272 Birds of Colorado 
of trees, whence it darts out after its insect prey. Some 
controversy seems to have arisen in regard to the 
situation of the nest : Aiken states, as is the case with 
the eastern bird, it is usually saddled on the outer fork 
of a horizontal bough, and in plain sight. It is somewhat 
deeper and more strongly constructed than that of the 
eastern bird, and is covered externally with leaves and 
bark, not, as a rule, with lichens. Fresh eggs are to be 
found at low elevations in the middle of June; but at 
Twin Lakes, Scott took a nest with three eggs on July 
llth. These, generally three in number, are white 
to pale cream, spotted and blotched with reddish. 
They cannot be distinguished from those of the eastern 
bird. 
Genus EMPIDONAX, 
Small Flycatchers—wings measuring from 2-25 to 3-25—with broad, 
flattened bills, the width of which across the nostrils is about equal 
to the culmen; wings long and pointed, the tenth (outer) primary 
between the fourth and sixth, the ninth to seventh the longest; tail 
even or slightly emarginate, shorter than the wings, generally about 
* to 8; legs and feet of normal size, the tarsus from +? to } the 
length of the wing, always exceeding the culmen and middle toe and 
claw. 
About thirty species and subspecies have been recognized, spread 
over the greater part of America, except the West Indies. Seven of 
these have been taken in Colorado. 
The members of this genus have a very similar coloration, varying 
from olive to dark grey above and from pale yellow to whitish-grey 
below ; they are also very nearly of the same size, and are consequently 
difficult to discriminate ; the following key, therefore, should be used 
with caution, and the description in all cases referred to before a 
satisfactory conclusion can be reached. 
Key oF THE SPECIES. 
A. Yellow wash of under-side richer, and distinctly extending over 
the throat ; size large (wing 2-85); tail emarginate. 
E. difficilis, p. 273. 
B. Yellow wash of under-side paler, not extending over the throat, 
which is markedly white. 
