THE SUMMIT OF THE YEARS 



stinct into greater activity. A still simpler explana- 

 tion is the suggestion that this instinct is feebler in 

 some birds than in others, and is feeblest of all in 

 those birds that build cup-shaped or basket-shaped 

 nests on stiff young maples newly planted by the 

 roadside. We are not to ascribe to an animal a 

 process of reasoning so long as there is a simpler 

 explanation of its conduct. 



When we have an early spring we plant and sow 

 early, and vice versa. We seem to think that the 

 birds choose to act similarly, and to nest early or 

 late as their judgment as to the weather prompts. 

 But they have no choice in the matter. A warm 

 wave brings them, and a cold wave retards them, 

 as inevitably as it does vegetation. The warmth 

 stimulates them to nest-building, for the reason that 

 it increases their food-supply; the more warmth the 

 more food, and the more food, the more rapidly 

 the egg develops in the mother bird. Heat hastens 

 the ripening of the egg as surely as it hastens the 

 ripening of fruit, and cold retards it to the same 

 extent. In cold, backward springs I note that the 

 robin lays only two or three eggs in the first nest; 

 in warm seasons she lays four or five. 



Pluck off the leaves of a tree in the early season 

 and new leaves will form; sometimes new blossoms 

 will come a second time. Rob a bird of her eggs and 

 she will lay another clutch, and still another, till the 

 season is past. I suppose that there is no more of 

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