Volume XVIII - 1952

At irregular intervals Crater Lake National Park is visited by huge numbers of Tortoise Shell Butterflies, Aglais californica Bdv. Previous invasions have been described by Scullen (1930), Constance (1931), and Lowrie (1951). Doubtless others have occurred without being recorded. The chronology of the 1952 invasion was very similar to that of 1951. The butterflies first began to appear about July 30 and seemed to reach their maximum abundance during the first week in August when prodigious numbers were to be observed in flight and resting on buildings. They were observed in abundance at the summits of Mt. Scott, the Watchman, and Dutton Cliff.

Doubtless these butterflies constitute an abundant source of food for several species of animals. During the last week of July and the first week of August there was a pronounced increase in the numbers of Clark's Nutcrackers, Nucifraga columbiana (Wilson), along the Rim Highway. On several occasions I have noted them feeding on the California Tortoise Shells which had been killed by automobiles. The same observation has been made by Ranger-Naturalist R. M. Brown. On August 10, Ranger Naturalist C. Warren Fairbanks saw three ravens, Corvus corax Linnaeus, feeding on these butterflies on the highway near Llao Rock. He also found six in the stomach of a Rainbow Trout, Salmo gairdnerii Richardson, caught near Eagle Cove on August 17. Ranger-Naturalist Brown also observed a Golden-Mantled Ground Squirrel, Citteilus lateralis (Say), taking one on August 7 near Hillman Peak. These ground squirrels were frequently observed to take butterflies which dropped from the radiators of automobiles at the checking stations. The use of butterflies as food by the Golden-Mantled Ground Squirrel, however, is apparently not unusual (Gordon 1943:27).

References

Constance, L. 1931. A butterfly pilgrimage. Nature Notes from Crater Lake, 4(2):3-4.

Gordon, Kenneth. 1943. The natural history and behavior of the Western Chipmunk and the Mantled Ground Squirrel. Oregon State Monographs, Studies in Zoology, No. 5. 104 pp.

Lowrie, Donald C. 1951. Butterflies of Crater Lake National Park. Crater Lake Nature Notes, 17:10-11.

Scullen, H. A. 1930. The California Tortoise Shell Butterfly. Nature Notes from Crater Lake, 3(3):2.

Under-surfaces of two closely related newts. A Mazama newt from Crater Lake at the left and a common Oregon newt on the right.

During the past two seasons many of the visitors to Crater Lake National Park have been able to get some first hand contact with one of the most distinctive and interesting animals of the Lake. This is a salamander or water-dog, oftentimes called the Mazama newt or Crater Lake newt; it is found no place in the world outside of the waters of Crater Lake. Believing that many of the visitors to the Park would be interested in this unusual animal, we have frequently exhibited living specimens during lectures in the lodge and the community building and the excitement that is invariably caused by the circulation of the jars of newts has indicated to us that these salamanders are indeed a real source of interest to our visitors. If one compares the Mazama newt (Triturus granulosus mazamae) with the common Oregon newt (Triturus granulosus granulosus) it is clearly evident that the two are very closely related. Indeed, the difference between the two is simply a matter of the pigmentation of the lower surface; the immaculate orange-yellow of the Oregon newt is replaced in the Mazama newt with varying amounts of dark pigment that appears to invade the under surface of the animal from the sides. This difference in pigmentation is illustrated in the photograph in which the under surfaces of the two kinds of newts are shown. It should be pointed out that the amount of black pigment on the lower surface of a Mazama newt is highly variable; some individuals have lots of it and others approach closely the pigmentation of the common Oregon newt.

Our best interpretation of the Crater Lake newt population assumes that hundreds of years ago some common Oregon newts were able to get into the Lake through an unknown route, probably during a period when the climate was much wetter. The steep, dry walls of the Lake Rim have apparently served as an isolating mechanism, allowing the Crater Lake newts to develop a different genetic composition and resulting in the pigmentation differences that now separate this group of water-dogs from the common Oregon newt. It is a very interesting fact that a specimen of the common Oregon newt collected within the Park boundaries as close as two and one-half miles from the Lake showed none of the under-surface black of a Mazama newt. This is surely a tribute to the isolating function of the caldera walls.

Our present knowledge of the life history of the Mazama newt is fragmentary, despite the fact that during the past years a good many members of the ranger-naturalist staff have searched the water and the shoreline of Crater Lake for such information. The smallest larvae that we have found in the Lake were collected in a partially cut-off pool behind the Government Boathouse on Wizard Island during the first week of September, 1951. Ten of these larvae had an average length of about 3/4 inch which indicated to us that they had hatched from the egg mass at least three weeks previously. It seems very probable that the eggs from which these larvae came had been laid during the summer, perhaps back in the spaces between the large blocks of lava where they would be found only with great difficulty.

In the water along the shore and in pools partially separated from the Lake, large larvae with an average length of about 3-1/4 inches are commonly found. Our limited data suggest that the small larvae observed in the pool on Wizard Island attain this size during their second season of growth, undergoing metamorphosis at that time. Associated with the large larvae in the water along the shore and in the partially cut-off pools on Wizard Island, may be found newly metamorphosed newts and adults of various sizes, including large, mature individuals averaging about 6-3/4 inches in total length.

If one lifts up the rocks and driftwood along the shore of Crater Lake he soon learns that the Mazama newts are by no means confined to the actual water of the Lake. Oftentimes they may be collected in large numbers under the debris along the shore, frequently in association with the long-toed salamander, Ambystoma macrodactylum. In this non-aquatic environment they appear desiccated and sluggish with extremely granular skins. We have considered the possibility that these semi-terrestrial individuals represent a definite stage in the life history of this newt; however, since no single age group is involved, it seems more probable that a transitory semi-terrestrial existence represents an aspect of the behavior of the Mazama newt at various times during its life.

On several different occasions we have observed large aggregations of the Mazama newt along the shore of the Lake. Usually these aggregations consist of semi-terrestrial individuals in groups of about twelve to fifteen out of the water and under rocks or pieces of driftwood. A somewhat different kind of aggregation was observed September 6, 1951, on the east side of Eagle Point where the shore of the Lake consists of a rocky beach covered with willows. Two hundred and fifty-nine newts were massed together in an area of water not more than thirty feet square, the vast majority of these being under a single flat rock about nine feet square, resting on other rocks in approximately one foot of water. Making up the aggregation were adults of varying sizes, large larvae and newly metamorphosed individuals.

On August 7, 1952, an enormous aggregation of Mazama newts was observed under rocks in the shallow water of about 15-20 feet of shoreline in Eagle Cove. We estimated that at least three hundred newts were involved in this aggregation and, as previously noted, all sizes from large larvae to the largest adults were present. At this time the significance of these aggregations is not understood.

From the zoological standpoint, the newts of Crater Lake are particularly interesting because they provide material for the determination of the time required for the genetical change that is necessary for the development of a subspecies. The collapse of Mt. Mazama has been accurately established by modern techniques as occurring between six and seven thousand years ago. This information clearly indicates that newts could not have entered the water of Crater Lake more than about six thousand years ago; moreover, considering the subsequent eruptions that brought about the formation of Wizard Island, it is highly probable that the Lake newt population was established much more recently. Indeed, the Mazama newts are doubtless one of the most clearly dated cases of subspeciation available any place in the world.