Page:Popular Science Monthly Volume 45.djvu/525

Rh to night-migrating birds. Probably no one artificial cause produces 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 incalculable. 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; (3) 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 definitely 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 presents 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 conditions is the best explanation of the comparatively small number of birds killed during the spring migration, when the inf requency 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 experiences of any other observer of similar phenomena. Still, even his graphic account fails to produce the sensations which possess