Food Habits Of Crater Lake Salamanders
By Dr. D. S. Farner, Ranger-Naturalist
Two species of salamanders, belonging to the genera Triturus and Ambystoma respectively, occur under the rocks at the waterline of Crater Lake. On August 17 and 24, 1946, 56 salamanders were collected for the purpose of examining their stomach contents.
Of the 27 Ambystoma examined, 19 of the stomachs contained material. Fourteen (74 percent) of these contained terrestrial arthropods, or fragments thereof. These were mostly insects such as ants, wasps, flies, beetles, etc. Usually there were parts of one or two animals only per stomach. Seven stomachs (37 percent) contained aquatic insect larvae. Two stomachs contained unidentifiable material only. One contained only a piece of andesite about one centimeter in length.
Of the 29 Triturus examined, there were 27 with food items in their stomachs. Sixteen (56 percent) contained the fresh-water shrimp, (Hyallela), (one to sixteen per stomach). Nine of these sixteen had no items other than Hyallela. Eight stomachs (30 percent) contained snails (one to 15 per stomach). In four of these, snails were the only item; in the other four, Hyallela was also present. Five (18 percent) contained aquatic insect larvae (Coleoptera, Trichoptera, and Diptera), one to three per stomach. Two contained caddis-fly larvae. In three of the five instances, the aquatic insect larvae were the only food items. Four (15 percent) contained terrestrial insects or fragments thereof (never more than one per stomach). In three of these, the insect, or fragment thereof, was the sole item; in the fourth, there were also two Hyallela. One stomach contained unidentifiable material.
The terrestrial arthropods, mostly insects, found in the stomachs of the salamanders are doubtless individuals which were either dead at the time of eating or were in a helpless and easily captured living condition on or in the water. In view of the fact that 74 percent of the Ambystoma stomachs with food contained such items and only 37 percent contained items would could have been taken alive it seems safe to conclude that the Ambystoma of Crater Lake is largely a scavenger taking mostly dead animals. Live food taken is that which moves slowly. Apparently fresh-water shrimp and snails, both abundant in its habitat, are not utilized. On the other hand, it appears that Triturus acts as a scavenger only rarely since only 15 percent of the stomachs contained terrestrial arthropods. Obviously the principal source of food for Triturus, at least at the time of year in which this study was conducted, consists of fresh-water shrimp and snails. Seventy-one percent of the stomachs examined contained either or both of these items. Aquatic insect larvae constitute the next most important item.
It is of interest to note that, in the stomachs of either species, neither aquatic Coleoptera nor Turbellaria were found; although both are abundant in the habitats of these species.
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