THE NOCTURNAL MIGRATION OF BIRDS. 507 



to night-migrating birds. Probably no one artificial cause pro- 

 duces more disastrous results than these beacons which guide the 

 mariner in safety, but prove fatal obstacles in the path of aerial 

 voyagers. 



The number of birds killed by striking lighthouses is incalcu- 

 lable. Over fifteen hundred have been found dead at the foot of 

 the Bartholdi Statue in a single morning ; while from Fire Island 

 (Long Island) light we have a record of two hundred and thirty 

 birds of one species black-poll warblers which met their fate 

 on the night of September 30, 1883. 



Reports from numerous lighthouses show (1) a great variation 

 in avian mortality at different localities ; (2) that as a rule no 

 birds are killed during clear nights ; and (3) that comparatively 

 few birds strike the lights during the vernal migration. The 

 fact that birds follow certain routes or highways of migration in 

 their journeys to and from the South doubtless explains their 

 absence or presence at a given locality ; indeed, it has been defi- 

 nitely ascertained that lights which are situated in known lines 

 of migration as, for example, the Bartholdi Statue at the mouth 

 of the Hudson River Valley prove far more destructive than 

 those which are placed far from the regular routes of migrating 

 birds. 



Through telescopic observations, to be mentioned later, we 

 have learned that when en route birds travel at an altitude of 

 from one to three miles above the earth. It is obvious, then, that 

 when their way is not obscured by low-hanging clouds they pass 

 too far above us to be attracted by terrestrial objects. It has been 

 noted that cloudy and especially rainy nights are most disastrous 

 to migrants, evidently because the formation of moisture at the 

 elevation at which they are flying must not only interfere'with 

 their progress, but in veiling the earth below robs them of their 

 landmarks, while the condensation of this moisture into rain pre- 

 sents an effectual check to flight. The birds then descend to a 

 lower altitude, and, should the storm be very severe, they are 

 obliged to seek the nearest shelter, and even may be driven to 

 earth wet, helpless, and dying. 



The influence thus shown to be exerted by meteorological con- 

 ditions is the best explanation of the comparatively small number 

 of birds killed during the spring migration, when the infrequency 

 of violent storms enables them to perform their journey with less 

 danger from exposure to the elements. 



The observations of Mr. William Brewster on the migration of 

 birds at the Point Lepreaux (Bay of Fundy) lighthouse have 

 never been exceeded in interest or value by the recorded expe- 

 riences of any other observer of similar phenomena. Still, even 

 his graphic account fails to produce the sensations which possess 



