Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. (X United States p Department of ^ Agriculture Forest Service Rocky Mountain Forest and Range Experiment Station Fort Collins, Colorado 80526 General Techinical Report RM-254 The Scientific Basis for Conserving Forest CamiWres American Marten, Fi and Wolverine in the Western United States C- o Abstract Ruggiero, Leonard R; Aubry, Keith B.; Buskirk, Steven W.; Lyon, L. Jack; Zielinski, Williani J., tech. eds. 1994. The Scientific Basis for Conserving Forest Carnivores: American Marten, Fisher, Lynx and Wolverine in the Western United States. Gen. Tech. Rep. RM- 254. Ft. Colhns, CO: U.S. Department of Agriculture, Forest Ser- vice, Rocky Mountain Forest and Range Experiment Station. 184 p. This cooperative effort by USDA Forest Service Research and the National Forest System assesses the state of knowledge re- lated to the conservation status of four forest carnivores in the western United States: American marten, fisher, lynx, and wol- verine. The conservation assessment reviews the biology and ecol- ogy of these species. It also discusses management considerations stemming from what is known and identifies information needed. Overall, we found huge knowledge gaps that make it difficult to evaluate the species' conservation status. In the western United States, the forest carnivores in this as- sessment are limited to boreal forest ecosystems. These forests are characterized by extensive landscapes with a component of structurally complex, mesic coniferous stands that are character- istic of late stages of forest development. The center of the distri- bution of this forest type, and of forest carnivores, is the vast bo- real forest of Canada and Alaska. In the western conterminous 48 states, the distribution of boreal forest is less continuous and more isolated so that forest carnivores and their habitats are more frag- mented at the southern limits of their ranges. Forest carnivores tend to be wilderness species, are largely intolerant of human activities, and tend to have low reproductive rates and large spa- tial requirements by mammalian standards. We must have information at the stand and landscape scales if we are to develop reliable conservation strategies for forest car- nivores. Ecosystem management appears likely to be central to these conservation strategies. Complex physical structure asso- ciated with mesic late-successional forests will be important in forest carnivore conservation plans. Immediate conservation measures will be needed to conserve forest carnivore populations that are small and isolated. Additional forest fragmentation es- pecially through clearcutting of contiguous forest may be detri- mental to the conservation of forest carnivores, especially the fisher and marten. Specific effects will depend on the context within which management actions occur. Keywords: American marten, fisher, lynx, wolverine, late- successional forest, old growth, conservation biology, fragmentation, wilderness, Martes americana, Martes pennanti, Lynx canadensis, Gulo gulo Cover: Fisher, lynx, and wolverine photos by Susan C. Morse of Morse & Morse Forestry and Wildlife Consultants, Marten photo by Dan Hartman. USDA Forest Service General Technical Report RM-254 September 1994 The Scientific Basis for Conserving Forest Carnivores American Marten, Fisher, Lynx, and Wolverine Leonard F. Ruggiero, Project Leader, Research Wildlife Biologist Rocky Mountain Forest and Range Experiment Station^ Steven W. Buskirk, Associate Professor Department of Zoology and Physiology, University of Wyoming L. Jack Lyon, Project Leader, Research Wildlife Biologist Intermountain Research Station^ William J. Zielinski, Research Wildlife Biologist Pacific Southwest Research Station^ ' Headquarters is in Fort Collins, Colorado, in cooperation with Colorado State University. ^ Headquarters is in Portland, Oregon. ^ Located in Laramie, Wyoming. " Headquarters is in Ogden, Utati. ^ Headquarters is in Berkeley, California. in the Western United States Technical Editors: Keith B. Aubry, Research Wildlife Biologist Pacific Northwest Research Station^ Received By: ^ f / Ir^dexing Er?nrH CONTENTS Page PREFACE viii CHAPTER 1 A CONSERVATION ASSESSMENT FRAMEWORK FOR FOREST CARNIVORES Background 1 Purpose 2 Overview 2 The Quantity and Quality of Existing Information 3 Geographic Limitations 3 Extensive Information From Few Studies 4 Small Sample Sizes and/or Highly Variable Results 4 Ambiguous Parameters and Problems of Scale 4 Definition of Terms and Inappropriate Inference 4 Inappropriate Methods 5 Management Considerations and Information Needs 5 Literature Cited 6 CHAPTER 2 AMERICAN MARTEN Steven W. Buskirk, Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming Leonard F. Ruggiero, USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Laramie, Wyoming Introduction 7 Natural History 7 Current Management Status 8 Distribution and Taxonomy 9 Distribution 9 Taxonomy 11 Population Insularity 11 Management Considerations 12 Research Needs 13 Population Ecology 13 Demography 13 Ecological Influences on Population Size and Performance 14 Population Sizes and Trends 14 Direct Human Effects 15 Metapopulations 15 Population Genetics 15 Management Considerations 16 Research Needs 16 Reproductive Biology 16 Phenology 16 Den Sites 17 Mating Systems and Behavior 17 Modes of Communication 18 Parental Care 18 Survival of Young 18 Management Considerations 18 Research Needs 18 Food Habits and Predator-Prey Relationships 18 General Foraging Ecology and Behavior 18 Seasonal, Supra-annual, Geographic Variation in Diets 19 Principal Prey Species 20 Habitat Associations of Principal Prey 20 Management Considerations 21 Research Needs 21 Habitat Relationships 21 General Considerations 21 Use of Major Vegetation Zones 21 Habitat Use in Relation to Sex, Age, and Season 23 Special Requirements and Spatial Scales 23 Effects of Forest Fragmentation 24 Response to Human Disturbances 24 Structural Features Relative to Succession 25 Use of Nonforested Habitats 26 The Refugium Concept 26 Management Considerations 26 Research Needs 26 Home Range 27 Variation in Home Range Attributes 27 Territoriality 27 Spatial Relationships Among Cohorts 28 Management Considerations 28 Research Needs 28 Movements 28 Management Considerations 28 Research Needs 28 Community Interactions 28 Management Considerations 29 Research Needs 29 Conservation Status 29 Literature Cited 30 CHAPTER 3 FISHER Roger A. Powell^ Department of Zoology, College of Agriculture and Life Science, North Carolina State University, Raleigh, North Carolina William J. Zielinski, USDA Forest Service, Pacific Southwest Research Station, Areata, California Introduction 38 Natural History 38 Current Management Status 39 Distribution and Taxonomy 40 Range 40 Historical Changes in Populations and Distribution 41 Taxomony 43 ii Management Considerations 43 Research Needs 43 Population Ecology 43 Population Densities and Growth 43 Survivorship and Mortality 44 Age Structure and Sex Ratio 45 Management Considerations 45 Research Needs 45 Reproductive Biology 46 Reproductive Rates 46 Breeding Season and Parturition 46 Den Sites 47 Scent Marking 47 Management Considerations 47 Research Needs 47 Food Habits and Predator-Prey Relationships 47 Principal Prey Species and Diet 47 Diet Analyisis by Age, Season, and Sex 51 Foraging and Killing Behavior 51 Management Considerations 52 Research Needs 52 Habitat Relationships 52 General Patterns and Spatial Scales 52 Forest Structure 53 Habitat and Prey 53 Snow and Habitat Selection 54 Elevation 55 Use of Openings and Nonf orested Habitats 55 Habitat Use by Sex, Age, and Season 55 Resting Sites 56 Management Considerations 57 Research Needs 57 Home Range 57 Home Range Size 57 Territoriality 59 Management Considerations 60 Research Needs 60 Movements 60 Activity Patterns 60 Movement Patterns 60 Dispersal 60 Movements and Reintroduction 61 Management Considerations 61 Research Needs 61 Community Interactions 61 Food Webs and Competition 61 Predation on Fishers 62 Management Considerations 62 Research Needs 63 Conservation Status 63 Human Effects on Fishers 63 iii Trapping 63 Forest Management 64 Conservation Status in the Western United States 64 Literature Cited 66 CHAPTER 4 LYNX Gary M. Koehler, 65005 Markel Road, Denting, Washington Keith B. Aubry, USDA Forest Service, Pacific Northwest Research Station, Olympia, Washington Introduction 74 Natural History 74 Current Management Status 76 Distribution, Taxonomy, and Zoogeography 77 Distribution in North America 77 Taxonomy 77 Zoogeography of Lynx in the Western Mountains 78 Management Considerations 79 Research Needs 80 Population Ecology 80 Population Dynamics of Snowshoe Hares and Lynx in the Western Mountains 80 Reproductive Biology 80 Mortality 82 Age and Sex Structure 83 Density 83 Management Considerations 84 Research Needs 84 Food Habits and Predator-Prey Relationships 84 Foraging Ecology 84 Prey Requirements and Hunting Success 84 Temporal and Spatial Variations in Diet 85 Management Considerations 86 Research Needs 86 Habitat Relationships 86 Components of Lynx Habitat 86 Foraging Habitat 86 Denning Habitat 88 Travel Cover 88 Management Considerations 89 Research Needs 89 Home Range and Movements 89 Home Range 89 Movements and Dispersal 91 Management Considerations 92 Research Needs 92 Community Interactions 92 Management Considerations 93 Research Needs 93 Conservation Status in the Western Mountains 93 Literature Cited 94 iv CHAPTER 5 WOLVERINE Vivian Band, Province of British Columbia, Ministry of Environment, Lands and Parks, Wildlife Branch, Victoria, British Columbia Introduction 99 Current Management Status 101 Conterminous United States 101 Distribution and Taxonomy 102 Distribution 102 Taxonomy and Morphological Variability 104 Management Considerations 104 Research Needs 104 Population Ecology 105 Reproduction and Natality 105 Sampling Problems and Population Characteristics 106 Natural Mortality 106 Trapping Mortality 108 Density and Population Trends 108 Managment Considerations 108 Research Needs 109 Reproductive Biology 109 Mating Behavior 109 Natal Dens 110 Management Considerations 110 Research Needs Ill Food Habits and Predator-Prey Relationships Ill Diets Ill Foraging Behavior 113 Management