INSTINCT AND INTELLIGENCE IN BIRDS 



89 



Desertion of the Young under the Impulse of Migration 

 The struggle of conflicting instincts is clearly shown when the 

 normal cycle is brought prematurely to a close by the rise of the 

 instinct of migration, when eggs or young are left in the nest to perish. 



Fig. 22. A Multiple — four-storied Nest of the Yellow Warbler (Dendroica 

 /Estiva), with a "parasitic" cowbird's egg in each compartment, but with proper 

 eggs in the first story only, illustrating the successive breaking of the breeding cycle 

 through fear, the beginning of three new cycles in succession, the new nest being built 

 in each case, and probably through association, on the site of the old, thus admirably 

 " concealing " the successive parasitic eggs. Original in the Field Museum of 

 Natural History, Chicago. 



The migratory impulse seems to " overlap/' and finally to replace the 

 proper parental instincts. The cycle is scamped near its close. 



