29 
is possible to find more or less complete remains of four distinct plum- 
ages in one and the same bird, without any one of them showing de- 
cided predominance. Thus traces of last winter plumage may persist 
while that of next winter is just appearing and the two summer ones 
present an ill-defined mixture. The seasonal changes are not simultaneous 
in all individuals and birds of the same sex, time, and place may show 
widely different plumage development. 
The plumage itself is soft and the wear very rapid. This is specially 
true of the light edgings that are much less resistant to abrasion than the 
dark parts. Even during the short period these summer plumages are 
worn the light feather edges which lend the most characteristic subspecific 
characters are often cut away until racial features are obscured, lost, or 
even apparently reversed as between races. Another and not the least 
important difficulty in studying these birds is the optical one of com- 
paring unlike surfaces, feathers in mass on one specimen against individual 
plumes in another, often with totally different backgrounds that entirely 
alter the relative visual impressions. The colour patterns are complicated, 
variable, and subject to great individual variation in both detail and 
general effect. Size is also a variable quantity in the ptarmigan. Careful 
measuring of large numbers of specimens may show average differences 
between the races, but in the birds examined the distinction is so swamped 
by individual variation as to make it an uncertain criterion for the identi- 
fication of individuals. A factor that may mislead the investigator is 
the common overgrowth of the bill and claws of all the ptarmigan. This 
seems dependent upon the condition of the grounds upon which the birds 
have recently fed. When the rocks and soil are covered with snow or the 
birds are living on the soft tundra moss both claws and bill, deprived of 
the contact with abrasive material, continue to grow and occasionally 
assume almost monstrous proportions, returning again to their normal 
size when grit is once more available. 
The species is strongly migratory and movement may start com- 
paratively early in the season, resulting in many birds of different origins 
mixing together and losing their racial groupings before they do their 
distinctive plumages. With all these sources of confusing variation it is 
evident that large series of specimens are necessary for a final or detailed 
study of the species — such a series as probably does not exist in our col- 
lections today. 
The present series consists of 105 summer-plumaged specimens from 
Arctic America, the islands to the north, western Greenland, Newfoundland, 
and a few more southern continental localities. On a purely colour basis 
they divide into two distinct groups; one strongly yellowish, the other 
decidedly and generally greyish. Of course, all individuals are not equally 
marked in these characters and there are numerous intermediate speci- 
mens whose reference to one group or the other is more or less uncertain. 
It is doubtful if any two authorities would agree on the allocations of 
some of these, or even that a single judge would make exactly the same 
decision at different examinations. A point to be stressed is that these 
uncertain birds do not occur only on intermediate ground between con- 
sistently constant racial groups where hybrids can be expected, but may 
occur sporadically anywhere even where pure racial strains would be 
