The details of structure taken from No. 23,785, of color from No. 23,788: Length, of 23,785 ♂, 4.80 when fresh, of skin, 4.25; wing, 2.25; tail, 2.25; bill above, .37; tarsus, .73; middle toe and claw, .50; hind toe and claw, .42. First quill, .70; second, 1.40; longest (fifth), 1.64. (Cape St. Lucas.)
Hab. Cape St. Lucas; San Diego; Fort Mohave, and Arizona; Sacramento, California (Ridgway).
This species scarcely needs comparison with any other, except, perhaps, V. pallens of Middle America, which, however, besides belonging to Vireonella, and not Vireo, as restricted, differs in many minor, but no less essential points. The coloration of the two is remarkably similar, but pusillus has
only one indistinct band on the wing, instead of two sharply defined ones. The bill is much smaller, and the tail longer, than in pallens. V. belli is less ashy above and less pure white beneath, the sides much more yellowish; the wing is also longer, and the tail much shorter. V. vicinior is much larger, with the wing longer than the tail, instead of shorter; the ash above has a bluish instead of a greenish cast; the lores are wholly grayish-white, etc.
Habits. The Least Vireo is a recently described species of its genus, and one in regard to whose history comparatively little has been ascertained. It was first met with at Cape St. Lucas by Mr. Xantus, and described by Dr. Coues in 1866. Dr. Coues assigns as its habitat Lower and Southern California, Sonora, and Arizona, at least as far north as Fort Whipple. Dr. Cooper also found it at Fort Mohave. Dr. Coues met with it fifty miles south of Fort Whipple, where he found it breeding abundantly. He gives no information in regard to its habits. Dr. Cooper states that he found it rather common along the upper part of Mohave River, in June, 1861; and in the following spring, about April 20, they began to arrive at San Diego in considerable numbers. In its habits Dr. Cooper thinks it greatly resembles V. gilvus, though it differs entirely in its song. The notes of those that he heard singing resembled very much those of the Polioptilas uttering a quaint mixture of the notes of the Wrens, Swallows, and Vireos. They also seem to possess more or less of imitative powers. At Sacramento he saw and heard, in the willows along the river, individuals which, from their peculiar notes, he had no doubt were of this species, but he did not verify his conjectures. His suppositions were confirmed later by the observations of Mr. Ridgway, who states that he found these birds the most abundant as well as the most characteristic Greenlet in the vicinity of Sacramento. It is a species, he adds, easily recognized, being in all respects quite distinct from any other. The character of its notes, as well as its habits, show it to be a true Vireo. Its song, though weaker, bears a great resemblance to that of the White-eyed. A nest of this species was found by him near Sacramento. It was placed about three feet from the ground, in a low bush in a copse of willows. Like all the nests of this genus it was pensile, being attached to and suspended from the twigs of a branch.
Two nests of this interesting species were also obtained near Camp Grant, Arizona, in 1867, by Dr. E. Palmer. They are wrought like all the nests of this kind, below the small forked branches of a tree, suspended from the extremity of its twigs. They each have a diameter of about three and a half inches, a height of two, with a cavity an inch and a half deep and two wide. The external portion, like the nests of the V. belli, is wrought with woven hemp-like vegetable fibres, strongly bound around the ends of the twigs and covering the entire exterior. Within this is placed a strong, firmly made basket, composed of slender strips of bark and long, fine, and flexible pine-needles, with a lining of finer materials of the same. In one of these nests
there were three eggs of the Vireo, and one of a Molothrus (obscurus?). The former were of a bright crystalline whiteness, marked with very minute and hardly discernible spots of red, and measure .69 by .56 of an inch. The egg of the Molothrus, except in its much smaller size, is hardly distinguishable from those of the common M. pecoris, and measures .75 by .56 of an inch.
In the other nest were also three eggs of the Vireo. They correspond in size, but are much more distinctly marked with larger spots of a dark red and reddish-brown. In this nest there is a somewhat larger proportion of fine strips of inner bark, and mixed with these are also a few silky insect cocoons, by means of which the nest is firmly bound around the twigs from which the whole is suspended.
Vireo vicinior, Coues.
ARIZONA VIREO.