Vol. XVII 
1900 
PALMER, The Maryland Vellow-throat. 231 
This was caused by the bird’s habit of perching on the long 
inclining leaves of wire-grass abundant in the marsh, bushes 
and twigs being uncommon. ~ Alternate contact of the sides of 
the body with the grass wears the yellow tips of the feathers 
leaving the centre of the body almost untouched. The con- 
stant perching of most individuals of tzchas and brachidactyla 
on generally horizontal twigs produces the same effect but evenly 
up to the breast. The Mississippi Valley birds, owing to the 
less harsh character of the vegetation mainly of the winter habi- 
tat, have in comparable specimens less of the yellow worn off 
than occurs in eastern birds. Some examples are, however, iden- 
tical in wearing with these two preceding forms. 
The more boreal habitat of érachidacty/a and its consequently 
much longer migration accounts for its greater size, its longer 
wing and longer outer primary. The relatively less radiating 
power of its northern home, with a diminished amount of sunlight, 
has also assisted, besides the more tropical character of its winter 
home. Spring and summer specimens from the southern portion 
of its range are paler and more bleached than in more northern 
examples of even date. The more northern birds are also more 
shy and more difficult to secure. 
In occidentalis the 4th primary is often longer than the next on 
either side, the 3rd, 2d and rst graduating quite evenly in a 
manner not seen in true ¢richas. In the Mississippi Valley a less 
pronounced similarity is evident on birds from the western portion 
of the valley; but to the northeastward the outward primaries 
become longer and the wing contour merges into the typical of 
brachidactyla. Yhe great elevation of the habitat of occidentalis, 
from 2000 feet up, has produced its greater size. Its practically 
short migration permits it to retain the ancestral wing contour ; 
but in the more northern birds and those of the Plains the 3rd 
primary is often the longest, and the wings are slightly more 
pointed. 
In melanops we have a richer colored and yellower bird, due 
undoubtedly to its more tropical habitat, as shown in all the south- 
ern forms. Food is of course the prime factor in determining the 
amount and character of the pigment of these feathers, but we 
have little evidence as to its precise relation to color values. 
