6 ECONOMIC ORNITHOLOGY. 



then, mounting high in the air, pursue their journey under cover of 

 the night. Birds direct their flight by coast lines and river valleys 

 which are easily distinguishable in clear weather. On favorable nights 

 these natural highways of migration are thronged by a continuous 

 stream of aerial voyagers passing from dusk until dawn. 



Looking through a telescope at the moon, one may see numbers of 

 birds cross its glowing surface. From such observations it is com- 

 puted that migrating birds fly at a height of from one to three miles. 



The eyesight of birds is so far superior to ours that we do not 

 realize its value to them while migrating. The height at which they 

 fly gives them command of a wide range of country, and on clear 

 nights they can undoubtedly distinguish its prominent features with 

 ease. But when fogs or clouds obscure these landmarks, they lose 

 their way. It is then that lighthouses prove beacons luring them to 

 destruction. The Bartholdi Statue, at the mouth of the Hudson 

 River, is directly in the path of the great streams of migrants which 

 flow up and down this natural highway of migration, and for this 

 reason is particularly destructive to birds which travel at night. On 

 one occasion after a storm no less than fourteen hundred birds were 

 picked up at its base, having been killed by striking the statue or 

 pedestal upon which it rests. 



But while sight is of the first importance to the older and more 

 experienced birds who know the way, young birds, who are making 

 the journey for the first time, doubtless rely on their hearing to guide 

 them. Birds' ears are exceedingly acute. They readily detect sounds 

 which to us would be inaudible. Almost invariably they respond to 

 an imitation of their notes, and, when under way, frequently chirp and 

 call. When we consider their power of hearing and their abundance 

 in routes of migration, it seems probable that at no time during the 

 night is a bird beyond the hearing of his fellow-travelers. The line 

 of flight once established, therefore, by the older birds, who leave first, 

 it becomes a comparatively easy matter for the younger birds to join 

 the throng. 



Economic Ornithology. — This branch of the study of ornithology 

 treats of the relationships of bird to man from the standpoint of 

 dollars and cents. Civilized man is Nature's worst enemy. He is a 

 disturbing element whose presence is a constant menace to the balance 

 of life. It is of the utmost importance, therefore, that we should 

 acquaint ourselves with the conditions which make a true equilibrium 

 and endeavor to sustain them when it proves to our advantage to 

 do so. 



The disastrous results which have followed man's introduction of 

 the English or House Sparrow in America, the mongoose in the West 



