By. James R. Slater and C. Frank Brockman.
The amphibians,including frogs, toads and salamanders, form an
interesting but little known and appreciated section of animal life in
Mt. Rainier National Park. Throughout the world there are some 2000
species of amphibians (1) and of this number Mt. Rainier National Park
is represented by twelve. Seven of these are salamanders, newts,
waterdogs etc. - tailed amphibians (Caudata) - while five species are
tailess amphibians (Salientia) - frogs and toads.
Of this small unit twelve species representatives may be found living
and breeding from the lowest elevations along the boundaries of the park
to has high as 6000 feet above sea level (2). The marshes of the lower
Canadian zone resound with a multitude of frog voices during the
breeding season in early spring, and hardly before the snow has
disappeared from around the small lakes and ponds in the Hudsonian zone
we may find the jelly-like masses of eggs of various frogs and
salamanders that breed at that elevation.
* * * * * * * * * *
(1) Nineteen species are listed as active in the state of Washington.
(Julius R. Slater, Professor of Biology, College of Puget Sound, Tacoma,
Washington.)
(2) No amphibians have been found above 6000 feet in Mt. Rainier
National Park. (Slater)
Most amphibians lay their eggs in the water of small pools, in lakes,
or in streams; though some find moist places upon the ground more suited
to their needs. Species of two genera follow the latter procedure in
Mt. Rainier National Park (1). The eggs of all other local amphibians
are laid in water. After a metamorphosis during which the animals are
transformed through various stages to the adult form, they leave the
water and spend more or less of their time on land.
Economically many amphibians are of great value to man. This is
particularly true of the frogs and toads which consume a great number of
insects that, in turn, do considerable damage to crops and vegetation in
general. Amphibians also aid man in the destruction of mosquitoes (in
the larval and pupal stages).
Many people confuse certain of the reptiles with amphibians and
because of this confusion they often regard these two groups of the
animal kingdom as one. However such is not the case. There is as much
structural difference between a reptile and an amphibian as there is
between a bird and a mammal but to many people, salamanders resemble,
superficially, the lizards, for neither possesses outward characters of
a truly distinctive kind, such as the feathers of a bird, the fins of a
fish, or the hair and mamary glands of a mammal. But while Salamanders
and lizards resemble one another to the untrained eye, the student of
these forms quickly sees great differences in the two groups. Briefly a
few obvious differences are as follows:
| Amphibians. |
Reptiles. |
|
1. Lay eggs in water or in moist places on land.
2. Have metamorphosis - going through several distinct changes from egg to air-breathing adult.
3. Skin slimy and not possesing scales.
4. Larvae breath by means of gills for a time.
|
1. Never lay eggs in water.
2. Young hatched or born with essential form of parent.
3. Skin scaly or plate-like.
4. No larval stage and hence no gills.
|
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(1) These two genera are Plethodon, of which two species are
native to the park (Western Red-backed Salamander, P. vehiculus and the
Washington Salamander, P. Vandykei), and Ensatina which is
represented by but one species native to the Park (Red or Oregon
Salamander, Ensatina eschscholtzii).
The number of eggs which are laid by amphibians varies with the
species and the individual, ranging from less than twelve to more than
20,000. The egg consists largely of yolk, which is usually dark, and is
surrounded by a gelatinous transparent membrane which absorbs water and
swells to a large size forming a jelly-like protective covering for the
egg. The form of the egg cluster also differs. In the case of the
Pacific Tree Toad (Hyla regilla), Western Red-backed Salamander
(Plethodon vehiculus), Pacific Coast Newt (Triturus torosus) and the
Long-toed Salamander (Ambystoma macrodactylum) the eggs are laid in
small clusters. Those of the Northwest Salamander (Ambystoma
gracile), Pacific Giant Salamander (Dicamptodon ensatus) (1) the Western
Spotted Frog (Rana pretosia) and the Western Wood Frog (Rana aurora
aurora) are laid in large masses, while the Northwestern Toad
(Bufo boreas boreas) lays its eggs in long strings.
