LIFE AND BEHAVIOR OF THE CUCKOO 
189 
The parental instincts are further modified at every point by 
intelligence, and if it be inferred that since we are here dealing 
largely with the instinctive activities of birds, we assume that 
their behavior is due to instinct alone, the impression would be 
grossly misleading and thoroughly false. 
The reproductive cycle is made up of a series of acts or chains 
of actions, which follow in a definite succession. Eight or more 
terms may be recognized, but the classification is unmiportant, 
so long as it is observed that they are serial and harmo7iious, and 
that anything which profoundly disturbs their normal attune- 
ment is disadvantageous, and may lead to disaster. If the dis- 
turbance is of a fundamental and permanent character, new ad- 
justments in the series must follow, if the species survive. 
The cycle may be graphically represented by a number of 
nearly tangent circles, each of which stands for a distinct sphere 
of influence or for a subordinate series of related impulses, as 
given in the simpified formula: 
1. Migration; 
2. Mating; 
3. Nest-building; 
4. Egg-laying in nest; 
5. Incubation and care of eggs; 
6. Care of young in nest; 
7. Care and education'^ of young out of nest; 
8. Migration. 
A partial descriptive analysis of the successive terms of the 
cycle and of the correlated instincts of parent and child are 
given in the table which follows, but it must be understood that 
in a complete catalogue of the separate or related instincts of 
wild birds, this list would be extended to much greater length, 
and that the selection of terms, especially Xos. 6 and 7, is con- 
ventional. 
