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the daily numbers of several species which migrate at the same time, 

 and plotting the totals. Fig. 2, A, represents such a curve, showing 

 the fluctuation of the April migration of 1891, based upon the 

 Flicker, Chipping Sparrow and Brown Thrasher, which were among 

 the most numerous species moving at this time. Fig, 2, B, is a curve 

 of temperature variation covering the same period, based upon the 

 daily maximum temperature. By comparing the two the coincidence 



Fig. 2. A = Migration Curve, B = Temperature Curve. 



of a marked increase in the number of birds with a decided rise in 

 temperature is at once apparent, the two curves being nearly parallel. 

 It will be noticed, however, that elevations in the migration curve 

 generally begin a little later than those in the temperature curve. 

 This shows graphically the well-known fact that "bird waves" occur 

 a day or two after a decided increase in temperature. 



BIRDS FOUND WITHIN TEN MILES OF PHILADELPHIA. 



For the more especial use of the members of the Delaware Valley 

 Ornithological Club, the following " local " list has been prepared 



