THE INDIAN SAND-MARTIN 239 



warblers, sand-martins, etc., will come in search of food 

 quite close up to a motionless human being. Mr. W. H. 

 Hudson relates in his Birds and Man how, when one 

 day he went into his garden and walked under the trees, 

 there was a great commotion among the little birds 

 overhead, who mobbed him in the manner they mob an 

 enemy. He discovered that the reason of this strange 

 behaviour on the part of the small birds that usually 

 paid no attention to him, was that he was wearing 

 a striped cloth cap, which the birds appeared to 

 mistake for a cat. It would almost seem that there is 

 so vast a difference in size between a tiny bird and a 

 human being that the former fails to recognise the 

 latter as a living object provided he keeps still. This 

 does not imply poor eyesight on the part of birds. The 

 minds and eyes of birds are almost invariably directed 

 on small things. Now, a man bears to a small bird 

 much the same relation as a horse three hundred hands 

 high would bear to a man. As regards detail, the 

 eyesight of birds is probably superior to that of men, 

 for each sand-martin seems never to mistake its nest, 

 although the entrance to it is merely one of several 

 score of holes scattered irregularly over the face of the 

 cliff. To the human eye these holes look all very much 

 alike, but each must possess minute peculiarities 

 which loom large in the eye of the sand-martin. 

 Whether or not the above explanation is the true one, 

 the fact remains that a human being can take up a 

 position within a few feet of the cliff without disturbing 

 the martins in their nest-building operations. 



Some birds, when busy at their nests, work with 



