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A study of the ecology of beaver in central British Columbia Cottle, Walter Henry 1951

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A STUDY OF THE ECOLOGY OF BEAVER IK CENTRAL BRITISH COLUMBIA by WALTER HENRY COTTLE A thesis submitted i n p a r t i a l f u l f i l m e n t of the requirements for the degree of Master of Arts in the Department of Zoology We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF ARTS. Members of the Department of Zoology THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1951 ABSTRACT Prior to the present work no studies had been made of the ecology of beaver ln the glaciated areas of the intermoun-ta l n plateau of B r i t i s h Columbia, F i e l d studies for th i s study were'carried out in the forested areas of the Cariboo and C h i l c o t l n D i s t r i c t s of the Province during the summers of 19^9 and 1950. In 1950 these studies were l i m i t e d to the trapllne of Mr. £. C o l l i e r , Meldrum Creek, B. C. Two p a i r of l i v e beaver were released on C o l l i e r ' s trapllne by the B r i t i s h Columbia Game Department i n 19^2 and by 1950 these had increased to twenty-one colonies in addition to animals harvested i n 1950* Studies were made of some con-di t i o n s a f f e c t i n g this Increase. Examination of areas inhabited by beaver shoxved that although water i s apparently important to the animals as pro-tection from the climate and for escape from certain enemies, i t also provides the means whereby the beaver store winter food. Records were kept of the water l e v e l s of nine beaver ponds and these showed that beaver dams act as ai regulating mechanism and tend to prolong the flow of water ln 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 a f f e c t i n g the rate of"growth' and reproduction of aspen was made. T a l l i e s were made of the stumps of the aspen trees cut i n 19*4-9 by beaver of twelve colonies and of trees i n sam-ple areas in stands available to these colonies. Such t a l -l i e s showed that beaver cut a l l sizes of aspen without prefer-ence 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 r e l a t i o n to the a v a i l a b i l i t y and to the rate of reproduction of aspen demonstrated that beaver on the study area occupy two somewhat d i s t i n c t habitats, namely lakes and streams. Populations on lakes tend to be stable as there i s s u f f i c i e n t reproduction i n 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 obser-ved to have increased the habitat suitable to a number o f other species of vertebrates. r / ACKNOWLEDGEMENTS The writer wishes to acknowledge the h o s p i t a l i t y of Mr. and Mrs. E. C o l l i e r which he enjoyed while engaged i n f i e l d studies during the summer of 1950. Thanks are extended also to Mr. M. L. Gibbons, Mr. S. Barrett, Mr. F. Hooker and Mr. J . wiggens, trappers who kindly supplied the writer with beaver carcasses; to other trappers who aided Mr. F. MacLeod and the writer i n the i r 19^9 survey; to Dr. W. A. Clemens, 'Dr. I. McT. Cowan and Mr. J . Hatter for t h e i r guidance and th e i r aid in preparing t h i s thesis; and to the B r i t i s h Columbia Game Department for f i n a n c i a l assistance. F i n a l thanks go to my wife through whose lnsistance this thesis was completed. i v TABLE OF CONTENTS INTRODUCTION 1 Systematic Position of Beaver 3 L i f e History 4 DEFINITION OF THE STUDY AREA 7 HABITAT REQUIREMENTS OF BEAVER , 9 Water and Food 9 Construction Materials 10 THE EFFECT OF BEAVER ON STREAM FLOW AND EROSION 13 FACTORS AFFECTING- GROWTH OF THE BEAVER POPULATION 20 FOOD HABITS 26 Sizes of aspen preferred .- 29 Wastage of Aspen 29 Distance Foraged for Aspen 30 Rate of Aspen U t i l i z a t i o n 30 Factors A f f e c t i n g the Growth and Reproduction of Aspen ..... 32 Rate of Growth of Aspen 36 Carrying Capacity 36 RELATION OF BEAVER TO SOME OTHER VERTEBRATES k2 PARASITES AND DISEASE 45 V CONCLUSIONS hb APPENDIX ^9 Beaver Trapllne Management .. ^9 LITERATURE CITED 56 v i FIGURES 1. Map showing location of study area » 8 2. The winter food cache of Colony 15, October 1950 . . . . 10 3 . A large beaver house l n Spout Lake near Lac l a Hache. 12 4-. The dam of Colony 2 i n August. Beaver had cemented the dam with mud during the summer months 16 5 . Marsh vegetation invading a drained beaver pond ...... 12> 6. A sedge meadow showing the remains of an old beaver dam i n the foreground 19 7. Increase In numbers of beaver colonies on the study area following Introduction of two pair i n 19^2 21 2>. The sequence in which colonies became established ... 22 9 . Sample from remains of old food cache, Colony 21 . . . . 2g 10. Aspen—size d i s t r i b u t i o n and size selected by beaver. 29 IH. U t i l i z a t i o n of aspen cut by beaver 29 12. Curve for computing the weight of bark and twigs from aspen trees "of various diameters 32 13. Reproduction of aspen and lodgepole pine in an area following f i r e 33 lM-. Reproduction of aspen on a good site two years af t e r cutting , 34-15. Lack of reproduction of aspen i n a conifer f o r e s t . Pond 13 .• 35 16. Lack of reproduction of aspen on a dry s i t e . Pond 13. 35 17. Growth of aspen • 3 b • l g . Map of Madden Lake 37 19. The dam of Colony 15. in May, 1950 52 20. Beaver fence constructed across an i r r i g a t i o n d i t c h . . 52' v i i 21. Sectional view of beaver fence showing po s i t i o n of metal bars 52 22. Suggested methods for pipes through beaver dams to control water l e v e l s 53 v i i i TABLES I. Materials used by beaver f o r construction of houses and dams * 11 I I . Volume of water held by and escaped from nine beaver ponds during the summer of 1950 • » • • • 15 I I I . Years during which colonies were established on the study area 21 IV. The occurrence of food items i n stomach contents of nineteen beaver trapped i n the spring of 1950 . . . . . . . 27 V. T a l l i e s of aspen cut by thirteen beaver colonies and the c a l c u l a t i o n of the mean amount of food material made available per colony 31 VI. Calculation of the annual Increment of aspen about Madden Lake (Colonies 20 and 21) * . 3& VII. Calculation of the carrying capacity of seven ponds.. 39 VIII. Broods of waterfowl observed on beaver ponds 4-3 A STUDY OF THE ECOLOGY OF BEAVER IN CENTRAL BRITISH COLUMBIA • INTRODUCTION The beaver (Castor canadensis) has long been an important fur resource of the hinterland of B r i t i s h Columbia. Overexploitatlon of the resource and destruction of habitat i n the past resulted i n a decline of the beaver population u n t i l the early 1930*s when in many areas of Central B r i t i s h Columbia beaver were scarce or extirpated. Since that time, with the aid of such management practices as r e g i s t r a t i o n of trapllnes, l i b e r a t i o n of l i v e beaver in depopulated areas, and from protection afforded by compulsory tagging of beaver p e l t s , this fur bearer has increased. At the present time beaver are.an Important item In the economy of many areas. Knowledge of the i n t e r r e l a t i o n of beaver with t h e i r environment i s required to properly manage the resource. A number of studies of the ecology of beaver have been made In the eastern hardwood forest and in the t r a n s i t i o n a l type forests bordering the Great Plains but l i t t l e or no c r i t i c a l work has been done within the environment c h a r a c t e r i s t i c of the heavily glaciated regions of the inter-mountain plateau of B r i t i s h Columbia. The present study was designed to ob-ta i n data that would lead to a better understanding of the ecology of beaver ln that region. Studies were made of the environment to determine the effect of beaver thereon, of the ecological features which influenced the location of beaver colonies, of the r e l a t i o n of beaver to other w i l d l i f e species and of the response of beaver to certain management techniques. P a r t i c u l a r atten-tion was paid to food consumption and to the reproduction and growth of the chief food species. A number of studies have been made of the feeding habits of beaver and workers agree that aspen (Populus tremuloldes ) ris the chief source of food of the beaver. Bradt (1937) using the mean number of trees per acre found i n aspen stands In-Wisconsln estimated that one acre of aspen would support one beaver approximately one year. He