Considerations 113 Research Needs 114 Habitat Relationships 114 Habitat Use 114 Impacts of Land-use Activities 115 Management Considerations 116 Research Needs 116 Home Range 117 Spatial Patterns 118 Communication 119 Management Considerations 119 Research Needs 119 Movements and Activity 119 Dispersal 120 Management Considerations 120 Research Needs 120 Community Interactions 121 Wolverine and Prey 121 Wolverine, Wolves, and Humans 121 Wolverine and Wilderness 121 Conservation Status 122 The Future of Wolverine Populations 122 V Acknowledgments 122 Literature Cited 123 CHAPTER 6 THE SCIENTIFIC BASIS FOR CONSERVING FOREST CARNIVORES: CONSIDERATIONS FOR MANAGEMENT Introduction 128 Spatial Relationships 128 Categories of Management Considerations 128 Habitat Management Considerations 128 Stands and Components Within Stands 128 Landscape Considerations 132 Population Management Considerations 132 Landscapes and Metapopulations 132 Fragmentation and Linkages 133 Detecting Carnivore Populations 133 Population Abundance and Trends 134 Population Dynamics and Habitat Management 134 The Effects of Trapping 134 Species Management Considerations 135 Regional Management 135 Reintroduction 135 Existing Populations 135 Conclusions: The Major Considerations for Management 136 Literature Cited 137 CHAPTER 7 INFORMATION NEEDS AND A RESEARCH STRATEGY FOR CONSERVING FOREST CARNIVORES Introduction 138 Overview of Existing Knowledge 139 Information Needs 139 Habitat Requirements at Multiple Scales 139 Community Interactions 143 Movement Ecology 144 Population Ecology and Demography 145 Behavioral Ecology 146 A Comprehensive Approach to Meeting Research Needs 147 General Research Considerations 147 Recommended Studies 148 Western Forest Carnivore Research Center 150 Literature Cited 151 APPENDIX A. Ecoprovinces of the Central North American Cordillera and Adjacent Plains 153 APPENDIX B. Fisher, Lynx, and Wolverine Summary of Distribution Information 168 APPENDIX C. National Forest System Status Information 176 vi Preface This book assesses the scientific basis for conserv- ing the American marten, fisher, lynx, and wolver- ine. It consists of literature reviews for each species and a discussion of management considerations and information needs. The species' accounts were writ- ten by recognized authorities who were asked to re- view and synthesize existing knowledge about the biology and ecology of each species, paying particu- lar attention to aspects of their natural histories that affect the conservation of populations in the western montane regions of the conterminous United States. In Chapter 6, we evaluate this knowledge base and discuss considerations for land managers. Chapter 7 describes what is critically needed to develop scien- tifically sound conservation strategies for each spe- cies. Throughout the text, we have used the term "un- published" as an integral part of a citation when ref- erence is made to a document that has not been peer reviewed and is not widely available as a printed document. We hope readers will find this helpful in evaluating the nature of a citation without constantly referring to the literature cited sections. Our efforts and those of our collaborators build on the foundation of information that has been es- tablished by others. In addition to the researchers who produced the information summarized in this book, we acknowledge the important contributions of Bill Ruediger and John Weaver. Bill is responsible for organizing the Western Forest Carnivore Com- mittee, a group dedicated to coordinating the activi- ties and concerns of state and federal agencies and various nongovernmental organizations. In his role as Threatened, Endangered, and Sensitive Species Program Manager for the Northern Region of the National Forest System, Bill also sponsored the de- velopment of useful literature reviews on the fisher, lynx, and wolverine. Finally, Bill suggested to Jack Lyon a method by which Forest Service Research could synthesize existing information on the fisher, lynx, and wolverine and develop a research ap- proach. The result was a contract with John Weaver, through the Intermountain Research Station, for a synthesis and recommendations for needed research. John's work stands out as an important contribution to our knowledge of forest carnivores. Both of these individuals have made significant contributions to the conservation of forest carnivores, and we are in- debted to them for their efforts. The material in Appendix C was developed through considerable effort by our management part- ners. Chris Jauhola and Diane Macfarlane of the Pa- cific Southwest Region of the National Forest Sys- tem led the management portion of our conserva- tion assessment team. We greatly appreciate their efforts. Special thanks to Erin O'Doherty of the Rocky Mountain Forest and Range Experiment Station for assistance in compiling the maps in Appendix B. We thank the British Columbia Ministry of Environment, Lands, and Parks, Wildlife Branch, especially Ray Halladay, for cooperation in producing the ecologi- cal stratification scheme presented in Appendix A. We also thank Tom Hoekstra and Mike Lennartz of Forest Service Research and Phil Janik and Dale Bosworth of the National Forest System for their guid- ance throughout the conservation assessment process. We gratefully acknowledge the contributions of our peer reviewers who spent much time comment- ing on earlier drafts of each chapter. For their help- ful suggestions we thank Sandra Martin, Rudy King, Martin Raphael, John Weaver, Greg Hayward, Rob- ert Pfister, John Squires, Diane Macfarlane, Nancy Warren, Keith Giezentanner, Donna Storch, Howard Hudak, Brian Giddings, Robert Naney, Lowell Suring, Ed Toth, Diana Craig, David Brittell, Ted Bailey, Jeff Copeland, Michelle Tirhi, Jeffrey Jones, Wil- Uam Krohn, Kerry Foresman, Bill Ruediger, and repre- sentatives of the Western Forest Carnivore Committee. Finally, special thanks to Lane Eskew, Station Edi- tor, for his expertise in all phases of book production and to Tracey Parrish for her tireless editorial assistance. Leonard F. Ruggiero Keith B. Aubry Steven W. Buskirk L. Jack Lyon William J. Zielinski vll Chapter 1 A Conservation Assessment Framework for Forest Carnivores Leonard F.(^ggiero,[uSDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Laramie, Wyoming] William J.(zielinski, USDA Forest Service, Pacific Southwest Research Station, Areata, California Keith B.^Aubry, USDA Forest Service, Pacific Northwest Research Station, Olympia, Washington Steven W.(Buskirk, Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming L. Jack(lyon, USDA Forest Service, Intermountain Research Station, Missoula, Montana BACKGROUND Controversy over managing public lands is nei- ther an unexpected nor recent development. In the 1970's, debate over land management began to fo- cus on the effects of timber management practices on wildlife. This was most evident in the Pacific Northwest where the pubUc was beginning to express strong concerns about the effects of timber harvest in late-successional forests on northern spotted owls and other vertebrates. The focus on all vertebrates and not just "game animals" distinguished these con- cerns from earlier wildlife-related issues. In 1976, Congress passed the National Forest Management Act, which mandated the maintenance of biological diversity on lands of the National Forest System. Regulations enacted pursuant to this law specified that viable populations of native and desirable non- native wildlife species would be maintained on plan- ning units (i.e.. National Forests) of the National For- est System. Thus, a statutory and regulatory basis was provided for appeals and litigation directed at what the public believed to be the negative effects of timber man- agement practices on wildlife. The many legal chal- lenges that ensued focused primarily on the harvest- ing of late-successional forests in the Pacific Northwest (see Meslow et al. 1981 for additional discussion). The USDA Forest Service responded to this situa- tion in 1981 by chartering a research and develop- ment program aimed at studying the role of old- growth forests as wildlife habitat (Ruggiero et al. 1991). Early research efforts of this program focused on the ecology of spotted owls, a species at the cen- ter of the most intense debate. Although research was underway, legal challenges disrupted forest manage- ment activities, and the controversy was played out in legal and political arenas. Science was not called on as part of the solution until nearly a decade later, after the development of a political impasse in one of the country's most important timber-producing re- gions. In 1989, in response to this impasse, an inter- agency agreement between the major land manage- ment agencies established the "Interagency Scientific Committee to Address the Conservation of the North- ern Spotted Owl." The charter of this group was later incorporated into law (Section 318 of Public Law 101- 121), and a conservation strategy for the northern spotted resulted (Thomas et al. 1990). In 1991, Con- gress intervened directly by commissioning the Sci- entific Panel on Late-Successional Forest Ecosystems, whose mission was to make broad recommendations about management of the remaining old-growth for- ests in the Pacific Northwest (Johnson et al. 1991). And, in 1993, President Bill Clinton intervened and 1 appointed a task force of scientists to evaluate the effects of alternative management scenarios for old- growth forests on all wildlife in the Pacific North- west (Thomas et al. 1993a). This intervention in- cluded an unprecedented visit by a U.S. president to the site of a regional forest management/ wildlife controversy for the purpose of facilitating its end (the Forest Conference convened in Portland, Oregon, on April 2, 1993). It is clear from these events that public concern over the effects of land management on wildlife is enor- mously important politically, economically, and sci- entifically. It is also clear that the conservation strat- egy for the northern spotted owl came too late. Nearly two decades passed from the first concerns over the conservation status of this subspecies until scientists were asked to develop a "scientifically credible" con- servation