Page:Popular Science Monthly Volume 60.djvu/335

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later, may be actually seen by powerful telescopes. Woods and hedgerows that were untenanted one day may become fairly alive with birds at daylight the next morning, showing that they have arrived during the night. They remain to feed and rest during the day, and, if the weather be favorable, may practically all disappear the next night. That they only venture on these journeys during clear nights is shown by the fact that on such nights very few birds are killed by lighthouses, monuments or other obstructions, whereas on cloudy or rainy nights, especially such as opened clear and later become overcast, thousands of birds become confused and dash themselves against these obstructions. Thus over 1,500 birds have been found dead at the base of the Bartholdi statue in New York harbor in a single morning, and 230 birds of one species—black-poll warblers—were killed in a single night (Sept. 30, 1883) by the Fire Island light. The Washington monument, although not illuminated at night, causes the death of hundreds of birds annually.

The height above the earth at which migrating birds travel has been made the subject of some interesting observations, the first of which appear to have been by Mr. W. E. D. Scott, on the night of October 19, 1880, at Princeton, New Jersey. In company with a number of visitors he was being shown through the astronomical observatory at that place, and after looking at a number of objects through the 91/-inch equatorial, they were shown the moon, then a few days past its full phase. His attention was at once arrested by numbers of small birds that could be more or less plainly seen passing across the field of observation. Most of the kinds seen were the smaller land birds, among which were plainly recognized warblers, finches, woodpeckers and black-birds. He was able to identify with much certainty the characteristic undulating flight of the goldfinch, and the broad boat-shaped tail of the purple grackle. The flight of the birds noted was apparently nearly at right angles to the field of observation, and they were passing at the rate of 4% per minute. As nearly as could be estimated their height above the earth was between one and two miles.

In the following year similar observations were made by Scott and Dr. J. A. Allen, but the results were not as striking, only 13 birds passing in any quarter of an hour. They were also apparently flying lower than on the first occasion.

Some years later observations on nocturnal flight were taken up by Mr. Chapman, who spent three hours on the night of September 3, 1887, at Tenafly, New Jersey. During this time 362 birds passed across the moon's face. Of these 233 were computed to be at a height of from 1,500 to 15,100 feet, and curiously the lowest birds seemed to be flying upward, as though they 'had arisen in the immediate