habit, to a less 

 extent, must to most people be familiar in the Gull 

 tribe, which also follow vessels for long periods, and 

 remain on the wing for hours, when looking out for 

 food. These birds are not always flapping their wings, 

 but glide or skim along with intervals of muscular 

 action ; while it is evident that they are greatly in- 

 debted to the supporting power of the air and its 

 force against the flight-feathers. Vultures, Eagles and 

 Buzzards, Falcons and Hawks have a different kind of 

 flight ; they either cleave the air at a great pace or 

 move along slowly but po-prerfuUy; and even if they 



