The urge to incubate is satisfied when the clutch is completed. 



This drive Thorpe ( 1951b :6) identifies as "the complex of internal and 

 external stimuli leading to a given behavior." The goal of appetitive be- 

 havior may be a performance of a particular act, e.g., copulation or egg 

 laying, or the attainment of a particular relation with something in the 

 external environment, e.g., incubating a suitable clutch of eggs. 



Obviously the whole of the action from the beginning of appetitive be- 

 havior to goal cannot be carried out on the level of instincts : the bird must 

 get from the place where a drive is awakened to the special companion, 

 object, or environmental situation where the appetite is sated. There is an 

 interval of time and space where learned behavior serves to guide the indi- 

 vidual. Mallard hens the world over have the same appetites when the ovi- 

 duct is with egg; universally this hunger is satisfied by egg-laying at the nest. 

 But each and every Mallard must learn the way to her own nest. It is in 

 this period between drive and goal "that the adaptive and individual vari- 

 able responses are found . . . where learning in all its variety enters into 

 the life-story of the animal. . . . Instinct and intelligence are thus inter- 

 woven to form the whole pattern of behavior of the individual" (Thorpe, 

 1951b:7). 



Appetites are awakened daily by many drives. There is the everlasting 

 requirement of food, the need for gravel and water, the urge to bathe and 

 preen. Such acts are nonsexual, repeated on a daily basis throughout life, 

 regardless of sexual status. The reproductive drive, on the other hand, is 



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