Soaking of branches by North American beavers (Castor canadensis): A behavioral strategy for increasing bark palatability and/or digestibility?

摘要

It has been suggested that beavers employ various behaviors to limit tannin ingestion (e.g. avoidance, sampling, soaking). This study focused upon beavers' soaking behaviors for red maple (Acer rubrum) and witch-hazel (Hamamelis virginiana) at 10 beaver sites at Allegany State Park, NY. In preference feeding experiments, selection of usually less preferred species (black cherry, Prunus serotina; red maple) was greater at sites that did not contain aspen on the landscape. To test soaking behaviors, beavers were offered 243 red maple and 243 witch-hazel sticks soaked 0, 2, or 4 days (81 sticks per treatment) over 6 weeks. Beavers preferred un-soaked red maple and 2-day soaked witch-hazel, and selected against 4-day soaked sticks from both species. Tannin diffusion assays failed to detect decreased tannin levels in soaked red maple and witch-hazel bark. However, tannin levels in un-soaked bark did correspond with results from feeding experiments and vegetation analyses, indicating a negative relationship between tannin levels and ingestion. This study is the first with results that correlate changes in beavers' preference for multiple woody species throughout the fall with changes in bark tannin levels.