358 V niversity of California Puilications in Zoology [Vol. 11 



which is at right angles to the body of the bird ; the greatest 

 width, which is at the turn, is about 5 millimeters. The after- 

 shaft is, as usual, downy, and very minute. The barbs are very 

 numerous on the shaft, there being thirty-six to forty-one per 

 centimeter on each side, about twice as many as in an ordinary 

 breast feather. The barbules, which, due to the closeness of the 

 ad.joining barbs, are very short, are also very closely set, there 

 being forty-three distals and twenty-nine proximals per milli- 

 meter. The proximal barbules (pi. 19, fig. 14) are 0.62 milli- 

 meter long, while the distals (pi. 19, fig. 15) are about 0.55 

 millimeter. As there is no downy portion on the main shaft, 

 the result of the structure described is a very stiff, compact 

 feather, quite different from the loosely netted feathers to be 

 found immediately in front of or behind the ruff. Euff feathers 

 from beneath the throat differ in having longer aftershafts and 

 in being larger and less densely inserted; they are not quite so 

 compactly woven as those of the sides of the head. The function 

 of the facial ruff is unknown, unless it be merely in the nature 

 of an ornament, which is unlikely, since mere aesthetic orna- 

 mention is strikingly lacking among the birds of prey. The 

 facial ruff is present in both sexes. 



Ear Coverts 

 Just in front of the facial ruff, extending from the corner 

 of the gape to the upper end of the facial ruff, is a group of 

 several dozen feathei-s known as ear coverts, which are wonder- 

 fully adapted to fulfill the functions for which they are designed. 

 Obviously it would interfere with hearing to have the ears 

 covered by normal, densely woven feathers, and, on the other 

 hand, it would be disadvantageous to have the large open ear 

 entirely exposed and unprotected. The ear coverts are perfectly 

 adapted to suit these conditions in that they are extremely loose 

 in weave, but form a network which, while it gives practically 

 no obstruction to sound waves, effectually protects the ear from 

 the entrance of even small particles of dust. The shaft bears 

 about twenty barbs per centimeter on each side, which, due to 

 the appression of their barbules, are entirely out of contact with 

 each other. The barbules (pi. 19, fig. 18) are short and undiffer- 



