142 Stone, Graphic Representation of Bird Migration. [April 
ary in June. These variations represent first the arrival of such 
early birds as the Meadowlark, Dove, Chipping Sparrow, Field 
Sparrow, etc., in the middle or latter part of March : then the 
Kinglets, Towhee, Chimney Swift, etc., in April, and finally in 
May the vast influx of Warblers and other birds, many of which 
remain but a few days and then pass on to the north; leaving us 
by the second week of June with only the summer residents. 
The departure of the several winter visitants during March and 
April is more than balanced by the arrival of species from farther 
south. 
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Fig. 2. Spring Migration at Germantown, Pa., 1888. 
A. Curve showing the number of species present. 
B do. based on the actwal number of species recorded each week. 
Co do. based on the average number of species seen per day, for each week. 
T. Curve of temperature variation, spring, 1888. 
DS § 
EE | 
N 
N, 
It will be seen from curve B, Fig. 2, that the number of 
species actually seen never equalled the number of species that 
were present, though it came very near it about the 1st of March 
and again about the middle of April. The prominent ‘drops’ in 
this curve during the winter and early spring will be found to 
correspond to spells of severe weather at those times. 
By comparing the three curves of Fig. 3, the remarkable simi- 
larity of the spring migration for the past three years can readily 
be seen. The number of species seen in the different years varied 
considerably, but this is more a function of the time that was 
