A study of preferential prey selection in Castor canadensis.

Abstract

The focus of this study was to investigate feeding preference of Castor canadensis with respect to species, number of trees foraged relative to the distance from shore, and the girth of foraged trees relative to their distance from shore. Wilderness State Park in Emmett County, Michigan, a coniferous dominated forest, and Grapevine point, a deciduous dominated forest on the property of the university of Michigan Biological Station in Cheboygan County, Michigan, were chosen due to their support of beaver activity. After dividing up transect of 68.2m by 20m at Wilderness State Park and 30m by 20m transect at Grapevine Point, it was found that there was a significant difference in proportions of foraged trees at Wilderness State Park (X2=169.7, X2=14.1, p<0.05, df=7). Further analysis showed significant difference in the proportions of foraged trees at Grapevine Point (X2=18.61, X2=15.5, p<0.05, df=8). When examined, the difference in the proportion of trees consumed ""near"" versus ""far"" relative to shore, at Wilderness State Park indicate no significance in the proportion of trees foraged in each either section (X2=1.57, X2=3.84, p>0.05, df=1). Conversely, significant preference for trees ""near"" the shore was shown at Grapevine point (X2=20.59, X2=3.84, p<0.05, df=1) Finally, in examining the mean girth of ""near"" versus ""far"" trees at Wilderness State Park, the mean girth of the ""near"" trees was 16.0 +15.0 and the mean girth of the ""far"" trees was 30.0 + 11.0. These data proved to be parametric, (skewness=0.090, kurtosis -0.954) analysis, showed a significantly larger mean in the ""far"" trees than in the ""near"" trees (T=4.604, df=75.9, p<0.0001). Conversely, a non-parametric equivalent showed no significant difference in the mean girths of ""near"" and ""far"" trees at Grapevine Point (skewness=4.026, kurtosis=23.705, Mann-Whitney U=377.500, p=0.654, X2=0.201, df=1). What can be shown is that beaver do prefer aspen trees when available and maple trees when aspen is not available. However, due to the difference in composition of the canopies of both sites, very little information can be extrapolated to discuss overall feeding preference in beavers.