recognized that continued growth of the aspen stands would influence t h i s figure. In the present study the writer attem-pted to determine the conditions required i n aspen stands for s u f f i c i e n t reproduction and growth, under conditions found i n Central B r i t i s h Columbia, i n order that such stands would not be depleted when under use by beaver. F i e l d studies were carr i e d out In the summer months of 1949 and 1950. During May and June of 19^ 9 the writer, accompanied by Mr. C. F. MacLeod v i s i t e d a number of trapll n e s i n the Cariboo and C h i l c o t i n D i s t r i c t s of B r i t i s h Columbia to learn of the types of habitat occupied by beaver and of the problems confronting trappers l n the management of beaver t r a p l l n e s . During the summer of 1950 the writer c a r r i e d out 3 more detailed studies concerning the r e l a t i o n of beaver to t h e i r environment and of t h e i r response to management. These studies were made on the t r a p l i n e of Mr. E. C o l l i e r where the v a r i a b i l i t y of habitats and the undocumented work of Mr.Collier In development of them rendered the area a t t r a c t i v e for ecolo-g i c a l and management studies. It i s hoped that the findings of t h i s study w i l l contribute to the advancement of beaver management i n B r i t i s h Columbia. SYSTEMATIC POSITION OF BEAVER The genus Castor Linnaeus (1758) i s the only l i v i n g genus of the rodent family Castoridae. It i s repre-sented i n Europe by Castor f i b r e Linnaeus (l / 5 9 ) and i n North America by Castor canadensis Kuhl ( l g 2 0 ) . In North America beaver frequent the wooded areas from Mexico to the northern tree l i m i t in Canada and Alaska. Four subspecies are said to occur i n B r i t i s h Columbia Castor canadensis canadensis Kuhl (1220), i n the Peace River area; C. c. saglttatus Benson (1933)* i * 1 the i n t e r i o r plateau; C. c. g'aclflcus Rhoads [189&), on the P a c i f i c coast and along parts of the Columbia River drainage; and C. jc. leucodontus Gray (1869), l i m i t e d to Vancouver Island. The present study was conducted within the area populated by Castor canadensis saglttatus. The population li-on the C o l l i e r t r a p l l n e developed from the stock planted In the area l n 194-2 and which was secured from the Bowron Lake Game Reserve, the type l o c a l i t y of the race (Benson, 1933)• LIFE HI3T0RY. The l i m i t e d evidence obtained during the study sug-gested that the l i f e h i s t o r y of the beaver i n Central B r i t i s h Columbia corresponds to that of beaver in other parts of North America. Seton (1929) states that beaver are monogamous, a l -though more recent evidence indicates that under certain con-d i t i o n s this i s not always the case. G r i n n e l l et a l (l9h&) i n C a l i f o r n i a found a f t e r removal of a large proportion of the males from an area p r i o r to the breeding season^that a l l f e -males taken from the same area aft e r the breeding season^were pregnant. From t h i s i t was concluded.that beaver are promls-cuous. However, at northern l a t i t u d e s , such as l n B r i t i s h Columbia, unrestricted movement of animals from pond to pond during the breeding season i s prevented by c l i m a t i c conditions and therefore i t Is Improbable that promiscuous breeding i e common. Animals l e f t i s o l a t e d by trapping operations i n the spring presumably f i n d new mates during the season of open water. Mating i s believed to take place i n February with p a r t u i t l o n i n May. The writer found a female trapped on . 5 May 12th to be approaching p a r t u i t i o n . In Washington, Dalquest (194-g) reports a captive animal bearing young on May 1 3 t h . On the other hand, G-rasse and Putraan (1950) report occasional l i t t e r s during the summer months. However, there Is l i t t l e evidence to suggest that late breeding, which would give r i s e to summer l i t t e r s , i s common in B r i t i s h Columbia. L i t t e r s usually are of three or four young. Asdell (19^-6) reports a mean of 3«68 - .12 with a mode of four. Bradt (1933) i n Michigan, a f t e r examining s i x t y - f i v e l i t t e r s , found a mean of 3»72. Hodgden (194-9) a f t e r examination of the u t e r i of 20 females found that the average number of p l a -cental scars was 3»95« Three pregnant females trapped on the study area i n the spring of 1950 bore f i v e , four, and four young, respectively. Young are born f u l l y . f u r r e d and p r e c o c l a l . They remain with the parent colony approximately two years and therefore are present i n the colony when the next l i t t e r is born. In the spring of t h e i r second year the young leave the parent colony to disperse (Bradt, 1947). After intensive studies of beaver colonies i n Michigan, Bradt says that the two-year old animals are forced out of the parent colony before the young of that year are. born. He says t h i s provides a systematic dispersal of vigor-ous young animals. A f u l l colony of beaver therefore includes a pair of adult animals, a number of year-old animals, and a number b of young of the year. The number of animals In colonies d i f f e r . Bradt (1933)» while working on the removal of.nuisance beaver i n Michigan found from one to twelve animals i n fif t y - s e v e n colo-nies. The mean number was 5»1 with a mode of six. In estima-ting beaver populations many agencies use a higher f i g u r e . On the other hand, the B r i t i s h Columbia Came Department has used the figure three per lodge to estimate populations. A new colony has less animals than one established two years or more; which has the three age groups present. Var i a t i o n i n l i t t e r size or loss of members of a colony can also cause The v a r i a -tion i n the number present In d i f f e r e n t colonies. No evidence of the numbers of animals per colony became available during the present study. 7 DEFINITION OF THE STUDY AREA The present study was confined to traplines l y i n g within the forested regions of the i n t e r i o r plateau of B r i t i s h Columbia within that area described by Halliday (1937) as the Central Douglas F i r Section of the Montane Forest, or by Munro and Cowan (19^7) as the Cariboo Parklands B i o t i c Area. In this region Douglas f i r of the i n t e r i o r type i s the chief domi-nant but there has been widespread replacement of t h i s species by lodgepole pine as a subcliraax following forest f i r e s . Aspen which also forma a subclimax, i s well d i s t r i b u t e d and forms s o l i d stands along creeks, about lakes, and i n other areas where growing conditions are favorable. Preliminary investigations were made i n 19^9 on a number of traplines i n various l o c a l i t i e s within t h i s region, whereas the study of 1950 was confined to the C o l l i e r trapline and centered about Madden Lake, a small body of water some twenty miles north of the Riske Creek Post Office on the C h i l c o t l n Highway. (See figure 1.) .The C o l l i e r trapline includes much of the watershed of Meldrum Creek and includes Meldrum Lake (a l t i t u d e 2,300 feet, approximately). The creek drains east"some twenty miles through a series of lakes and marshes to the Fraser River. The s o i l in the area i s sparse and i s for the most . g part/"" of the podsolic type^being derived from g l a c i a l deposits re s t i n g mainly on Tertiary lavas. The area i s very rocky and i s unsuitable for any agriculture except possibly grazing. Several "swamp hay" meadows on the watershed have in the past been cut for hay by ranchers residing at the settlement of Meldrum Creek, B r i t i s h Columbia. To follow Page 2. BPfT/SH COLUMBiA 2 * ^ ~ m m * = * Scale of Mt'/es Figure 1. 