DIVIDED INTO GROUPS 2h7 
plumaged birds can only be recognized by 
their sizes, general colour, mode of flight, man- 
ners, postures, and notes, and these character- 
istics, especially the notes, can only be got by 
practice, though to read them all up is of 
the greatest use. 
The males of most species differ more or 
less in plumage and size from the females. 
The wmmature plumage of all young birds 
is different to that of the adult, and the size, 
of course, of the young is less. 
The winter plumage of many birds differs 
from that of the spring (breeding-time) and 
summer. 
The characteristic mode of flight, plumage, 
mannerisms, notes and sizes of the birds never 
vary (albinism and freaks are rare). 
The matertals of the nests of a few birds may 
vary, the nearest at hand being sometimes 
utilized, but the large majority always use 
the same materials. 
The shape, and outside and inside measure- 
ments (especially the latter) of the nests are 
constant, and typical, so that after some prac- 