The egg, usually fertilized externally in the case of frogs (2) and
internally in the case of salamanders, soon develops into the larva
(tadpole stage) with gills and tails but lacking legs. The larva grows
rapidly after hatching, at first living upon the nutriment of the yolk
sac which is stored in its own abdomen. If the egg is laid in water the
newly hatched larva, after a period that may encompass several days or
several weeks, escapes from the gelatinous mass which surrounded the
original egg and swims about freely. After using the nutriment of the
yolk the newly hatched larva feeds upon the green algae scum that is
generally found in ponds. The mouth parts of the tadpole are quite
different from those of the mature adult, being several rows of spiny
tooth-like projections with which the tadpole scrapes at the water
plants that serve as food at this stage. During this period the larva
grows rapidly. Fore and hind legs develop simultaneously. In the
tailess group (frogs and toads) the fore legs are hidden for a time
beneath the gill chambers. Even after the animal has reached maturity
the fore legs are shorter than the hind legs. This is different in the
case of the tailed amphibians whose fore and hind legs are of about
equal length upon maturity. The final stage of the metamorphosis comes
after a period of varying duration - from a few days to several months,
depending upon such factors as the temperature of the water and the food
supply; wherein the gills are lost and the animal assumes its final
adult, air-breathing form.
* * * * * * * * * *
(1) Although Slater has not taken eggs of this species as yet Storer
has a picture labeled as the eggs of this species in "Amphibia of
California".
(2) The American Ribbed Toad (Ascaphus truei) has internal
fertilization.
In the case of frogs and toads, of course, the tail as well as the
gills are absorbed. This absorbed material is used to build legs.
Where the eggs are laid on land, the larval stages of growth and
metamorphosis occur within the egg membranes. The young are then
hatched as small duplicates of the adult.
In addition to confusing the amphibians with the reptiles the public
has associated many peculiar superstitions with amphibians. This is
particularly true of the toads, for many people still believe that
toads, if handled, will cause warts. That, of course, is absolutely
false. Toads do possess glands which secrete a slimy acrid fluid which
serves to deter the various enemies of the toad from harming them. The
fluid is very distasteful and acts in a disagreeable manner on the
membranes of the throat and mouth. If a toad is picked up by some
animal, the resultant sensation is anything but pleasant, due to this
secretion. The toad is usually dropped hastily and rarely is a second
attack made by the marauder in question. The "warts" found on toads
contain these glands. After handling toads it is always best to wash
the hands or at least keep them away from the tender membranes of the
nostrils or eyes because some of this fluid may be carried to these
places and the effects will not be pleasant. All amphibians have such
glands in one form or another though they are more pronounced in the
case of the toad.
Among the many interesting facts regarding amphibians that may be
mentioned are the following:
1. A tadpole, at certain stages in its metamorphosis, has the power
of regeneration. That is, it can grow a reasonably efficient toe or leg
if that member has been snipped off.
2. Frogs hibernate in winter in soft mud, and in medieval times it
was thought that these amphibians were derived or generated from the
ooze and mud of swamps.
3. A frog can easily make a jump of twenty times its length as
compared to the average man's jump of about two times his length.
4. The female frog never sings. It is the voice of the male that one
hears during the mating season. However, in the case of the American
Ribbed Toad (Ascaphus truei) both sexes are voiceless.
5. Some frogs croak under water by forcing the breath across the
vocal cords alternatingly between the mouth chamber, or an air sac under
the chin, and the lungs.
6. The tongue of the frog is attached at the front of the lower jaw,
and when the mouth is closed the tongue lies flat and pointing down the
throat. In this manner the frog gets the use of the full reach of his
tongue in catching insects.
7. The frog fills his stomach completely about four times each
twenty-four hours.
8. Mortality of tadpoles is very high. They have innumerable enemies
and it is said only about one out of every hundred reaches maturity.
9. Some tree toads can be heard for a mile or more. If man had a
voice that would carry as well as this, in proportion to his size, he
could stand in Paradise Valley and, with an ordinary voice, be heard in
New York City!
10. The adults of Plethoden (Western Red-Backed Salamander and
Washington Salamander) and Ensatina (Red or Oregon Salamander) do not
have lungs or gills even though they live on land and use free oxygen
from the air. The entire moist skin acts as a respiratory surface,
since it is very thin and does not have an adhering layer of fat, as in
a warm blooded animal.
* * * * * * * * * *
- ACKNOWLEDGEMENTS -
The National Park Service wishes to gratefully acknowledge the
assistance of Professor James R. Slater of the College of Puget Sound,
Tacoma Washington, in the preparation of this issue of Mt. Rainier
National Park Nature Notes.
Professor Slater is our northwestern authority in this field. He has
studied and collected amphibians extensively throughout the Pacific
Northwest and a considerable portion of his time was spent in Mount
Rainier National Park. Largely through his interest and generous
cooperation with the naturalist department of Mt. Rainier National Park,
it was possible to prepare that section of our Park Encyclopedia which
deals specifically with amphibians of this region. This issue of Nature
Notes was arranged largely from that material. (C.F.B.)