9 HABITAT REQUIREMENTS OF BEAVER WATER AND FOOD of UJQ-"b*" * The presence*Is apparently Important to beaver not only to afford protection from the climate and for escape from certain enemies but also because i t provides the animals' means of storing winter food. Although a l l types of fres h -water bodies may be inhabited by beaver,by the construction of dams on small creeks they extend the aquatic environment to favorable sources of th e i r preferred foods. Although water i s necessary the presence of certain woody plant species also i s important since these are required for winter food. In Central B r i t i s h Columbia, trembling aspen (Populus tremuloides) and a number of species of willow (Sallx spp.) are the species most used f o r t h i s purpose. Aspen and.willow are cut for the winter food supply during September and October. The trees are dragged into the water and are p i l e d adjacent to'the house where they form the winter food cache. F i g u r e 2. The w i n t e r f o o d cache o f Colony 15, October 1950. CONSTRUCTION MATERIALS In the c o n s t r u c t i o n o f houses o r o f dams, beaver were found to have been v e r y a d a p t a b l e and t o have u t i l i z e d m a t e r i a l s on hand as shown i n Table I . T h i s Table l i s t s items found to have been used i n c o n s t r u c t i o n o f a number of houses and dams. Logs from o l d food caches were found to be an Im-p o r t a n t m a t e r i a l i n the c o n s t r u c t i o n o f houses. Where banks are s u i t a b l e , b e a v e r o f t e n were found t o c o n s t r u c t bank burrows I n s t e a d o f the c h a r a c t e r i s t i c house. 11 Table I . Materials used by beaver for construction of houses and dams. Material Number of Houses Number of Dams Dry willows 18 1 ^ Green willows 6 5 Green aspen lb 12 Asp.en from old food caches 17 7 Conifer logs 3 2 . Alder 2 Roots of water l i l y 2 Mud l g l h Grass and sedges l g 1M-Aquatic plants 7 10 Bones l Rock 3 Boards l TOTAL l g 14-Figure 3» A large beaver house in Spout Lake near Lac l a Hache, B. C. 13 THE EFFECT OF BEAVER ON Sl'REAM FLOW AND EROSION Beaver are capable of producing extensive changes In t h e i r environment. On creeks where beaver construct their c h a r a c t e r i s t i c dams the water which such dams impound often has had f a r reaching effects upon the ecology and the land management of the watershed. Beaver are commonly credited with s t a b i l i z i n g the water flow of the creeks they inhabit but l i t t l e information sub *A».fc^ '«i4* i s available to docramont t h i s b e l l e f a During the present study, although i t was Impossible to make controlled studies of the .influence of beaver upon the watertable or upon the s t a b i l i z a t i o n of stream flow, every opportunity was taken to make observations upon these matters. Records were kept by the writer from May 15th to October 1 0 t h , 195° of the water leve l s of nine beaver ponds and of Madden Lake, a l l of which are maintained by beaver dams. In t h i s way the volume of water which was held by the dams and the amount which escaped through these, thereby contributing to the regulation of the flow i n the creek, was determined. During the summer months the water leve l s showed a day to day v a r i a t i o n i n accordance with weather conditions.. In addition to t h i s a seasonal trend i n l e v e l s was detected. Water lev e l s i n most beaver ponds apparently drop during the f a l l and winter months. Water from the spring freshet i s thereby held i n f i l l i n g up the ponds to the l e v e l of the top of the 14 dams. Subsequently, however, the flow over the dams Is f r e -quently so heavy as to damage them and thus reduce the volume of water which might have been held from the freshet. Following the freshet of 1950, on the study area, beaver repaired the dams and thus raised the water l e v e l s u n t i l by early summer level s had reached the highest point. At the same time the flow of the creeks decreased u n t i l by midsummer more water escaped from the ponds through the porous dams, by seepage through the substratum and by evaporation, than entered the ponds. Thus leve l s dropped. In this manner the dams acted to maintain the flow of water in the creeks. This phenomenon i s i l l u s t r a t e d by Table II which shows the volume of water stored, In addition to that present May 15th , by nine beaver ponds r e s u l t i n g from the rebuilding of dams from May 15th to July 1 s t . The Table also shows the volume of water which escaped from the ponds from July 1st to October 1 0 t h . Much of this volume contributed to the main-tenance- of the flow of the creeks during the summer and f a l l months. The Table Indicates that where the l e v e l of a lake or other large body of water Is maintained by a beaver dam the presence of the dam may have a profound e f f e c t on the flow of water i n the creek draining the lake. If repair work on dams done by beaver during the summer months i s composed mainly of sticks water f i l t e r s through the dam f a i r l y r a p i d l y . However, i f , as i n Colony 2, shown i n figure ^, the dam i s heavily cemented with mud l i t t l e 15 water may be l o s t . . " . In addition to prolonging the flow of water, e v i -dence shows that over a period of years beaver are important agents i n the b u i l d i n g up of v a l l e y bottoms into f l a t meadows. A noticeable feature along the many creeks of forested areas of the C h i l c o t i n plateau^are the! numerous swamp meadows, many of which have been formed behind old beaver dams. Table I I . Volume of water held by and escaped from tnine beaver ponds during the summer of 1950. Colony Area of Water Water held Water escaped Number May 15 to July 1 July 1 to Oct. 11 1 12 acres 3.0 acre feet (pond abandoned) 2 5 acres O.g acre feet 1.6 acre feet 4- 26 acres 7.6 acre feet g.b acre feet 5 6 acres 1.3 acre feet 3.3 acre feet 15 g acres 2.0 acre feet 3»g acre feet 16 10 acres -O.g acre feet 2 .3 acre feet IS 29 acres 4-.g acre feet no October reading Madden Lake 100 acres -g.O acre feet 77.0 adre feet 2 acres 4.0. acre feet no October . reading » One acre foot approximately equal to 4-5*000 cubic feet 16 Figure The dam of Colony 2 in August. Beaver had cemented the dam with mud during the summer months. when beaver dam a stream the pond which i s formed immediately begins to c o l l e c t s i l t and debris from the water and thus the pond begins to f i l l . Such material, along with the remains of plants which l a t e r grow i n the water, c o n t r i -butes to building up the subaqueous strata. After oond number one was abandoned by beaver in July the water l e v e l drooned and a heavy layer of th i s material was exposed i n shallow areas. The writer found areas newly flooded by beaver were soon invaded by free f l o a t i n g aouatlc plants including U t r i -cular l a vulgaris, Lemna. minor, Lemna t r l s c u l c a , F o n t l n a l l s sp. 17 and various algae. Older ponds were found to support many ad-d i t i o n a l aquatic plant species including Myrlophyllum exalbe-scens, Polygonum natans. Potamogeton pectlnatu6, P. panorml-tanus, P. Rlchardsonil. Ranunculus aquatilus, Chara vulgaris, Hippurls vulgaris, Sparganlum simplex, and Nuphar polysepala. About the margin of such ponds marsh vegetation, Including Carex spp. and many associated species had become established. Examination of three drained beaver ponds showed that following draining, marsh species soon invade the exposed bottom, as shown in.figure 5» to form wet sedge meadows. Accu-mulation of thi s plant material gradually has f i l l e d up the depressions formerly occupied by many such ponds. Evidence of old beaver dams across the creeks draining Cotton's Meadow and T i l l Meadow (see trapllne map) and a number of smaller meadows on the study area suggests that repeated flooding has often contributed to bu i l d i n g up sedge meadows, many of which cover large areas. Racey (1935) states that Horseshoe creek i n the Ch i l c o t i n D i s t r i c t of B r i t i s h Columbia has been made into a series of meadows by the action of beaver and that these mea-dows now support a heavy growth of Carex spp. and associated species. According to Wilde et a l (1950) such sedge meadows may r e s i s t invasion by the surrounding forest for many decades. P r i o r to the establishment of the coniferous forest on such areas, there i s a slow encroachment of willow, alder and Figure 5. Marsh vegetation invading a drained beaver pond. mesophytic shrubs. Seton (1929) reports that ln Yellowstone Park bea-ver ponds deserted i n 1903-04- were well formed meadows by 1912 and by 1921 the ground was s o l i d and the dams obliterated. According to Ruedman and Shoemaker (193^) the broad f l a t a l l u v i a l plains of the Troy River Valley of the Cat s k i l l region of Eastern United States are the work of beaver rather than the bottoms of pr e h i s t o r i c g l a c i a l lakes as previously assumed. They add, however, that much of t h i s may have been the work of giant pleistocene beaver (Castoroldes ohloensls) and that the process of meadow building progressed over a period of twenty-five thousand years. 