strategy. The necessary commitment to sci- entific research, which is essential as the basis for any defensible conservation plan, was made too slowly. The resultant socio-political turmoil was likely avoid- able, at least in part, and the controversy would not have been so intractable if better scientific informa- tion had been available earlier. Concerns about wildlife conservation in relation to forest management are limited neither to the Pa- cific Northwest nor to spotted owls. Appeals and le- gal challenges of timber management activities, rela- tive to effects on wildlife, are now common through- out the country. The potential for re-enactment of the Pacific Northwest/old-growth scenario exists throughout the western United States. And there is growing public sentiment that serious attention to the conservation of biological diversity is long over- due outside the Pacific Northwest. PURPOSE To address this situation, the USDA Forest Service decided in 1993 to evaluate what is known about the biology and ecology of several species or groups of species that are potentially sensitive to the effects of forest management, including the harvest of late-suc- cessional forests. This so-called conservation assess- ment process is directed at interior cutthroat trout, bull trout. Pacific salmon, forest owls (flammulated, boreal and great-gray), marbled murrelet, northern goshawk, and forest carnivores (marten, fisher, lynx, and wolverine). The forest carnivores are included in this group because of their relatively large area requirements, their association with late-successional forests, and the relative lack of information available for conservation planning. In addition, most of the geographic ranges of forest carnivores (about 65% for the marten and fisher) are found on public lands, and the marten, fisher, and lynx have been judged to be at medium to high-viability risk due to the reduc- tion of old-growth forests in the Pacific Northwest (Thomas et al. 1993a, 1993b). The conservation assessment process is intended to produce three specific products for each of the species in question: an overview of the existing state of knowledge with regard to species biology and ecol- ogy; a discussion of the management considerations stemming from this knowledge; and recommenda- tions for research needed to fill voids in existing knowledge. Our mandate did not include the devel- opment of specific management recommendations and none appear here. The conservation assessment process is intended to lay the foundation for devel- oping conservation strategies for species of concern. Thus, knowledge voids are assessed in this context, and the research recommendations are intended to address the information needed for developing sci- entifically defensible conservation strategies. Conser- vation strategies build on conservation assessments by incorporating new information that results from assessment recommendations and by prescribing specific conservation measures needed to ensure population viability and species persistence. Re- search designed to fulfill assessment recommenda- tions will result in an understanding of the ecology of each species. Only then can we determine whether particular silvicultural practices are consistent with forest carnivore population persistence and whether they may be used to manage each species' habitat. OVERVIEW The developing paradigm of conservation biology forms the basis for the forest carnivore conservation assessment. And, as outlined in the contents, we have attempted to address those biological and ecological topics that are central to the issue of maintaining vi- able populations of the species in question. Each spe- cies account (Chapters 2-5) addresses what is known about population ecology and demography, behav- ioral ecology, habitat requirements, movement ecol- ogy, and community interactions. These classes of information are fundamental to conservation plan- ning. Knowledge of habitat requirements is essen- tial for understanding the resources needed for spe- 2 cies persistence. Community interactions mediate the use of these resources and hence must be understood for reUable conservation planning. Community in- teractions in the form of predator-prey relationships also can have a direct effect on population persis- tence. The vital rates of natality and mortality, along with an understanding of how the environment in- fluences these rates, constitutes basic information for developing models of population persistence. And an understanding of how movement ecology relates to the potential connectedness of populations within metapopulation structures is equally basic to under- standing population dynamics and estimating per- sistence probabilities. Finally, because behavior me- diates all interactions between organisms and their environment, understanding fundamental behav- ioral patterns is important to understanding species' ecology. In each of these broad categories, we have also tried to identify areas where information basic to conservation planning is currently lacking. It would be ecologically naive to assume that knowledge in any of the above areas could be ex- trapolated with equal validity to all populations across the geographic ranges of each forest carnivore species. Rather, we assume that ecotypic variation exists within these species. Although the amount of this variation is unknown, we stress its potential sig- nificance in formulating of conservation strategies. Accordingly, we have adopted an ecological stratifi- cation scheme (Appendix A) that we believe repre- sents the major physiographic and ecological influ- ences likely to effect ecotypic variation. Species dis- tribution patterns are superimposed on this ecologi- cal stratification in Appendix B. For reasons presented above (see Chapter 7 for additional discussion), we have also used this framework to make geographically ex- plicit research recommendations in Chapter 7. By do- ing this, we are stressing that important ecological differences may exist among species populations and we are also cautioning against overextrapolation of research results. An important feature of our ecological stratifica- tion is the explicit delineation of important ecoprovinces that span the Canada-U.S. border. For- est carnivore populations in the United States repre- sent the southern portions of species' ranges that are centered in Canada. This distribution pattern has important implications for conservation planning, and international cooperation in developing conserva- tion strategies seems appropriate. The ecological frame- work provided here should facilitate such cooperation. We have focused on the western U.S., exclusive of Alaska. The Tongass National Forest in Alaska is cur- rently involved in important analyses of long-term species viability for marten and other species (Inter- agency Viable Population Committee-Iverson, pers. comm.). We have focused on the western contermi- nous United States because concerns about habitat reduction and landscape modification through man- agement appear to be most urgent in this area. More- over, all four forest carnivore species are sympatric in portions of this area, thus affording the opportu- nity for ecosystem studies that examine the common elements of their ecologies, including a common prey base. THE QUANTITY AND QUALITY OF EXISTING INFORMATION Research findings like those reviewed in this book must be evaluated in terms of the quantity and qual- ity of information available on any given topic and for any given location. Such an evaluation should form the basis for judgments about the reliability and salience of information relative to decision-making or conservation planning (see Romesburg 1981 for a pertinent discussion). We have taken steps through- out this assessment to help the reader evaluate the quantity and quality of the information presented. There are at least six ways in which research results can be misleading or misinterpreted and thus mis- applied in a conservation assessment. These are dis- cussed below. Geographic Limitations Existing information may be the result of research conducted at only one or a few geographic locations. Research results from a specific geographic area may be unreliable or even misleading when applied to other locations. The risks associated with such ex- trapolations generally increase as distances increase and ecological conditions become increasingly dis- similar. This is equally true when numerous studies have been conducted in the same geographic loca- tion. Although numerous studies may add to the re- liability or breadth of knowledge as it applies to the geographic area of investigation, multiple studies from the same or very similar study areas do little to increase the value of the resultant information rela- tive to other geographic areas with different ecologi- cal conditions. 