Behavior, Activity Patterns and Foraging Strategies of Beaver (Castor canadensis) on Sagehen Creek, California

DOCTORATE DISSERTATION:A study of the behavior, activity patterns, and foraging of beaver was conducted at Sagehen Creek...adult beavers were radio-collared These data were used in investigating den use, resting associations and activity patterns. Beavers utilized from 20 to 60 percent of the identified resting sites in their home ranges with burrows being used preferentially over bank lodges and lodges...Beavers tended to be crepuscular to nocturnal with the level of activity gradually decreasing as the night progressed. A mid-morning to early afternoon period of activity, preceded by several hours of inactivity, was detected. It is hypothesized that this diurnal period of activity represents bouts of coprophagy intermixed with activities such as self and mutual grooming, and den cleaning All age-sex classes spent the greatest percentage of their time in personal maintenance behavior, with kits spending significantly more time on these activities than did adults or yearlings. Colony maintenance activities were performed by all age-sex classes, but kits spent less time than did adults or yearlings. The seasonal rates of performance of three food-related behaviors (cutting willows, transporting willow, and feeding on grass, and three non-food-related activities (grooming, swimming, and resting) differed among age classes. With seasons combined, kits spent less time acquiring willow than did adults or yearlings and more time eating grass than did adults. Kits spent more time than adults or yearlings in swimming, and more time than two-year-olds or adults in resting. Grooming behavior was performed less frequently by kits than by adults... It is hypothesized that the kits small size, which makes them more vulnerable to predation and at risk for hypothermia, may in part be responsible for these differences in their behavior. Two adult beavers were maintained in captivity for metabolic trials. Average daily forage consumption rates were lower for both animals when they were eating aspen than when they were fed willow Nutritional analysis of food detected little difference between aspen (Populus temuloides) and willow with the exception of total dietary fiber content, which was 1.4 times higher in willow than in aspen. Habitat use was determined by stream survey, colony mapping, and vegetation surveys. A GIS system, containing 15 layers of information was developed. Information pertaining to the biomass and productivity of preferred beaver foods and to beaver foraging activity was developed Bank lodges, found in nine of the colonies, accounted for 8 percent of indicators found and comprised 45 percent of all dwelling sites located. Beaver foraging was examined at various distances from water for three groups of plants: 1. small and 2. large aspen trees and 3. all willow. The ratio of mean stem size cut to mean stem size available was greater than one for all distance categories and for all plant groups, indicating that large branches were always preferred. Beavers cut significantly larger material than they avoided for all plant groups and all distance categories. Positive correlations between distance from water and mean size of stems harvested were found for all three plant groups. Negative correlations between distance and the percentage of available stems cut were found for all size classes of aspen saplings and for three of five size classes of large aspens Beavers selected, at all distances from water, aspen stems that were more profitable than those not harvested, but they selected willow stems of equal or less profit than those left standing. A positive correlation between distance from water and mean profit of stems cut was found only for aspen saplings. The impact that beavers have upon their food resources was evaluated for three colonies Though the beavers feeding activities caused occasional loss of willow bushes, colony-wide decreases in aspen and willow biomass were not found. Instead, the amount of willow and aspen available at each site increased gradually. Thus, model predictions of the initial loss of willow at Hobart Mills and Trestle-Wyethia colonies and the eradication of aspen at Wallet-Rockslide colony were not substantiate by field observations. When the entire creek was considered, willow use appeared to be on a sustained yield biomass as did aspen use when aspen represented only a portion of the diet Sagehen Creek and its associated vegetation appears to be capable of sustaining a viable beaver population over time. It is recommended that model refinements, including the development of site-specific regression equations for biomass and productivity, and a feeding-rate regression equation specific for beaver, be made to improve the accuracy of model predictions