This study was initiated to establish some basic factors concerning beavers which would aid in understanding changes in population numbers. It was desired to obtain optimal and maximal growth rates, to determine the caloric requirements necessary for maintenance, growth and reproduction, to establish "normal" values for various blood constituents and to correlate variations in these constituents with growth and nutrition. In order to maintain beavers in captivity specially designed pens were constructed and a ration formulated and fed to the animals in a pelleted form. Growth rates were established from the weight increases of several yearling beavers and these were compared with data presented in the literature. Only one rate was established for a kit owing to the difficulty in obtaining young beavers, however, this was supplemented with published data. Body weights were regressed against several body measurements and organ weights were regressed against body weights in order to establish the relative rates of gain for different body components. The caloric requirements necessary for maintenance were established for several beavers of different body weights and these were correlated with the quantity of natural beaver foods required for maintenance and growth. The digestibility and time of food passage was also determined for the pelleted ration. "Normal" values for 25 different blood constituents and tests were determined on an age and seasonal basis. These values were discussed in terms of growth, nutrition, stress and disease and compared with published data obtained for other species . These studies indicated that the beaver has a relatively-fast growth rate and has the ability to efficiently utilize foods high in fiber content. It showed a close similarity to other herbivores, especially those with large caecums, the site of extensive cellulose degradation. Minor physiological adaptations to its semi-aquatic type of life were also indicated. / Science, Faculty of / Zoology, Department of / Graduate

Prior to the present work no studies had been made of the ecology of beaver in the glaciated areas of the intermountain plateau of British Columbia, Field studies for this study were carried out in the forested areas of the Cariboo and Chilcotln Districts of the Province during the summers of 1949 and 1950. In 1950 these studies were limited to the trapllne of Mr. E. Collier, Meldrum Creek, B. C. Two pair of live beaver were released on Collier's trapline by the British Columbia Game Department in 1942 and by 1950 these had increased to twenty-one colonies in addition to animals harvested in 1950. Studies were made of some conditions affecting this increase. Examination of areas inhabited by beaver showed that although water is apparently important to the animals as protection from the climate and for escape from certain enemies, it also provides the means whereby the beaver store winter food. Records were kept of the water levels of nine beaver ponds and these showed that beaver dams act as a regulating mechanism and tend to prolong the flow of water in Meldrum Creek. A number of techniques were used to determine the food habits of beaver on the study area and these revealed that although beaver consume mostly the bark of aspen and willow, a number of other foods were taken. A study of the conditions affecting the rate of growth and reproduction of aspen was made. Tallies were made of the stumps of the aspen trees cut in 1949 by beaver of twelve colonies and of trees in sample areas in stands available to these colonies. Such tallies showed that beaver cut all sizes of aspen without preference and that the mean weight of barks and twigs made available by cutting was approximately thirty-seven hundred pounds per colony. Studies of the rate of cutting by beaver In relation to the availability and to the rate of reproduction of aspen demonstrated that beaver on the study area occupy two somewhat distinct habitats, namely lakes and streams. Populations on lakes tend to be stable as there is sufficient reproduction in the large stands available to maintain the stand during use by beaver. Populations on creeks eat out their food supplies and are thus forced to emigrate. By developing the aquatic habitat beaver were observed to have increased the habitat suitable to a number of other species of vertebrates. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (M.S.) in Ecology and Environmental Science--University of Maine, 2003. / Includes vita. Includes bibliographical references (leaves 67-72).

Thesis (Ph. D.)--University of Michigan, 1936. / Typescript. Includes bibliographical references (leaves 84-86).

Thesis (PH. D.)--University of Michigan, 1936. / Caption title. Thesis note on label mounted on p. 139. "Reprinted from Journal of mammalogy, vol. 19, no. 2, May 14, 1938." "Literature cited": p. 162.

The beaver (Castor canadensis Kuhl) is subjected to a widely fluctuating energy regime in the northern portion of its distribution. During the summer the animal has free access to an abundant food supply in the form of growing plant material, while during the winter the food supply is limited to a store of cached saplings. The working hypothesis of this study was that seasonal shifts occur in energy expenditure such that it is highest during the summer when an abundant food supply is readily available. In the Mackenzie Delta, Northwest Territories, growth was found to be rapid in the summer and absent in the winter. A winter weight loss characterized immature animals. Fat was deposited in the autumn, maintained during the winter and mobilized in the spring. Animals were lean during the summer. Thyroid gland weights were high in the summer and low in the winter. It was concluded from these data that metabolic energy expenditure is high during the summer and low during the winter. A consideration of possible extrinsic causes of this annual pattern and the finding that the beaver ceases to grow during the winter when on a constant ration made available ad libitum led to the conclusion that the pattern is an inherent property of the beaver at northern latitudes. The thyroid gland was hypothesized as the major effector of the annual pattern within the organism. Light intensity was hypothesized as the environmental factor that times the level of energy expenditure to environmental conditions. No major seasonal changes in thyroid activity, food intake or growth were observed in California beavers maintained under Vancouver climatic conditions and a constant ration made available ad libitum, but Arctic beavers maintained under the same conditions showed a growth cessation, a 40% reduction in food intake and a depression in thyroid activity during the winter. This is consistent with the conclusion that the annual metabolic pattern observed in northern beavers in the field is an inherent attribute. Manipulation of light conditions had no detectable effects on California beavers, but exposure of Arctic beavers to constant darkness resulted in a reduction of food intake to zero after 17 and 22 days, a weight loss and a complete muscular paralysis of unknown nature. No body temperature drop occurred. Exposure to constant incandescent light after 24 days of darkness returned these effects to normal. The thyroid hypothesis was questioned because food intake dropped to zero rather than to a low basal level during the depression. It was hypothesized that the muscular paralysis represents a peripheral control of activity that reduces winter activity to a minimum. Continued exposure of the Arctic beavers to light during the winter resulted in rapid growth and high food intake during that period. It was concluded that in nature decreasing light intensity in the autumn induces a metabolic depression in the northern beaver and increasing light intensity in the spring dispels it. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (M.S.)--Oregon State University, 1992. / Typescript (photocopy). Includes bibliographical references (leaves 87-90). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 1994. / Typescript (photocopy). Includes bibliographical references (leaves 87-90). Also available on the World Wide Web.

Thesis--Leyden.

An unsuccessful attempt was made to culture cellulolytic bacteria from the caecum of the beaver. The caecum is the site of cellulose digestion in this herbivorous rodent. Cellulose digestion takes place on the surface of the food particles as demonstrated by the erosion of the surface of cellulose paper in artificial caeca. The rate of digestion of cellulose was measured using chromic oxide as a food marker. A variation in cellulose digestion of values from zero to 43 per cent was obtained; this variation appeared to be influenced by the health status, the diet, and perhaps the readiness with which a particular animal accepted the regimentation imposed by the experimental procedures. Cellulose unquestionably contributes to the energy available to the beaver from food material ingested. The digestible energy from cellulose appears insignificant. / Science, Faculty of / Zoology, Department of / Graduate