YOSEMITE TOAD. Bufo canorus Camp

Field characters.—Size medium; total length 3 inches or less. A short broad raised gland (parotoid) on each shoulder behind ear membrane; space between parotoid glands not more than width of one of them; muzzle rounded in side view; pupil round. Male: Skin quite smooth, with few 'warts'; ground color above olive green with dots of black; under surface grayish white with scattered small spots of black. Female: Upper surface with irregular patches of black (pl. 60d, e), each outlined with white and marking the position of a low rounded wart; ground color light brownish; under surface chiefly clear white. Voice: Spring song a sustained melodious trilling, with rapid rhythm.

Occurrence.—Common resident in Canadian and Hudsonian zones from near Chinquapin and Tamarack Flat eastward to Tioga Pass. Lives in or about wet meadows. Solitary except at spawning season.

The Yosemite Toad was a second notable discovery among the amphibians found by our party in the Yosemite region. This species is quite different in appearance from the California and Northwestern toads, which live along the west and east flanks of the mountains, and its range is separated by some miles on either hand from those of the other two. The range of the present species includes most of the Canadian Zone and all of the Hudsonian, extending from near Chinquapin and Tamarack Flat eastward to Tioga Lake, and ranging altitudinally from about 6700 feet to as high as 10,350 feet (at Vogelsang Lake).

This species may be separated easily from other toads and frogs of the region by the shape and position of the two large parotoid glands which are located on each 'shoulder' immediately behind the ear membrane (pl. 60d, e). These glands are but little longer than they are broad and the space between them does not exceed the width of one gland. In the other two toads of the region the parotoid glands are proportionately longer and are more widely separated. Neither the tree-toads (Hyla) nor the frogs (Rana) possess these glands at all.

There are marked differences between the two sexes in the Yosemite Toad. Indeed they are so great that to a casual observer the male and female might be taken as belonging to distinct species. As with other kinds of toads, the females are somewhat larger than the males; but the greatest difference is in coloration. The male has very few obvious 'warts' and the skin on its upper surface is plain olive green marked with minute scattered dots of black, each of which is rimmed with white. The female, on the other hand, has the back and sides thickly marbled with irregular but clearly defined patches of black outlined by white. Low rounded warts of dark color are centered in these areas of black. The ground color between the spots varies from dull brown to white. Whether these marked differences in coloration and markings are maintained at other times of the year is not known definitely, though the few animals collected in early spring and in autumn would indicate that such is the case. In some species of amphibians such as the California Toad the male takes on a green-colored smoother-skinned appearance in the breeding season and then reverts to a condition more like the female for the remainder of the year. The males of the Yosemite Toad, as is true of all other true toads (genus Bufo), develop on the upper side of the 'thumb' and two adjacent digits of the fore limb an area of roughened brown skin during the breeding season.

The Yosemite Toad undoubtedly hibernates for a considerable period of time during the winter months, when snow covers the higher country and the temperature goes below the freezing point. Our observations were not continued in the higher altitudes long enough to determine the actual dates of spring emergence and fall disappearance. On May 20, 1919, we visited Peregoy Meadow and found the males there already out and trilling loudly; on September 3, 1915, at Vogelsang Lake, a single individual was collected. In all probability some of these toads emerge toward the end of April and a few may be out until early October. The hardihood of the species is indicated by the way in which the adults jubilate in the melting snow water during the spring and early summer months.

The winter season is spent in some retreat in the ground, presumably below the frost line; any individual toad which chances to seek a shelter above that level will in all probability be killed when the cold of winter freezes the upper ground. During that part of the summer not devoted to egg laying the toads spend the day solitarily in damp situations at the surface of the ground under logs or stones. A toad seen abroad during the day near Porcupine Flat quickly betook itself to a pool of water beneath a log. Several small individuals were observed on a hot, dry, sandy flat near Ragged Peak in July, and near Vogelsang Lake one individual was found beneath a rock in a damp heather patch 20 feet from a stream.

Immediately or very soon after emerging from their winter hibernation these toads repair to pools and small streams in the wet meadows, and continue there until the eggs are deposited or even longer. The males precede the females, as at Peregoy Meadow there were many males present on May 20, 1919, while the only females found were small non-breeding individuals. At Tamarack Flat, May 25, 1919, an adult female was found at the base of a rotted tree stump fully 200 yards from the edge of the nearest meadow and 200 feet above it in altitude, while males were heard trilling in the meadow that same evening. On June 15, 1915, a chorus of these toads was heard near Peregoy Meadow, although egg laying had been accomplished some time previously. At Snow Flat on June 28, 1915, and near Ragged Peak on July 9, 1915, other toads were heard in song. At the head of Lyell Cañon on July 16, 1915, numbers of Yosemite Toads were found in a small pond, and some at least of the females were engaged in laying their eggs.

