OCTOBER, 1902. 
TFIE MIGRATION OF lURDS. 
255 
Explanation of Plates.* 
Plate I. 
Curves drawn from observations collected by means of the 
telescope at Ann Arbor, IMicb., Detroit, Mich., Lake Forest, 111., 
and Heloit, Wis. These curves show the numlier of birds flying 
in ])eriods of fifteen minutes. 
Plate 11. 
Same as plate I. for Madison, Wis., with the exception that the 
curves have in each instance been reduced to the same number 
of hours after moon-rise. 
Plate III. 
A combined curve of three successive observations taken it 
Madison, Sept. 11, 12 and 13, 1897. The curve has again been 
reduced to hours after moon-rise. This combined curve brings 
out more strikingly the general conditions observed at Madison 
with reference to the influence of topography upon the number of 
birds flying. 
Plates IV. and V. 
In plates IV'. and V. each circle represents the field of observa- 
tion as seen through the telesco]>c wdien focused on the moon. 
Each line in the circle represents the flight of one bird, the heav- 
ily shaded end showing the direction toward which the bird is 
flying. The broken lines represent the flight of birds that appeared 
out of focus. The data from which these two plates were made 
were taken at Beloit, May I2, 1900. 
Plates VI. and VII. 
Same as plates IV. and V. for Beloit, May 11, 1900. 
Plate VIII. 
Same as plates IV. to VII. from data collected at Madison at 
various times from April 8, 1898, to May 9, 1900. The arrows 
outside of the circle show the approximate direction for the period. 
It is to be noted that there are two main directions followxxl, the 
one predominating in April, the other in May. 
*For a clear uiuleistanding of the plates it will be necessary to keep 
the method of observation in mind. See pages 198 to 199 in text. 