3 Extensive Information From Few Studies While single studies may provide important knowledge, insight, or even understanding, multiple studies provide scientific corroboration of these re- sults. Accordingly, reliable bodies of knowledge are usually based on well-documented concordance among results of independent investigations. It fol- lows that a literature review based on 10 studies does not reveal as strong an information base as the same review based on 20 or more studies. This is equally true when one or a few studies cover many topics, as is the case in many natural history studies (especially of the thesis or dissertation genre). This situation leads to copious citations and the documentation of findings across a broad array of topics, sometimes creating the false impression of an extensive body of information. Small Sample Sizes and/or HIgtily Variable Results Small sample sizes are related to anecdotal infor- mation in that the resultant information may fail to represent a meaningful or common natural condi- tion or event. And, when little is known about a spe- cies, this type of inherently unreliable information tends to be repeated and applied without the neces- sary qualifiers. For example, our knowledge about the denning habitat requirements for lynx is based on very few actual den sites. In spite of this, some authors will cite the studies involved and portray our knowledge on this topic as much more solid than it actually is. In many cases, this kind of situation goes undetected by decision-makers or readers of review articles or management-oriented overviews. Similar problems occur when larger sample sizes reveal highly variable findings, which are then reported as a simple mean value without appropriate statistical qualifiers and professional interpretation. Ambiguous Parameters and Problems of Scale Some parameters are inherently ambiguous, and conclusions based on data resulting from the mea- surement of such parameters can be misleading. For example, simple occurrence of animals in some habi- tat says little about habitat requirements, and even intensive measures of parameters like density can sometimes be misleading (Van Horne 1983). In spite of this understanding, observations of animals oc- curring in particular environments are sometimes incorrectly reported as indicative of specific habitat requirements or a lack thereof (see Chapter 7 for ad- ditional discussion). Similarly, a species may conduct different activities in different habitats, as in the case of foraging and denning habitats. These habitats may be strikingly different but both are essential. A general description of the habitat requirements of the species should consider the availability of each type and their spatial juxtapositions. Problems of scale arise when individuals within populations are sampled and the resultant param- eter estimates are applied to the entire species. This seemingly obvious and easily avoidable problem is quite common, especially when ecological results are applied or interpreted in a management context (Ruggiero et al. 1994). Definition of Terms and Inappropriate Inference The issue of old-growth forest as important habi- tat for forest carnivores is laden with philosophical and semantic problems that can hinder communica- tion about habitat requirements. "Old-growth" is a stage of forest development characterized by large components (e.g., logs, snags, live trees) and struc- tural complexity (e.g., vertical and horizontal). These attributes vary as a function of vegetation type, site conditions, and disturbance history. Thus, in general, old growth is a concept rather than a specific set of conditions. Old-growth characteristics develop gradually as forests mature, so that there is no spe- cific threshold where mature stands become old growth. Thus, the characteristics of late-successional forests (including the oldest forests) are what inter- est us as habitat for forest carnivores. In order to fo- cus on the structural and compositional features of forest habitats, we have chosen to use the term late- successional forests when referring to mature and older forests that possess the attributes listed above. Our work requires the definition of three additional terms: fragmentation, dispersal, and den site. "Frag- mentation" occurs when a large expanse of habitat is transformed into a number of smaller patches of smaller total area, isolated from each other by a ma- trix of habitats unlike the original (Wilcove et al. 1986:237). The process of fragmentation includes loss of stand area, loss of stand interior area, changes in relative or absolute amounts of stand edge, and changes in insularity (Turner 1989). "Dispersal" is 4 important because it connotes the successful estab- lishment (usually by juvenile animals) of a breeding territory in an area distant from the natal area. "Na- tal den sites" are important because they play a key role in recruitment by providing parturition sites. Inappropriate inferences about dispersal are made when authors confuse the long-distance movement capability of animals with their ability to successfully disperse. Inappropriate inferences about habitat re- quirements for denning are made when authors use the term "den" in reference to resting sites that are not associated with parturition or rearing of young. Similarly, there are important ecological differences between natal den sites (used for parturition) and other den sites that are used subsequent to parturition. Inappropriate Methods Using the wrong method to address the right ques- tion can result in inaccurate or incomplete answers. Questions about population structure and area re- quirements, for example, are germane to conserva- tion planning. Information about area requirements is best obtained by well-designed (i.e., sufficient data over appropriately long time-periods) radio-telem- etry studies. However, telemetry studies are expen- sive, and much information about the area require- ments of forest carnivores has been derived from re- locations of marked animals. There is an important distinction here with regard to the quality of result- ing information. Similarly, questions about popula- tion structure have often been addressed by examin- ing the carcasses of trapped animals. The quality of inferences from such data is questionable because the structure and dynamics of exploited populations dif- fer from unexploited populations in ways that are poorly understood. For the reasons discussed in this section, we have tried to provide a realistic view of the actual scien- tific knowledge base that forms the foundation of the species-account narratives. We have done this in each species account by including a tabular summary of existing studies by topic and including information on study location, duration, methodology, and sample size. Similarly, in Chapter 7 (table 1) we have represented the geographic distribution of existing knowledge for all 4 species in 10 topical areas of spe- cial importance to conservation planning. We have also asked the authors of each species account to pro- vide their thoughts about management consider- ations that follow from the state of knowledge and to provide their recommendations about information still needed for develoment of conservation strate- gies for each species. In addition, we present a syn- thesis of these management considerations and in- formation needs in Chapters 6 and 7, thus giving the reader two perspectives on these important aspects of the assessment. MANAGEMENT CONSIDERATIONS AND INFORMATION NEEDS As alluded to above, the state of scientific knowl- edge on forest carnivores carries with it certain im- plications for land management. Because the quan- tity and quality of information available for the west- ern United States is limited, one such implication is that the conservation status of forest carnivores is it- self uncertain. Thus, empirically based management strategies for species conservation cannot now be developed, and a significant commitment to research is needed. This need for much additional information through research leads to a practical dilemma. Conservation planning draws on information from all aspects of a species' ecology. Accordingly, for little-studied (and difficult-to-study) species like the forest carnivores, the list of information needs is long indeed. And the need to replicate some studies to generate regionally generalizable information only expands the list of needed research. The dilemma, then, is how to be scientifically rigorous in prescribing needed research while also recognizing the practical limits of avail- able resources and acknowledging real questions about the feasibility of collecting certain crucial in- formation (e.g., vital rates for wolverine populations). Long lists of needed studies for even a single species are difficult to prioritize and often lead to a piecemeal approach to research whereby knowledge gaps persist. Problems of consistency and comparability arise, and studies are conducted on an opportunistic rather than a comprehensive and well-integrated basis. Our solution to this problem is to avoid long "laun- dry lists" of needed research (although detailed in- formation needs are included in each species account) in favor of a comprehensive, programmatic approach to producing the information needed for develop- ing conservation strategies for forest carnivores. In reality, most well-designed studies address multiple objectives or multiple information needs. Thus, we believe that for each species a few highly integrated and compreherisive studies replicated in the geo- 5 graphic areas of concern will satisfy existing infor- mation needs for conservation planning (see Chap- ter 7 for additional discussion). We believe this ap- proach will result in high levels of consistency, a com- prehensive body of knowledge, and optimal use of available resources. Unfortunately, it will also take considerable time, expense, and effort. This should not, however, deter managers from developing con- servative interim guidelines that will maintain fu- ture options. LITERATURE CITED Johnson, K.N; Franklin, J.F.; Thomas, J.W. [et al.]. 1991. Alternatives for management of late-succes- sional forests of the Pacific Northwest. A report to the Agriculture Committee and the Merchant Ma- rine and Fisheries Committee of the U.S. House of Representatives; 1991 October 8. Corvallis, OR: College of Forestry, Oregon State University; Se- attle, WA: College of Forest Resources, University of Washington; La Grande, OR: U.S. Department of Agriculture, Pacific Northwest Research Station; New Haven, CT: School of Forestry and Environ- mental Studies, Yale University: The Scientific Panel on Late-Successional Forest Ecosystems. 59 p. Meslow, E.C.; Maser, C; Verner, J. 1981. Old-growth forests as wildlife habitat. In: Transactions of the 46th North American Wildlife Natural Resource Conference; 1981. Washington, DC: Wildlife Man- agement Institute; 46: 329-335. Romesburg, H.C. 1981. Wildlife science: gaining re- liable knowledge. Journal of Wildlife Management. 45(2): 293-313. Ruggiero, L.F.; Hay ward, G.D.; Squires, J.R. 1994. Viability analysis in biological evaluations: con- cepts of population viability analysis, biological populations, and ecological scale. Conservation Biology 8(2): 364-372. Ruggiero, L.F; Aubry, K.B.; Carey, A.B. [et al.]. 1991. Wildlife and vegetation of unmanaged Douglas- fir forests. Gen. Tech. Rep. PNW-285. Portland, OR: U.S. Department of Agriculture, Pacific Northwest Forest and Range Experiment Station. 533 p. Thomas, J.W; Forsman, E.D.; Lint, J.B. [et al.]. 