Food Habits and Nightly Emergence Activity
in a Family of Beavers (Castor canadensis)
in the Taiga of SoutheasternManitoba.
Taiga Biological Station, Department of Zoology, University of Manitoba, Winnipeg, Manitoba R3T 2N2
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Sahulka, D. 1998. Food Habits and Nightly Emergence Activity in a Family of Beavers (Castor canadensis) in the Taiga of Southeastern Manitoba. University of Manitoba, MSc. Thesis:142 pp.
Conclusions: food selection and nutrients;
The family of beavers under study consumed a diverse number of plant species including trees and aquatic plants and were selective in their food habits both in terms of species consumed and plant parts consumed seasonally and yearly. These findings suggest that boreal beavers may be opportunistic herbivores (as Jenkins 1975 suggests) when the food supply is diverse, choosing those species which meet their energy and nutritional requirements at a particular time.
While beavers may have different nutritional requirements over he course of a year (e.g. - lactating females in the spring) differences in food selection by male and female beavers were not found to be statistically significant in this study.
Beavers at Wallace Lake do not appear to be constrained by nutrient availability in the plant species they consume. Most of the plant species and plant parts had adequate levels of nutrients as described by Robbins (1993) with two exceptions. Potassium levels in the bark of some of the plant species did not meet minimum requirements and adequate phosphorus levels were found only in the leaves of deciduous tree species in the growing leaf stage.
Nutrient levels in food consumed by beavers is hypothesized as a probable factor influencing food selection in terms of species and plant part selection. Noticeable differences in potassium, sodium, copper and iron levels and the potassium:sodium ratios. As well, there were observed differences in some of the nutrient levels between the bark and leaves of the tree species. The leaves were noted to have greater levels of potassium, magnesium, phosphorus, sulphur and copper than in the bark for each tree species while the bark had much lower potassium:sodium ratio. Pinus buds were also noted to have very high levels of crude protein and sodium.
By consuming a wide variety of species and plant parts the beavers in the study may be ensuring that they will not be affected by nutrient deficiencies. Thus, determining food selection based on nutrient contents in plants appears to be much more complex and may involve several factors at once, including soil fertility, moisture regimes and topography at each site.
Conclusions; feeding site selection:
The comparisons conducted between beaver run (experimental) sites and non-beaver run (control) sites showed no significant differences between the sites in terms of tree densities and diameters lower height indicating that these factors do not appear to influence feeding site selection.
There were observed differences in stump densities between control and experimental sites with stumps found at 21-30 and 11-30 m from the water's edge respectively. Species availability, topography and site history were postulated as potential factors influecing the distance beaver traveled to harvest food.
However, only five sites of each were measured for this study. It may, therefore, be beneficial to conduct a larger survey to determine whether factors such as tree species, density and diameters influence feeding site selection and distance traveled for food harvested by beavers. As well, studies should be conducted to determine whether feeding sites and harvesting distance may be selected by the beavers based on other physical and chemical site factors.
Conclusions; emergence times:
Nightly emergence from the lodge by beavers appears to be correlated with the time of sunset, with most emergence by the beavers occurring 30 to 150 minutes prior to sunset. Weather conditions appear to have little influence on nightly beaver emergence; however, further study may be required.
These management recommendations are based on the information obtained from this study. However, it should be noted that this information may be relevant only to the particular family of beavers under study and additional data are required to make broad generalizations about beaver for management purposes.
1. Beaver appear to be very opportunistic in food habits and may consume a diverse array of plant species. Therefore, a survey of beaver habitat should be conducted to determine which plant species the beaver are utilizing prior to any habitat management decisions being made.
2. A variety of factors such as nutritional value of plant species, soil fertility, moisture regimes and topography should be taken into account when developing management programs for beaver.
3. When preparing habitat management designs for beaver, changes in yearly and seasonal food choice should be taken into account.
4. When conducting research on beaver in northern climates it is best to start daily studies 90 minutes prior to sunset.
This page created October 28, 2000.
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