WESTERN SKINK. Plestiodon skiltonianus Baird and Girard

Field characters.—Scales flat, thin, and not ridged or beaded, overlapping (shingled) and forming a very smooth body covering; body and tail evenly tapered to slender tip of tail; both pairs of legs short, scarcely longer than diameter of body (pl. 58a). Adults: Head coppery red; body olive brown above, bluish green on sides, pale beneath; tail pinkish red (pl. 12c). Young: Head and body dark brown, with two sharply defined yellowish stripes along back; under surface pale blue; tail brilliant blue (pl. 12b). Total length of adults: Head and body up to 4-1/8 inches, tail to 6-3/8 inches.

Occurrence.—Common resident throughout western part of Yosemite section, from Lagrange and Pleasant Valley eastward to Yosemite Valley. Forages in shaded places, in leafy debris in thickets and under trees; has retreats under stones, logs, boards, etc., and down rodent burrows.

Most interesting among the several species of lizards in the Yosemite region is the Western Skink, a peculiarly smooth-bodied reptile, notable for its brilliant coloration and for the great difference in color pattern between young and old individuals. (See pl. 12b, c.)

The young are commonly referred to by naturalists as "blue-tailed skinks," since the tail is bright blue. The back of the young is dark brown, relieved by two long stripes of golden yellow. The adults, on the other hand, show no trace of blue on the tail and seldom any indication of striping on the body. The tail in the older animals is salmon pink, the head coppery red, while the body is plain greenish olive. A greater age contrast in one species could scarcely be imagined. This sharp difference in coloration led to the description of the "red-headed skink" of the Yosemite Valley as a distinct species, Eumeces gilberti (Van Denburgh, 1896, pp. 350-352). The entire absence of small (that is, young) individuals of the "red-headed" skink and of very large "blue-tailed" skinks, the capture of several individuals of intermediate size and coloration (green-bodied yet with indications of striping), and the fact that in a related species of skink inhabiting eastern North America a parallel change in coloration is known to occur, lead now to the conclusion that the two 'forms' found in the Yosemite region are but different phases of growth in one and the same species. In the northwestern part of California only the striped-backed, blue-tailed phase of the skink is known to occur.

The Western Skink is conspicuously smooth-bodied. The head merges imperceptibly into the 'shoulder' region, and the body and tail are evenly and finely tapered to the slender tip of the latter. The scales everywhere are thin and lie so closely against the body that the animal can slip through a person's fingers as if oiled. It can also slip through the piles of dead leaves, in which it often seeks its insect food, with the greatest ease. The legs are small and short, particularly in the adult, where they scarcely exceed in length the greatest diameter of the body. Locomotion is accomplished more by wriggling or squirming movements of the body than by use of these diminutive legs. The tail of the skink, as in most other local lizards, will break off if the animal be handled roughly, and will wriggle interestingly for some time. Individuals are sometimes met with in nature in which the tail has been broken off and later partly regenerated. Such animals can be recognized by the stubby form of the tail.

The local range of the Western Skink extends from the westernmost rocky outcrops on the foothills near Lagrange and Pleasant Valley eastward to Yosemite Valley. In the latter place the skink has been found as high as 4500 feet, at Inspiration Point (Van Denburgh, loc. cit.). A dried skin of this species was picked up at Snelling by one of our party, but otherwise no evidence of its existence out on the plains of the San Joaquin was forthcoming.

Skinks are in the main cover-seeking reptiles. They do not often forage in the open; they may come out, however, toward twilight of warm summer days. The rock fences built in many parts of the foothill country afford admirable shelter and forage grounds for many of these lizards, as does likewise the boulder talus along the north wall of Yosemite Valley. In the latter place, however, the skinks live on the ground between the rocks, in the debris consisting of accumulated oak leaves and pine needles; they do not go out on the surfaces of the rocks as do the swifts (Sceloporus occidentalis). Skinks are also to be found beneath fallen tree trunks or in slight excavations (burrows of other animals probably) under rocks lying on open ground. Logs or rocks in pastures or on grassy hillsides quite often afford retreats for one or two of these lizards. In the 'mother lode' district some individuals take shelter in the heaps of shale at old prospect holes.

Several skinks were obtained in mouse traps set on the ground under bushes for the capture of small mammals. These particular individuals either stumbled into the traps or else were attracted secondarily by ants and other insects which had gathered to feed on the bait (rolled oats). Still other individuals were obtained when we tore open dead and rotting tree trunks lying on the ground.

Western Skinks, particularly the blue-tailed youngsters, are able to run with considerable speed when frightened and upon open ground. But the normal movements, especially of adults, are rather slow and heavy. On several occasions we had chances to watch individuals which were undisturbed and engaged in foraging. The animals moved in a hesitating manner, proceeding this way and that, advancing and then remaining quiet for a second or two, usually going around rather than over small rocks and other obstacles, even if of less than an inch in height. These particular lizards kept their heads close to or even upon the ground, and one in the course of its meanderings was seen to snap up small insects from time to time. One red-headed skink was seen gliding over the surface of a black-oak log in strong sunlight, one afternoon in June. As the animal breathed a shimmering play of light was reflected from its smooth scales.