1990. A conservation strategy for the northern spotted owl. Portland OR: A report prepared by the Inter- agency Scientific Committee to address the con- servation of the northern spotted owl. U.S. Depart- ment of Agriculture, Forest Service; U.S. Depart- ment of Interior, Bureau of Land Management, Fish and Wildlife Service, National Park Service. Wash- ington, DC: U.S. Government Printing Office. 427 p. Thomas, J.W; Raphael, M.G.; Meslow, E.C. [et al.]. 1993a. Forest ecosystem management: an ecologi- cal, economic, and social assessment. Portland, OR: A report prepared by the Forest Ecosystem Man- agement Assessment Team. U.S. Department of Agriculture, Forest Service; U.S. Department of Commerce, National Marine Fisheries; U.S. De- partment of the Interior, Bureau of Land Manage- ment, Fish and Wildlife Service, National Park Ser- vice; Environmental Protection Agency. 794-478. Washington, DC: U.S. Government Printing Office. Thomas, J.W.; Raphael, M.G.; Anthony, R.G. [et al.]. 1993b. Viability assessments and management con- siderations for species associated with late-succes- sional and old-growth forests of the Pacific North- west. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 523 p. Turner, M.G. 1989. Landscape ecology: the effect of pattern on process. Annual Review of Ecological Systematics. 20: 171-197. Van Horne, B. 1983. Density as a misleading indica- tor of habitat quality. Journal of Wildlife Manage- ment. 47: 893-901. Wilcove, D.S.; McLellan, C.H.; Dobson, A.P 1986. Habitat fragmentation in the temperate zone. In: Soule, M.E., ed. Conservation Biology: The Science of Scarcity and Diversity. Sunderland, MA: Sinauer Associates, Inc.: 237. 6 Chapter 2 iM American Marten Steven W.(Buskirk, Department of Zoology and Physiology, ^nlversity of Wyoming, Laramie, Wyoming^ Leonard F.(Rugglero, USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Laramie, Wyoming INTRODUCTION Natural History The American marten {Martes americana), also called the marten or American sable, is a carnivo- rous mammal about the size of a small house cat. Its total length is between 500 and 680 mm and it weighs 500-1400 g as an adult, depending on sex and geog- raphy (Buskirk and McDonald 1989; Strickland et al. 1982). The male is 20-40% larger than, but otherwise similar in appearance to, the female. Both sexes are furred with glossy hair of medium length, are tan to chocolate in color, and have an irregular neck or throat patch ranging from pale cream to bright am- ber. Its face is pointed and foxlike in shape, its torso is slender, and its legs and tail are intermediate in length and darkly furred. Each foot has five toes, all of which touch the ground, and the claws are light in color and semiretractable (Buskirk 1994; Clark and Stromberg 1987). Although its close relatives include skunks and other species with powerful scent glands, the marten, even when frightened, produces odors only weakly perceptible to humans. The American marten is one of seven species in the genus Martes, within Family Mustelidae, Order Carnivora (Corbet and Hill 1986). Along with the Eurasian pine marten (M. martes), the sable (M. zibellina), and the Japanese marten (M. melampus), it belongs to a group of closely related species called the "boreal forest martens" (Buskirk 1992). These four species replace each other geographically from west to east across the circumboreal zone from Ireland to Newfoundland Island, and they exhibit close simi- larities of size, shape, and ecology (Anderson 1970). The genus Martes is distinguishable from other North American mustelids by the presence of four upper and lower premolars. The only other Martes in North America is the much larger-bodied fisher (M. pennanti), which occupies similar habitats but has a smaller geographic range. The American marten is broadly distributed. It extends from the spruce-fir forests of northern New Mexico to the northern limit of trees in arctic Alaska and Canada, and from the southern Sierra Nevadas of California to Newfoundland Island (Hall 1981). In Canada and Alaska, its distribution is vast and continuous, but in the western contiguous United- States, its distribution is limited to mountain ranges that provide preferred habitat. American martens occupy a narrow range of habi- tat types, living in or near coniferous forests (Allen 1987). More specifically, they associate closely with late-successional stands of mesic conifers, especially those with complex physical structure near the ground (Buskirk and Powell 1994). Martens may in- habit talus fields above treeline (Grinnell et al. 1937; Streeter and Braun 1968) but are seldom or never found below the lower elevational limit of trees. In Alaska, but not elsewhere, martens have been re- ported to occur in early post-fire stages that have few living trees where tree boles have fallen to the ground in dense networks or where herbaceous growth is dense (Johnson and Paragi 1993; Magoun and Vernam 1986). The diet varies by season, year, and geographic area. In summer, the diet includes bird eggs and nest- lings, insects, fish, and young mammals. In fall, ber- ries and other fruits are important foods. And in win- ter, voles, mice, hares, and squirrels dominate the diet. In some geographic areas, single prey species are especially important because of their high avail- ability— for example, snowshoe hares (Lepus americanus) in Manitoba (Raine 1981) and deer mice {Peromyscus maniculatus) on Vancouver Island (Nagorsen et al. 1989). Martens hunt for small mam- 7 mals by traveling on the ground or snow surface. Prey that live beneath the snow, such as voles, mice, and shrews, are caught by entering access points to the subnivean space created by coarse woody debris and other structures (Com and Raphael 1992; Koehler et al. 1975). Martens make occasional forays into trees and have good tree-climbing abilities (Grinnell et al. 1937). Community interactions between martens and other vertebrates are not well understood. Predation on American martens seldom is directly observed or inferred from marten remains in fecal pellets or cast- ings. But the threat of predation is thought to be strong in shaping habitat-selection behaviors by martens (Buskirk and Powell 1994). This is in part because of documented predation on Eurasian pine martens (Brainerd 1990) and because of the strong psychological avoidance of open areas by American martens (Hawley and Newby 1957), which is gener- ally inferred to be an evolved response to predation threats. Predation on martens by coyotes (Canis latrans), red foxes (Vulpes) (Ruggiero, unpubl. data), and great-horned owls {Bubo virginianus) (Baker 1992) has been documented. Unlike martens, these species are generalists associated with a broad range of habi- tats including early successional and fragmented landscapes. Martens occur locally sympatrically with various other mustelid species, but competitive in- teractions involving limiting resources have not been reported. Martens tend to be shy and have been called "wil- derness animals" (Thompson-Seton 1925); even people who live in marten habitat may seldom see them. However, martens occasionally seem fearless of humans and approach closely. They may be strongly attracted to human structures and human foods, so that they at times seem locally abundant and tame (Halvorsen 1961). But this impression usu- ally is transient. Marten tracks in snow, which are distinctive to experienced observers, follow circui- tous routes over their large home ranges, staying close to overhead cover and investigating openings to the subnivean space where coarse woody debris penetrates the snow surface. Although they are agile climbers of trees and cliffs, they mostly travel on the ground (Francis and Stephenson 1972). Martens are active at various times of day and night and appear to be flexible in their activity patterns (Hauptman 1979). In comparison with the fisher, the marten engages in more arboreal and subnivean activity (Strickland and Douglas 1987), eats smaller prey (Clem 1977), and associates more strongly with coniferous stands. Both species are similarly intolerant of vegetation types lacking overhead cover (Buskirk and Powell 1994). American martens have been trapped for fur since aboriginal times and are primarily known as furbear- ers over much of their range. Their distribution has contracted and then recovered in parts of their range, but it is smaller today than at the time of European contact. Martens have been especially impacted by human activities in the Pacific Northwest. The knowledge base for the marten in the western United States, excluding Alaska, is the strongest of the forest carnivores considered in this assessment (table 1). Current Management Status Neither the American marten nor any of its local populations are protected under the Endangered Species Act. Likewise, as of 15 July 1991, this species had not been listed in any appendices to the Con- vention on International Trade in Endangered Spe- cies of Wild Flora and Fauna, or in the International Union for the Conservation of Nature and Natural Resources Red List of Threatened Animals (Wilson and Reeder 1993). In most state and provincial juris- dictions in western North America where it occurs, the American marten is managed as a furbearer (Ap- pendix C, table 4a). This management generally al- lows martens to be taken by trap, but not by firearm, and involves the use of one or more of the usual measures: licensing of trappers, seasonally closed, requirements that pelts or carcasses be submitted for sealing inspection, and assignment or registration of traplines (Appendix C, table 4a; Strickland and Dou- glas 1987). In five western state jurisdictions (Cali- fornia, Nevada, New Mexico, South Dakota, and Utah) martens may not be legally taken in any area of the jurisdiction at any time. California classifies the marten as a furbearer but has had no open sea- son since 1952. Only two other states have given the marten a formal listing: "Protected" in Utah and "En- dangered, Group 11" in New Mexico. Several federal land management agencies in the western conterminous states, representing a range of jurisdictional powers, assign special management status to the marten. Pursuant to the National Forest Management Act of 1976 and 36 CFR Ch. II, Part 219.19 a. 1., many forest