26 DwiGutT, Moult of Quails and Grouse. ne 
I. Every species has a definite sequence of plumages and of 
moults. 
II. Moult is periodical systematic feather growth. 
III. Moult is complete or incomplete. 
IV. Plumage is renewed by moult. 
V. Plumage is modified by wear. 
A word has already been said about each species having a 
definite series of plumages and of moults. ‘This is found to be 
true of every species of Grouse and every species of Quail, plum- 
age being renewed by feather-growth at definite periods while 
between them it is subjected to all the destructive influences of 
abrasion and fading which I have summed up under the word wear. 
It has been possible for me to reach these conclusions by an 
examination of the large series of Tetraonide in the American 
Museum of Natural History, thanks to the kindness of the Curator 
of Zoology, Dr. J. A. Allen, who has afforded me every facility. 
I must confess that the study of moult from museum skins presents 
many difficulties. The loss of feathers from the birds when fresh 
and the crowding together of parts of the skin, especially of the 
wings, obliterates many details or renders their demonstration 
impossible without serious mutilation, of the specimens when once 
dried. Fortunately a few specimens of Colinus, Dendragapus 
and Sonasa in my own collection were studied before they were 
skinned so that I am able in a measure to make up the serious 
shortcomings of dried skins. 
Before taking up the Grouse and Quails individually it will be 
well first to consider their moults in general and then discuss their 
plumages, the same fundamental principles being applicable to 
all of them. 
Among the Tetraonide two distinct periods of moult may be rec- 
ognized in adults and two others in young birds occurring shortly 
after they leave the nest. The one which occurs in adults at the 
end of the breeding season is complete, just as it is In all species 
of North American birds, and is known as the Postnuptial Moult; 
the other, which is seldom complete in any species and in the 
Tetraonide chiefly confined to a very limited area of the head and 
throat, is known as the Prenuptial Moult. In the Quails the 
prenuptial moult includes very little beyond the sides of the head 
