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A Capture-Recapture Analysis of a Mountain Beaver Population in Western Oregon

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A Capture-Recapture Analysis of a Mountain Beaver Population in Western Oregon AN ABSTRACT OF THE THESIS OF BILL PERTL LOVEJOY for the DOCTOR OF PHILOSOPHY (Name of Student) (Degree) in Zoology presented on (Major) Title: THE CAPTURE-RECAPTURE ANALYSIS OF A MOUNTAIN BEAVER POPULATION IN WESTERN OREGON Abstract approved: Redacted for privacy Dr. Robert M. Storm This report summarizes the results of a field study of a popula- tion of the Pacific mountain beaver, Aplodontia rufa pacifica, from August 1965 through August 1967.The study site consisted of a 13. 5- acre grid on a logged over area in the Coast Range Mountains of Benton County, Oregon.The report also includes new data on the postnatal development, growth, and behavior of two litters of mountain beavers born and raised in captivity. The field study involved the mark-release-and-recapture method using a rotational system of live-trapping on a weekly basis. A total of 5, 144 trap-nights yielded 872 captures of 181 individuals. Of this total, 109 were adult animals and 72 were juvenilesMales outnumbered females 61.9 percent to 38. 2 percent. Population estimates were determined by direct enumeration and, ranged from a low of 41 in mid-winter to a high of 54 in July. Densities varied from 2.60 to 3.43 animals per acre.Transients made up a considerable portion of the catch.Longevity records of 5 to 6 years were estimated for wild mountain beavers. Adult males had an average home range size of 0.80 acres, adult females 0.42 acres.The home range of juveniles averaged 0.31 acres.Males made longer forays during the summer months when activity was also at a peak.Overlapping of home ranges was common. Male Aplodontia were in breeding condition throughout January, February, and March. Estrus females were available by about mid- February.Lactating females were observed from 8 April through 27 May. Young Aplodontia are weaned at 6-8 weeks of age and emerge from their burrows the following 2 weeks. The earliestdate of capture of a young in the field was 3 June. The growth curve of the young was characterized by a rapid increase during the first 8 weeks, followed by a gradual decline, and eventually reached a plateau in 4 months at 69 percent of the adult weight. Animals were classed as juveniles, yearlings, or adults based on their body weights, character of pelage, and breeding condition. Aging of mountain beavers on the basis of weight alone was con- sidered impossible due to the wide range of size within each age class.The average yearling weighed about 710 g, or 88 percent of the adult mean weight of 806 g.Adult males were consistently heavier than females.The largest male weighed 1130 g; the largest female weighed 1070 g.The body weights of adult Aplodontia were at a seasonal low during their reproductive period in the spring and at a high in mid-summer when food was most abundant. Attempts to breed Aplodontia in captivity were unsuccessful due primarily to the hostile behavior of the females. 0 1972 Bill Pertl Lovejoy ALL RIGHTS RESERVED A Capture-Recapture Analysis of a Mountain Beaver Population in Western Oregon by Bill Pertl Lovejoy A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy June 1972 APPROVED: Redacted for privacy Professor of Zoology in charge of major Redacted for privacy Head of DepartMent of Zoology Redacted for privacy De.Fn of Graduate School Date thesis is presented Typed by Ilene Anderton for Bill Pertl Lovejoy ACKNOWLEDGEMENTS I wish to extend my sincere appreciation to my major professor, Dr. Robert M. Storm, for his continued guidance and encouragement during the course of this study. I also wish to thank Dr. Hugh C. Black and the Forest Research Laboratory for providing technical assistance, equipment, and transportation during the performance of the field work.Dr. Edward F. Hooven, also with the Forest Research Laboratory, made many of the observations involved in the growth study. Mr. John R. Thompson of the Thompson Timber Company generously granted permission to conduct the study on his property. Dr. Wayland L. Ezell and La Rea Dennis Johnston of the Oregon State University Herbarium provided identification of many of the plant specimens collected on the study siteDrs. Rodger Shomake and James Wernz identified the ectoparasites found on the mountain beaver s. I would like to acknowledge with thanks the contributions of the following people: Drs. Elver H. Voth and Sheldon R. Johnson, who share a common interest in the mountain beaver. Dr. Don H. Helfer, Department of Veterinary Medicine, who performed the necropsies and provided medical advice in the treatment of captive animals. Dr. Ronald Nussbaum, for helpful advice in the handling of statistical data. Mr. Chris Maser, whose knowledge of the Oregon