19 F i g u r e b. A sedge meadow showing the remains o f an o l d beaver dam In the f o r e -ground. 20 FACTORS AFFECTING- GROWTH OF  THE BEAVER POPULATION As the present heaver population on the study area was established by the release of two pair of l i v e animals i t was possible to follow the population increase and to detect features of the environment which Influenced the location of beaver colonies. : In September 1942 the B r i t i s h Columbia Game Depart-ment released four beaver on the C o l l i e r t r a p l l n e to re-estab-l i s h beaver thereon. Although the sexes of the animals were unknown, l a t e r evidence suggests that two males and two females were l i b e r a t e d . From these two pair the animals increased so that i n 1950 there were 21 active colonies on the tr a p l l n e in addition to the f i f t e e n animals harvested during the open sea-son of 1950. C o l l i e r reported that shortly a f t e r the l i b e r a t i o n beaver became established at the point of release and l n addi-tion a colony appeared in a pond (#13) eight miles away. Table III l i s t s the years during which successive colonies became established. The increase ln number of beaver colonies on the study area from 194-2 to 1950 i s represented i n figure 7. This Increase i s compared to the p o t e n t i a l Increase at two rates, one assuming four young survive from each l i t t e r to establish two colonies l n thei r second year, and one assuming two young 21 Table I I I . Years during which colonies were established on the study area. Year .Colonies established (See t r a p l l n e map.) Colonies Abandoned 19^2 2 1 #1,.#13. 1945 5 1 #7, #11, #20. 1946 g 2 . #g, #12, #lg. 1947 12 .3 #3, #9, #10, #16. 1948 16 4 #2, #5, #6, #21. * ' 1949 l g 5 #15, #17, #19, #25, #6, #12. 1950 21 6 #4, #23, #24, #26, #1, #3, • #27, #2g. #13, #23. survive from each l i t t e r to establish one colony i n t h e i r second year. It was observed that the actual Increase lay between these two rates. This conforms with the findings of other workers (Bradt, 1947; Bailey, 1927) who agree that the mortal-i t y among beaver i s low in newly established areas. Emigra-ti o n , natural losses, and trapping (1950 f i r s t year of trap-ping) each year cause an increasing discrepancy between the p o t e n t i a l and the observed rate of increase. A number of factors were found to determine the To follow Page 21. / / 19+2. '9+3 t&?S 194-7 /9+9 ISSO J9S/ //VC#£AS£~ IN NUMBERS OF B£A\/£R COLOA//£S OA/ STUDY fOUOU/A/6 //Vr#ODVCT/OA/ OF TU/O PrtfX /A/ /S4-2.. Figure 7. 22 s u i t a b i l i t y of s i t e s for the establishment of new colonies. Dispersing two-year old animals may or may not e s t a b l i s h colo-nies near the parent colony. For example, before establishing colonies transient beaver of Colony 13 In 19^2, of Colony 7 In 19^5* and.of Colony IS i n 19^b passed through several areas, which were suitable as they were l a t e r developed by other bea-ver.A Animals of other colonies settled i n s i t e s near the parent colonies. Observations of the l o c a t i o n of twenty-four beaver colonies on the study area showed that each was estab-li s h e d in a natural pond i n a creek, in ponds formed behind dams constructed by C o l l i e r , or i n lakes. Of the twenty-four colonies, eighteen had enlarged the o r i g i n a l area of water by damming the outlet. The current of water escaping from a. pond seemingly i s the stimulus which causes beaver to dam the outlet. As the l e v e l r i s e s and water escapes about the material already in place, the same stimulus probably causes the animals to mass more sticks and mud. A dam i s often so constructed which i s apparently much higher than the heeds of the animals. During the 19^9 survey the writer observed a number of beaver colonies established in ponds where only l i m i t e d quantities of aspen or willow were available to the animals. Apparently the presence of the pond i s a stronger Inducement to beaver to colonize an area than i s the presence of an ade-quate food supply. C o l l i e r has taken advantage of t h i s fea-ture and has been able to hold many of the dispersing, animals on his trapline by constructing a number of dams, in favorable locations, on creeks so as to form ponds which have l a t e r been occupied. Beaver appear intolerant of a high population den-s i t y so that even though there i s much, habitat available the number of colonies w i l l not exceed a certain density. Neither * the writer nor a number of trappers whom he contacted.have observed more than two active colonies on a moderate size lake (up to approximately three hundred acres) or more than four active colonies per mile of creek. Probably t h i s saturation point i s related to a t e r r i t o r i a l behavior of beaver which has not yet been investigated. This intolerance to a high population density appears to be the chief factor l i m i t i n g the number of beaver colonies on the study area. It i s l i k e l y this saturation point tendency that has rendered commercial beaver farming impractical as reported by Bradt (1947) and Grasse and Putman ( 1950) . Once established, colonies appear to be reasonably permanent. An examination of five ponds to determine the cause of abandonment during 1949 and 1950 ( l i s t e d in Table IV) revealed that each was vacated only under such adverse condi-tions, as heavy trapping, food exhaustion, irreparable damage to the dam. Colony #6 (abandoned 1949) Examination of the area adjacent to the pond showed that the food species had been depleted. Aspen and willow were 24 abundant about the nearby lake and It i s l i k e l y that the a n i -mals moved to this more favorable habitat. Colony #12 (abandoned 1949) This colony was located.in a small pond surrounded by a mixed forest of conifers and aspen. Investigation showed that most of the aspen and willow adjacent to the pond had been removed and apparently the animals moved to a more favor-able habitat. Colony #1 (abandoned 1950) Beaver disappeared from this colony approximately July 1 s t . During the open season of 1950 one adult female (pregnant) and one adult of undetermined sex were removed. A l -though the remaining animals vacated the area and the location was not reoccupied during the balance of the summer, i t i s pos-sible that the area w i l l be reoccupied i n 1951. Colony #3 (abandoned 1950) After the spring freshet of 1950 beaver raised the l e v e l of the pond but the escaping water washed out the dam. This dam, b u i l t by C o l l i e r i n 1946, was constructed of gravel and lacked any reinforcement. After several unsuccessful attempts to repair the break beaver abandoned the area. Colony #13 (abandoned 1950) A mixed stand of conifers and aspen once surrounded this colony. P r i o r to the study, beaver had removed a l l aspen 25 for a distance of for t y yards from the pond and i n addition had cut a number of small Douglas f i r and lodgepole pine. Five animals were trapped during the open season of 1^50 and any others apparently emigrated. Colony #23 (established and abandoned 1950) This colony was located on the creek draining Madden Lake. I t was established i n May 1950 and was abandoned in late August when the water l e v e l of the pond dropped, due to exces-sive subterranean drainage. 