110 



MICHIGAN SURVEY, 1908. 



and the imovement of its high and low areas, and since "low pressure 

 is generally accompanied by clouds and rain, while areas of high pres- 

 sure are cloudless" it will be seen that this important element is also 

 associated with the baromptric pressvire. Thus we see that the four 

 striking factors which influence migration, namely temperatuTe, direc- 

 tion of wind, condition of the weather, and barometric pressure are 

 correlated and work together, the same factors being always associated 

 together and giving the same results. 



To determine the true relation of these factors to migration we 

 must discover the most fa,voi*able conditions for this movement, and 

 then we can correlate the atmospheric changes which are taking place 

 with the corresponding migratory movement. Of course many birds 

 are constantly passing to the south throughout the fall, irrespective 

 of the weather conditions, but the changes which will set great num- 

 bers moving onward simultaneously niilist be the ideal conditions for 

 migration. If this be true the time to study this relation of the weather 

 is during the great waves. 



TABLE or BIRD WAVES. 



Date. 



Aug. 2.3 

 24 

 25 

 26 



Aug. 30 



31 



Sept. 1 



Sept. ") 

 6 



Sept. 12 

 13 



Sept. 16 



Sept. 18 



Barometer. 



Tempera- 

 ture, F. 



I-IEST BIRD WAVE. 



SECOND BIRD WAVE. 



29.8 

 30.1 

 30.1 



56 

 46 

 52 



THIRD BIRD WAVE. 



30.1 



30.1 



39 

 42 



FOUKTH BIRD WAVE. 



30.2 

 30.4 



42 

 26 



FlfTH BIRD WAVE. 



30 I 50 



SIXTH BIRD WAVE. 



29.8 i 52 



Wind. 



N. W. 



N. 

 N. E. 



N. W. 

 N. W. 



N. W. 

 W. 



.N. E 



Sky. 



Clear. 

 Clear. 

 Clear. 

 Cloudy. 



Clear. 

 Clear 

 Cloudy. 



Partly cloudy. 

 Clear. 



Clear. 

 Clear. 



Cloudy. 



Clear. 



1. Influence of Wind. A reference to the table of bird waves shows 

 that on six d^ys of the thirteen during which large waves were ob- 

 served, the wind was from the northwest. Two days were without 

 appreciable wind, on two, the wind was from the northeast, and upon 

 other days it was from the north, east, and west, but upon none of 

 them was it from the south, southeast, or southwest. A northwest 

 wind prevailed the first two days of the first wave, the third and fourth 

 days being without wind. The second wave commenced with a north- 

 west Avind, which changed to north on the second, and to the north- 



