INCUBATION BEHAVIOR. 57 



A crested male relieved his blond-ring female between 6 h 50 and 8 h 40 m in the morn- 

 ing and relinquished the nest for the night between 2 h 40 and 4 h 15 m in the afternoon. 

 The average time of relief in the morning was 7 h 30 m , and the average time in the after- 

 noon was 3 h 30 m . The total time during the day devoted to incubation by the male varies 

 from 2^ hours to 8f hours; the average period being 6 hours daily. During the period 

 of alternation (daytime) the male occupied the nest three times as long as the female. 

 The number of reliefs by the male during the day varies from 1 to 9, with an average 

 number of 3^. The length of time spent on the nest in these reliefs varies from 1 minute 

 to 6-J hours. There were 8 intervals of 4 to 7 hours, 23 intervals of 1 to 3 hours, and 25 

 intervals of less than 1 hour in length. As a general rule the early reliefs were short and 

 the later reliefs rather long. 



A bronze-wing male began relief between 7 and 8 h 45 m in the morning, the average 

 time being at 8 a. m. He retired for the night from 12 h 15 m to 3 h 20 m in the afternoon, 

 the average time being at 2 p. m. The average number of reliefs during the day were two. 

 The total time spent on the nest during the day varied from 3-| to 6f hours; the average 

 being 5^ hours. The shorter intervals of relief occurred in the morning, while the later 

 periods were generally the longer ones. (SS4, R 18, R33.) 



The time of early-morning relief, as well as the time when the male retires for 

 the night, is probably influenced by light conditions, such as the length of the day, 

 clear or cloudy weather, etc. The bronze-wing male put in a shorter day than did 

 one of the passenger males of the first pair; his early-morning relief averaged a 

 half-hour later, while he retired for the night much earlier. He also spent less 

 actual time on the nest during the day. The bronze-wing record covered the 

 period from Dec. 16, 1905, to Jan. 3, 1906; the passenger record concerns incu- 

 bation during February, when the days were appreciably longer. The daily records 

 sometime state the character of the weather, but the cases are too few to allow of 

 any conclusions as to the effect of the clearness or cloudiness of the day. In the 

 bronze-wing record it is noted that the male once relieved at 6 h 30 m a. m., shortly 

 after lighting the gas during an early-morning inspection. It is stated that this 

 very early relief was probably due to the light. 



INITIATIVE IN INTERCHANGE. 



In the majority of cases the records do not state which bird was responsible 

 for the interchange at incubation. From the available records it may be stated 

 that either bird may take the initiative in leaving the nest or in resuming nest duty. 

 In the bronze-wing, both birds took the initiative in resuming incubation more fre- 

 quently than in leaving the nest, while the reverse was true for a crested-blond-ring 

 pair. In the latter pair the male showed more initiative, both in leaving and in taking 

 the nest, while in the bronze-wing pair both birds initiated the changes a nearly 

 equal number of times. The female often leaves the nest early in the morning, 

 before the first relief, in order to defecate, but she returns to nest duty at once. 



When a bird takes the initiative in resuming nest duty, the mate often exhibits 

 some stubbornness in giving up the nest upon demand. The female exhibits the 

 most stubbornness and reluctance in leaving. Often the male is forced to give 

 up the attempt to take the nest, and he is sometimes forced to crowd in and push 

 her off the nest. In one case the female resisted for 15 minutes before leaving. 



