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Reptiles and Amphibians of Yosemite National Park (1946) by Myrl V. Walker


If we were to ask the average person how he distinguished the lizards from the snakes he would probably reply that the lizards are reptiles which have four legs and can run over the ground, while snakes are legless and only crawl. This happens to be true for the lizards found in Yosemite National Park, but in other sections of the United States there are legless lizards, lizards with only two legs, and lizards that are not only without legs, but in addition are blind and burrowing. A more careful observation of lizards and snakes will reveal that the lower jaw bones of all lizards are solidly joined in front, while in the snakes the lower jaws are held together by a somewhat elastic type of cartilage. A further difference which may be observed between the lizards and snakes of Yosemite is that the lizards have eyelids which they can close over the eye, while the snakes are without these movable eyelids. This distinction does not hold true in other sections of the United States.

A majority of the lizards deposit eggs which are left to hatch without further attention from the parent; however, a few lizards produce their young alive. Included in this latter group are some of the horned lizards, commonly but erroneously called horned toads.

Nearly everyone is well acquainted with the fact that a number of the lizards easily break off or “throw” their tails when roughly handled or pursued by an enemy. This seems to be a method of self preservation and does no particular harm to the lizard, for it will in time proceed to grow another tail, although the new member may be slightly smaller and with scales more variable in size and character.

Although some of the lizards are herbivorous, they are for the most part insectivorous and few people ever stop to realize their economic value in the control of insect pests. All forms found in Yosemite are prolific insect eaters and are active mostly during the daylight hours. Lizards are cold blooded and must of course hibernate during the cold winter months when temperatures drop below certain levels of tolerance.

Lizards are very interesting and are easily studied, but they are difficult to maintain in captivity for any great length of time. Many will attempt to bite if roughly handled, and their small sharp teeth may puncture the skin and draw blood, but otherwise they are harmless. In fact, the only poisonous lizard in the entire United States is the Gila monster which is found in the arid and desert regions of the southwest.

The different species of lizards are not so abundant in Yosemite National. Park as they are in areas that are warmer and more arid, so that we are able to list only nine species native to this area. Even one of those may have reached the park as a result of being introduced by man.

Sceloporus (See key for species)

In Yosemite everyone is aware of the existence of a number of small lizards commonly called by such names as spiny swifts, scaly lizards, fence lizards, or blue-bellied lizards. They belong to the genus Sceloporus and because they are so much alike few people ever try to distinguish the different forms. For that reason no attempt is made to discuss each species separately but all are considered in a general manner.

Four species of Sceloporus are found in Yosemite National Park. Three of them are closely related and are grouped into the blue-bellied lizard division, while the other one is commonly called the mountain lizard, although perhaps a better name might be brush lizard. The name blue-bellied lizard is of course descriptive and refers to the blue under-markings so characteristic of this form. The name fence lizard is applied to one species because cf its interesting habit of congregating in the vicinity of or on rail or log fences. Here these lizards climb about either to sun themselves or to secure certain insect food.

The three species of blue-bellied lizards seem to have each selected a particular niche in the Yosemite region. The western fence lizard is found in the lower elevations on the western side of the Park, up to and including the floor of Yosemite Valley. The Pacific blue-bellied lizard tends to occupy the space above the fence lizard, that is, from the Yosemite Valley up to and including

[click to enlarge]
From Slevin: The Amphibians of Western North America. Courtesy of the
California Academy of Sciences
the areas with elevations comparable to the rim of the canyon. Here it shares this zone with the mountain lizard; however, the latter is definitely an underbrush or ground form, while the former is at home among the big talus boulders or on the rough rocky areas at this elevation.

The third species of blue-bellied lizard, the Tenaya blue-bellied lizard, is a large form occupying a rather limited and restricted zone of higher elevation in the vicinity of Merced Lake, Washburn Lake, Tenaya Lake and Glen Aulin. It is apparently well adapted to the open and well lighted areas of glacially polished rocks at this elevation. This last species is of particular interest in view of the fact that Yosemite National Park has been designated as the type locality for this form.

The Sceloporus lizards are all small, the mountain lizard seldom reaching a length of five inches. The blue-bellied lizards are larger, being from six to eight inches in length, with the body averaging from three to four inches and the tail from three to five inches. All are covered with small scales and the dorsal scales usually have a ridge or “keel” running down the center of the scale which ends in a short but sharp projecting spine. This is soon discovered when one attempts to rub them the “wrong” way.