plans in Regions 1, 2, 4, 5, and 6 of the National Forest System have designated 8 1, the marten as an ecological indicator species (e.g., Gallatin National Forest) or a "high-interest species" (e.g., Wasatch-Cache National Forest). These special designations are listed in Appendix C. Regions 2 and 5 have placed the marten on their regional foresters' "sensitive species" lists. Sensitive species are those for which continued persistence of w^ell-distributed populations on National Forest System lands has been identified as a concern. Other regulations or agency policies are not spe- cific to martens but affect their conservation; for ex- ample, trapping is prohibited in most units of the National Park System. Also, trapper access is de- creased, and de facto partial protection provided, by prohibitions of motorized travel in Research Natu- ral Areas on National Forests and in wilderness ar- eas established pursuant to the Wilderness Act of 1964. DISTRIBUTION AND TAXONOMY Distribution Anderson (1970, 1994) reported that the American marten came to North America by way of the Bering Land Bridge during the Wisconsin glaciation, which ended about 10,000 years ago. During the Wiscon- sin, martens extended much farther south and lower in elevation than they do today (Graham and Gra- ham 1994), occurring in what is now Alabama. The current geographic range is temperate to arctic and spans the continent from east to west, including off- shore islands (Hall 1981). The main part of the distri- bution comprises the boreal and taiga zones of Canada and Alaska. South of this vast area, the dis- tribution becomes insularized, with fingers and is- lands following western mountain ranges south- Table 1.— The knowledge base for American martens in the western United States, excluding Alaska, by subject. This includes studies for which the subject was a specific objective of the study; incidental observations are not included. Sample size is number of animals studied, or for food habits, number of scats or gastrointestinal tract contents, unless stated otherwise. Sample sizes for dispersal include only juveniles. Theses and dissertations are not considered separately from reports and publications that report the some data. A total of 26 studies (*) are represented in this table, discounting redundancies. Topic, author Location r^ethod Duration Sample size Home range & habitat use 'Burnett 1981 NW Montana Telemetry(hr)' 18 mo, 11 *Buskirk etal. 1989 SE Wyoming Telemetry 2 winters 8 'Campbell 1979 NW Wyoming Telemetry(hr) 15 mo. - 4 Marking 17 XIark 1984 NW Wyoming Marking 18 mo. 5 •Corn and Raphael 1992 S Wyoming Searches 3 mo. 43 subnivean access sites *Fager 1991 SW Montana Telemetry(hr) <1 yr. 7 Marking 37 'Hargis 1981 C California Snow-tracking 2 winters 35 km of tracks 2-5 martens •Hauptman 1979 NW Wyoming Telemetry(hr) 12 mo. 4 •Hawley 1955 NW Montana Marking(hr) 21 mo. 69 *Koehler and Hornocker 1977 Idaho Marking 7 mo. 13 Snow transects 255 track observations 'Koehler et al. 1990 N Washington Snow transects 4 mo. 1 1 track observations 'Martin 1987 N California Telemetry 28 mo. 210 resting sites. 10 individuals 'Newby 1951 Washington Marking 36 mo. 4 'Sherburne and Bissonette 1 993 NW Wyoming Searches 8 mo. 70 subnivean access sites Home range & habitat use 'Simon 1980 N California Telemetry(hr) 16 mo. 8 'Spencer 1981 N California Marking 15 mo. 14 Telemetry(hr) 4 'Wilbert 1992 S Wyoming Telemetry 14 mo. 190 resting sites, 1 1 individuals Demography Campbell 1979 NW Wyoming Marking 15 mo. 17 Clark 1984 NW Wyoming Marking 18 mo. 39 Fager 1991 SW Montana Marking 12 mo. 37 (Continued) 9 Table 1 .—(continued). Topic, author Location Method Duration Sample size Hoi iri+mnn 1070 l\l\A/ \A/\//^mir\r^ iNvv vvy^iiiiiiy I VIdl KM ly 1 ^ 1 1 ID. 9n Hawley 1955 NW Montana Marking 21 mo. 69 •Jonkel 1959 NW Montana Marking 10 mo. 161 'Marshall 1948 Idaho Carcass 36 mo. 124 Simon 1980 N California Marking 16 mo. 18 *Weckwerth 1957 NW Montana Marking 12 mo. 45 Food habits Campbell 1979 NW Wyoming Scats 4 mo. 145 •Gordon 1986 Colorado G.I. tracts 6 mo. 32 Hargis 1981 C California Scats 2 winters 91 Hauptman 1979 NW Wyoming Scats 12 mo. 233 Food habits Koehler and Hornocker 1977 Idaho Scats 7 mo. 129 •Marshall 1946 NW Montana Scats 1 winter 46 Marshall 1948 Idaho Scats 36 mo. 19 G.I. tracts 20 Martin 1987 N California Scats 28 mo. 100 •Murie 1961 NW Wyoming Scats Multi-year 528 Newby 1951 Washington Scats 3 mo. 95 VC7. 1 . II KJK^ 1 o 1 1 1 1 i\J, 1 7 •Remington 1951 Colorado Scats 15 mo. 198 Sherburne 1993 NW Wyoming Scats 8 mo. 69 Simon 1980 N California Scats 16 mo. 99 WonLfu/or+h 1 0S7 N\A/ K/lontr^nn INVV IVIV^'I IIVJI \\J OL^O lo 1 9 mn 1 ^ 1 1 \KJ , OU 1 •Zielinski 1981 N California Scots 15 mo. 428 Burnett 1981 NW Montana Telemetry 18 mo. 6 Jonkel 1959 NW Montana Marking 10 mo. 11 Natal dens •Ruggiero, in review S Wyoming Telemetry 72 mo. 14 natal dens, 6 females ' hr = home range size reported ward. The southern Umit of distribution of martens coincides roughly with that of coniferous tree spe- cies, for example Picea engelmannii in the southern Rocky Mountains, that develop stand conditions with which martens associate (c.f. Hall 1981 and Little 1971, Map 37-W). The distribution of the American marten has un- dergone regional contractions and expansions, some of them dramatic. On balance, the American marten has a smaller distribution now than in presettlement historical times (Gibilisco 1994); the total area of its geographic range appears similar to that early in this century, when it was at its historical low. American martens have reoccupied much of southern New England with the aid of transplantation after being absent for much of the 1900's. Farther to the north- east, however, martens have undergone numerical and distributional declines (Thompson 1991). Mar- tens are endangered or extinct in mainland Nova Scotia, and on Newfoundland, Prince Edward, and Cape Breton Islands (Bergerud 1969; Dodds and Martell 1971; Gibilisco 1994; Thompson 1991). The status of martens in the maritime provinces has been attributed to the logging of late-successional conif- erous forests and to trapping for fur (Bissonette et al. 1989; Thompson 1991). Consistent with this, the ex- pansion of the range of martens in southern New England is thought to be related to forest succession that has taken place there for about the last century (Litvaitis 1993). Martens were lost from large areas of the north-central United States during the late 1800's and early 1900's, primarily as a result of forest loss (Berg and Kuehn 1994) to logging and agricul- ture. Since about 1930, the range of martens in this 10 region has slowly expanded as forests succeeded to conifers. The marten is now extirpated from seven states where it occurred historically: North Dakota, Illinois, Indiana, Ohio, Pennsylvania, New Jersey, and West Virginia (Clark et al. 1987; Thompson 1991). In the Shining Mountains, Northern Rocky Moun- tain Forest, Utah Rocky Mountains, and Colorado Rocky Mountains ecoprovinces, (Appendix A), dis- tributional changes have apparently been of small scale. Only the Tobacco Root Mountains of Montana reportedly have lost an historically present marten population (Gibilisco 1994). In the Georgia-Puget Basin, Pacific Northwest Coast and Mountains, and Northern California Coast Ranges ecoprovinces, (Ap- pendix A), distributional losses have been major. Martens now are scarce or absent in the coast ranges of northern California, where they were once com- mon. Evidence for this loss is provided by the near complete absence of marten sightings from the coast ranges since 1960 (Schempf and White 1977) com- pared to the early part of this century (Grinnell et al. 1937). This apparent range reduction involves parts of Humboldt, Del Norte, Mendicino, Lake, and Sonoma Counties, and it corresponds closely to the distribution oi M. a. humboldtensis, a subspecies rec- ognized by both Hall (1981) and Clark et al. (1987). Therefore, this apparent loss may jeopardize a named taxon, the Humboldt marten. Because trapping has been illegal in California since 1953, and because marten sightings in northwestern California have decreased rather than increased during this period of protection, trapping could not have accounted for the decline in marten numbers in northwestern Cali- fornia in the last 40 years. Therefore, loss of late-suc- cessional forest to logging must be considered the most likely cause. Some range expansions have occurred through transplantation of martens, but other transplants have only hastened range expansions that were oc- curring naturally (Slough 1994). Still others were at- tempted to populate vacant habitat but have failed to produce persistent populations (Berg 1982; Slough 1994). Areas that currently have marten populations established by transplantation include Baranof, Chichagof, and Prince of Wales Islands in Alaska (Burris and McKnight 1973; Manville and Young 1965) and the Black Hills of South Dakota (unpubl. data in Fredrickson 1981). Translocation has proven an effective conservation tool if sufficient numbers of animals are translocated, and if quantity and quaUty of habitat at the release site are adequate (Slough 1994). Taxonomy All systematic studies of this species have been based on morphology, especially skull and dental measurements; no biochemical studies of phylogeny have been completed to date. In the first half of this century, the American marten was classified as from two (Merriam 1890) to six species (Miller 1923), but today it is considered a single species {Martes americana) (Clark et al. 1987; Hall 1981). Up to 14 sub- species have been recognized (Hall and Kelson 1959), but Hagmeier (1958, 1961) and Anderson (1970) con- sidered these distinctions arbitrary, and Clark et al. (1987) recognized only eight subspecies in two "sub- species groups." The "caurina" subspecies group in- cludes those (M. a. caurina, humboldtensis, nesophila) in the Rocky Mountains, Sierra Nevada, and the coastal Pacific states. The "americana" subspecies group includes all other subspecies (M. a. abietinoides, actuosa, americana, atrata, kenaiensis). Only two of the eight subspecies recognized by Clark et al. (1987) were separated from others by geographic barriers in presettlement times: M. a. nesophila, on the Queen Charlotte Islands, British Columbia, and the Alexander Archipelago; and M. a. atrata, on New- foundland Island. The others intergrade with each other along lengthy zones of subspecies contact. Population Insularity Our knowledge of isolated populations is almost certainly incomplete and may not include important natural or human-caused cases. Population insular- ity can only be inferred because true insularity re- sults from a lack of movement among populations, and the absence of movements is impossible to prove. Martens occur or occurred on several ocean islands that were connected to the mainland during the Wis- consin glaciation. These include Vancouver, Graham, and Moresby Islands off the coast of British Colum- bia, and Mitkof, Kupreanof, and Kuiu Islands in southeast Alaska (Alaska Department of Fish and Game, unpubl. data; Hall 1981). In the Atlantic, these include Newfoundland, Anticosti, Prince Edward, and Cape Breton Islands (Gibilisco 1994; Hall 1981). In addition, martens occupy several islands in the Alexander Archipelago, including Baranof, Chichagof, and Prince of Wales Islands, to which they were introduced in 1934, 1949-52, and 1934, respectively (Alaska Department of Fish and Game, unpubl. data; Burris and McKiught 1973; Manville and Young 1965). 