THESIS WINTER ECOLOGY OF BIGHORN SHEEP IN YELLOWSTONE NATIONAL PARK Submitted by John L. 01demeyer In partial fulfillment of the requirements for the Degree of Master of Science Colorado State University December 1966 COLORADO STATE m~IVERSI1Y December 1966 WE HEREBY RECOl-lEEND 'lRAT lliE 'IHESIS PREPARED UNDER OUR SUPERVISION BY J onn L. 01demeyer ENTITLED tt'v-linter ecolo&;,( of bighorn sheep in yellowstone National ParkU BE ACCEPTED AS FULFILLING nus PART OF 'mE ~UIIill"LENTS FOR THE DillREE OF EASTER OF SCI~CE. CO:TJli ttee on Graduate Work --- - Examination Satisfacto~ Pennission to publish this thesis or any part of it must be obtained from the Dean of the Graduate School. PJL,ORADO STATE UN !VEKS ITY LI BRARIES i ABSTRACT WIN TER ECOLOOY OF ID:GHORN SHEEP IN YELLOVlS'IDHE NA TI ONAL PARK A bighorn sheep study was conducted on the northern winter range of yellowstone National Park, TNY01~inE from JIDle 1965 to June 1966. The objectives of the study were to census the bighorn population, map the winter bighorn distribution, detennine plant conposition and utilization on irnportant bighorn winter ranees, observe daily feedine habits, and assess the effect of competition on bighorn sheep. ~o hundred twen~ nine bighorn sheep wintered on the northern winter range. These herds were located on Nt. Everts, along the Yellowstone River, on Specimen Ridge, and along Soda Butte Creek. The ewe to ram ratio was 100: 78, the ewe to lamb ra tic waS 100: 47, and the ewe to yearling ratio was 100: 20. Range analysis was done on HacHinn Bench, Specimen Ridge, and Druid Peak. Range condition was best on Specimen Ridge and poorest on Druid Peak. Grass utiliza tion varied from 50 per cent on lvlacllirm Bench to over 80 per cent on one key area on Druid Peak. Browse utilization was over 60 per cent throughout t..~e winter ranGe. Grasses made up 61.4, forbs 17.2, and shrubs 21.5 per cent of the bighorn's diet. The most important forage plants were b1uebunch whea tgrass (Agrogrron spicatwn), Idaho fescue (Festuca idahoensis), phlox (Fhlox sp.), Douglas rabbi tbrush (Chrysotharnnus viscidiflorus) , and winterfat (Eurotia lana ta). Competition between elk and bighorn Sheep was mild during the study. Because of lighter than normal ii sno-wfall, elk were not forced to occupy bighorn winter ranges. Compe- ti. tion wi th eli.: waS greatest on Speci.llen Ridge, where over 200 elk spent most of the winter. John L. Oldemeyer Deparu~ent of Fishe~ and Wildlife Biology Colorado State University Fort Collins, Colorado December, 1966 iii ACKNGlLEDGE}iEN TS I am indebted to the National Park Service, the National Wildlife Federation, the Wildlife Management Insti tute, and the Yellowstone Lib~ and Museum Association for financial support of the project. ~Iecessary facilities at Yellowstone National Park were made available to me for use during the study, and the generosi ty of Park officials was greatly appreciated. Dr. Douglas L. Gilbert was my major professor and introduced me to the possibilities of the bighorn sheep study. Dr. Gilbert was instrmnental in securing financial assistance and provided guidance, encouragement, technical suggestions, and cr! tical review of the manu­ script. I am grateful to ¥.r. Dwight R. Smith for suggestions and technical assistance. His journey with me into bighorn cOWltry was of great assistance