THE AMPHIBIANS
PACIFIC TREE-TOAD. Hyla regilla Baird and Girard
Field characters.Size
small; total length 2 inches or less; ends of toes with small rounded
discs. Coloration extremely variable, ranging from pale light gray
through vivid green and brown to nearly black; a dark streak is always
evident on side of head extending from tip of nose at level of eye to
behind ear membrane; under surface white, unspotted, blackish on throat
in males; back may or may not be marked with dark streaks or spots.
Voice: Song note a loud, raucous kreck-ek, repeated at frequent
intervals; call note a single low prolonged, guttural
kr-r-r-eck.
Occurrence.Distributed
throughout the Yosemite section without regard to life zone. Recorded
from Snelling eastward across Sierra Nevada to Walker Lake and up to
10,600 feet altitude on Conness Mountain. Lives chiefly in damp
situations and on the ground, seldom being found in trees or even in
bushes. Essentially solitary except when spawning.
The Pacific Tree-toad is one of the very few species
of animals in the Yosemite section which ranges uninterruptedly from the
San Joaquin plains to the highest passes of the Sierra Nevada. Of other
land vertebrates only the Gambel White-footed Mouse, the Red-shafted
Flicker, and the Western Chipping Sparrow can be said to do the same.
The range of the Pacific Tree-toad is most remarkable when we remember
that it is a 'cold-blooded' animal which has a body temperature always
close to that of its environment, while each of the other species
mentioned has a heat-regulating mechanism which maintains its body at
practically constant temperature irrespective of that of the
surroundings.
At Snelling the air temperature at different seasons
of the year varies from slightly below freezing to above 110° F.,
while on Tuolumne Meadows it undoubtedly goes below 0° F. in winter
and may reach above 85° F. in summer; yet tree-toads are found in
both of these places. The animals keep to moist situations near the
surface of the earth, where the temperature fluctuations are somewhat
less than those given, and in freezing weather must of necessity seek
shelters below the frost line. Even so, the Tree-toads must be subject
to considerable variation in the temperature of their surroundings. The
hardihood of these diminutive creatures is indicated by the fact that in
Yosemite Valley on February 28, 1916, when there was two feet or more of
snow on the Valley floor, tree-toads were chorusing in open marshy ponds
below the Royal Arches; and on Mount Hoffmann on June 29, 1915, their
voices were heard coming from beneath deep snow banks on the north side
of the mountain. On July 8, 1915, several were croaking in a small lake
covered almost completely with ice on Conness Mountain at 10,600 feet
altitude. By way of contrast it may be mentioned that on May 27, 1915,
at Snelling, when the air was to us uncomfortably hot, tree-toads were
heard in voice near the river margin.
Among all the toads and frogs of the Yosemite region
the Pacific Tree-toad may be known at a glance by the expanded discs on
the ends of all its toes and by the presence of a streak of dark color
which extends along the side of its head, at the level of the eye, from
the tip of the nose to behind the ear membrane. These features are
evident at all ages, from the smallest individuals recently transformed
from tadpoles to the largest adults.
Many amphibians use their voices almost exclusively
during the spawning season, but the Pacific Tree-toad is likely to be
heard at any time of year, being silent, if at all, only during the dry
hot days of late summer. Thus, in Yosemite Valley, the notes have been
heard by us in February, May, June, October, and December; at Snelling
in January and May; at Chinquapin in May and June; about Tuolumne
Meadows in July; at Vogelsang Lake on August 30; and at McGee Lake and
Ten Lakes in October. During the fall months the single note is usually
the only one heard, while from January to June the two-syllabled song
note, as well as the call, is given commonly.
The call-note consists of a single prolonged guttural
syllable, kr-r-r-r-eck, which it requires a second or two to
pronounce. This note is uttered at irregular intervals, by isolated
individuals when in their retreats and by members of a group in a pond
or marsh when their song chorus has been interrupted.
The 'song' note is a two-syllabled kreck-ek
given in faster time than the call and repeated at short intervals.
There is slightly less emphasis on the second note, which drops in pitch
and ends abruptly. When a number of Hylas are in a marsh or pool
together, their notes tend to be given in unison, so that there is a
continued series of notes, every alternate note being slightly stressed.
Such a chorus may continue for a long period, but more often it is
interrupted, ceasing rather abruptly and then beginning again after a
period of quiet. If a person walks out into a meadow where tree-toads
are chorusing, the voices soon cease. One or more call notes with an
interrogative inflection are given, and then there is silence. If the
observer stands absolutely still, the animals will shortly resume their
singing. The chorus begins as it ended, with a few call notes; then one
individual commences his song, to be quickly followed by another, and in
five seconds or so the place resounds with the chorus once more.
The tree-toad is quite the strongest voiced of any of
our amphibians, though it is the smallest in point of body size among
the tail-less forms. Only the males sing, although females may give the
low call note. The males when held in the hand are seen to possess loose
folds of black skin on the throat. When the animal is singing, this skin
is inflated to form a pouch which swells out beyond the chin and is kept
continuously inflated while the notes are being given. The pouch
evidently acts as a resonator and helps to give volume to the sound.
The eggs of the tree-toad are laid during the spring
months. No egg masses were seen anywhere in the region, but it seems
likely that the individuals living in the higher altitudes spawn at much
later dates than those in the lowlands. On August 20 and 23, 1915, at
Merced Lake, small tree-toads, measuring between one-half and
three-fourths of an inch in length, were found in numbers. These were
animals which had but recently changed to the adult condition, and which
had undoubtedly come from eggs laid during the same season.
Among the specimens of this species collected in the
Yosemite region are two individuals taken at Merced Grove Big Trees and
Porcupine Flat, respectively, which after being preserved are nearly 2
inches (1-7/8 and 1-15/16) in total length and are fully as large if not
larger than any we have seen from anywhere. The cup-like discs or pads
at the ends of the toes on these animals are unusually large and
conspicuous and in life must have been fully twice the diameter of the
toes themselves.
In Yosemite Valley on October 13, 1915, scores of
half-grown Hylas were seen in a saw grass swale. There were also many
grasshoppers there and it was often difficult to distinguish a toad from
a grasshopper until the individual was scrutinized closely. The
tree-toads exhibited much variation in color, ranging from uniform
bright greenish yellow to dark brown; some were coarsely mottled with
dark and light brown.
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