2b FOOD HABITS A number of techniques are useful in the study of the food habits of beaver. A directrapproach through the examina-tion of the stomach contents of beaver taken by trappers i s In-dic a t i v e of the foods u t i l i z e d i n the spring months. However, this method i s not'accurate as the materials are f i n e l y ground and are d i f f i c u l t to i d e n t i f y . A search for t e r r e s t r i a l plants cut by beaver during the summer gives some evidence of foods u t i l i z e d during that season. Each of these methods, however, f a i l s to detect the use of soft foods obtained from submergent aquatic plants. winter foods can be Investigated through the analysis of the winter food caches. Unfortunately, a close scrutiny of the new food, caches in the f a l l could not be made in the present study as th i s might have disturbed the animals. Analysis of the remains of old food caches on the other hand, does not y i e l d quantitative results as many of the larger items are used i n construction work. However, such analyses showed that aspen was the chief source of winter food. A quantitative study of the aspen u t i l i z a t i o n was possible by the t a l l y of stumps of t£ees cut by beaver. Examination of the contents of the stomachs of nine-teen beaver trapped in A p r i l and May, 195°» showed that the beaver had consumed mostly the bark and twigs of aspen and w i l -low along with a number of other Items, as l i s t e d in Table IV. 2 7 Table IV. The occurrence of food items i n stomach contents . of nineteen beaver trapped i n the spring of 1950* Species Part Occurrence i d e n t i f i e d i n number of stomachs Populus tremuloides Bark and twigs 1 9 Salix sp. Bark and twigs 1 9 G-ramineae Stems and leaves Carex spp. Stems and leaves 3 Scirpus sp. Stems 2 Equisetum sp. Stems 2 Nuphar polysepala Rhizomes 2 Pinus contorta Leaves 2 Plcea sp. Leaves 2 Pseudotsuga t a x i f o l l a Leaves 1 Thu.la p l l c a t a Leaves 1 Betula sp. Bark 1 Hlppurls vulgaris Stems 1 Miscellaneous Leaves 2 Fish Skeleton 1 f i g u r e 9. Sample from remains o f o l d f o o d cache, Colony 21. D u r i n g the summer months the a n i m a l s were found t o c u t v e r y few aspen t r e e s , but c u t t i n g o f o t h e r p l a n t s p e c i e s found i n c l u d e d w i l l o w ( S a l l x s p p . ) , a s t e r ( A s t e r c o n s p l c u u s ) . r o s e bush (Rosa sp_. ), Saskatoon bush ( A m e l a n c h i e r sp>). a l d e r ( A l n u s s i t c h e n s l s ) , v e t c h ( V l c l a a m e r l c a n a ) , and mushroom (Agaricaceaej. Cut fragments o f pondweeds (Potamogetan spp.) found f l o a t i n g i n beaver ponds suggested t h a t the a n i m a l s consumed p a r t s of these a q u a t i c p l a n t s . Aspen s t i c k s predominated among m a t e r i a l s found I n the remains o f o l d w i n t e r f o o d caches, a l t h o u g h a l l caches con t a i n e d many s m a l l t w i g s from w i l l o w . I t i s l i k e l y t h a t w i l l o w made up a l a r g e r p ercentage o f the o r i p i n a l cache and due to I t s s m a l l s i z e a g r e a t e r p r o p o r t i o n of i t had been consumed than o f aspen. Pond l i l i e s (Nuphar p o l y s e p a l a ) . g r o w i n g from o l d food caches i n d i c a t e d t h a t beaver, a t t i m e s s t o r e the 29 large rhizomes of these plants for winter food. SIZES OF ASPEN PREFERRED A study of the size classes of aspen cut by beaver for winter food was made i n an attempt to determine i f there was any preferred s i z e . Data were obtained through a t a l l y of the stumps of a l l trees cut by thirteen colonies in 19^9. This was compared with the.relative abundance of the size classes available as determined by a t a l l y of trees on sample areas located on predetermined s t r i p s within the aspen stands. Beaver cut trees of a l l diameters without choice, although figure 10 suggests they select diameters from two to three Inches. This apparent preference was l i k e l y a r e s u l t of the writer having overlooked many inconspicuous cuttings of small diameters. WASTAGE OF ASPEN Wastage of aspen by beaver varies with the diameter of the tree. Small trees (less than approximately three inches) were cut and the whole tree removed to the water. Large trees were cut but only the tops and branches were removed to the water. Beaver apparently f i n d the bark of the trunks of such trees unpalatable. A number of trees cut by beaver^lodge against adjacent standing trees and do not f a l l to the ground and are so wasted. Such wastage was found to be greatest among trees four to f i v e inches i n diameter. Presumably large trees, To f o l l o w Page 29. Figure 10 To f o l l o w Page 29, 5 UTILIZATION Of ASPEN CUT BY B£AVEP O t i s / i o . *S/Z£~ CLASSES INCHES • — rULLY UT/LIZED — /*S1GT/S1LLY 1/r/LtZEO — CELLED rtA/D WAST€D F i g u r e 11. 30 because of their greater weight, crashed to the ground. Small trees, because of their size, were manipulated to the ground and removed. . Figure 11 i l l u s t r a t e s the u t i l i z a t i o n and the wastage.:;of aspen of d i f f e r e n t diameters. DISTANCE FO RAG-ED FOR ASPEN ' For the most part aspen on the Meldrum Creek waters-shed Is limited to narrow belts along creeks and about the mar gins of lakes. Only at a few points was i t found that beaver had t r a v e l l e d a distance greater than twenty yards.overland to cut aspen trees. Other workers, as reviewed by Hlner (1936), have found that beaver w i l l forage several hundred yards from water. Evidently on the study area the distance beaver w i l l forage away from water does not govern the amount of aspen available to them. RATE OF ASPEN UTILIZATION To determine the mean rate at which beaver colonies on the study area cut aspen, a t a l l y was made of a l l stumps of trees cut by thirteen colonies during 194-9. The mean amount cut per colony was considered as the average rate per year at which each colony u t i l i z e s aspen. To re l a t e the number of trees cut and the diameter trees cut to the amount of food material made available, refer ence was made to the work of Aldous (193&) at the Lake States Forest Experimental Station, Ely, Minnesota. Aldous cut the Table V. T a l l i e s of aspen cut by thirteen beaver colonies and the calculation of the mean amount of food, material made available per colony. Colony Number Years Esta-SIZE CLASSES (INCHES) blished 0-1 1-2 2-3 3-4 4-5 5_b b-7 -7-8 8-9 others 1 8 10 23 66 61 57 39 12 3 2 2 2 13 45 49 25 26 25 20 9 4 6 3 3 1 25 104 31 17 7 8 2 1 2 5 13 11 10 11 16 11 3 1 4 6 1 1 13 29 12 7 12 16 5 7 7 b 87 , 127 37 24 13 7 10 3 24 120 151 58 8 2 13 8 5 94 78 44 38 13 2 15 1 16 16 19 37 5 1 1 lb 3 5 14 19 18 16 114 7 18 4 9 44 28 17 22 14 5 3 20 21 5 2 23 67 1*3 70 60 53 27 10 7 8 Totals 77 428 848 448 326 248 142. 47 15 29 Pounds twigs/ bark and size class .16 2.1 5.6 12.5 25.0 37.5 66.0 91.0 122.0 125.0 Food material 12 899 4749 5600 8150 9300 9372 4271 1839 3625 Total food material cut--47,817 pounds; the mean per colony—3»b78 pounds or approximately 3^700 pounds 32 bark and twigs from seventy-four aspen trees ranging i n d i a -meters from one to seven Inches and was able to construct a graph giving- the amount of food available from aspen trees of various diameter. The graph i s reproduced i n figure 12. The mean amount of food material made available by the cutting of each colony per year, i n the present study, was calculated t i n Table V) using this r e l a t i o n and was found to be appro-ximately thirty-seven hundred pounds. FACTORS AFFECTING- GROWTH AND REPRODUCTION OF ASPEN The rate of growth and reproduction of aspen stands when under use by beaver are governed by a number of conditions. In some instances these may determine whether or not the stands survive. Aspen was found to be a subclimax species i n the forest succession on the study area and evidence showed that i t w i l l be succeeded by lodgepole pine, Douglas f i r or spruce. According to Harlow and Harrar (194-1) aspen i s a short-lived species maturing at from f i f t y to sixty years, whereas .the^coni-fers mature in a much longer period and thus w i l l outlive the aspen. Kittredge (1938) found that aspen reproduces large-l y by sucker.growth from roots of previous stands destroyed by cutting or by l i g h t burning. Figure 13 shows aspen and lodgepole pine reproduction following a l i g h t burn. The rate of reproduction was found to depend upon the s i t e , the s o i l To f o l l o w Page 32 5 6 7 a 9 AVERAGE DIAMETER - INCHES CURVE rex? COMPUTING THE: WEIGHT OF BARK AND TWIGS FROM ASPEN TREES OF VARIOUS DMMETERS (fro* Aido«* isia) F i a n r e 12. 33 Figure 1 3 . Reproduction of aspen and lodgepole pine i n an area f o l l o w i n g f i r e . type and other f a c t o r s . A c c o r d i n g to S t o e c k l e r (l94g) aspen i s most respon-s i v e to r i c h loams although i t i s found on a wide v a r i e t y of s o i l s . I t r e q u i r e s c o n s i d e r a b l e moisture and i s v e r y I n t o l e -r a n t to shading so that r e p r o d u c t i o n i s best where a stand i s c l e a r cut. F i g u r e 14 i l l u s t r a t e s the r e p r o d u c t i o n of aspen by sucker growth from the r o o t s of a previous stand cut by beaver of Colony 20. 