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


FROGS

The frogs, unlike the toads and tree-toads, must always remain close to permanent pools of water. Although their skin allows them to leave the water temporarily and to bask on floating logs or debris, they must ever so often moisten themselves by plunging into the pool. When it comes to the matter of protection, frogs are far more dependent on pools of water than are the toads and tree-toads, for they escape from most of their enemies by diving into the water and hiding either under rocks, or going down to the bottom of the pool where they either partially or completely bury themselves in the muddy ooze and are lost to the sight of most enemies.

Unlike the toads, they are not warty nor do they carry an extra supply of water with them. They do not have digging tools on their hind feet, nor have they developed any poison glands comparable to the toads. They are far more at home in water than on land, and their long hind legs push them through the water with remarkable speed.

Nearly everyone has at some time or another seen the large jelly-like masses of frogs eggs in quiet streams or pools, and upon returning a few days later, noticed the great number of tiny tadpoles. In the warmer regions these larva mature at the end of the first summer, but in the higher and colder elevations, where the summer seasons are short, they pass the first winter as tadpoles, becoming adults some time the second summer.

Three species of frogs are found in Yosemite National Park, although one form is confined to the lower elevations. One of these frogs reaches sufficient size to be considered of some value for food, and outside the Park these frogs have sometimes been collected in large numbers and furnished to the markets. The other two frogs found in the park are much smaller and are of economic value only because of the number of insects or insect larvae they destroy, or in their value as fish food. It has been found that trout in the higher mountain lakes and streams feed heavily on the small frog tadpoles, and in many instances, sooner or later, almost eliminate the frogs from these lakes.

CALIFORNIA RED-LEGGED FROG
Rana aurora draytonii

CALIFORNIA RED-LEGGED FROG
[click to enlarge]
From Slevin: The Amphibians of Western North America. Courtesy of the
California Academy of Sciences
CALIFORNIA RED-LEGGED FROG

The California red-legged frog is by far the largest frog found in the Yosemite National Park. They sometimes measure four or five inches in length. The adults may be readily identified by the red and pink markings on the underside and inner side of the big hind legs. They are light to dark hi-ewe above and with large or small black spots on the dorsal surface and on the thighs. They appear to be much more hump-backed than the other two species of frogs found in Yosemite.

The red-legged frog seems to show a preference for the big ponds alongside streams that are filled to their maximum during the high water and flood stages in the spring. They seem to he more of a pond or lake frog, rather than a stream frog, and seldom are found in association with swiftly running water.

The California red-legged frog does not appear to be very abundant in Yosemite National Park, and thus far has been found only in the lower elevations: in fact, our first museum accession of this frog was not made until 1938 when specimens were taken at Swamp Lake. Other specimens have since been taken in Miguel Meadows and Sand Pit Lake. Perhaps careful collecting will prove that this frog is more widespread than our records thus far have seemed to indicate.


YELLOW-LEGGED FROGS
Rana (See key for species)

CALIFORNIA YELLOW-LEGGED FROG
[click to enlarge]
Photo courtesy Calif. Acad. of Sci.
CALIFORNIA
YELLOW-LEGGED FROG

These two species of frogs appear to be so closely related that it seems unnecessary to treat them separately; hence they are discussed only in a general manner. They are moderate sized frogs with an average length of three inches or less. They are blackish, dark green or brown above, and with a few rather indistinct markings. The markings on the underside are more distinctive, being yellow or whitish, with the yellow underside of the hind Legs being their most diagnostic characteristic. The most apparent characteristics which distinguish the two species are as follows:—The California yellow-legged frog has an ear membrane which is quite rough and with a “pebbled” texture; the hind leg is rather long, and in addition this frog lives largely below 6,500 feet in elevation. The Sierra yellow-legged frog has an ear membrane which is relatively smooth, not pebbled; the hind leg is only moderately long, and they live at elevations mostly above 6,500 feet.

The range of the California yellow-legged frog, especially in the lower elevations, allows it to remain active throughout the entire year, but the Sierra yellow-legged frog must hibernate for long periods either along the shore lines or in the bottom of muddy pools and lakes in the high alpine country. These streams and lakes are sometimes almost completely frozen for several of the mid-winter months.

SIERRA NEVADA YELLOW-LEGGED FROG
[click to enlarge]
Photo courtesy Calif. Acad. of Sci.
SIERRA NEVADA
YELLOW-LEGGED FROG

The yellow-legged frogs are probably the most common amphibians of Yosemite National Park, especially in the vicinity of streams, pools, and lakes; and furthermore, they range from the lowest elevations up to 11,500 feet where specimens have been taken in the small lake near the base of Mount Lyell. They are of course most abundant along stream banks and lake shores as all fishermen and hikers are well aware, not because they see the frogs, but rather because they hear them as they “plunk” into the water, one after another, to find shelter and protection.



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