2i 8 BIRD BEHAVIOUR 



such are particularly apt to appear in localities not 

 normally frequently by their species, as I found in 

 the case of the invasion of India in the late 'nineties 

 by Baer's White- eyed Pochard (Nyroca baeri), most 

 of the specimens I obtained being young birds. 

 Birds also often range for a time north of their 

 breeding-haunts in autumn, and may even fly out 

 into the Atlantic from our coasts, only to perish 

 or come back utterly exhausted. 



There is thus a good deal to be said in justification 

 for the statement that young birds " wander almost 

 at random," and that most of them are probably 

 destroyed before the next spring ; and the dangers 

 of a long migration may be the chief reason why 

 birds are more numerous, but less fertile, in the 

 tropics, where there is not this wholesale risk to 

 be faced annually. Of course there is a. good deal 

 of local movement even in the tropics, but not 

 much is known about this as yet, and the journeys 

 are inevitably far less risky. 



It has been pointed out that the reason why 

 day-birds so often migrate by night is that by so 

 doing they utilize hours which would in any case 

 have to be spent without food, and thus economize 

 time and strength ; but the ever-present danger 

 of Gulls, Carrion-Hawks, and Crows, some or other 

 of which are always to be found along every coast, 

 all on the alert to note signs of weariness in birds 

 they ordinarily would have no hope of capturing, 

 must surely have something to do with this, and 

 it is to be noted that in all groups the larger or 



