664 ANIMAL LIFE IN THE YOSEMITE 



The Yellow-legged Frog is the commonest amphibian in most parts of 

 the Yosemite section. Its total range is slightly less than that of the Pacific 

 Tree-toad; but its numbers, especially at the higher altitudes, far exceed 

 those of the smaller species. This frog is the species most likely to come 

 to the attention of fishermen and others who may walk along the banks 

 of Sierran streams and lakes. 



The Yellow-legged Frog may best be identified by the characters which 

 it lacks when compared with other species of frogs and toads from the 

 same region. (See pi. 60&.) It differs from the Spadefoot in having a 

 round instead of an elliptical pupil, from the California and Yosemite 

 toads in the absence of enlarged glands on its shoulders and of prominent 

 'warts' on the back, from the tree-toad in not having expanded adhesive 

 discs on its fingers, and from the Red-legged Frog in having no dark 

 spot on the ear region, no ridges along the back, and no red in its coloration 

 (save in individuals afflicted with the disease known as "red-leg"). The 

 characteristics of the two local subspecies of Yellow-legged Frog are set 

 forth in footnote 44. 



During the daytime these frogs are to be seen sitting quietly on rocks 

 or other places close to the water. If a person is walking along the shore 

 of a stream or pond his attention is usually first drawn to the animals 

 when one of them 'plops' into the water and makes for the bottom. In 

 the higher zones one's progress along the bank of a pool is announced by 

 a series of splashes ten to twenty-five feet ahead, as the numerous frogs in 

 quick succession take to the safety of the water. Once under the surface 

 a few quick strokes of the hind legs with their broad foot-webs put the 

 frog under some sheltering rock. The mottled pattern of the upper surface 

 is quite protective in character when the animal comes to rest. When once 

 on the bottom the frog is likely to remain there quietly unless further 

 disturbed. When the frog is in motion, either jumping or swimming, the 

 yellow color on the legs shows contrastingly against the dark upper surface 

 of the body, but it is almost entirely masked when the frog is at rest. 



Certain of the lakes in the higher parts of the Yosemite contain large 

 numbers of Yellow-legged Frogs in both the tadpole and adult conditions. 

 It is a commonly repeated observation that frogs, in tadpole form at least, 

 do not occur in lakes which are stocked with trout. Adult frogs are some- 

 times found around the margins of such lakes and they occur in numbers 

 along the shores of streams inhabited by trout, but the advent of fish in 

 a lake sooner or later nearly or quite eliminates the frogs. It seems prob- 

 able that the fish prey upon the tadpoles, so that few or none of the latter 

 are able to reach the stage at which they transform. The frogs which live 

 along the streams probably spawn in small temporary pools in the meadows 

 which the trout cannot reach. 