11 Examples of insular populations on the mainland are more difficult to identify, partly because the dis- persal abilities of martens on land are more subject to interpretation than are their abilities across water. Still, biologists are generally agreed that over 5 kilo- meters of treeless land below the lower elevational limit of trees acts as a complete barrier to dispersal (Gibilisco 1994; Hawley and Newby 1957). On this basis, several mainland populations can be identi- fied that likely have been isolated since late Pleis- tocene or early Holocene times. These include the Bighorn Mountains in north-central Wyoming (Clark et al. 1987) and the Crazy Mountains, Big Belt Moun- tains, and Little Belt Mountains in Montana (Gibilisco 1994). The Bighorn Mountains are separated from other populations to the northwest by arid shrublands along the Bighorn River. Martens oc- curred in the isolated Tobacco Root Mountains in Montana in historical times but now are apparently extinct (Gibilisco 1994). Martens in Colorado, New Mexico, and southern Wyoming are well isolated from those in the northern Rockies by the Green River- Wyoming Basin complex, an important zoo- geographic barrier for other boreo-montane mam- mals as well (Findley and Anderson 1956). Gary (1911) identified a potentially isolated population on the eastern White River Plateau of Colorado. These naturally isolated marten populations in the montane southern part of the range result from sev- eral interacting processes. The coniferous forests to which martens are now limited are high-elevation relicts of more extensive forests that existed during the late Pleistocene (Wright 1981) but have since con- tracted. Today's montane boreal forests are sur- rounded by low-elevation, nonforested lands, which are complete barriers to marten dispersal (see Habi- tat section). Because of these barriers martens are not likely to have reached the montane islands, even over millennia. Therefore, these isolated populations are believed to have persisted since late Pleistocene or early Holocene time. Some mountain ranges that lack extant populations of martens have yielded fossil or subfossial remains of this species, providing insight to the prehistoric distribution (Graham and Graham 1994; Patterson 1984). The persistence of some iso- lated marten populations, and the extinction of oth- ers, suggests the importance of sufficient habitat that can support populations large enough to outlast the processes that push small populations toward extinc- tion. These processes include inbreeding, genetic drift, Allee effects, and stochastic events (Gilpin and Soule 1986). Inbreeding refers to matings among closely related individuals, which is inevitable in small populations. Drift refers to random changes in allele frequencies in small populations resulting from random sampling during gametogenesis and syn- gamy. Allee effects result from low probabilities of animals finding mates at very low densities. Sto- chastic events are more or less unpredictable envi- ronmental conditions that affect size or structure of populations. Lastly, some parts of the distribution of martens appear to have been isolated from others by human- caused habitat fragmentation. These include the iso- lation of martens on the Olympic Peninsula from those in the Cascades (Sheets 1993) and the isolation of martens in western California and Oregon, if they still exist, from those farther north (c.f. Clark et al. 1987; Gibilisco 1994; Hall 1981). In addition, the mar- ten population in the Blue Mountains of southeast- ern Washington and northeastern Oregon likely now is isolated from that in the mountains east of the Snake River (Gibilisco 1994). Management Considerations 1. The marten has undergone an apparent range reduction in northwestern California that may threaten the Humboldt marten, M. a. humboldtensis. This reduction likely is attributable to loss of habitat through the cutting of late-successional forest. 2. The geographic distribution of martens in Wash- ington, Oregon, and northwestern California has been dramatically reduced. This reduction likely is attributable to loss of habitat through the cutting of late-successional forest. 3. Several populations in the western United States are known or hypothesized to be isolated. Insularity decreases population persistence times relative to those of otherwise similar populations that receive episodic ingress (Diamond 1984). Therefore, isolated populations may be especially vulnerable to human actions, particularly where the population is small and the carrying capacity of the habitat is reduced. Special management consideration, including main- tenance of the carrying capacity of the habitat, must be given to these populations. 4. Known isolated populations include some that have persisted since prehistoric times, others that have been created by human-caused fragmentation of formerly contiguous habitat, and still others that 12 have been established by transplantation. Popula- tions that have persisted since prehistoric times likely represent locally adapted forms and warrant greater protection than those created by transplant. 5. Martens are apparently extinct in some isolated habitats where they occurred in historical times. Spe- cial management approaches, including transplan- tation, may be appropriate for these areas. 6. Logging is commonly regarded as the primary cause of observed distributional losses in historic times in the western contiguous United States. Fire, insects, and disease are other important causes of tree death in the western conterminous United States, but the effects of these disturbances on martens have been studied little. Because logging is unique among these disturbances in removing boles from forests, and because of the importance of boles in contributing physical structure to habitats, logging likely is more deleterious to habitat quality for martens than other disturbances. Trapping has contributed to distribu- tional losses in other areas, including the north-cen- tral states and eastern Canada. Research Needs 1 . Develop better methods for monitoring marten populations, including presence or absence, relative abundance, and components of fitness. More reliable knowledge is needed regarding the current distribu- tion of martens in the western United States, espe- cially in the Pacific States and the southern Rocky Mountains. 2. Investigate systematic relationships among populations, especially those that are partially or completely isolated, in order to recognize locally adapted forms or taxonomically recognizable groups. This could also provide site-specific knowledge of rates of genetic exchange. 3. We need information about the factors that af- fect persistence of isolated populations. Specifically, we need knowledge of how duration of isolation, population size and demography, and variation in these attributes affect persistence. 4. Extant populations isolated from other popula- tions by water or land present an opportunity to ex- amine population persistence in relation to area, habi- tat characteristics, and duration of isolation. Knowl- edge of these will improve our ability to address the dependency of marten populations on mesic conif- erous forests (Ruggiero et al. 1988). POPULATION ECOLOGY Demography Most females first mate at 15 months of age and produce their first litters at 24 months (Strickland et al. 1982). For mammals, this is a prolonged time to sexual maturity. Taylor's (1965) allometric equation for mammals gives a predicted maturation time for a 1-kg mammal of 5 months. But even yearling fe- males, up to 78% in some studies (Thompson and Colgan 1987), can fail to produce ova. Females >2 years also may not ovulate, with pregnancy rates as low as 50% in years of environmental stress (Thomp- son and Colgan 1987). The course of spermiation in relation to age has not been studied. Among 136 litters reviewed by Strickland and Douglas (1987), the mean size was 2.85, and the range 1-5. This litter size is about that expected on the ba- sis of body size; allometric equations by Sacher and Staffeldt (1974) and Millar (1981) predict litter sizes for a 1-kg mammal of 2.5-3.0. There is some evidence of age-dependent litter size, with a peak at about 6 years, and senescence at >12 years (Mead 1994). Breeding can occur at ages up to 15 years (Strickland and Douglas 1987). A maximum of one litter is pro- duced per year, compared with an allometrically pre- dicted litter frequency for a 1-kg mammal of 1 .4/ year (Calder 1984). By multiplying litter size by litter fre- quency, Calder (1984) expressed natality rate for ter- restrial placental mammals as a function of body size; a 1-kg mammal is expected to produce 3.4-3.9 off- spring/year. By this standard, the yearly reproduc- tive output of pregnant female martens (mean = 2.9) is low. Longevity statistics depend heavily on whether the population is captive, wild and trapped, or wild and untrapped (Strickland