34 Figure 14. Reproduction of asr>en on a good s i t e two years a f t e r c u t t i n g . Aspen t r e e s growing among c o n i f e r s reproduce slowly due to overshadowing. When such t r e e s are cut by beaver there i s l i t t l e I f any r e p r o d u c t i o n as was found l n the case of Colony 1 3 . (See f i g u r e 1 5 . ) Aspen on dry m i n e r a l s o i l grow and reproduce slow-l y . F igure l b shows cuts made of aspen growing on a dry slope. Here r e p r o d u c t i o n was l i m i t e d by l a c k of moisture. 35 F i g u r e 15. Lack o f r e p r o d u c t i o n o f aspen i n a c o n i f e r f o r e s t Pond 13. F i g u r e l b . Lack of r e p r o d u c t i o n of aspen on a d r v s i t e . Pond 13. 3° RATE OF GROWTH OF ASPEN The mean rate of growth of aspen on the study area was determined by measuring the diameter and counting the an-nual rings of 379 stumps of various diameters. Samples were taken from a number of s i t e s . Figure 17 i l l u s t r a t e s the mean age-diameter r e l a t i o n -ships of the 379 trees of diameters from one-eighth Inch to seven inches. The l i n e was calculated using the formula: slope i s equal to the sum of ^ /N . The formula assumes the "x" intercept i s "0" and i t takes into account the increased variance i n diameter with age. A discrepancy i n the d i s t r i b u t i o n of the points about the l i n e occurs among tree^s twenty to fo r t y years of age and i s due presumably to adverse conditions of growth preva-lent then. CARRYING CAPACITY Knowing the mean rate of growth of aspen, the mean rate at which beaver u t i l i z e aspen, and the amount of aspen available i t was possible to calculate the approximate carrying capacity of 'the aspen about each pond. To determine the amount of aspen available to each colony, the pond and the adjacent area was mapped on squared paper and the areas of the pond and of the aspen stand were thus obtained. T a l l i e s were made of the trees on sample To f o l l o w Page 3b. 4 6 i 11 /O — i — 20 — i 30 e in 40 SO Fears 60 ~ i — 70 G#OVr/i OF *SPFH Figure 17 . 37 s t r i p s through each stand and the t o t a l aspen available was calculated, as shown by Table VI. Figure 18 shows the-area of aspen about Madden Lake. From the mean rate of growth and from the amount of food available from each size class (Aldous 1938) the annual increment of each: size class was calculated. Applying these figures to the aspens each'stand was obtained.. Table V i l l u s -trates the ca l c u l a t i o n of the annual increment of aspen about Madden Lake. Table VII l i s t s a number of conditions e x i s t i n g at certain colonies studies and. these include the area of the pond occupied, the area of aspen available, the annual incre-ment of aspen stands i n terms of food material, and. the mean amount of aspen cut per colony by thirteen colonies. In addi-t i o n to these, the age of each pond i s given and the amount of. food material made available by cuttings of each of these colonies i n 1949. -The quotient of the annual increment by the mean amount cut per colony was taken to represent the carrying capa-c i t y of each area. Table VII shows that aspen stands about larger bodies of water are more l i k e l y to support beaver without be-coming depleted than are small areas where less aspen i s a v a i l -able. Although d i f f e r e n c e . i n the dominant size classes and d i f -ferences i n density of trees probably contribute to a conside-rate v a r i a t i o n in the annual increment per acre of various To follow Page 37-V s A Jodaepo/e. pine., \ *i£LDAVM LAKC f — jca/fe r eel dspen NORTH 'oc/gefio/e p,„a a/oncf j/toi-e. M A D D E N L / W E Sca/e . jo chaws = J rnch area ojpe/? - -ts acres area water - too Qcrej /odg»po/e pine. L£6£NO Figure 18, A>e aver dam Nearer Jo doe. buiJdm a edge hm&er typ& rtyu/ trail Table VI. Calculation of the annual increment of aspen about Madden Lake (Colonies 20 and 2 1 ) . Size Classes (Inches) 0-1 1-2 2-3 3-4 4-5 5-6 b-7 7-8 S-9 Others Number of trees available (cruise) 8,6l4 15,230 13,956 10,734 4,022 2,393 980 516 84 180 ^ ~ Increment weight bark per years .125 .144 .225 .350 .556 Ml -994 1.21 1.35 1.25 Total Increment 1,077 2,193 3,140 3,774 2,236 1,629 974 624 113 225 T o t a l — 15,9^5 pounds or approximately lb,000 lbs Table VII. Calculation of the carrying capacity of seven ponds Colony Years Area of Area of Annual Incre- Mean amount Amount cut Approxi-Number Esta- Water Aspen ment of aspen Cut by 12 by colony mate bllshed (acres) (acres) stands (bark, colonies l n 1949 carrying twigs, pounds) (bark, twigs, capacity ; pounds) (colonies) 2 2 5 • 5 900 3,700 5,500 Less than 1 3 3 10 5 3,200 3,700 2,500 Less than 1 15 1 8 4.5 3,600 3,700 1,700 1 lb 3 10 3.8 1,500 3,700 2,900 Less than 1 18 4 29 14 4,000 3,700 3,200 1 20 21 5) ) 2) 100 48 16,000 7,4oo (two colonies) 9,900 4 4 26 • 8 8,000 3,700 2 40 stands i t i s only where large stands of aspen are available that the annual increment of the stand i s equal to or greater than the mean amount u t i l i z e d per colony;- Reference to the Table also shows that such large stands were available only about the larger beaver ponds. Larger stands of aspen were available to colonies 18, 20, 21 and 4 located in flooded meadows or lakes than were to Colonies 2, 3, 15, and l b l o c a -ted i n small ponds l n creeks. Table VII also gives the amount of food material cut by each colony during 1949. Variation in t h i s figure may. have been due to: 1. Variation i n the number of animals i n each colony. 2. Variation i n the amount of aspen used i n construc-tion work. 3 . Variation i n the amount of aspen cut and wasted. Colony 15 had been established one season when the study was made and therefore i t i s l i k e l y that only one pair of beaver were in the colony in 1949, thus less aspen was cut than by other colonies. A large volume of aspen was cut by Colony 2 where wastage was high due to trees becoming lodged against adjacent standing trees. . These Investigations show that beaver on the study area occupy two somewhat d i s t i n c t types of habitat, namely lakes and streams. Beaver populations located In lakes or flooded meadows are probably stable as there i s s u f f i c i e n t reproduction ln the large aspen stands available to them to 41 I* replenish the stand when under use.by beaver. Populations located In creeks are probably not stable as there i s i n s u f f i -cient reproduction l n the stands to prevent them being deple-ted when, under use by beaver. 42 RELATION OF BEAVER TO  SOME OTHER VERTEBRATES Observations made during the study showed how the a c t i v i t y of heaver affected the habitat of several other spe-cies of w i l d l i f e . Muskrats (Ondatra zlbethlcus) were found associa-ted with beaver i n a l l ponds on the study area. By enlarging ponds beaver had increased the' habitat available to these ani-mals. Where beaver inhabit marsh areas they may increase or decrease the capacity of the area for muskrat. Evidence indicated that i n some areas shalloxtf flooding enhanced growth of the marsh vegetation, the food of the muskrat, whereas i n other areas excessive flooding had drowned out much of this vegetation. J e l l i s o n (1949) reports that tularemia has been found to be epidemic among muskrats in overpopulated marshes. In addition he showed that the. causative organism, B acterlum r  tularense. can be contracted by beaver from water. Presumab-l y i f t h i s disease were to become epidemic among muskrat i n marshes also occupied by. beaver, the beaver population would become exposed to i n f e c t i o n . Beaver ponds provide habitat for a number of spe-cies of* waterfowl. Eight species of ducks were observed with broods on beaver ponds. These are l i s t e d in Table VII. 43 Barrow's golden-eye, mallard, green-winged t e a l , and b u f f l e -head were the species most frequently seen, each pond support-ing at- least one brood of one of these species. Lesser scayp ' were common on flooded meadows. According to Pirnie' ( 1 9 3 5 ) small crustaceans and aquatic insect larvae are important food f o r young ducks. Plankton trawl samples from the water of beaver ponds showed a r i c h fauna of these organisms available to broods there. During August, molting and birds i n f u l l eclipse plumage were numerous on those beaver ponds which supported heavy growths of duck food, plants. Table. VIII. Broods of waterfowl observed on beaver ponds, Species Numbers of Broods on Number of Beaver' Ponds Barrow's golden-eye 9 on 9 Lesser scaup 9 on 6 Mallard 6 on 6 Green-winged, t e a l b on 5 Bufflehead 5 on 5 American baldpate 2 on 2 Ringneck 1 on 1 P i n t a i l 1 on 1 44 Controversy exists regarding the effect of beaver on sport f i s h i n g . On the Meldrum Creek watershed beaver l i k e -l y made l i t t l e change in the sport f i s h i n g as a l l lakes i n the area are shallow and are unsuitable for trout which i s the common sport f i s h in Central B r i t i s h Columbia. The watershed was found heavily populated by squawflsh (PtTchocheilus  oregonensls). Apparently beaver only increased the area of water available to this coarse f i s h . 