144 Libby, Nocturnal Flight of Migrating Birds 



I April 



were the birds numerous enough to be seen two at a time, though 

 this happened once during each evening. Not infrequently cur- 

 rents of air seemed to aid or retard their flight. One bird was 

 seen to move backwards across the field as a slowly flying bird is 

 sometimes seen to do from the window of a swiftly moving train. 

 Many of them sailed instead of flying across, occasionally flap- 

 ping their wings to steady themselves. 



On account of the short time each bird was in sight, and the 

 difficulty of estimating their relative distances, not many of them 

 could be identified. More Swamp Blackbirds were identified 

 than any other, and next to them were the Meadowlarks, of which 

 several flocks were observed. Besides these theie were the Crow 

 Biackbird, Sparrow Hawk, Yellow Hammer, and one species of 

 Duck. Many of the birds, from their size and flight, must have 

 been Warblers, but it was impossible to further identify them. A 

 number of birds resembling Gulls were observed in large flocks, 

 but nothing could be determined as to the species. The single 

 Sparrow Hawk seen was moving leisurely along in no particular 

 direction except that he seemed to be following the main stream 

 of birds. His hesitating appearance showed how well concealed 

 were his intended victims, though he had sufficient intimation of 

 their presence to keep him on the track. A more thorough 

 acquaintance with the appearance of the birds in flight would 

 have added greatly to the value of the observations. 



How the birds are guided in their nocturnal flight is per- 

 haps the most puzzling question which rises in the mind of the 

 observer. There are two possible solutions of this problem. 

 They may be guided by the stars, or by the contour of the country, 

 the lakes and river valleys. Certain it is that cloudy, and espe- 

 cially foggy nights are not favorable for flight. Birds lose their 

 way and wander from their course as seamen do when there is 

 neither sun nor star to guide them. It may be accepted as set- 

 tled that birds are not possessed of an infallible instinct that 

 guides them, otherwise they need not be disturbed by a fog. 

 The results of the observations just cited show the same thing. 

 That birds do wander from their course is seen from the great 

 variety of directions taken by them during the night. Certainly 

 not all in a given flock fly in one unvarying direction. Individ- 