fauna was instrumental in locating a suitable study site. Mr. Richard Newman and many others, whose assistance and companionship in the field made the hours spent there even more pleasurable. And finally my wife, Martha, who made it all possible-- Merry Christmas. TABLE OF CONTENTS Page_ INTRODUCTION Literature Review 3 STUDY AREA 6 Location 6 Environment 6 Climate 7 Vegetation 10 Soils 19 Vertebrate Fauna 20 METHODS AND MATERIALS 23 Field Methods 23 The Field Plot 23 Trapping Procedure 24 Handling 30 Shock Treatment 33 Weather Record 34 Field Notes 34 Growth Study 35 RESULTS AND DISCUSSION 37 Trapping Results 37 Trap Mortalities 41 Movement Patterns and Home Range Sizes 41 Home Range Concepts 41 Home Range Methods 43 Home Range Results 44 Dispersal Movements 54 Population Sizes and Densities 55 Population Estimates 57 Densities 61 Survival and Longevity 65 Sex Ratios 66 Age Structure 67 Reproduction 68 Breeding Habits 68 Gestation and Litter Size 72 Weaning and Emergence of Young 73 Page Growth and Development 74 Physical Development and Behavior 75 Growth Rates 83 SUMMARY AND CONCLUSIONS 91 BIBLIOGRAPHY 95 APPENDIX I 101 APPENDIX II 104 LIST OF FIGURES Figure Page FrontispieceA young male Aplodontia rufa pacifica, showing typical feeding posture. 1. Distribution of seven subspecies of Aplodontia rufa and location of the study area.(After Godin, 1964). 2. Mean monthly temperature and monthly precipitation 11 at the study site from August 1965 through August 1967.The shaded area indicates the monthly temperature range. 3. View of the north-facing slope showing the large 12 amount of slash still present over much of the area. Photograph taken in May 1966. 4. View of the area showing various stages of Douglas 13 fir regeneration.Photograph taken in October 1965. 5. A food cache of freshly clipped sword-fern outside a 17 burrow entrance.Sword-fern was the mountain beavers' principal winter food item and began appearing in these neatly stacked piles in November. 6, A Douglas fir seedling clipped by a mountain beaver. 18 Western hemlock on the study site was also utilized occasionally as a food item. 7. Live-trap grid at the Thompson Tree Farm Study 25 Area.The grid encloses 13.50 acres and is sub- divided into 15 blocks, each containing four trapping stations (solid circles). 8. A runway set with the trap open at both ends to 27 receive an animal from either direction.The traps were covered with strips of black plastic during the winter to protect the animals from rain or snow. Figure page 9. A mound of soil pushed from a recently excavated 28 tunnel.Fresh mounds such as this are a sign the animals are enlarging or renovating their burrow system. 10. This wire mesh trap manufactured by the National 31 Live Trap Company was the type used in this study. This young mountain beaver had been feeding on bracken fern when disturbed.Note the long vibrissae extending out the side of the trap. 11, The handling cage shown here was designed to 3Z restrain a mountain beaver during the ear-tagging, measuring, and weighing procedures.The animal in the cage for this photograph is a Douglas squirrel. 12. Monthly capture record of animals taken during 40 regular weekly grid-trapping.Weekly trapping was discontinued from January through May 1967. 13. Trap-revealed movements of three adult male 49 Aplodontia rufa pacifica.The solid circles represent capture sites, the numbers indicate the number of captures at each site.An arrow indicates where the animal was captured last. 14. Trap-revealed movements of three adult male 50 Aplodontia rufa pacifica,Symbolism as in Figure 13. 15. Trap-revealed movements of five adult male 51 Aplodontia rufa pacifica showing the limited range of animal No. 25 and the relatively wide range of No. 198.Animal No. 102 and No. 116 are examples of apparent home range shifts.Symbolism as in Figure 13. 16, Trap-revealed movements of four adult female 52 Aplodontia rufa pacifica,showing the more restricted movement patterns of females. Symbolism as in Figure 13. Figure Page 17. Trap-revealed movements of two juvenile male and 53 three juvenile female Aplodontia rufa pacifica. Animal No. 128 is an example of an apparent dispersal movement. Symbolism as in Figure 13. 18. Monthly changes in population size. No data avail- 60 able for the period from January through May 1967. 19. Distribution of captures of 181 mountain beavers on 63 17.52 acres of the Thompson Tree Farm Study Area.Only the site of first capture shown for animals caught more than once. 20. A sexually mature female mountain beaver showing 71 the circles of dark hair surrounding each of the six mammae. These mammary hairs are visible only during the spring and summer months.This female was photographed in August. 21. Two-day old Aplodontia rufa pacifica, born to a 77 captive female on 3 April 1966.The young at this age are naked, pink, and quite helpless.
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