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much difificulty in the open air. The observations of most of these 

 naturalists were made in the Central and Southern States, where even in 

 summer the nights are of considerable length. In our northern lati- 

 tude, on the other hand, the short duration of the hours of darkness 

 at this season compels the birds to seek more promptly the rest so much 

 needed after the incessant activities of the long bright day. 



At this hour the inside of the ventilating shaft is too dark to permit 

 one to see anything of its occupants, but on the 20th of May last I was 

 fortunate enough to find them almost all at home in the daytime. The 

 weather was cold with a light rain, and, as the swifts are very suscept 

 ible to a fall in the temperature, only a few score ventured out to circle 

 round the building or take a short turn over the city. Entering one of 

 the ducts through a trapdoor in the attic, a journey of a few feet on 

 the hands and knees was well repaid by the view within the shaft. The 

 tower is an octagonal one, built of stone lined with bricks, the space 

 within being about 8 feet across. Up through the centre passes an iron 

 smoke-pipe from the furnaces in the basement. This is about 3 feet in 

 diameter, so that the mtervening space leaves ample room for a view of 

 the wall lighted by the little windows at the top where the swifts find 

 entrance. All round the inside the birds were clinging against 

 the wall, shoulder to shoulder, covering every available inch from a 

 short distance below the windows down to about 10 feet above my 

 head, a rSpace of probably 18 feet in height. Many were continually 

 fluttering in and out, knocking each other off and beating about in the 

 dim light with endless flapping and twittering. The wall surface covered 

 would be about 470 square feet. Audubon in making a rough computa- 

 tion of the number of a flock roosting within a hollow tree which he 

 visited near Louisville, Ky., allows 32 birds as the number resting on 

 each square foot of surface. At this rate the census of the Ottawa 

 colony would reach 15,040. I believe, however, that this is consider- 

 ably over the mark. On several evenings I took the time occupied by 

 the flock in entering the tower, which proved to be about 16 minutes. 

 If there were as many as 15,000, it would require something over 15 

 birds to pass in during each second, The openmg is a small one, about 

 I foot by 3, and it seems hardly possibly that they can crowd in at such a 

 rate, though th,ev certainly go faster than one can count. Probably 9,000 



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