CXCVl 
APPENDIX. 
the first bird which was observed in change ; by the end of the first week in 
June the summer plumage of the females was generally complete, and a change 
had commenced in a few of the males ; some of the latter were however 
killed, as late as the middle of June, in which no alteration of their winter 
plumage had taken place. The distribution of the coloured plumage of 
summer corresponds both in the male and female with the Ptarmigan, the 
same parts of both species remaining white ; but there is much difference in 
the colour itself ; the upper plumage of the Ptarmigan is cinereous, with 
undulating and narrow black lines and minute spots, whereas in the 
Rock Grous each feather is black, cut by transverse broad lines or bars of a 
reddish yellow, which do not reach on either side so far as the shaft, and have 
spaces of black between them, broader than the bars themselves ; the feathers 
are tipt with a light colour in the male, approaching to white in the female. 
The tail consists of fourteen feathers, which do not undergo changes from 
season. In the greater number of individuals, the whole fourteen are black with 
white tips, but in occasional specimens, the two middle ones are entirely white, 
and in others partly black, and partly white ; and this has been found to be the 
case in individuals of a pack, others of which had not the same peculiarities. 
It is, doubtless, in consequence of this accidental variation that “ rectricibus 
atris apice albis, intermediis totis albis” forms erroneously a part of the specific 
character of the T. Rupestris in Gmelin. The superior and inferior tail 
coverts are very long, exceeding occasionally the length of the tail itself; 
these feathers change from white in winter to the same colour as the upper 
plumage in summer. 
The average length of the male specimens is 13| inches ; of females 12| ; 
both sexes are inferior in size to the Lagopus ; the two species resemble 
each other in the formation and colour of the claws and bill, and in the 
naked space above the eye, terminated by a dentated membrane, larger and 
more conspicuous in the male than in the female. 
The ground colour of the egg of the Rock Grous, is a pale reddish brown, 
irregularly blotched and spotted with darker brown. 
