1914] Chandler: Feathers of Circus hudsonius 357 



heat and protection, and to produce a smooth automatically ad- 

 justable surface to the air. do not need, and do not have, the high 

 development and numerous adaptive modifications and adjust- 

 ments of the more specialized wing and tail feathers. The gen- 

 eral loose structure and weak form of the barbules is character- 

 istic throughout. Going from the middle or lower back to the 

 nape and crown, there is a gradual increase in number of barbs 

 per unit of measure, accompanied by a correlative decrease in 

 length of barbules, the rasult being increasingly compact feathers. 

 A similar tendency is shown in the feathers of the under parts. 

 The belly and flank feathers are very long and fluffy, lying flat 

 on the body. The lower breast feathers are shorter and more 

 compact, and are inserted more nearly perpendicularly to the 

 body contour; and the upper breast feathers have these tenden- 

 cies emphasized, they being short, compact, and inserted directly 

 perpendicular to the body contour, the shaft traversing an are 

 of 90 degrees to bring the well-developed terminal portion to 

 lie flat. This thick, loo.se covering produces a high degree of 

 elasticity and ability to smooth over irregularities of contour, 

 resulting in a smooth surface with a minimum of unnecessary 

 friction. The contour feathers of the under side of the pygostyle 

 are specialized to serve as under tail coverts, while the terminal 

 row of back feathers is considerably modified to serve as upper 

 tail coverts. 



MODIFIED FEATHERS OF THE HEAD 

 F.vci.VL Ruff 



Some of the mo.st interesting modifications of feathers to be 

 found in this bird are those of the head, surrounding the eyes, 

 ears and mouth. 



Running around the head ventrally, beginning on either side 

 just above and back of the ear, and encircling the throat, is a 

 peculiar facial ruff, composed of specially modified feathers. 

 The latter are very numerous and closely inserted, and project 

 almost perpendicularly from the body of the bird. They then 

 turn at right angles, so that the broader terminal portion lies 

 flat on the surface. The feathers are elongate and narrow, the 

 total length being from 16 to 18 millimeters, 10 millimeters of 



