BLUE-BELLIED LIZARDS. Sceloporus occidentalis Baird and Girard⁴⁰

Field characters.—Of typical lizard form. Tail (when not injured) slightly more than length of head and body. (See pl. 57b.) Scales on upper surface, and sides of body and tail, with conspicuous ridges or 'keels'; 51 or fewer scales in longitudinal row from back of head to line across back of thighs; scales on back of thigh keeled. General coloration above dark brownish or blackish, patterned with lengthwise rows of spots of blackish brown; under surface of body (especially in males) with more or less deep blue. Head and body 3 to 3-3/4 inches; tail 3-1/2 to 5 inches in adult males.

Occurrence.—Common almost throughout the region. Forage on trunks of trees, on fences, or on rocks.⁴⁰

The Blue-bellied Lizard is perhaps the best known of the typical lizards here in the west, being common throughout the settled districts of California, where it is known as the fence lizard. The two common names of the reptile just given refer respectively to the blue color on the under surface of the body in the male and to the animal's habit of coming out on rail fences and on similar above-ground structures upon which it can climb about and hunt for insects.

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⁴⁰Three subspecies of Blue-bellied Lizard live in different parts of the Yosemite region. Their general appearance is much the same, especially as compared with other lizards in the region, and but little is known concerning their life histories. For these reasons the three are treated together. The characters given below apply particularly to adult males, which sex may be distinguished by the presence of two enlarged plates on the under side of the tail behind the anal opening.

WESTERN FENCE LIZARD, Sceloporus occidentalis occidentalis Baird and Girard, the form which inhabits the northwestern half of California, is to be found in the western part of the Yosemite section, where it occurs from Snelling and Pleasant Valley eastward to, and including, Yosemite Valley. It may be distinguished by the greater amount of light color on the under surface of the hind limbs, on the chest, and between the dark patches on the belly. Also the blue patch on the throat is divided, as a rule, not solid. This and the following subspecies are ordinarily to be seen on tree trunks, fences, logs, and boulders.

PACIFIC BLUE-BELLIED LIZARD, Sceloporus occidentalis bi-seriatus Hallowell, the subspecies common in southern California, reaches the eastern end of the Yosemite section around Mono Lake. Our party took specimens at Mono Lake Post Office. It is characterized by somewhat larger size than the preceding and by darker coloration on the under surface. The thighs, middle of belly, and chest are gray or blackish, and the blue patch of the chin is never divided in the mid-line.

TENAYA BLUE-BELLIED LIZARD, Sceloporus occidentalis taylori Camp, is a subspecies known at present only from the high country about Merced and Washburn lakes, Tenaya Lake, and Glen Aulin, and from Little Yosemite Valley. It is recognizable at once by its solidly bluish black under surface and dark back (without conspicuous spotting). The highest station of observation, on the ridges above Merced Lake toward Mount Clark, was 8800 feet in altitude. This subspecies is to be seen chiefly on sunlit granite boulders.

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Under original conditions the Blue-bellied Lizards lived chiefly upon and around rocks and trees, and this is still true in most of the Yosemite region. The Tenaya Blue-bellied Lizards of the higher altitudes are almost exclusively rock dwellers, whereas the Fence Lizards at the lower levels on the west slope inhabit tree trunks, downed logs and, of course, rail fences where these are available. Only seldom are these animals to be found on the ground. There is thus with lizards, as with other vertebrates, an ecologic segregation. The present species inhabits places above ground, while skinks, whip-tails, and alligator lizards live on the ground. In the high mountains the Tenaya Lizard when active resorts to the granite boulders, while the Mountain Lizard (Sceloporus graciosus) is chiefly terrestrial, and the Mountain Alligator Lizard strictly so.

Fig. 61. Cross-section of the Sierra Nevada through the Yosemite region showing the distribution of some reptiles and amphibians which are either restricted to or find their maximum abundance in single life-Zones. (click on image for an enlargement in a new window)

The fences built about pastures in the forest belt, especially those made of split rails, are often occupied by numbers of these lizards. On one occasion a member of our field party, while working in the neighborhood of the McCarthy ranch east of Coulterville, estimated that there was one lizard to every 50 feet of a given fence.

In the territory occupied jointly by the Mountain Lizard (Sceloporus graciosus) and representatives of the present group, the Blue-bellied Lizards outnumber the smaller species. On the upper parts of the boulder talus along the north side of Yosemite Valley beneath Eagle Peak the proportion was about 25 of occidentalis to 10 of graciosus. On a trip to Clouds Rest, from 6 to 12 Tenaya Blue-bellied Lizards were noted to each Mountain Lizard.

Fence Lizards are abroad and active during all the warmer months of the year, but they spend the winter season, even at the lowest altitudes, in hibernation. On January 8, 1915, two were found in a damp place beneath a log at Snelling, "stiff in hibernation," as the collector says in his notes. As soon as the days of spring come, with the sunlight and warmth which induces growth in plants and activity in insects, these lizards begin to venture forth from their winter retreats. At first they are abroad only for a short time during the warmest of the mid-day hours, but by the middle of summer in the foothill country they are active at, or shortly after, sun-up and thenceforth throughout the day, even until well after sundown. In Yosemite Valley in 1916 several were abroad at the end of April, and at El Portal they were out in numbers on May 2 the same year. The latest seasonal record is of several abroad at Sweetwater Creek on October 28 (1915).

With the Tenaya Blue-bellied Lizard in the higher altitudes the season is shorter. Our earliest record for the species is May 16 (1919), when one was seen at Sierra Point. On May 18 that year numbers of males were in evidence in Little Yosemite Valley. A note made on August 28, 1915, near Washburn Lake states that these lizards had not become active until about 9 o'clock in the morning. The last appearance of the species seasonally, in 1915, was on October 1, when one was obtained at 7300 feet in the Tuolumne Cañon below Glen Aulin.

The male Blue-bellied Lizard has a curious habit of alternately raising and lowering the forepart of the body by straightening and then flexing the fore legs. When the body is lifted up in this manner the coloring on the under surface may be glimpsed. Once, in Little Yosemite Valley (May 18, 1919) several males (of subspecies taylori) were seen going through an even more elaborate performance than that just described. These particular lizards had puffed out their bodies and throats to about twice their natural size. Then they worked up and down several times on all four legs. Thereafter they deflated somewhat and continued the exercise, on the front legs alone. Although this movement is common, its purpose is as yet without a satisfactory explanation. From the momentary display of the bright color on the under surface of the body one might infer it to be a courting antic, comparable to the spreading of wings and tail, with consequent exhibition of bright markings, which is to be seen in many species of birds in the mating season.