DISTANCES TRAVELLED 121 



to shift a short distance to an area where rains are 

 prevalent, if such change is desired. It would seem 

 that any bird could choose among these diversified 

 haunts one suited to its needs, and in fact many do 

 linger in such regions. That others press on into the 

 summer weather of the south temperate region may 

 be explained only by belief that flight is not labori- 

 ous, and that they delight to wander. It is possibly 

 merely an outgrowth, or, better, a continuation of 

 the wandering instinct that has carried them to 

 breeding grounds in areas where for part of the year 

 the season is inhospitable. 



Mortality Among Migrant Birds 



Without great reflection it is obvious that the 

 migrant bird, in traversing hundreds, perhaps thou- 

 sands, of miles of land and water, is subject to many 

 more perils and dangers than if the same indi- 

 vidual were able to remain in one locality. Storms, 

 unfamiliar coverts, and exposure to the attacks of 

 winged and four-footed enemies, to say nothing of 

 the possibility of becoming lost while crossing broad 

 stretches of water, annually destroy our smaller 

 migrants in untold thousands. To enable mainte- 

 nance of a species at the necessary maximum to pre- 

 vent its disappearance from the earth, it is required 

 that each pair shall produce a sufficient number of 



