WILD LIFE OF ORCHARD AND FIELD 



in the tropics, since when one set is staying there 

 the other is absent, owing to the alteration of arc- 

 tic and antarctic seasons. 



How do we account for the existence of this habit, 

 with its strange anomalies? No one has been 

 able to do it satisfactorily thus far, and I do not 

 mean to add any guessing, but, instead, to try to 

 give some idea of the method of bird-migration; 

 for, though we do not yet understand the why, we 

 have learned a great deal as to the how. 



I. THE SPRING MIGRATION NORTHWARD. 



Observers in Central America and the West 

 Indies, where most of our absent birds spend their 

 winter, tell us that in March and early April they 

 begin to find their voices and to gather in little 

 bands which flit northward in an uncertain way 

 until finally the movement grows steady. 



Now, this is just the time when the tropical resi- 

 dents are mating and preparing to build their nests, 

 so that whatever social force there may be in ex- 

 ample is all towards influencing the restless emi- 

 grants to settle down where they are; but it has 

 no such effect. This is also the time, since the 

 rainy season is at hand, when vegetation springs 

 into flower and fruit after the long drought, in- 



