LUTHER BURBANK 



in Iowa, for example, you will find the last flight 

 of migratory birds, comprising the various species 

 of wood-warblers and vireos, the orioles, and the 

 scarlet tanager, making their appearance between 

 the tenth and fifteenth of May each year, quite 

 without regard to the advancement of the season. 



And a few months later you will note, if you 

 are observant, that these and the other migrants 

 disappear in the fall, having taken up their return 

 voyage at about the same calendar period year 

 after year, although in one season the September 

 days may be as hot as August and in another 

 season they may have the chill of November. 



Countless generations of heredity have fixed 

 in the mechanism of the bird's mind the instinct 

 that impels it to migrate at a fixed season ; and no 

 transient or variable conditions of the immediate 

 environment can alter that instinct, even though, 

 in a given case, its alteration might be vastly to 

 the advantage of the individual. 

 Even Unto Death 



As proving the latter point, and as further 

 illustrating the force of the instinctive time-sense 

 under consideration, let me recall the case of the 

 martins to which reference was made in an earlier 

 chapter — the case in which these birds starved to 

 death because in a particular season drought pre- 

 vented the hatching out of their insect food. 



[186] 



