EASTERN HOUSE WREN 123 



normally accomplished in 13 days. Based on the rate of gaseous ex- 

 change the most favorable incubation temperature for rapid develop- 

 ment falls between 35° and 37.8° C. On the basis of Kendeigh's com- 

 putations, if we take into account the total amount of oxygen absorbed 

 and assume the respiratory quotient to be 0.72, development at a con- 

 trolled temperature of 37.8° C. would require only ten days, while 

 at 32.2° C. it would require 18 days. Temperature is an important 

 factor in determining the length of incubation. Reports by different 

 observers present a variation in the length of the incubation period 

 from 11 to 15 days, but this discrepancy can be explained in part 

 through the lack of proper consideration in the factors involved and 

 especially through the lack of accurate determination when incubation 

 actually starts. 



Baldwin and Kendeigh (1927) made a detailed study of the be- 

 havior of nesting house wrens, including their attentiveness and in- 

 attentiveness. Their information was obtained by direct observations 

 and from continuous records secured by the use of special apparatus 

 involving the principle of thermoelectricity to determine the presence 

 or absence of the birds from the nest. It seems desirable to quote their 

 statements at considerable length. 



The differentiation between the periods of attentiveness when the bird is actu- 

 ally engaged in nesting activities and the periods of inattentiveness when it is 

 feeding or resting is best developed with the female for it is she who is most 

 active in the reproduction of the species. 



After the female becomes mated with the male, she soon begins to carry in 

 lining for the nest, the rough part of which has been begun or finished by the male 

 some time previous. The female, however, does not carry nesting material into 

 the box continuously for long at a time, getting her food at odd moments when 

 she is looking for material. On the contrary, she works assiduously at building 

 the nest for a period of a few to several minutes, and then goes off and hunts 

 actively for food for herself, only to come back when this period is ended to carry 

 more material for another stretch of time, and so on. While building her nest she 

 is not concerned with looking for food. Likewise, when she is away looking for 

 food she does not concern herself with nesting duties. She usually spends a 

 great deal longer time away from the box than at the box during this phase of 

 her nesting activities. 



The same holds true for the days during which she is laying her set of eggs. 

 Her inattentive periods are usually much longer than her attentive periods, 

 although she comes to the box at regular intervals throughout the day. As her 

 set nears completion and the duties of incubation approach, the inattentive 

 periods gradually shorten, and the attentive periods not only lengthen but become 

 more numerous. 



The day on which the eggs hatched the activities during the early 

 morning started at the normal rate. However, at one nest studied, 

 beginning at 7 : 11 her record indicates considerable uneasiness. 



The reason for this became apparent when at 7 : 35 the first young bird was 

 found to have just broken out of the shell. All of her eggs hatched during the 

 rest of the day. The number of her attentive and inattentive periods during the 



