200 ON SOARING FLIGHT. 



aside from these general considerations the birds occasionally furnish 

 evidence of a much more convincing character. Thus on one of the 

 calmest mornings I ever knew I saw two vultures make an attempt to 

 soar in circles at a height of about 100 feet above the earth. In order 

 to maintain and increase their altitude they continued to flap vigor- 

 ously for about three minutes, after which, having risen to a height of 

 200 feet, they ceased flapping and continued rising. A third vulture 

 now approached the spot, flapping as it came, and began soaring imme- 

 diately beneath the other two, over the same spot above which their 

 flight began, but at a lower elevation. But unlike the other two, it did 

 not flap at all, but rose steadily from the first. The elevation in this 

 case evidently had no influence on the character of the flight, and the 

 fact that the last vulture soared steadily at the exact spot where three 

 minutes before the two others were unable to soar at all offers strong 

 presumptive evidence that the first two had effected some change in 

 the .condition of the atmosphere at that spot before the third one 

 entered it. On another occasion, in a moderate wind, three vultures 

 being frightened from a carcass, began soaring in circles near the earth 

 above a meadow. During the early part of their flight they flapped 

 vigorously, but after a time ceased flapping entirely, and rose steadily 

 along a course slanting with the wind. When they had reached a 

 considerable altitude a fourth passed beneath them in direct flight, and 

 continued on until it reached the identical spot at which the three had 

 begun their ascent by flapping. It at once began soaring and rising 

 rapidly, but was not under the necessity of flapping as the others had 

 been". As it ascended it followed directly in the course the others 

 had taken. 



On another occasion with light winds prevailing I witnessed the 

 ascent of two flocks of vultures near the Dan E.iver, Virginia. The 

 first flock, which numbered fourteen birds, rose after some preliminary 

 flapping from a wide alluvial plain near the banks of the river. The 

 second flock, numbering fifteen birds, rose from the slope of a hill 

 about 3,000 feet distant. After each flock had continued soaring for 

 some minutes, all the birds above the slope of the hill began flapping 

 and iu a very short while began to disperse. And now a singular 

 thing took place. Each bird on leaving the spot sailed directly toward 

 the spot from which the first flock had ascended, and each of the fifteen 

 birds as it reached the spot, at an elevation varying from 75 feet to 200 

 feet, was seen to rise as if buoyed up by an ascending current, and 

 each at once turning upon a circle began to follow the course taken by 

 the birds of the first flock. Only two out of the fifteen flapped their 

 wings at all and all. rose steadily, and soon, with those of the first 

 flock, formed a column of vultures, slanting in the direction the wind 

 was blowing and reaching to a height of iierhaps 1,000 feet. Here w© 

 may suppose that the vultures upon the hillside began flapping because 

 the supply of heated air which buoyed them up became exhausted, and 



