128 BULLETIN 195, UNITED STATES NATIONAL MUSEUM 



passeriform birds including two house wrens. A male secured on 

 June 11, 1933, weighing 13.3 grams had 1,271 contour feathers, the 

 latter weighing 0.6 gram. Another male, obtained on July 9, weigh- 

 in 11.5 grams, had 1,178 contour feathers weighing 0.7 gram. 



Poole (1938) in studying the ratio of wing area to weight and the 

 effect of this ratio on flight, determined the wing area of a house wren 

 weighing 11.0 grams to be 48.40 square centimeters. The wing area 

 per gram is shown to be 4.40 square centimeters. As a means of com- 

 parison it is interesting to note that in the case of the loon, a poor 

 flier, there is the ratio of only 0.56, while that of Leach's petrel, which 

 spends much of its time in flight, has a ratio of 9.47. 



Temperature. — Kendeigh and Baldwin (1928) made an exhaustive 

 series of temperature readings of the house wren in connection with 

 their study of temperature control. For this work they used specially 

 devised thermometers and thermocouples. 



The average temperature of wrens during the first day after hatching 

 is 98.6° F. This gradually increases with the age of the young, and 

 by the time they are 15 days old the average temperature is 106.7° F. 

 According to these authors : 



The body temperature of young house wrens vary several degrees during the 

 first few days out of the shell, but by the time they are ready to leave the nest 

 their temperatures are not only higher but distinctly less variable. 



The development of a resistance in young house wrens against cold follows the 

 sigmoid growth curve. This development of temperature resistance is due 

 primarily to the mass of body increasing faster proportionately than the external 

 dissipating surface, to the development of a feather covering, to the development 

 of an internal dissipating surface probably under nervous respiratory control, 

 and to the production of heat in the metabolism of the bird. * * * No efficient 

 resistance against extreme heat is developed in young house wrens, although 

 the rapid respiration from the lungs and air sacs probably serves toward this 

 end. 



According to Kendeigh (1934) the standard temperature of adult 

 house wrens taken at complete rest and without food in the alimentary 

 tract is for the males 104.4° F. (40.2° C.) and for the females 

 105.0° F. (40.6° C. ) . He says further : 



These values are fairly constant under various conditions, but may be lowered 

 at night when the bird is inactive and without food for several hours. * * * 

 Emotional excitement, muscular activity, extremely high air temperature, and 

 the digestion of food cause a rise in body temperature, while starvation and 

 extremely low air temperature produce a decrease. * * * Under natural 

 conditions a slight correlation exists between variations in average bird and air 

 temperatures from day to day ; but the variation in the average bird temperature 

 may amount to only a few tenths of one degree while the average air temperature 

 may vary 20" F. (11.1° C.) or more. Even this slight correlation may not be a 

 direct one but dependent upon variations produced in the amount of activity of 

 the bird from day to day. 



