104 BEHAVIOR OF PIGEONS. 



The male of the pair X-W 1 did not participate in nesting and his sexual advances 

 were repelled, yet incubation developed in due time. A hybrid male paired with 

 another male by mistake, courted for a month without inducing a response, and 

 then began incubation with objective deficiencies. Inadequate sexual expression 

 may result in delay or lack of incubation. The male hybrid cited above illustrates 

 delay. A bronze-wing pair were separated and each remained in a state of sexual 

 readiness for 45 days without inducing the impulse to sit. When the rise of the 

 sexual passion is not synchronous in the two birds, the rise of incubation is timed 

 in reference to the beginning of "sexual activity" and not with the rise of the sexual 

 impulse. 



Though incubation is a result of preceding activities, it is not an invariable 

 result. A male mourning-dove courted and united with his mate in several cycles, 

 but refused to participate in either nesting or incubation. A pair may mate, 

 court, unite, and construct a nest, but proceed no further with the cycle. Other 

 cases are mentioned in which the only defect consisted of a lack of incubation 

 on the part of the male. We are thus forced to assume that incubation and sexual 

 activity may vary in relative strength, even though they stand in a causal relation. 

 Incubation results from the sexual activities, but the two impulses are not neces- 

 sarily proportionate in strength. Incubation may be normal when the preceding 

 conditions were somewhat deficient, while incubation may be weak or absent 

 when the previous acts were normal. 



Incubation and sexual activity are also mutually exclusive and antagonistic 

 phenomena. The two never occur together. Coition ceases immediately as 

 incubation begins. The rise of sexual activity during incubation disrupts the 

 cycle, and the sex activities generally appear shortly after incubation terminates. 

 The resultant advantage of this relation is obvious; but one can not explain the 

 mechanism of the antagonism in terms of its consequents or advantages. Neither 

 can the relation be explained in terms of the mutual exclusiveness of the activities 

 per se; for, in the early periods of incubation, the eggs are often left uncovered for 

 sufficient time to allow coition. The antagonism must be conceived as obtaining 

 between the two "dispositions." 



Whitman has suggested a conception (Chapter VIII) which is not wholly 

 unsatisfactory in explaining these relations. Incubation is due to "exhaustion" 

 resulting from the previous sexual or reproductive activity. Incubation is thus 

 a result, and the two must necessarily be mutually exclusive impulses. Neither 

 does it follow that the strength of the two tendencies are always proportionate, 

 for exhaustion and recuperation could well depend in part upon factors other than 

 the degree of sexual activity. In fact, the author regards exhaustion merely as the 

 primary or germinal condition from which incubation arose. Other supplementary 

 factors were added in the process of evolution before the primary condition could 

 be utilized in the manner in which it is manifested in pigeons. Whitman would not 

 only admit, but also assert, that the incubating behavior of pigeons is to be ex- 

 plained only "in part" in terms of exhaustion and recuperation. 



