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REPORT OF THE CHIEF OF ENGINEERS. 
orbital ring, instead of being pure white, are of a dull white, strongly inclining to 
fulvous. The green of the sides is much mixed with or replaced by brown; the uni er 
parts generally are of an impure white, the result of a general admixture of brow n. In 
fact, extreme examples of cassini are colored so much like huttoni that upon a coloi 
basis alone it would be difficult to distinguish them. 
There are a sufficient number of specimens at hand showing the above characters to 
prove beyond a doubt that cassini is entitled to rank of some kind ; in other words, that 
it is not a mere accidental plumage of solitarius. For be it noted, as stated by Pro¬ 
fessor Baird of the type, that solitarius as it is colored in the East never approaches 
the above. The color peculiarities of cassini are to be regarded then as entirely beyond 
and independent of individual variation. But, to complicate matters, nearly every 
author who has had occasion to treat of Western birds has noticed specimens, evidently 
not typical cassini, which he has referred with more or less doubt to solitarius. thus, 
specimens of so-called solitarius are before us from Washington Territory, Oregon, 
California, Nevada, Utah, Wyoming, Arizona, &c. Some of these are certainly very 
close to solitarius, and I have always presumed the occurrence of that species in the 
West to be a matter that admitted of no doubt. But a recent careful examination 
of all these specimens shows not one that can fairly be called typical of that bird. 
In such specimens the back is of a varying shade of green; the head is more or less 
ashy in contrast, while the under parts are of a purer white than is the case with typ¬ 
ical cassini. It is to be remarked, however, that not only is it scarcely possible to find 
two of these doubtful specimens that agree 'with each other, but bv means of them a 
series can be formed that appears to grade directly from the typical cassini towards 
and almost, if not quite, into solitarius. The percentage of specimens.of which the 
statement holds good that they are more like solitarius than cassini is quite small. 
Nearly all the intermediate specimens are really identifiable with cassini; in fact, of 
twenty-nine specimens in the collection which have been labeled indifferently cassini 
and solitarius, I find that twenty are referable to cassini, and cannot by any means 
be identified with solitarius. Of the remaining nine, three are so nearly intermediate 
that they might with about equal propriety be assigned to either, leaving six with a 
decided leaning toward solitarius. It needs, however, but an instant’s comparison of 
these with the ordinary Eastern solitarius to show that although closely resembling 
that species, it would be going too far to say that they are typically the same. In 
connection with the rest of the series they are clearly intermediate, but on the solita¬ 
rius side of the line. 
The testimony of the series as a whole seems to show pretty conclusively that the 
solitary vireo proper does not occur in the West, aud that all specimens which have 
been so identified are either cassini or are intermediate betvveeu the two; the latter 
class, in fact, furnishing the evidence that the two inter-grade, and hence that cassini 
is a variety of solitarius. 
The only alternative would be to throw cassini out entirely aud refer all Western 
specimens to solitarius. But, in our judgment, typical specimens of cassini are now too 
numerous and show too decided and constant differences to warrant such a procedure. 
The habitat of Cassin’s vireo may receive a moment’s attention. Its summer home 
appears to be strictly limited to either slope of the Sierra Nevadas, from Washington 
Territory to Southern California. I can tiud no specimens (including under the head 
of cassini all individuals hitherto supposed to be solitarius ) from the Rocky Mountains 
in spring or summer* 
As a migrant in fall the occurrence of the Cassiu’s vireo in the latter range is not sur¬ 
prising, or no more so than that of several other Sierra Nevadan birds, as Junco hyemalis, 
Turdus pallasi nanus, Dendroica townsendi, aud occidental^ , &c. 
I have alluded in a foot-note below to a specimen, the coloratiou of which is inter¬ 
mediate between solitarius aud plumbeus. Such specimens do not appear to be as com¬ 
mon as in the instance of the Cassin’s vireo, but I have seen too many such to render 
the relationship of the two former birds at all doubtful in my own mind. With its 
notable increase of stature, and the laying off of nearly all the bright tints that dis¬ 
tinguish solitarius,plumbeus might well pass for a different species, but for the fact that 
specimens of unquestionable intermediate character have been repeatedly taken; so 
that consistency would seem to demand that its near relationship to solitarius should 
be formally as well as tacitly admitted. Although this race possesses au average 
size considerably in excess of solitarius, the latter occasionally leads well up to its 
smaller individuals. Turdus pallasi, with its race auduboni, furnishes precisely the 
same phenomenon of increase of size coincident with a mountain habitat. 
Of the two Western varieties of the solitary vireo, plumbeus appears to be the best 
marked. This is not because typical examples of it are any more readily recoguizable 
than of cassini, but because intermediate specimens of the former appear to be fess com- 
* A specimen, Xo. 11,004 of Xat. Mus. Res., taken at Fort Bridger in May by Drexler, was labeled 
solitarius and so referred to by authors. This I ascertain upon examination to be the plumbeous 
vireo ( \ . solitariusplumbeus). Its colors are those of plumbeus, with the addition of a slight admixture 
of green, it being in fact intermediate between that form and solitarius. 
