BRITAIN'S BIRDS AND THEIR NESTS. 281 



their running, or when perching on some prominent point, 

 the Wagtails one and all keep up a continuous up-and- 

 down movement of the tail. In the Common Sandpiper 

 similar but less pronounced actions may be noted, and 

 the Redstarts frequently display rapid sideways movements 

 of the tail. But in none is the habit so marked and so 

 continuous as in the case of the Wagtails, which, indeed, 

 take their name from it. No very satisfactory explana- 

 tion exists as to the origin and reason of the habit. 

 As regards the flight of this and other Wagtails, it need 

 only be said that it is of an extraordinaiy ' switchback " 

 nature, consisting of short but steep rises and falls in 

 quick alternation. In addition to the characteristic call- 

 note there is also a brief but pleasing song. The food con- 

 sists mainly of insects and various small aquatic creatures. 



In winter the Pied Wagtail forsakes some of the more 

 northern and elevated regions of the British Isles, and 

 decreases over most of the remainder. Some of the move- 

 ments are of quite a local character, but there is a distinct 

 southward tendency, and the bird thus becomes more 

 numerous in winter than in summer in the extreme south. 

 Even from that part of the countiy there is, however, a 

 considerable amount of transmarine emigration in autumn. 

 In the return jom^ney in spring it has been established 

 that the males arrive some days before the females. This 

 is probably the case with the majority of our migrants, 

 and the order is believed to be reversed in autumn, 

 except that young birds of both sexes usually depart 

 long before any of the adults. 



Hair and feathers form the lining of the nest of dry 

 grass, moss, and the like. The whole is occasionally 

 placed in the open meadow, but generally in a sheltered 

 situation on a bank. Sometimes it may be in a crevice in 

 a wall or rock, or on a thatched roof or a tree-stump. The 



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