Foraging Behavior of Beavers (Castor Canadensis), Plant Secondary Compounds, and Management Concerns

Abstract

I examined how secondary metabolites in trees influenced food selection of beavers, whether selection patterns were consistent with recent theories of plant-defense investment, and whether a chemical extract could be used as a feeding deterrent. I used cafeteria-style experiments to examine beaver food preferences for six species, quaking aspen, willow, mountain alder, white fir, lodgepole pine, and Jeffrey pine; over four treatments, intact stems, stems with leaves removed, a methanol extract from bark, and a methanol extract from leaves. Quaking aspen was significantly preferred across all treatments, Jeffrey pine was significantly avoided across all treatments except the bark-extract treatment, and the bark extract of mountain alder was significantly avoided. Height growth rates and leaf lifespan of experimental trees were locally estimated and were not significantly different between the three deciduous species or the three coniferous species. Beavers selected significantly more deciduous than coniferous species across all treatments except the bark-extract treatment. A regression indicated a stronger relationship in selection of leaf extracts was present for leaf lifespans than height growth rate. In feeding experiments designed to examine the potential of an extract from Jeffrey pine as a repellent, beavers significantly avoided aspen stems painted with extracts from the bark and needles of Jeffrey pine when compared with controls. As a follow up, all aspen at two sites were either left untouched, painted with an extract from Jeffrey pine, or wrapped with chicken wire. The treatments significantly altered beaver food selection. These results are consistent with the hypothesis that food selection is influenced by secondary metabolites, that long-lived leaves are more protected from herbivory than short-lived leaves, and that chemical extracts from trees might be used as feeding deterrents. The greatest potential repellent ex-tracts are from long-lived leaves from slow-growing trees, or bark from species specifically avoided by beavers.