CHAPTER V. 



INCUBATION BEHAVIOR. 



The time of beginning incubation is not always synchronous with the appear- 

 ance of the first egg; it differs for the two birds, it varies with the species, and it 

 seems to be highly variable within a species. The early incubation is often irreg- 

 ular, but in the later stages the eggs are covered almost continuously. Copula- 

 tion ceases with the advent of the eggs, but nest-building is continued for the first 

 half of the period. Both birds participate in the incubation of the eggs. At night 

 the female covers the eggs, while the male normally roosts on the perch as far 

 from the nest as possible. During the day the male and female alternate in the 

 task, though the male occupies the nest the major portion of this time. These 

 activities are described in detail under the topics which follow. 



EARLY INCUBATION. 



The wild passenger-pigeon (Ectopistes) begins to incubate a day or two in advance 

 of laying, and the male takes his turn on the nest just as if the eggs were already there. 

 In the common pigeon the sitting usually begins with the first egg, but the birds do not 

 sit steadily or closely until the second egg is laid. The birds do not, in fact, really sit on 

 the first egg, but merely stand over it, stooping just enough to touch the egg with the 

 feathers. This peculiarity has an advantage in that the development of the first egg is 

 delayed so that both eggs may hatch more nearly together. 1 



A female passenger-pigeon began to make a nest on a Monday. She sat much on that 

 day and almost constantly all day on Tuesday. She was sitting again on Wednesday; on 

 this latter date the male seemed to be off duty and did not come near the female on the 

 nest, although he sat for a long time on the nest during the middle of Monday and Tuesday. 

 The egg was laid after 4 p. m. on Wednesday. In another instance, a female passenger- 

 pigeon was on the nest in the early morning. The male sat during the middle of the day, 

 as if he were in charge of an egg, though the nest was empty. I found the female on the 

 nest at 3 p. m., and she remained on from this time, laying her egg at 4 h 52 m p. m. of this 

 same day. In still another case a pair of passengers accepted a nest on one day. On the 

 next, I saw the male on the nest at 1 l h 30 m a. m., and he remained there until 3 or 4 o'clock, 

 or perhaps until later. The egg was laid that day between 4 and 5 p. m. (SS 4.) 



Fulton (op. cit., p. 41) comments upon this subject as follows: 



"As a rule, it is found that the sooner pigeons' eggs are allowed to commence the process of incu- 

 bation after being laid the better, certainly not later than 5 or 6 days. Further, as to the time during 

 which they may be allowed to remain uncovered after incubation has once commenced, this is 

 regulated by the stage which has been reached. In the early days eggs may have become cold and 

 remained so for 24 hours, and even more, and yet not be injured; but as the date of hatching 

 approaches even 1 or 2 hours of desertion by the covering bird may cause the egg-tenant to perish ; 

 though even within 24 hours of the time of hatching we have known marvelous instances of the vital 

 power of squabs being preserved, even though the egg may have been stone-cold for a few hours." 



On the third day of incubation, i. e., on the day of the laying of the second egg, a pair 

 of bronze-wings were in full swing proceeding in regular order with incubation, not leaving 

 the nest except by exchange of relief, and sitting (not standing). The day following 

 the laying of the first egg was one of fairly regular incubation, but the sitting was not 



1 Woods Hole Biological Lecture, p. 327. 

 5 53 



