REPRODUCTIVE CYCLE. 101 



FIDELITY OF PAIRING. 



A pair of birds normally remain faithful to each other during the reproductive 

 cycle and then maintain their relations in the succeeding cycles of the season. It 

 has been noted, however, that the female may desert a mate defeated in fight for 

 the stronger male. We are not definitely told whether the matings are spontane- 

 ously continued in subsequent years, but often probably they are not. This 

 fidelity of pigeons is at once explicable on the basis of the principles developed 

 in the previous section. One does not need to postulate an "instinct of fidelity" 

 to account for the circumstance that pigeons act as if actuated by well-developed 

 ethical ideals. During a reproductive cycle there is little opportunity for illicit 

 intercourse, for the reason that the sexual impulse is suppressed during incubation, 

 i.e., it is limited to the first week of each cycle. Their reciprocal activity in courting 

 and nest-building keeps them in proximity to each other and relatively isolated 

 from others. At the time there is little likelihood that any other birds would be 

 simultaneously disposed, except when such pairs are members of large flocks. 

 At the end of the first cycle the rise of the sexual impulse will be closely synchronous 

 in the two members of the pair, and this impulse generally develops while the pair 

 is still kept together by the necessity of caring for the young. Fidelity is thus 

 a necessary result of the synchroneity of impulses and the proximity to each other 

 and the isolation from others which result from the cycle. As a matter of fact, 

 illicit copulations with paired birds do occur; and we know further that a pairing 

 may be broken up and a new mating be almost immediately obtained. These 

 facts are readily explicable on the basis of the conception already developed. 



FUNCTIONAL INTRA-RELATIONSHIP OF ACTIVITIES. 



The various activities of the cycle are presumably woven together in some sort 

 of a causal nexus. In the analysis of these relations we need to distinguish between 

 the impulse or disposition, the objective sensory stimuli which excite it, and the 

 resulting behavior. By an impulse we mean any intraorganic condition predispos- 

 ing the organism to a certain line of behavior. Both the stimulus and the impulse 

 necessary to any act may thus be a result of previous activity. The utility and 

 validity of this distinction will be obvious from the subsequent discussion. 



FEEDING. 



The initial act in feeding on the part of the old birds consists of presenting the 

 open beak to the young. The conditioning factors of this act are both internal 

 and external. The external stimuli are an attitude of helplessness, certain cries, 

 flapping of the wings, and the teasing contact of the beak of the young. The favor- 

 able internal condition is a full crop. The relative amount of cooperation of the 

 two is highly variable. On the one hand, the parents may respond to vigorous 

 and insistent appeals of the young when they have nothing to give. Again, the 

 internal stimuli may become so strong, the desire for relief so compelling that the 

 parents will attempt to force food upon their unwilling progeny, may return to 



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