108 BEHAVIOR OF PIGEONS. 



left the nest, but were still being fed during the second incubation period. One of these 

 young birds, No. 560, was observed to participate in this incubation when only 38 days old, 

 and the activity was continued for more than a week. This act was a genuine case of 

 incubation, as was shown in several ways. It occurred after the nest had been deserted by 

 both of the young; the young bird took up such a position as to cover the eggs completely; 

 and it exhibited the usual incubation behavior of ruffled feathers and an attitude of holding 

 its ground, when the hand was placed in the nest. Further observation showed that the 

 two old males were driving the other young bird (a nest-mate) in the attempt to wean it, 

 but that they were, at the same time, most anxious and eager to feed No 560, and that 

 this feeding was almost invariably followed by attempts to mount and copulate with the 

 young bird. This situation continued for some time, and finally the young bird was itself 

 observed to attempt the complete sexual response; only its muscular inability to bear the 

 weight of the male prevented any copulatory success. The first successful coition was 

 observed when the young bird was about 3 months old. The motive to this unusual pro- 

 longation of the feeding on the part of the old males was primarily sexual. The young 

 bird was at first primarily interested in the food, but the continuance of the activity finally 

 aroused a sexual response before maturity. This abnormal sexual attitude of the old birds 

 toward the young is probably a result of their unnatural sexual relation ; the pair consisted 

 of two males. Possibly the awakened sexual impulses would have found a normal outlet 

 in a pair consisting of male and female." 



(B) Some of the activities are designed to arouse the appropriate attitudes 

 in the mate. As noted previously, each bird possesses the behavior potentialities 

 of both sexes, and the system awakened depends upon the behavior of the mate. 

 Driving and charging stimulates coyness and submissiveness. Hugging and "jump- 

 ing over" tend to arouse the necessary stooping attitude in the female; and the 

 movements adapted to secure sexual union are the outcome of the contact stimuli 

 incident to the mount. 



(C) The billing, preening, and pecking at certain feathers on the wings and 

 tail seem more of the nature of a self-excitatory process. These parts are the 

 sensory regions involved in certain reflexes incidental to mounting, and it is thus 

 possible that the act of preening is designed to stimulate these areas and arouse 

 the sexual inclination. 



(D) The activities preceding coition are highly uniform for various species, 

 and this fact will suggest the conception that they are adapted to secure certain 

 results in the progression of events in the cycle. The activities immediately "sub- 

 sequent" to contact, however, exhibit many specific variations, and one may 

 therefore suspect that they serve no particular function in the cycle, but are the 

 specific modes of expression of the neural energy released in the orgasm. When no 

 definite result is to be achieved, variability in response may be permitted. 



EGG-LAYING. 



Some of the acts in egg-laying are adapted to the purpose at hand, while others 

 are probably incidental but necessary results of the labor involved. The prelim- 

 inary symptoms of ovulation are stimulated mainly by the presence of the egg, 

 but probably in part by antecedent conditions, because these symptoms were more 

 than once observed when no eggs were produced. 1 The stimulus to ovulation 



1 The possibility that ova were set free in the body-cavity is not excluded by the author's data. 



