352 University of California Publications in Zoology [Vol. 11 



CONTOUR FEATHERS OF TRUNK 

 Upper Parts 



The ordinary contour feathers covering the trunk of the bird, 

 which are useful for warmth and protection and for presenting 

 a smooth and more or less elastic surface to the air, are much 

 less developed than the wing and tail feathers hitherto 

 described. In these feathers the downy aftershaft reaches its 

 maximum of development, covering, as it does, over half of the 

 under side of the feather. Though there is quite a wide varia- 

 tion between extreme types of these non-specialized feathers, as 

 for instance between the crown, back, and shank feathers, there 

 is every gradation between them, and it will suffice to describe 

 one t.ypical example, and then discu.ss the modifications on 

 different parts of the trunk. 



Taking a feather from the middle of the back as an example, 

 we find that it may be at once distinguished from any of the 

 feathers so far considered, with the exception of some of the 

 smaller upper coverts, by the large proportion of the downy 

 basal portion, and by the loose way in which tlie differentiated 

 barbs are held together. 



The calamus is very short for the size of the feather, being 

 approximately 3.5 millimeters long. The shaft is comparatively 

 slender, measuring, on the under side, about 0.47 millimeter in 

 width at the umbilicus, but rapidly decreasing to about 0.3 

 millimeter, after which it decreases slowly. As in the case of 

 the primaries, the upper side of the shaft is narrow, measuring 

 about 0.3 millimeter at the umbilicus, and quickly decreasing 

 to 0.2 millimeter or less. The under side of the shaft is grooved 

 for a few millimeters above the umbilicus. The total length 

 of the shaft in a feather from the middle of the back is about 

 55 millimeters. 



The vanes are practically equal in size, but the barbs of the 

 outer vanes are inserted at a slightly more acute angle with the 

 shaft, being, therefore, of greater length and fewer in number 

 on the inner vane. 



The terminal portions of the more basal barbs are downy, 

 some of the filamentous barbules, of which there are from twenty- 



