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.