The Sceloporus lizards, like many of the other lizards, have that ability to break or throw their tails when attacked by an enemy, and to regenerate or grow a new tail just in case such an emergency might arise again. These lizards are of economic value because of the large number of insects they destroy. But they are in turn preyed upon by several of the snakes and by some of the hawks, owls, and shrikes.

Phrynosoma blainvillii frontale

The small horned lizard, more commonly called horned toad, seldom exceeds three to four inches in total length. It is probably better known to the average person than any other of our North American lizards. Its flattened form and peculiar appearance with its set of tiny sharp pointed horns are so distinctive that it is usually recognized at a glance.

It ordinarily dwells in the more open, arid, rocky and sandy areas, and where the temperature remains rather warm. Few places in Yosemite offer the ideal habitat for this lizard, and although a few specimens have been taken on the floor of the Valley, it is questioned whether or not these should be considered valid records. It is feared that the specimens might have been carried in by some tourist who, later tiring of the “pets,” turned them loose in the Valley where they were able to maintain themselves long enough to be observed by several people, and occasionally recaptured and added to the research collection.

These small lizards feed on a variety of small insects, especially ants, and for that reason they are easily kept in captivity. They will soon become very tame and will

[click to enlarge]
From Slevin: The Amphibians of Western North America. Courtesy of the
California Academy of Sciences
even take small insects such as flies or beetles from the fingers. Although they often live in very arid regions, they will take water readily when in captivity.

Unlike some of the other horned lizards, this species deposits eggs instead of producing the young alive, although it is believed that the eggs hatch very shortly after being laid.

The horned lizards or horned toads are probably best known for their peculiar habit of “squirting blood from their eyes,” and the California horned lizard seems to be one of the best performers in this respect. Many people have looked in vain for the place where a horn had supposedly punctured the skin and drawn blood on the hand of a person holding a specimen. Little did they realize that the tiny drops of blood had been forcibly ejected from the delicate eye membranes of the horned lizard, perhaps because it was very much irritated or unusually angry.

Gerrhonotus (See key for species)

The two species of alligator lizards found in Yosemite National Park are very similar in general appearance and are therefore not considered separately in this bulletin. The alligator lizards are the largest lizards in the Yosemite region. They sometimes reach a length of twelve inches. Although some whip-tail lizards may also measure up to twelve inches, they are much more slender and with a shorter body and longer tail than the alligator lizards.

The common name alligator lizard is quite applicable for these lizards surely resemble a small alligator, not only in their general appearance, but in their actions as well. When fully grown the head is large and wider than the body and gives them a look of ferocity. The scales are relatively heavy and thick for a lizard of this size, and the lengthwise series are very distinct. Because of their short and rather weakly developed legs and feet, they move somewhat awkwardly and with a wriggle or crawl that has caused them to receive the common name of snake lizard.

They live up to their ferocious appearance by being rather irritable, and they will charge and strike at almost any object that is moved into a position before them. They have a series of sharp pointed teeth, but they are so short that they will seldom draw blood unless the lizards are aroused to the extreme by handling or abuse.

These lizards seem to be most active in the late afternoon or evening, at which time they come from their shady retreats or shelters under brush or low growing trees and shrubs to forage largely on insects. They do not venture far into the open but keep within “a dash or two” of cover or protection. They usually remain on the ground, but in dense thickets or fallen underbrush they have been observed climbing through the twigs apparently in search of insect or other food.

The alligator lizards have a long slender tail which is easily “parted” when attacked by their enemies; however, the power of regeneration soon produces a tail nearly as long as the first one, but the new part seems to be poorly supplied with nerve fibers and not capable of the spasmodic jerks for attracting an enemy like the original caudal appendage.

A few differences between the two species are perhaps worth mentioning. The two species seem to occupy different altitudinal ranges in the Park with the San Diego alligator lizard being found in the Yosemite Valley and below, while the Sierra alligator lizard ranges from the Valley up to elevations as high as Washburn or Merced Lakes, and even to 10,000 feet on the west ridge of Red Peak. If live specimens are available for observation, the two species are easily distinguished by eye color, for in the San Diego alligator lizard the iris of the eye is yellow and without dark pigment, while the eye of the Sierra alligator lizard is dark and appears nearly black. A further difference is the fact that the San Diego alligator lizard deposits eggs, while the Sierra alligator lizard produces the young alive. This seems to be the natural specialization of those forms ranging into the higher and colder elevations where damp and cold habitats would greatly hinder or prevent the hatching of eggs.

The alligator lizards belong to the interesting family known as the Anguidae. They are poorly represented in North America. Some of their closest relatives are the strange glass-snake or joint-snake of the eastern portion of North America, and the small limbless, burrowing lizard of the Pacific Coast region.