and delight. Dr. Harold W. Steinhoff offered guidance and suggestions for the project. His efforts are greatly appreciated. Dr. Elmer E. Remmenga offered encouragement and suggestions for which I am grateful. Mr. Robert E. Howe, fonnerly Park l'lBJ'lagement Biologist at Yellow­ stone, guided the im tial study plan. His ass:is tance, guidance and encouragemen tare greatly apprecia ted. I am gra teful to ¥...r. William J. Ba:nnore Jr. for assistance and support. His experiences 'Working on the northern Yellowstone winter range and his guidance in the field were invaluable in completing the range work. Many persormel of Yellowstone National Park afforded help and. assistance. Special thanks go to Mr. Gary Brown, ~.r. Gordon Boyd, and iv Mr. Ted Scott. Mr. Richard Weaver helped. in rr~ng the distribution maps. Others who gave assistance in some way were Mr. Richard Blatt, Mr. Victor Barnes, Mr. Olin Bray, and Dr. Hal Prostka. Mr. Kermsth Greer of the Montana Fish and Game Commission permitted me to use cia ta he had assembled on stomach samples of elk collected in Yellowstone National Park. My wife, Carole, patiently typed an1 read the manuscript and recorded range composition data for me in the field. Her patient understanding and encouragement and enjoyment of life in Yellowstone National Park added much extra pleasure and satisfaction to the study. v =CD o io til = vi TABLE OF CON~TS ABSTRACT. • 1i ACKNCWLEOOE2-lmTS • • • iv LI ST OF TABUS • xi LIST OF FIGURES xii II,TRODUCTION • 1 ffiYSICAL D~RIP'lION 5 Rocky MOlIDta.in bighorn sheep • 5 Biotic communi ties • • • 6 Transition Zone 7 Canadian Zone • B Hudsonian Zone • • • 8 Arctic Alpine Zone • • • • • • 9 Geology and NOW1ta.in Systems • • • • 9 Clima.te • • 11 The Study Area • • • • 13 Range Study Si te 5 • 15 Eagle's Nest Rock • • • 15 Yl8.cMinn South Slope • '_6 Q'Jart.z Creek • 16 Crystal Creek • • 16 Druid South Slope 16 Druid Ridge 17 HEntODS k\1D HATEHIALS 18 Observations by Helicopter • 19 Plant Composi tion • 19 Range Utilization 20 Pellet Group Count • 22 Food Habits • • • 22 viii POPULATION AND DISTRIBUTION • 24 Summer 24 Winter • • • • • 25 Nt. Everts Herd • 26 yellowstone River Herd • 29 Spec:iJnen Ridge Herd 35 Soda Butte Creek Herd • 35 THE WINTER RANGE • 40 Hacllarm Bench • • 40 Plant Composition. • 40 Plant utilization • • • 41 Snow Cover • • • 43 Animal Use • • • 47 Spacirnen RidGe • • • 47 Plant Composition • • 47 Plant Utilization • • 51 Snow Cover • • 51 A.ni..rn.a.l Use • • • • • • • 53 Druid Peak • • • • • 54 Plant Composi tion • • • • 54 Plant Utilization • • • • • • • • • 59 Snow Cover • • • 60 Animal Use • • • • • • • 60 ECOLOGY • • • 62 Reprod uction • • 62 Food Habits • 66 Habitat • 69 Competi ti on 72 Competi tion with Elk • 72 COIt1peti tion with Other Ungulates 76 Predation 77 Disease • • 78 Popula tion Ih.,rnami cs • • • 80 ix BEHAVIOR •• . 83 Seasonal ¥dgration . 83 Herd Composi tion . 85 Daily Ac tivi ti as • • • . • • . • • 86 Activi ty Patterns •••••• . • • • . 86 Local Movements •• • • • • • • • . • • • . 87 Interrelationships with Other An:ilnals . 87 HANAG EHEll T . 89 su:r~:ARY . 92 LI TERA lURE CITED . 98 APPENDI CES • . 102 Appendix A. Bighorn Sheep Field Form . 