On May 20, 1919, numbers of male Yosemite Toads were congregated in the wet meadows on either side of the ridge east of Chinquapin. During the preceding winter gophers from the adjacent slopes had moved down and occupied the grassy meadows, but with the spring break-up and melting of the snow the place had become untenable for the gophers, who had moved up onto the hillsides once more. Their tunnel systems were left as subterranean 'pipes' which carried off much of the water from the melting snow banks to the creek in the bottom of the cañon. These gopher tunnels served also as shelters for the toads. The latter when partially hidden in the entrances to the tunnels or even when they sat quietly on the open grassland were quite invisible to our eyes, so well did their pattern of coloration match the greens and browns of the meadow.

The mating song of the Yosemite Toad is a sustained series of ten to twenty or more rapidly uttered notes, constituting a 'trill,' and the whole song is repeated at frequent intervals. The notes, though mellow in character, carry well considering the size of the animal and have a ventriloquial quality which makes it difficult to locate any one animal by sound alone. When a number of males are giving their songs in the same place the songs overlap one another so that the general chorus is continuous. There is some difference in the pitch at which the several members of a group sing, varying perhaps with the size of the individual toad. The general effect of a chorus is rendered more pleasing to our ears by these variations, while the ensemble is even sleep-inducing in effect, as we can testify from experience. The notes recall the courting song of the Texas Nighthawk.

If a person walks out onto a meadow where toads (Bufo) and tree-toads (Hyla) are both 'singing,' the chorus soon comes to an abrupt termination. If he stands stock still for a while the Hylas will resume, but the Bufos do not ordinarily begin again until the intruder has quitted the vicinity. The animals probably get first knowledge of the approach of a person by the vibrations which his footfalls produce in the ground, and, as the water-logged ground in a meadow readily transmits such vibrations, the toads are on their guard long before the observer can get within sight of them.

As intimated above, the toad chorus, at different levels, may begin at least as early as May 20 and last until July 9; and, according to our experience, singing is carried on quite through the daylight hours and into early evening at least.

The Yosemite Toad spawns in late spring or in summer, depending somewhat upon the local climate. Specimens collected on May 24 to 26, 1919, at Tamarack Flat showed no signs of breeding. On June 22, 1915, numerous tadpoles and one recently metamorphosed young toad were seen at Mono Meadow. One female taken near Porcupine Flat June 28, 1915, had already laid most of her eggs. On July 16, 1915, at the head of Lyell Cañon several individuals were depositing eggs.

Our collection of Yosemite Toads includes 20 males and 28 females. Upon the basis of total length the representatives of each sex fall into several size groups which are quite probably age groups as well. These groups indicate that about four years is required for a toad to reach adult size, that males are always somewhat smaller than females of the same age, and that the females do not begin to spawn until more than 2 inches (50 mm.) in length, when they are presumably three years old.

Among the females taken are three which measure less than one inch (20, 22, and 23 mm.) in length. When it is recalled that toads are small at the time they transform from the tadpole stage, it seems highly probable that these three individuals came from eggs of the preceding season and so represented animals one year old or thereabout. Another group of 12 ranges from about 1-1/2 to 2 inches (33 to 49 mm.) in length; in neither of these two size groups did any of the individuals show that eggs were being, or had been, developed. The third group, of 9 animals, measures about 2-1/2 inches (57-62 mm.) in length; and the fourth of four individuals about 3 inches (70 to 74 mm.). In both the latter groups the animals were in breeding condition and contained eggs.

Male toads in the collection fall into two groups: 2 to 2-1/4 inches (50 to 55 mm.), and around 2-1/2 inches (58 to 64 mm.) in length. These specimens were practically all collected in meadow ponds or streams and were breeding animals, for they have roughened brown areas on the inner digits of the fore limb. They are thought to represent animals three and four (or more) years of age. No males were obtained which could be called younger than these. Such individuals would probably be found by careful search on the upper slopes some distance from the breeding ponds.

The food of the Yosemite Toad includes a wide variety of insects and the like. One individual captured at Porcupine Flat, June 29, 1915, contained 2 Tenebrionid beetles, several weevils of different species, numerous large ants and one centipede, besides some red fir needles probably taken incidentally.