Cnemidophorus tessellatus tessellatus

The whip-tailed lizard is found only in the extreme western portion of Yosemite National Park and barely reaches the lower end of Yosemite Valley. These lizards are ordinarily considered most at home in the arid and more desert types of country; however, a few individuals occupy the foothill regions and lower valleys. Typical habitats are not present in Yosemite National Park, but a few specimens have been taken from the more open, sandy and warmer sections along the western boundary.

The whip-tailed lizard is the swiftest of all the lizards in this region. Because of its specialization in slender body form, long slender tail, and modified leg and foot—such modifications all assisting in the attainment of speed—it is well known and readily recognized by all those who are the least interested in natural history. Its habit of lifting its tail off the ground and actually using it as a rudder or counter-balance when running rapidly is an especially interesting adaptation. When these lizards are seeking food they move cautiously but somewhat “jerkily,” and at that time they drag their long slender tails, so that they leave an interesting but characteristic “trail pattern” when moving over fine dry sandy soil.

The head and snout is long and slender. They have a habit of “poking” the sharp pointed snout into holes or crevices and at the same time darting out their delicate tongue. The body measures only three to four inches, but the tail reaches a length of from seven to ten inches, thus giving them an overall length of from ten to fourteen inches.

The whip-tail lizard feeds largely on insects such as grasshoppers, ground beetles, spiders, ants, larvae and so forth, and they seldom if ever leave the ground to crawl into brush or trees or even up and over the larger boulders. They most certainly are typical ground dwellers. They are abundant and widely distributed over most of the plains, prairie and sandy desert country of North America, and they exhibit such great variations in marking and scale characteristics that they are one of the most perplexing divisions of the lizard group in this country.

They are easily distinguished from all other lizards in Yosemite National Park by the fact that they have eight lengthwise rows of fairly large, rhomboid-shaped belly scales, while all other of our lizards have numerous rows of relatively small belly scales.

Eumeces gilberti gilberti

Because of its change in color pattern from young to adult, and because of the irridescent play of color often observed on the smooth and shiny scales, this lizard is one of the most interesting in Yosemite National Park. Its habits are such, however, that very few people ever have the opportunity to see these lizards except in cages or preserved collections. These lizards, commonly called “skinks,” seldom venture far from shelter. They seem to remain under cover most of the day but come out into the open to forage for food in the late afternoon or evening. Their food is composed largely of

[click to enlarge]
N. P. S. Photo by Anderson
insects which they locate on the ground among piles of dead leaves and down brush, or amongst the rubbish accumulated in the cracks between large boulders.

For a shelter they usually seek out thin flat rocks on fairly open hillsides, and several specimens may sometimes be located under a single slab of shale. They also take advantage of fallen logs, and may be found under the rotting logs, or even between the loosened bark and the log itself.

It is believed that these lizards deposit only a small number of eggs, and there is some indication that the females may curl up around the eggs and thereby assist in their incubation.

The skinks seem to be well adapted for quiet movement through fallen leaves or underbrush. The head is long and slender and merges into the body without any noticeable change. The body continues evenly and the tail tapers gradually. The legs are short and closely set. The scales are very smooth and glossy, and sometimes in bright sunlight, show an interesting display of irridescent coloring. Their entire makeup enables them to glide and wriggle their way through leaves and debris with ease and with hardly a perceptible rustle.

The young are marked so differently from the adults that in the past some difficulty was encountered in recognizing the different species. The young or immature Yosemite skink is dark brown to nearly black, but with four sharply defined light lines or stripes along the back. The belly side is pale blue to whitish but the tail is often brilliant blue, this latter characteristic often attracting immediate attention. As these skinks mature, usually during the second or third year, they gradually change color. The head becomes reddish to copper in color; the body turns brown to olive-green; they lose their stripes entirely, and the tail becomes somewhat greenish. These colors, unfortunately, often change or fade considerably in museum specimens kept in strong preservatives.

Although Eumeces gilberti was first recognized and described by Van Denburgh in 1896, and was the first species of vertebrate to have ” Yosemite National Park designated as its type locality, it was lost in the synonomy of Eumeces skiitonianus until brought out again by Taylor in 1936.

Skinks in our Museum collection have been taken in or near the following locations: Tenaya Canyon, Yosemite Valley, Mirror Lake, Bridalveil Fall, Mather Ranger Station, Arch Rock Ranger Station, foot of El Capitan, near Swamp Lake, Miguel Meadows, and near the Government Center. In the summers of 1944 and 1945 both adults and young were observed on several occasions emerging from behind the large Sequoia section just to the right of the Museum door.

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