DEFECTIVE CYCLES. 85 



then began incubation of the eggs on January 29, and normal conduct was exhib- 

 ited thereafter. In the second cycle the one female laid on February 27 and 29 

 and the supposed male did not begin incubation until March 3, when she too laid 

 an egg. Another pair (E) mated and went through all the preliminaries, even to 

 the symptoms of laying. Neither bird laid, however, but incubation began at 

 the usual time. For the most part both birds sat on the nest at night and exchanged 

 with each other during the day. This incubation persisted for the usual time, 

 when a new cycle was started and one of the pair laid eggs. In another case both 

 females laid in one nest and exchanged with each other as if male and female. 

 The preliminary activities of courting, uniting, and nesting are abnormal in one bird, 

 and they find no normal reciprocal response in the other. Following these, the 

 production of eggs may be lacking in one or both of the pair, although some of 

 the correlated behavior may be present. The production of eggs may be stimulated 

 in both birds, and when this occurs the previous masculine behavior is associated 

 with delayed laying. The impulse to incubate develops in both birds, although 

 eggs are lacking. This impulse was not awakened in one bird until after the delayed 

 laying. Incubation persisted in spite of defective alternation, and also, in the case 

 of one of the females of "pair D," in spite of an empty nest and being driven away 

 and having the box covered. 



(3) Several times this season and in different pairs, such as ring-dove X Japanese turtle, 

 tur-orient. X tur-orient. hybrids, orientalis X turtur, guinea X guinea hybrids, etc. (and 

 formerly crested pigeons, which laid several times before sitting steadily), I have seen eggs 

 laid and incubation begun, and in the course of a few days or a week the eggs were deserted. 



In the case of the turtur-orientalis hybrids, the offenders were young birds. They 

 began by laying and sitting well for a few days or a week, then beginning a new nest and 

 laying again, and again incubating for a short time. I believe this is due to having "an 

 abundance of rich food," and to eating more than is really needed, thus bringing forward 

 a set of eggs that would, under normal nourishment, not develop until the previous set 

 hatched and the young were reared. After the birds have repeated this several times, and 

 as the season is more advanced, they become exhausted to an extent that allows of a normal 

 course of incubation. As an example of this, two pairs of Japanese turtle X European 

 turtle, and also one of the reciprocal cross, have repeated the short abnormal course four 

 or five times, but they are now at work in normal time. 



(4) The time of incubation, or rather the time that the old bird will continue her sitting, 

 can be varied somewhat as the result of excessive feeding. The bird becomes unsteady in 

 sitting and then begins a new cycle, and in several cases I have found pairs of birds produc- 

 ing a second and even a third set of eggs in the same nest. One pair of crested pigeons, for 

 example, after they had sat a week on one set of eggs, laid two more in the same nest; and 

 then after a week or ten days more laid a third pair of eggs in the same nest. These birds 

 were kept indoors and had plenty of stimulating food, hemp and canary seed; and I saw 

 no other reason than the easy conditions under which they were kept which should lead 

 them to break the cycle in this way to stop the sitting on one set of eggs and renew the 

 sitting on another set of eggs in the same nest. 



(5) A pair consisting of a ring-dove and a Japanese turtle have twice raised young, 

 and each time they have laid again before the young were out of the nest. As a result, the 

 later eggs were deserted and the young were thus given more time to get out of the way, 

 and then other eggs were laid which were properly incubated. 



7 