45 PARASITES AND DISEASE During the study the carcasses of nineteen heaver trapped during the open season of 1950 were examined f o r para-sit e s and for evidence of disease. Erickson (1944) i n a review of the parasites of beaver reports only six species of helminths from beaver and of these two were single records from animals i n zoological gardens. The small nematode Travassos^s amerlcanus, which was found In large numbers i n the stomachs of a l l the beaver examined by the writer are reported to be common to beaver of a l l Worth America. The hookworm C astogstrongylus c a s t o r l . was found in the caeca of seven beaver examined by the writer. Erickson also reports t h i s species as a common parasite of beaver. The large fluke Stichorchls subtrlouetrum reported by Cowan (1941) as common In beaver from Vancouver Island was found in the caeca, of eleven beaver examined by the writer. No evidence of injury, attributable to the pre-sence of these I n t e s t i n a l worms, was found i n the preserved carcasses examined. A single specimen of an uni d e n t i f i e d female Acantho-cephalan was found attached to the mucosa of the ileum of a female adult beaver trapped at Horsefly, B. C. No evidence of mortality among beaver, due to bac-t e r i a l Infection came to the writer's attention during the present study, although J e l l l s o n (1949) reports that the ani- . mals are susceptible to tularemia, a disease common among rodent 46 CONCLUSIONS 1. Observations during the present study suggested that bea-ver show a saturation point type of population l i m i t . I t . i s l i k e l y that t h i s Intolerance to high density has been the chief factor l i m i t i n g the number of beaver colonies in the study area. 2. The release of two pair of l i v e beaver on the C o l l i e r trap-l i n e was successful i n re-establishing the population thereon. Conditions governing the dis p e r s a l of beaver have not ;aitL been determined, but the presence of a body of water appeared, essential i n the location of new colo-nies. The presence of adequate food supplies seemingly had l i t t l e influence, 3. The presence of beaver dams on the Meldrum Creek watershed was found to prolong the flow of water i n the creek. Addi-t i o n a l water held i n ponds, when beaver repaired the dams following the spring freshet, tended to escape through the porous dams and so prolong the flow. 4. On the C h i l c o t l n Plateau beaver dams have probably been agents in building up many marshy meadows located along creeks. Evidence indicated that accumulation of s i l t and plant debris in beaver ponds tends to b u i l d up the sub-aqueous strata. • when exposed such areas are invaded, by fl marsh plant species and thus form sedge meadows. 47 5. On the study area beaver occupy two somewhat d i s t i n c t habi-tat s , namely lakes and streams. The s t a b i l i t y of the bea-ver population i n each of these habitats i s apparently related to the s t a b i l i t y of t h e i r food supply. 6. Once established, beaver colonies appeared to be reason-ably permanent and s i t e s were abandoned only when colonies were under adverse influences. 7. In Central B r i t i s h Columbia aspen and willow are the chief sources of winter food for beaver. On the study area the depletion of the available supply of these species has l i k e l y been a factor leading to the abandonment of a num-ber of ponds by beaver. 8. In areas where the conditions for the reproduction and growth of aspen are adequate, beaver populations on lakes w i l l l i k e l y be stable as there i s s u f f i c i e n t reproduction i n the large stands of aspen available to replenish the stand when under use by beaver, whereas populations i n streams w i l l tend to be-less stable as there i s insuf-f i c i e n t reproduction in the small stands to prevent them being depleted when under use. 9. T a l l i e s of the stumps of a l l aspen trees cut by beaver of twelve colonies i n 1949 and t a l l i e s of the trees i n sam-ple areas located i n aspen stands available to these 4g colonies indicated that beaver there showed no preference to any p a r t i c u l a r diameter of aspen trees. 10. Examination of cuts of aspen trees made by beaver showed that wastage of aspen was greater with larger diameter trees. 11. The development of habitat by beaver has resulted i n an Increase i n the habitat suitable to a number of other species of vertebrates. 49 APPENDIX BEAVER TRAPLINE MANAGEMENT As most hinterland areas of B r i t i s h Columbia are now l a i d out i n registered traplines, management of beaver i s carri e d out through the registered trappers with each trap-l i n e forming a management unit. Only non-arable areas are suitable f o r the manage-ment of beaver as here the a c t i v i t i e s of the animals do not c o n f l i c t with agriculture or some other pursuit of man. Con-versation with trappers, during the 1949 survey, showed that the settlement of arable lands l y i n g within registered trap-l i n e s has resulted i n areas within these t r a p l i n e s being made inaccessible to the trappers, i n beaver flooding a g r i -c u l t u r a l land, and i n private property trappers operating within registered t r a p l i n e s . It i s esse n t i a l that when a p p l i -cation i s made for ali e n a t i o n of crown lands l y i n g within a registered t r a p l i n e a proper evaluation of the land f o r a g r i -c u l t u r a l purposes and for the management of the fur resource be be made by the land inspector i n order that the land 4s put to proper use. In the Cariboo and the C h i l c o t i n d i s t r i c t s of B r i t i s h Columbia beaver frequently dam creeks draining mea-dows which are cut for hay. The lease holder whose hay i s -50 flooded usually destroys the heaver. To protect the Interests of the trapper a program of nuisance beaver control i s needed. When possible, nuisance beaver should be removed by livetrapp i n g as such animals can be used as stock to esta-b l i s h beaver wherever required. A number of l i v e traps have been designed and found s a t i s f a c t o r y . Plans for these have been drawn up by Couch (194-2) and are avai l a b l e . A l l animals livetrapped should be tagged i n order that records kept of the movements of such i n d i v i d u a l animals w i l l contribute to the knowledge of the population. Small numbered monel metal ear tags have been used successfully by a number of workers. Aldous (194-0) suggests punching holes one quarter of an inch In diameter through the webbs of the hind feet. A large number of combinations are possible using two punches each through a separate webb. The sex of beaver i s often d i f f i c u l t to determine because of the presence of a false cloaca. The method sug-gested by Young (1936), of ins e r t i n g the l i t t l e f inger into the cloaca and f e e l i n g for the baculum or the vaginal opening, was used by the writer and found sa t i s f a c t o r y . A number of techniques have been used successfully by E. C o l l i e r to control movements of beaver on his t r a p l l n e . Since 194-5 he has been able to Induce dispersing animals to es t a b l i s h new colonies at a number of suitable s i t e s along creeks. This he did by constructing earth dams, reinforced with f i r boughs,^which were high enough to hold one foot or 51 so of water. The presence of such ponds he found s u f f i c i e n t to cause beaver to est a b l i s h colonies. Figure 19 shows the dam of Colony 15 i n May 1950. This dam was started by C o l l i e r i n 19*8 and was taken over by beaver i n 19*9. Harris and Aldous (1946) suggest the construction of a temporary house by digging a trench from the creek up the bank several feet and then covering i t with brush, sod, and d i r t . The writer aided C o l l i e r in the design and construc-ti o n of a fence across an i r r i g a t i o n d i t c h to prevent beaver from moving up the ditch. As suggested by Bailey (1927) the fence was of standard small mesh hog wire fencing and i t ran across the d i t c h at right angles and up the bank on either side approximately t h i r t y - f i v e yards. Because beaver are able to cut away any wood used i n construction of the fence, the parts about the water, the parts to receive most attack by beaver, were made of steel and concrete as shown i n figure 20. Figure 21 shows the po s i t i o n of the iron rods used to prevent beaver moving upstream and yet allow debris car r i e d by the water to pass. C o l l i e r reported that a similar fence in the same posi t i o n had been successful for a number of years u n t i l i n 1949 the i r r i g a t i o n d i t c h was enlarged and the fence not repaired. 