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

Fic. 22. A MULTIPLE—FrOUR-STORIED NEST OF THE YELLOW WARBLER (Dendroica 
@istiva), 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. 
