86 BEHAVIOR OF PIGEONS. 



(6) Any serious fright or disturbance is likely to cause desertion. In a pair of mourning- 

 doves it was noted that the eggs were deserted on the second day of incubation as a result 

 of disturbance by dogs. A pair of homers deserted their young when 10 days old in order 

 to return to a former nest. Other pairs, however, failed to desert their eggs in similar 

 circumstances (Chapter X). A change in the position or character of the nest may also 

 cause desertion of eggs or young (Chapter XII). (R 7, R 18, SS 10, Em 7.) 



(7) Two male mourning-doves, after the normal end of their breeding season, 

 indulged in all the preliminaries of courting, uniting, and nesting, but failed entirely 

 to incubate, or else did so quite spasmodically. It is noted that this phenomenon 

 occurred only with males which were unusually prolific and unusually successful 

 in fertilizing eggs (see under "Prolongation of the Breeding Season in Wild Pigeons," 

 Chapter I). At the period of the subsidence of the reproductive impulses, it was 

 found that the sexual proclivities were still vigorous and found expression, while 

 the incubating impulse was extremely weak and sometimes failed altogether. It 

 is thus possible that, in the disintegration of the reproductive series of acts at 

 the end of the season, the incubating impulse tends normally to disappear first, 

 or that we are here dealing with males in which the sexual impulse is relatively 

 much stronger than usual. From the short account of the phenomenon the latter 

 interpretation is to be preferred, though one is not justified in making a decision. 



(8) In his breeding experiments the author frequently removed the eggs 

 shortly after being laid and had them hatched under a pair of "brooders." This 

 removal of the eggs generally disrupts the cycle immediately. To assure the dis- 

 ruption, however, the nest-box is usually temporarily displaced or removed. In 

 the treatment of the topic, "Length of the Mating Period," in Chapter I, 27 such 

 cases are listed. Many hundreds of cases could have been obtained from the 

 "breeding records." In one case it is stated that the female persisted in sitting 

 for some time (probably 10 days) afterwards. The breaking of the eggs usually 

 produces the same effect; 4 such cases are listed in the same place cited above, while 

 in one case the new cycle was postponed for about 10 days. 



