Food Habits of Brown Bears on Northern Admiralty Island In
Total Page:16
File Type:pdf, Size:1020Kb
FOOD HABITS OF BROWN BEARS ON NORTHERN ADMl,RALTY · I SLANP. , SOUTHEAST.~LASKA ·A THESIS. Presented -to ~he Faculty of the University of Alaska in Partial Fulfillment o·f the Requirements for the Degree of MASTER OF SCIENGE By Thomas M. McCarthy,· }).S. F.iirbanks; Alaska December-1989 FOOD HAB~TS OF BROWN BEARS ON NORTHERN ADMIRALTY ISLAND, SOUTHEAST ALASKA By Thomas Michael McCarthy RECOMMENDED: APPROVED: FOOD HAB.rrs ()F B~QWN BEARS ON NORTHERN A1)~~llAL'J:'Y ··IS.LANl;);. SOtrrliEA&T .'~S~· ·A THESIS Presented ·tro 'the Faculty of the University of Alaska in Partial Fulfillment o£ the Requirements for the Degree of MASTER OF SCIENGE By Thomas.M. McCarthy,· ~.s. Fairbanks, ·Alaska · D~cember·1989 ABSTRACT The food habits of brown bears on northern Admiralty Island in Southeast Alaska were studied through analysis of fecal samples collected in 1984 and 1985. The diets of two groups of bears were examined, those that used low elevation habitats and anadromous fish streams, and those that remained at higher elevations throughout the year. Selected forage items observed in the diets were analyzed for nutrient content. While most bears used the protein-rich salmon resource, bears at high elevations substituted deer, small mammals, and plant species and parts high in nitrogen. Both groups of bears appeared to seek a high energy diet during the fall pre-denning period. In the second phase of the study, captive brown bears were used in feeding trials to determine the digestibilities of 4 natural forages; sedge (Garex lyngbyaei), skunk cabbage (Lysichitum americanum), devil's club berries (Oplopanax horridus), and salmon (Oncorhynchus sp.). Dry matter, protein, and energy digestibilities were highest for salmon and lowest for sedge. 3 TABLE OF CONTENTS ABSTRACT .......•...•...•.•..••.•••..•.•.•••..•..•..•..•.•.....• 3 LIST OF TABLES ...•.•.•....•..•.•..•.•...•.••••.......•..•...... 5 LIST OF FIGURES ....•..•••......•..•...••..••..•...•.....•...... 6 ACKNOWLEDGEMENTS •....•...••...•.....•..•.........•............•7 CHAPTER I. INTRODUCTION .........•...•.•....•..........•......10 Study Site............................................... 14 Vegetation...........................................14 Mammals ..............................................16 Human Use ............................................18 CHAPTER II . BROWN BEAR FOOD HABITS ON ADMIRALTY ISLAND S.E. ALASKA ............•••........•••....•.....•. 22 Study Area and Methods ...................................24 Results and Discussion................................... 29 Elevation Class One <&1 ) Scats ...................... 29 Elevation~ Two (&z) Scats ......................34 Forage analysis ......................................37 Conclusions ..............................................40 CHAPTER III. DIGESTION OF FOUR NATURAL FORAGES IN THE BROWN BEAR ...•..........•..•.•........•.•......•..45 Methods ..................................................4 7 Results and Discussion..................•................ 51 CHAPTER IV. CONCLUSIONS •..•...•.••••.•.•...•.•••..••..•..•.•• 63 LITERATURE CITED ........•.•.•••...•.••••••.••.......••.•...... 66 APPENDIX ..•........•...•...•••.•.•.•.•.•••••.•.•...•.•.•...•.. 74 4 LIST OF TABLES Table 2-1. Seasonal frequency of occurrence of major foods identified in brown bear scats collected below 400 m elevation in the Hawk Inlet area of Admiralty Island, Southeast Alaska, 1984-85 ..................................... 32 Table 2-2. Seasonal frequency of occurrence of major foods identified in brown bear scats collected above 400 m elevation in the Hawk Inlet area of Admiralty Island, Southeast Alaska, 1984-85 .....................................35 Table 2-3. Nutrient values of major food items in brown bear diets on northern Admiralty Island, Alaska, 1984-85 .....................................39 Table 3-1. Composition of individual food items and mixed diets fed to brown bears in digestibility trials conducted at the Yashington Park Zoo, Portland, Oregon, 1985 .............................. 52 Table 3-2. Apparent dry matter, crude protein and gross energy digestibilities of the basal diet (Zu/Preem omnivore chow) used in brown bear feeding trials conducted at the Yashington Park Zoo, Portland, Oregon, 1985 ....................54 Table 3-3. Apparent digestibility of dry matter, crude protein, and gross energy of experimental diets fed to captive brown bears at the Yashington Park Zoo, Portland, Oregon, 1985 ......... 55 Table 3-4. Estimated partial digestibilities for dry matter, crude protein, and gross energy of individual trial forages fed in mixed diets to captive brown bears at the Yashington Park Zoo, Portland, Oregon, 1985 .........................56 Table 3-5. Comparison of apparent dry matter digestibilities of forages with different NDF and ADF concentrations ..................................... 