103 Appendix B. Supplemental Food Habit Observation Form • • 104 Appendix C. Bighorn Sheep Habitat Description Form 105 Appendix D. Point Quadrat on Paced Transect Form . lOS Appendix E. Daubenmire Quadrats Form •• • • • • • • •• 107 x LIST OF TABLES Table Page 1 Nurllber of bighorn sheep in northern Yellowstone National Park, 1903-1955 4 2 Lamar Ranger Station weather swnmary and snowfall at Tower Ea.1l Ranger Station, 1964-1966 l2 3 Observations of bighorn sheep on the yellowstone National Park summer range, 1965 2.5 4 Location and numbers of bighorn sheep on northern Yellowstone winter ranges, 1965 and 1966 26 5 Plant composi tion on two bighorn winter range sites on HacMirm Bench, Yellowstone National Park, 1966 44 6 Plant composition on ~o bighorn winter range sites on SpecL.~en Ridge, Yellowstone National Park, 1966 48 7 Plant composition on two bighorn winter range sites on Druid Peak, Yellowstone National Park, 1966 55 8 Grass and browse utilization and pellet group counts on ~~portant bighorn sheep winter ranges in Yellowstone National Park, 1966 57 9 Monthly food habits of bighorn sheep in yellowstone Na tional Park, 1966 67 10 Area food habits of bighorn sheep in Yellowstone Na tional Park, 1966 68 11 Bighorn sheep habitat preferences on Yellowstone National Park winter ranges, 1965-1966 70 12 Winter food habits of Yellowstone elk 75 13 Winter sex and age ratios of six bighorn sheep herds 81 xi LIST OF FIGURES Figure Page 1 Northern part of Yellowstone National Park showing study area and winter distribution of bighorn sheep. 14 2 Distribution of bighorn sheep on Mt. Everts, yellowstone National Park, 1965-66. 27 3 Typical winter range of the Mt. Everts bighorn sheep herd, Yellowstone National Park. 28 4 Typical winter range of the yellowstone River bighorn sheep herd, Yellowstone National Park. 28 ~ .:::> Distribution of bighorn sheep on Reese Creek, yellowstone National Park, 1965-66. 31 6 Distribution of bighorn sheep on the lower Yellowstone Hi ver, Yellowstone National Park, 1965-66. 32 7 Distribution of bighorn sheep on the upper yello'Wstone Ri ver, yellowstone National Park, 1965-66. 33 8 Distribution of bighorn sheep near Slough Creek and on SpeciJnen Ridge, Yellowstone National Park, 1965-66. 34 9 'IYPl-ca1 winter range of the Specimen Ridge bighorn sheep herd, Yellowstone National Park. 36 10 Typical winter range of the Soda Butte Creek bighorn sheep herd, yellowstone National Park. 36 11 Distribution of bighorn sheep on lower Soda Butte Creek, Yellowstone National Park, 1965~6. 37 12 Distribution of bighorn sheep on upper Soda Butta Creek, Yellowstone National Park, 1965-66. 38 13 Range exclosure on Mac}!inn Bench, Yellowstone National Park. 42 14 Browsed condition of winterfat on MacMinn Bench, yellowstone National Park. 42 15 Bighorn lamb digging through snow on MacMinn Bench, yellowstone National Park. 16 Sparce ground cover on Maclunn Bench, Yellowstone National Park. 46 xii Figure Page 17 Crystal Creek photo plot before winter grazing in October 1965, Yellowstone National Park. 52 18 Crystal Creek photo plot after winter grazing in May 1966, Yellowstone National Park. 52 19 Bighorn ram mingling with ewes during the breeding season. 63 20 '!Wo bighorn rams during the breeding season. 63 xiii 1 Chapter! rn TRODUCTION Little has been done in Yellowstone National Park to manage Rocky Mountain bighorn sheep (Ovis canadensis canadensis) since the studies during the late 1930l s and early 1940's by Mills (1931) and Gammill (1941).