es PaLtMER, The Maryland Vellow-throat. 219 
of the length and character of the migration, avd have been caused 
by migration. 
While the color values as here given (largely psychological 
characters) exist strongly in the males, many of the females 
show a tendency in the same direction. The females of formosa 
especially are very like the males and are thus further advanced in 
this species, but many of the older females of other species exhibit 
a tendency toward the marking and coloration of the males of 
their respective species. This is especially true of the more tropi- 
cal forms. ‘The strong color differences between the sexes of 
most of the forms are evidently derived from the superior activity 
of the male, plus the necessary secretive characteristics of the 
female. Where, however, the showing off habits of the males 
are slight, natural selection has permitted the females to acquire 
an almost similar plumage to the males, as in formosa. The 
subdued character of the song of this species, its secluded habi- 
tat and its ground habits have permitted the female to attain 
nearly similar plumage conditions and has retarded greater spe- 
cialization of the male. 
Judging from all the characters, the forms? and poliocephala 
groups would seem to be the least specialized, while occidentalis 
and brachidactyla occupy the other extreme. 
Another interesting feature is shown in the comparative lengths 
of the tails and wings, non-migratory lowland forms having rela- 
tively shorter wings and longer tails, while mountainous dwell- 
ing and high northern forms have relatively longer wings and 
shorter tails. These characters, dependent upon altitudinal and 
northern habitats, are less strong in the immature, but are attained 
by age and experience. 
The white and slaty crown band of the ¢r7chas group changes in 
Mexico and lower California to a yellow band, which in Central 
America is entirely lost, the green of the back becoming greatly 
intensified and abruptly joining the facial black. 
THE TRICHAS GROUP. 
Their abundance, and the low bushy-ground nature of their 
habitat fit these birds to take advantage of general climatic 
