SOME COMMON BRITISH BIRDS 87 



are used as organs of locomotion, in the whales they serve as 

 balancers. 



The fashion in which birds carry their legs during flight 

 should be specially noticed. The " perching-birds " or " Passeres " 

 alone draw up the feet close to the abdomen, others carry them 

 stretched out under the tail, as may easily be seen in gulls and 

 herons, or stuck out on each side as in the short-legged puffins. 



The carriage of the neck similarly varies. Thus in the herons 

 it is bent up, so that the head touches the back, while in the 

 storks, and in the goose and its relatives the ducks and swans, it 

 is carried stretched out at its full length. 



Birds prefer to fly against the wind ; and, while some can 

 only sustain flight by a vigorous use of the wings, others con- 

 trive to sail over large areas without a single wing-beat. The 

 sparrow and the gull afford interesting contrasts of this kind. 



Some birds can hover stationary over a given spot for a very 

 considerable time ; and this is especially true of the kestrel, 

 one of our commonest hawks, which, on account of this habit, 

 is known as the ' Wind-hover." This power is of immense 

 advantage, for thereby the bird is enabled to thoroughly search 

 the ground for food before passing on. 



SEASONAL CHANGES OF PLUMAGE 



That many birds assume two very distinct liveries in the 

 course of the year, while others, as the spring approaches, 

 become perceptibly brighter in hue, is a matter of common 

 knowledge. But the means by which their changes are affected 

 are by no means so well known. 



The common sparrow displays seasonal changes of plumage 

 to which special attention should be directed. In the spring 

 the male develops a conspicuous black throat, and is generally 

 much more vividly coloured than during the autumn and winter 

 months. This change is due to a very curious cause. If a bird 

 be examined directly after the autumn moult the feathers of the 

 throat will be found to be black throughout their length, save at 

 the tips, which are greyish-white ; while, similarly, the feathers of 

 the head, and upper parts generally, have a tawny fringe. As the 



