Boreal Beavers (Castor canadensis):
Home Range, Territoriality, Food Habits and Genetics
of a Mid-continent Population
Taiga Biological Station, Department of Zoology, University of Manitoba, Winnipeg, Manitoba R3T 2N2
Present address: Dr. Michelle Wheatley, Director of Wildlife Management, Iqaluit, TN, X0A 0H0
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Wheatley, M. 1994. Boreal Beavers (Castor canadensis): Home Range, Territoriality, Food Habits and Genetics of a Mid-continent Population. Unpubl. PhD. Thesis, University of Manitoba: 350 pp.
I studied beavers (Castor canadensis) in the boreal forest of eastern Manitoba from 1986 to 1992. I captured and ear tagged 60 different beavers, and outfitted 42 of these animals with transmitters. I collected sufficient data to determine summer home range size for 34 beavers and to determine fall home range size for 27 beavers. I examined: methods of delineating beaver home range; the effects of season, habitat, sex and age class on home range size; whether beavers were territorial; food selection by beavers; and genetic relatedness within the beaver population in my study area.
I compared estimates of beaver home range size and shape using four different methods: grid; minimum convex polygon (MCP); modified minimum area (MMA); and the Jennrich-Turner ellipse. The grid gives the smallest estimate most often and the ellipse or minimum convex polygon give the largest. The ellipse works best for home ranges with only one area of concentrated use near the centre. The MCP and MMA work best when the distribution of observations is a regular shape, with no protruding arms. The grid method is most suitable for animals with irregularly shaped home ranges or home ranges with several areas of concentrated use, and appears best suited for use with beavers.
Summer home range areas average 10.34 ha and fall averaged 3.07 ha. Thirty-seven of 38 beavers had core areas in summer, and 21 of 27 had core areas in fall. Home range size and core size were positively correlated in both summer and fall. Summer home ranges were significantly larger than fall home ranges, with fall home ranges being centred closer to the lodge than summer ranges. Winter home ranges were restricted to less than 0.25 ha around the lodge.
Summer home range size was positively correlated with fall home range size, and summer and fall core sizes were also positively correlated. Percent of area in the core and percent of activity in the core were similar for all habitats and sex and age classes in summer.
Beavers living in river habitat had the largest summer and fall home ranges. Those living in pond habitats had the smallest summer home ranges but did not differ from lake beavers in the fall. Adult males usually had the largest home ranges, and adult females the smallest in both seasons. Adult females usually had home ranges centred closer to the lodge, and adult males farther from the lodge, than other family members.
In 6 years and over 600 days of observing beavers, I never observed any evidence of aggressive behaviour among beavers. Some overlap of home ranges occurred, especially on the river, but most home ranges were almost exclusive to a family group. I found no evidence that scent mounds delineated territory and no evidence to prove the presence of territories. I hypothesize that mutual avoidance is more likely than territorialism.
Beavers in the taiga show a preference for Populus tremuloides as a primary food in both spring and summer. In spring Pinus banksiana is also consumed. P. tremuloides leaves are the preferred summer food and P. tremuloides bark and P. banksiana growing tips are preferred in spring. Beaver food choices appear to maximize protein intake and minimize potassium to sodium ratio. This strategy may serve to foster growth during the relatively short period of high protein availability.
DNA fingerprinting studies of 60 beavers showed a mean band sharing coefficient (BSC) among unrelated beavers of 0.36 ± 0.087, and among known first order relatives of 0.62 ± 0.099. Beavers of unknown relationship in the population had a mean BSC of 0.40 ± 0.107, significantly smaller than known first order relatives, but significantly larger than the value for unrelated animals. Further study is needed to determine what role the relatedness plays in limiting territorial behaviour.
This page created March 2, 1999.
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