HUTTON VIREO. Vireo huttoni huttoni Cassin

Field characters.—About half size of Junco; tail decidedly shorter than body. Plumage nearly uniform greenish olive, only slightly darker above than below; eye partially surrounded by light color; two pale bars on wing (pl. 50c). Movements deliberate; does not habitually twitch or flutter wings as does Kinglet. Voice: Song of male a hoarse, drawling zee'-ey, zee'-ey, zee'-ey; and again, zi-ew; zi-ew, zi-ew; these notes intoned monotonously in long series; there is also a low harsh call note.

Occurrence.—Fairly common resident locally in Upper Sonoran and lower Transition zones on west slope of Sierra Nevada. Observed near Coulterville, about El Portal, in Yosemite Valley, and at Gentrys. Lives almost exclusively in live oaks and golden oaks. Solitary or in pairs.

Four species of vireos or 'greenlets' are found in different portions of the Yosemite section during the summer months, but only one, the Hutton Vireo, remains in the region through the winter as well. This vireo is almost exclusively an inhabitant of the live oaks and golden oaks and this choice of habitat is doubtless the basis for the continuance of the bird here during the winter moths. These 'evergreen' oaks furnish forage in the form of insects throughout the year, as is shown by the number of warblers and kinglets which resort to these trees during the colder months. The Hutton Vireo, by being restricted to this type of tree, is assured of food in all seasons, and does not need to migrate.

The Hutton Vireo is the greenest of our four species. It is smaller than the Cassin and the Warbling and larger than the Least Vireo, and although it resembles the Cassin in possession of a light eye ring and two bars on the wing (pl. 50c), its much greener coloration makes it readily distinguishable from that gray and white-toned species. Its voice is absolutely distinct from that of any of the other three.

The Hutton Vireo bears a remarkable resemblance to the Ruby-crowned Kinglet. The two species are of about the same general tone of coloration and have in common a light eye ring and two light bars on the wing; but the vireo is somewhat larger, has the appearance of big-headedness and has no bright crown-patch such as is worn by the male kinglet. In demeanor the two birds are at most times strikingly different, and the voices are not likely to be confused at all. The deliberate vireo occasionally flutters its wings but never so frequently or nervously as does the smaller bird. During the winter season both of these birds are to be found in the oaks, and so, on occasion, may be compared in life, side by side.

The range of the Hutton Vireo within the Yosemite section is not extensive. The westernmost station at which we observed the species was Blacks Creek, west of Coulterville, and the easternmost was the talus slope on the north side of Yosemite Valley, near Rocky Point. In the winter of 1914 (December 28), one was recorded at 4500 feet altitude on the Big Oak Flat road, and on October 21, 1915, one was found at Gentrys, 5800 feet, also on that road. The species was seen in greatest numbers at El Portal, probably because of the abundance of evergreen oaks in the vicinity.

The restriction of the Hutton Vireo to oak trees seems to be practically complete; not one of our ten recorded observations of the species list it as being seen elsewhere than in one or another kind of these trees. It forages occasionally in black oaks, but more commonly in the non-deciduous oaks. In Yosemite Valley, individuals were discovered by following up the characteristic monotonous drawling song, in June, July, and December. All observed were at the lower end of the valley, west of Yosemite Falls.