216 
SLATE-COLOURED HAWK. 
irregular, and swiftly ; preys on lizards, mice, and small birds, 
and is an active and daring little hunter. It is drawn of full size, 
from a very beautiful specimen shot in the neighbourhood of 
Philadelphia. The bird within his grasp is the Tanagra rubra , 
or Black-winged Red-Bird, in its green or first year’s dress. 
In the spring of the succeeding year the green and yellow 
plumage of this bird becomes of a most splendid scarlet, and 
the wings and tail deepen into a glossy black. For a particular 
account of this Tanager, see Vol. I. p. 192, of the present 
work. 
The great difficulty of accurately discriminating between 
different species of the Hawk tribe, on account of the various 
appearances they assume at different periods of their long 
lives, at first excited a suspicion that this might be one of 
those with which I was already acquainted, in a different 
dress, namely, the Sharp-skinned Hawk just described; for 
such are the changes of colour to which many individuals of 
this genus are subject, that, unless the naturalist has recourse 
to those parts that are subject to little or no alteration in the 
full grown bird, viz. the particular conformation of the legs, 
nostril, tail, and the relative length of the latter to that of the 
wings, also the peculiar character of the countenance, he will 
frequently be deceived. By comparing these, the same species 
may often be detected under a very different garb. Were all 
these changes accurately known, there is no doubt but the 
number of species of this tribe, at present enumerated, would 
be greatly diminished, the same bird having been described 
by certain writers, three, four, and even five different times, 
as so many distinct species. Testing, however, the present 
Hawk by the rules above mentioned, I have no hesitation in 
considering it as a species different from any hitherto described; 
and I have classed it accordingly. 
The Slate-coloured Hawk is eleven inches long, and 
twenty-one inches in extent; bill, blue black; cere and sides 
of the mouth, dull green; eyelid, yellow; eye, deep sunk 
under the projecting eyebrow, and of a fiery orange colour; 
upper parts of a fine slate ; primaries, brown black, and, as 