52 F i g u r e 20. Beaver f e n c e c o n s t r u c t e d a c r o s s an i r r i g a t i o n d i t c h . To f o l l o w Page 52. 53 It i s doubtful that such a fence would be e f f e c t i v e to control the dispersal of the two-year old beaver as Bradt (19*7) found that these animals often t r a v e l overland away from water. Such structures placed in natural water courses are governed by Chapter 3^1 (Water Act}, Paragraph 37, Section 'g' of the B r i t i s h Columbia Statutes, 194-8, and permission for t h e i r construction must be had from the Comptroller of Water Rights, V i c t o r i a , B, C. In some locations beaver raise the l e v e l of the water i n t h e i r ponds higher than Is apparently required and as a res u l t much aspen about the margin of such ponds i s drown-ed, thus reducing the amount of available food. To prevent thi s Bailey (1927) suggests placing a four to seven-Inch drainage pipe through the dam as shown i n figure 2 2(a). The Intake of the pipe i s protected by a wire screen and rocks placed over i t . The rocks break up the current of water entering the pipe thus preventing beaver from plugging I t . A pipe placed through the dam, as shown i n figure 22(b) has been reported successful. Water enters the pipe through nume-rous holes i n the part projecting into the pond. These devices could be used in areas where beaver occupy muskrat marshe! to prevent the beaver r a i s i n g the water enough to drown out the marsh vegetation. The method commonly used to census the beaver popu-l a t i o n of an area consists of a count of the active houses or To. follow Page 53. (6) . SUGGESTED METHODS FOR PfPES r/S&OUGV BEAVEA DAMS TO COA/TROL WATEf? LEVELS Figure 22. • 5 4 bank dens. Such a count i s made i n October, or November when the presence of the food.caches indicate which colonies w i l l have beaver In them the following winter. As the number of beaver-pelt seals issued to a trap-per i s based on t h i s cenus, i t should be made by an o f f i c i a l of the Game Department. The great area of B r i t i s h Columbia makes such a census impractical and an al t e r n a t i v e i s neces-sary whereby each trapper makes the annual census of his area and an o f f i c i a l of the department makes a periodic check of a l l areas. Controversy exists regarding the optimum numbers of beaver to harvest from a population each year. Harris and Aldous (1946) working i n the Black H i l l s of South Dakota, recommend keeping the number of animals at a minimum, usually one p a i r per colony. Bradt (1947) in Michigan.suggests to harvest one t h i r d of the animals on an area ( t o t a l population calculated at fi v e r p e r colony). In Manitoba (Guymer, 1950) a s l i d i n g scale i s used whereby a higher percentage of the animals are removed from trap l l n e s having a large number of colonies. A "rule of thumb" used by many trappers Is to har-vest one animal per colony each year. This approximates Bradt 1 s suggestion and should allo\\r an increase where possible. ^successful trapping program f o r any area y i e l d s a substantial harvestjyet maintains the-optimum numbers of colonies. The success of any trapping scheme w i l l be mani-fested only af t e r , a number-of years of trapping during which 55 time the records kept of the annual censuses w i l l show the trend of the population. 56 LITERATURE CITED ALDOUS, S . E . 193^. ALDOUS. S. E . 1940. ASDELL, S. A. 1946. . BAILEY, V. ' 1927. BENSON, S. B. 1933. ' BRADT, G. W0 1533. BRADT, G. W. 1947. COUCH, L. K. 1942. COWAN, I. Mc. 1941. DALQUEST, W. 1948. ERICKSON, A. 1944. GRASSE, J . E, .1950. GRAY, J. E . 1869. GRINiMEL, J., 194S. w. B. Beaver food u t i l i z a t i o n studies. Jour. WUdl. Mgt. 2(4):2lb-222. A method for marking heaver. Jour, "wild'l. Mgt. 4(2):145-148. Patterns of Mammalian reproduction. Comstock Publishing Co., I t h i c a New York. Beaver habits and experiments in beaver culture. U.S.D.A. Tech. B u l l . 21. A new race of beaver from B r i t i s h Columbia. Jour. Mammal. 14:320-325. Report on nuisance beaver control. Mich. Acad. Sci. Let. 17:509-513-Beaver management i n Michigan Game Divi s i o n . Mich, Dept. Conservation, Lansing, Mich. Trapping and transplanting l i v e beaver. U.S. Fish and Wildl. Ser. Conserv. Bull . 3 0 . Report on some diseases and parasites of game birds and furbearing mammals i n B r i t i s h Columbia. Report of B. C. Game Comm. for 1941:40-45. Mammals of Washington. .Univ. Kansas Press. Parasites of beaver with note on Paramphi-stoma ca s t o r ! (Kofoid and Park, 1947), a synonym of Stichorchls subtrlquetrum. Am. Mid. N at. 33:625. and E . F. Putman. Beaver management and ecology In Wyoming. Wyoming Game and Fish Commission, B u l l . 6. On the white-toothed American beaver. Gray Ann. and Mag. N at. H i s t . Series 4, 4:293, J . S. Dixon, and J . M. Linsdale. Fur bearing mammals of C a l i f o r n i a . Vol. 2, Univ. C a l i f . Press. 57 GUYMER, W. 1950. HALLIDAY, W.• E. D. Letter to the writer, October 2 3 . 1937. A forest c l a s s i f i c a t i o n f or Canada. Forest Service B u l l . 8 9 . Dept. Mines and Resources, Canada. HARLOW, w. M. and E. S e Harrar. 194-1. Textbook of Dendrology. M c G - r a W r - - H i l l Book Co. Inc. New. York and London. HARRIS, D. and S. E. Aldous. :9k HI'NER, L. E.-1936. HODGDON, K. W. 1949. JELLISON, W. L. 1949. KITTREDGE, J . S 1932. KUHL, H. 1820. LINNAEUS, C. 1750-. Beaver management ln the Northern Black H i l l s of South Dakota. Jour, w i i d l . Mgt. 10(10:348-353-Observations of the foraging habits of bea-ver. Jour. Mammal. 19:317-319. Productivity data from placental.scars In beaver. Jour. Wllds.lMgt. 13.(4) :4l2-4l4. Report on tularemia. Proc. Int. N. W. Conf. on Disease of Nature Communicable to Man. The i n t e r r e l a t i o n of habitat, growth rate, and associated vegetation In the aspen com-munity of Minnesota and Wisconsin. Ecol. Mono. 8(2):l51-246. Beitrage zur Zoologie und Verglelchanden Anatomie (P.64) Frankfurt .am Main. Systerna Naturae. 10th Ed. Pi 58. MUNRO, J 0 A. and I. McT. Cowan. 1947. PIRNIE, M. D. 1935. A review of the b i r d fauna of B r i t i s h Columbia. B r i t i s h Columbia P r o v i n c i a l Museum, V i c t o r i a , B. C. Special B u l l . No.2. Michigan waterfowl management. Game Di v i s i o n , Dept. Conserv. Lansing, Mich. RACEY, K. 1935. Notes on some mammals of the C h l l c o t l n , B. C. Can. F i e l d Nat. 5 0 ( 2 ) : 1 5 . 58 RHOADS 1898. Contributions to a r e v i s i o n of the North American Beavers. Trans. Amer. P h i l . Soc, RUEDMANN,. R. and w. J . Shoemaker, 1935. SETON, E. 1928. STOECKELER, J . H. 1948. Beaver dams as geological agents. S c i . Man. 881292):523-525. Lives of Game Animals. Vol. IV, P. 473-L i t e r a r y Guild of America, N. Y. (1937). The growth of quaking aspen as affected by s o i l properties and f i r e . Jour. Foresty 46:727-737. WILDE, S. A., C. T. Youngberg, and J . H. Hovlnd. 1950. Changes l n the composition of ground water, s o i l f e r t i l i t y , and forest growth produced by the construction and removal of beaver dams. Jour, w i l d l . Mgt. l4(2 ) : 1 2 3 - 1 2 9 -YOUNG, F. W. 1936. I d e n t i f i c a t i o n of the sex of beaver. Mich. Ag. Exp. Sta. Sp. B u l l . 279:1-8. N O R T H 0 M I L E S TR A P L I N E i h. i > i \ i * 11 Tra i ( Edge of Fore.5"fc Typ' C d b i n I r M * c j d t ( O h D l t c K Mead o w B e a v e r Lodcje/ B e a v e r Dom E R I C C O L LI ER M E L D R U M C R E E K . B . C . 1950 

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