THE WINTER RHUBARB 99 



ILLUSTRATIONS FROM BIRDLAND 



Perhaps the all-importance of this inherent 

 tendency to gauge habits in accordance with the 

 calendar will be more clearly apprehended if we 

 cite another illustration from the organic world. 



Take the migrations of birds as a familiar 

 instance. If you watch the birds at all, you have 

 doubtless noted that the migrants that come to 

 temperate regions from the tropics arrive each 

 spring in your neighborhood at a date that you 

 may fix in advance with almost entire certainty. 



The hardier birds, to be sure, such as the robin, 

 the bluebird, and the meadow lark, retire before 

 the blasts of winter somewhat unwillingly and 

 they begin their northward migration at a period 

 that may vary by a good many days or even 

 weeks according to the forwardness or backward- 

 ness of the season. But the coterie of tender 

 birds orioles, vireos, wood robins, tanagers, fly- 

 catchers which spend the winter in the region 

 of the Equator, must begin their northward 

 migration without regard to the climatic condi- 

 tions, inasmuch as their winter home is a region 

 of perpetual summer. 



They start northward merely in obedience to 

 an instinctive time sense that has been implanted 

 through long generations of heredity, and they 



