304 INSECTIVOILE. 



those that play on the surface of the water or hover near it 

 in the air. 



The legs of the wagtails are placed behind the centre of 

 gravity of their bodies, as is the case in all birds which run 

 rapidly, in consequence of which they would have difficulty, 

 or at least labour, in recovering themselves by mere muscular 

 exertion when they bring their bills to the ground, as they 

 must often do in picking up their food. The tarsi, as has 

 been noticed, are long in proportion to the size of the birds ; 

 but the neck and bill, instead of being so long as to enable 

 the latter to reach the ground while the axis of the body is 

 horizontal, are so short, that the shoulders must dip much when 

 the bill is brought to a level with the feet. A bird so formed 

 would be very apt to tumble forwards, if it had not some 

 means of working a counterpoise ; and that counterpoise is 

 the tail. When that is expanded and struck forward against 

 the air, it acts in nearly the same manner as a wing, and 

 pulls the body of the bird backwards, so that the head is 

 raised with comparatively little effort. All birds that have 

 the same length of tarsi in proportion to that of the neck 

 and bill have a similar action of the tail ; but as that struc- 

 ture, and also the habit of picking up food on a level with 

 the feet, is more remarkable in the wagtails than in any 

 other British birds, the motion of the tail is more powerful 

 in them, and the tail is also longer in proportion. But the 

 habit may be seen in very many birds, both in enabling them 

 to raise the head and to retain it in an erect posture. The 

 magpie is a familiar instance, and so is the peacock which 

 would tumble backwards if he were to raise the body in the 

 same manner when the tail is down as he does when it is 

 erected and spread. 



PIED WAGTAIL (Motcicilla alia). 

 A figure of the male bird in its summer plumage is given 