59 5 LIST OF FIGURES Fig. 1-1. Study site at Hawk Inlet, northern Admiralty Island, Southeast Alaska...................13 Fig. 2-1. Frequen~y of occurrence, by season, of major food types in the diets of brown bears, as determined through analysis of scats collected from below 400 m elevation at Hawk Inlet, Admiralty Island, Southeast Alaska, 1984-85 .................... 30 Fig. 2-2. Frequency of occurrence, by season, of major food types in the diets of brown bears, as determined through analysis of scats collected from above 400 m elevation at Hawk Inlet, Admiralty Island, Southeast Alaska, 1984-85 .................... 31 6 ACKNOWLEDGMENTS The Alaska Department of Fish and Game provided funding for this project. Additional support was provided by the Territorial Sportsmen, Inc. of Juneau, Alaska. I would like to express my sincere thanks to Dr. Frederick C. Dean for his time and effort throughout this project. His ecological insights and editorial abilities have been invaluable. Fred's door has always been open when direction was asked, and independence provided when desired. Fred has become a good friend to me and my family. I would also like to thank Dr. John Schoen for securing funding for this project, for his assistance in the field, and for sharing his keen understanding of brown bear ecology. John's knowledge of, and concern for, the resources of the Tongass National Forest have been an inspiration to me throughout this work. It has been a privilege to work closely with him. Committee members Dr. David Klein and Dr. Robert White provided helpful suggestions, laboratory expertise, and much appreciated manuscript review. The body of this thesis is comprised of two manuscripts prepared for 7 8 submittal to The Journal of Wildlife Management. While I was responsible for field-work, data collection and analysis, and manuscript preparation, the contributions by Drs. Dean, White, and Schoen to the project's planning and review were substantial. I am honored to be able to list them as co-authors of these publications. I am indebted to LaVern Beier for his field assistance and for keeping me in one piece during this study. Additional field assistance was provided by Harriet Quasney'. Dr. Thomas Hanley of the U.S. F. S. Forest Sciences Lab in Juneau provided expertise, suggestions, and encouragement, in addition to much needed laboratory space. Gordon Noyes and the staff of the Washington Park Zoo are sincerely thanked for allowing, and assisting with, the digestibility study. Booboo and Sarah, the zoo's bears, are thanked for tolerating the experience. I appreciated the support of all our family and friends who helped us endure. Finally, my unending thanks to my wife, Danelle, and my sons, Keegan and Kyle, for sharing the experience, enduring the rain, coping with scats in the freezer, and for making our Hawk Inlet camp a home. For Leone McCarthy 9 10 CHAPTER I INTRODUCTION Admiralty Island, in Southeast Alaska, supports one of the largest, relatively undisturbed populations of brown bears (Ursus arctos) in North America. Nearly 85% of the island's 2,734 km2 was placed in national monument wilderness status by the Alaska National Interest Lands Conservation Act (ANILCA) of 1980. The monument and the national forest lands that make up most of the island, are administered by the United States Forest Service (USFS). The Alaska Department of Fish and Game (ADF&G) began a study in fall 1981 to determine seasonal distribution, habitat preference, and den site and home range characteristics of brown bears on the northern portion of Admiralty Island (Schoen and Beier 1982). Age, sex, and body measurements were also recorded. To date, 68 bears have been captured, equipped with radio collars, and released. Data obtained through radio relocation from fixed-wing aircraft were used to determine movements, home ranges, and habitat use. Southeast Alaska brown bears are generally believed to follow a typical pattern of movement between spring and fall denning:(l) they leave high country dens in spring to feed on newly emergent vegetation along beaches and tidal flats; (2) they move upward in early summer to feed on new vegetation; (3) they return to lower elevations to feed on spawning salmon in midsummer; and (4) they return to alpine areas to 11 feed on vegetation prior to denning. However, Schoen et al. (1986) identified a small portion of radio-collared bears that did not use coastal salmon streams during the summer but remained in the interior regions of the island. The terms "coastal" and "interior" are used to differentiate between the 2 groups of bears. Increased use of higher elevations, extensive foraging on berries, and a