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Mountain beavers are strictly vegetarian in food habits, eating most types of herbage which grow near their burrow. I found the vegetation cut for drying in neat piles around the entrance holes or upon nearby rocks or logs. All the stems of the material in any one pile pointed in one direction. Around the hole would be several piles; each contained the same species of plant and may have indicated the size of the load carried by the individual. As a rule, the material constituted plants which grew in the immediate vicinity; on one occasion, however, red elderberry cuttings were observed 45 yards from the nearest shrub.

Foliage collected and eaten by mountain beavers covers a wide variety of plants. Availability seems to be the important factor in the type of food selected. In each of the locations the materials collected varied in direct proportion to the species growing nearby. Although the area adjacent to the burrows at Vidae Falls and Castlecrest Gardens supported great numbers of Lewis’ monkeyflower, in no case, was I able to find cuttings of this species. But my captive animal ate this plant quite readily. At the location on the south slope of Munson Ridge, three of the burrow entrances were located under a green-leaved alder; but no traces of this shrub were identified in the bunches of cuttings.

Although F. Lyle Wynd reports that false green hellebore is fatal to live stock (Nature Notes Volume 2, No. 2 August 1929) and that most species of Aconitum are poisonous to animals and human beings (Nature Notes Volume 2, No. 3 September 1929), both monkshood (Aconitum columbianum), and false green hellebore, (Veratrum viride Ait.), were eaten by the captured beaver without apparent maleffect. Monkshood was identified, also, in the bunches of drying vegetation at Castlecrest.

Twice daily at 7:00 A.M. and 10:00 P.M., from August 20 to August 26, examinations were made of the food piles at the Munson Ridge location to determine if the mountain beaver was active during the daytime. These observations showed that most of the activity of cutting and stacking occurred during the night; only once, on August 24, were new cuttings found at the night examination.

Each morning from August 11 through August 27, the materials appearing at the eleven holes at the Munson Ridge location were counted and marked. The marking was done by writing the date on a prominent leaf with pen and ink. By means of this counting and marking, it was possible to note the number of pieces of vegetation cut and stacked and the length of time required for the material to dry before it was taken into the burrow. During this period, the mountain beaver collected over 3246 pieces of vegetation.Dicentra stems amounted to nearly 25% of the material gathered and Valerianafollowed with nearly 24%. On August 22, alone, 488 pieces were piled. Note Table I.

Table I – Material gathered at the Munson Ridge location by one mountain beaver during the period of August 11 through August 27. These figures list the number of stems of each of the species and not the bulk of the plant cut by the mammal.