191-1] Chanrller: Feathers of Circus huchonius 331 



PTERYLOGRAPHY 



Before entering into a discussion of the structural modifica- 

 tions in the feathers of Girmis hudsonius, a few words about 

 the general pterylography of the genus will not be out of place. 

 In common with the Accipitres in general, Circus is character- 

 ized by the presence of aftershafts, a permanent covering of 

 down feathers not confined to tracts, and a circlet of feathers 

 at the apex of the oil gland. In working out the ptervlosis of 

 various accipitrine birds, Nitzseh (1867) stated that the general 

 pterylographic characters of C. pygargus {^^ cyaneusf), C. aeru- 

 ginosus, and C. cinerarius {^cineraceus?) essentially agree 

 with those of Milvus, Pernis, and A&tur, especially in the narrow 

 form of the tracts; in the presence on the dorsal portion of the 

 spinal tract of two divergent rows of feathers which reach the 

 scapular fork ; in the small size of the lumbar tract ; and in the 

 shortness of the inner branch of the inferior tract. Circus may 

 be distinguished from the majority of the Acciptres (Elanus, 

 Elanoides, Regerhinus, and Gypa'etus excepted) by the presence 

 of lumbar powder-down patches in two symmetrical tracts on the 

 sides of the pelvis, the posterior portion of the spinal tract run- 

 ning between them. Each patch tapers off anteriorly into a 

 narrow band which reaches the shoulders. The tarsus is feath- 

 ered one-third down in front, and is essentially naked behind, 

 the head is fully feathered, the base of the gape is furnished with 

 bristles, and the face is given a rather owl-like expression by 

 the presence of a facial ruff. 



MOULTS 



An examination of about twenty-five skins in the University 

 of California Museum of Vertebrate Zoology indicates that 

 Circus hudsonius moults but once a year, this being in July. 

 Three specimens showed new feathers in process of growth, one 

 from San Jose, California, taken July 12 ; a second from Modoc 

 County, California, at an altitude of 7000 feet, taken July 29; 

 and a third from Kenai, Alaska, taken August 4. The two Cali- 

 fornia specimens are in process of moulting both the definitive 



