FAUNA OF THE ALEUTIAN ISLANDS AND ALASKA PENINSULA 125 



lands, the Shumagins, and other neighboring island groups, and 

 west in the Aleutians as far as the Islands of the Four Mountains. 



We had suspected that birds from the Islands of the Four 

 Mountains might have developed new characteristics due to iso- 

 lation. Ground color of the plumage of birds taken on these is- 

 lands in early summei differs in tone from that of evermanni or 

 ridgivayi (of the Commander Islands) — although there is a slight 

 olivaceous cast, the predominating shade is yellow-brown. The 

 ground color also differs from that of specimens of nelsoni from 

 Unalaska and farther east, tending to gray rather than to red 

 in overall effect. Such differences, if real, are too insignificant 

 to warrant naming a new form. They can best be referred to a 

 slight deviation from the usual in nelsoni. There is a similar situa- 

 tion at Kodiak and neighboring localities, where nelsoni shows an 

 approach to dixoni (of southeastern Alaska), because the ground 

 color of nelsoni has a slightly grayish cast. 



The females of each Aleutian form cannot readily be distin- 

 guished, but there is a discernible difference between females of 

 nelsoni (which represent the darker forms) and the females 

 of the middle Aleutians (which represent the pale forms). On 

 female nelsoni, barring is black, broad, and in contrast ; whereas, 

 on the pale forms, the barring is less sharp, and the bars tend to 

 be discontinuous with a softer effect. 



Spring-plumage changes in Nelson's rock ptarmigan come much 

 later than the changes in willow ptarmigan. A 1-pound speci- 

 men, collected on Ushagat of the Barren Islands group on May 

 11, 1936, was still mostly white. On May 7, 1925, I found, on 

 Unimak Island, that the plumage was still nearly all white. On 

 May 14, 1925, males were seen with well-speckled plumage, but 

 it was a long time before these birds attained full summer dress. 

 On June 6, in the Izembek Bay region on Alaska Peninsula, 

 males still had considerable white in the plumage, but the females 

 had changed completely into summer plumage. A female taken 

 on Dolgoi Island, May 24, 1937, contained well-developed eggs. 



Nelson's rock ptarmigans are largely inhabitants of the high 

 mountains, .though they are not confined to the steeper parts. 

 They are often found on gentler middle slopes — in this respect, 

 they resemble the rock ptarmigan of interior Alaska. 



Lagopus mutus yunaskensis 



The Yunaska rock ptarmigan was described by Gabrielson and 

 Lincoln (1951) on the basis of a specimen collected by Gabriel- 

 son on Yunaska. As might be suspected, although it is grayer 



