122 BULLETIN 50. UNITED STATES NATIONAL MUSEUM 



L[agoptts] m[utus] dixoni Salomonsen, Medd. Grjzinland, cxviii, No. 2, 1936, 4 in 



text. 

 Lagopus mutus americanus Hellmayr and Conover, Cat. Birds Amer., i, No. 1, 1942, 



205, part (syn. ; distr.). 

 Lagopus rupestris Shortt, Contr. Roy. Ontario Mus. Zool., No. 17, 1939, 12 (Alaska; 



Yakutat Bay region). 



LAGOPUS MUTUS EUPESTRIS (GmeUn) 



Rock Ptarmigan 



Adult male, summer plumage. — Like that of L. m. dixoni, ,but paler 

 and grayer, the brown markings hair brown to dull grayish olive-brown. 



Adult female, summer plumage. — Similar to that of L. m. dixoni but 

 upperparts more grayish, the general appearance being more grayish 

 than brownish and with the black blotches much larger. In worn plumage 

 some of these birds are almost black above. Breast, sides, and upper 

 abdomen whitish or only very pale ochraceous-buff barred with heavy 

 black bars. Occasional specimens are found, especially in the far north- 

 ern part of the range, that are not to be distinguished from L. m. nelsoni, 

 having more of the brownish color, but most of these brown specimens 

 are first-year birds. 



Adult male, autumn plumage. — Similar to the summer male but slightly 

 browner, the vermiculations averaging finer, giving an appearance of 

 greater uniformity to the upperparts and breast. 



Adult female, autumn plumage. — More hair brown, less marked with 

 black than summer females; many of the dorsal feathers only vermicu- 

 lated with blackish. Apparently this plumage is never (?) fully present, 

 as by the time many of the black summer feathers have been replaced 

 by the vermiculated hair brown ones, the white feathers of the winter 

 plumage begin to appear as well. 



Adult male, winter plumage. — Entirely white except for the blackish 

 loreal stripe extending through and behind the eye, and the rectrices, 

 which are dark clove brown; feathering of tarsi and toes longer and 

 denser than in summer plumage. 



Adult female, winter plumage. — Similar to the winter male but without 

 the black loreal stripe. 



Female, first autumn plumage. — Browner and more narrowly barred 

 with blackish above and on the breast than the adult female in autumn ; 

 outer primaries more pointed and often with one or more of the juvenal 

 remiges retained. 



Juvenal (unsexed). — Differs from the female in first autumn plumage 

 in having the upperparts with bright ochraceous edges and bars on the 

 otherwise blackish feathers; breast, sides, and flanks ochraceous-buff, 

 brightest on the breast, barred with fuscous; remiges dark hair brown 

 to grayish clove brown externally mottled with pale bufify. 