and Douglas 1987). Captive martens as old as 15 years and a marten 14.5 years of age from a trapped wild population have been re- ported (Strickland and Douglas 1987). This is high, by mammalian standards; the allometric equation developed by Sacher (1959) predicts maximum lon- gevity for a 1-kg mammal of 11.6 years. Therefore, American martens are long-lived. However, these figures say little about the life expectancy of new- born martens in the wild. For 6,448 trapped martens from the Algonquin region of Ontario, Strickland and Douglas (1987) reported a median age for both males and females of <1 year. These data suggest the young age at which martens in trapped populations die. 13 The age structure of wild populations depends heavily on whether the population is trapped. Among trapped populations, trapping commonly is the primary mortality source, causing up to 90% of all deaths (Hodgman et al. 1993). Fager (1991) re- ported that 27-100% of marked martens in his three study areas in southwestern Montana were caught by fur trappers during one trapping season. In spite of the high proportion of young animals in trapped samples, heavy trapping over several years tends to selectively remove old animals and skews age struc- tures toward young animals (Strickland and Douglas 1987; Strickland et al. 1982). As a result, structures of trapped populations respond mostly to timing and intensity of harvest. Harvested populations are af- fected by resources such as prey populations only when the resources fall to levels below those that can support the low marten numbers maintained by trap- ping (Powell 1994). At the same time, Powell (1994) pointed out that single-year recruitment responses to high or low prey abundance can be reflected in age structure for years to come. Sex structure likewise is difficult to infer from data from trapping, because of its inherent sampling bi- ases. Males are more likely than females to be taken by trapping (Buskirk and Lindstedt 1989), so that trapped samples show a higher proportion of males than is in the population. As a result, populations subjected to high trapping mortality usually are skewed toward females. Still, live-trapping studies have inferred population sex ratio by comparing numbers of animals captured, by sex, with the num- bers of captures of those animals, by sex. Males tend to exhibit more captures per individual caught than do females. Archibald and Jessup (1984) showed that the ratio of males to females in their study popula- tion did not differ from 1, whereas fur trappers from their area captured predominantly males. Powell (1994) predicted that even sex ratios would be the general case for untrapped populations. Ecological Influences on Population Size and Performance Food availability gives the best evidence of eco- logical influences on population attributes. Weckwerth and Hawley (1962) reported a decrease of about 30% in numbers of adult martens, and of about 80% in numbers of juvenile martens, over a 3- year period when small mammal numbers dropped about 85%. Likewise, Thompson and Colgan (1987) reported a decline in marten numbers in uncut for- est of about 85% in the face of a synchronous decline in prey biomass estimated at over 80%. Thompson and Colgan (1987) also found that food shortage had a stronger effect on resident males than on females, whereas Weckwerth and Hawley (1962) observed effects on both resident males and females. Thomp- son and Colgan (1987) also observed food-shortage effects on pregnancy rate, ovulation rate, age struc- ture, and home-range size. This phenomenon could be important in conservation strategies, because in some forest types, dramatic fluctuations in the mar- ten prey base have been documented (Nordyke and Buskirk 1991 ; Weckwerth and Hawley 1962). This could represent a special concern as a stochastic influence on the persistence of small or isolated populations. Henault and Renaud (in press) examined the rela- tionship between body condition of martens in Que- bec and the relative proportions of deciduous and coniferous forest where they lived. They found a positive relationship between the weights of martens and the coniferous component of their habitat. They inferred that coniferous habitats conferred better body condition on martens than did deciduous- dominated habitats. Strickland et al. (1982) reported various endopara- sites and an incidence rate of 11% for toxoplasmosis, and 1.4% for Aleutian disease, but pointed out that none of these has ever been found to be a substan- tive mortality source for martens. Zielinski (1984) reported that about one-third of the martens he sampled had been exposed to plague, but he noted no deaths, even among the animals with the highest antibody titers. Fredrickson (1990), however, ob- served a dramatic die-off of martens on Newfound- land Island, which he attributed to canine distemper. Population Sizes and Trends Densities of marten populations have been esti- mated mostly by attempts at exhaustive trapping and marking, or by telemetry. These estimates do not as- sure that all martens in a study area are detected; therefore the estimates should be considered conser- vative. Francis and Stephenson (1972) estimated the density of martens in their Ontario study area to be 1.2-1.9/kml Also in Ontario, Thompson and Colgan (1987) estimated the density of martens to vary from 2.4/km2 in the fall of a year of prey abundance to 0.4/km^ in the spring of a year of prey scarcity. 14 Archibald and Jessup (1984) estimated the fall den- sity of resident adults in their Yukon study area to be 0.6/km^ the same as that found by Francis and Stephenson (1972). Soutiere (1979) reported the den- sity of adult residents to be 1.2/km^ in undisturbed and selectively cut forest but only 0.4 /km^ in clearcut forest. These values show some consistency across geographic areas and are remarkably low, even by comparison with other mammalian carnivores, which tend to occur at low densities. Peters (1983:167) showed that, for terrestrial carnivores, population density scales to the -1 .46 exponent of body mass; so a 1-kg carnivoran is expected to occur at a popula- tion density of 15 /km^. The observed densities of American marten populations are about one-tenth of this. Therefore, martens occur at very low densi- ,ties by carnivoran standards, and even lower densi- ties if compared to mammals generally. Even unharvested marten populations undergo marked changes in density. In addition to the six- fold fluctuation reported by Thompson and Colgan (1987), Weckwerth and Hawley (1962) reported a four-fold change in density in Montana. Indeed, one of the goals of managing trapped populations is to decrease population fluctuations (Powell 1994), which may have important implications for habitat relationships and dispersal. Few data sets allow evaluation of population trends over long periods, and this dearth of data is a serious constraint on conservation planning. Data on harvests for furbearers are notoriously sensitive to fur prices (Clark and Andrews 1982), and data on catch per unit effort are gathered by few if any juris- dictions. Several methods of population monitoring have been tried with martens, involving measure- ment scales from presence-absence (Jones and Raphael 1993) to ordinal (Thompson et al. 1989) and ratio (Becker 1991) estimators. Ordinal and ratio-scale population estimation remain largely the province of research. Detection methods summarized by Raphael (1994) include tracks in snow (Becker 1991), smoked track plates (Barrett 1983), and baited cam- era stations (Jones and Raphael 1993). Direct Human Effects Trapping is the most direct avenue by which hu- mans affect marten populations. Because of the ef- fects described above, populations trapped at inter- mediate intensities are characterized by lower den- sities, a predominance of females, and altered age structures relative to populations under untrapped conditions (Powell 1994; Strickland and Douglas 1987; Strickland et al. 1982). However, the effects of trapping on demography are strongly influenced by the timing of harvest. Early season trapping tends to selectively remove juveniles, but seasons that extend into late winter or spring begin to remove more adults. Likewise, early trapping tends to selectively remove males, but trapping after the onset of active gestation shifts toward selective removal of females. Direct human effects on marten populations also in- clude highway accidents (Ruggiero, unpubl. data). Metapopulations Metapopulation structure implies an arrangement of populations that collectively persists, with indi- vidual units that undergo episodic extinction and recolonization (Brussard and Gilpin 1989). No such metapopulations of martens have been described, but their existence in the western United States is plau- sible, especially where patches of high-quality habi- tat are separated by habitat that is traversed by dis- persing animals only at infrequent but ecologically meaningful intervals. Using metapopulation con- cepts to plan for conservation of martens has merit; however, we need far more information on dispersal attributes for martens, and these data are scarce. Population Genetics Only one study has examined genetic variability of American martens. Using allozyme electrophore- sis, Mitton and Raphael (1990) found high variabil- ity in a population in the central Rocky Mountains, with 33% of the loci examined showing some vari- ability, and a mean multi-locus heterozygosity of 0.17. Mean multi-locus heterozygosity reported by Kilpatrick et al. (1986) for terrestrial carnivorans was 0.01. But the sample size for the Mitton and Raphael (1990) study was small {n = 10), which may explain the large heterozygote surpluses relative to Hardy- Weinberg predictions. The lack of more complete knowledge of population genetics means that there is little basis for evaluating genetic variability of populations in relation to conservation status. Genetic data also could provide useful insights into relatedness and rates of genetic exchange among populations. Effective population size (N^) is a conceptualization of how a real population should be affected by in- breeding and genetic drift relative to an idealized 15 population (Crow and Kimura 1970). Neither nor Ng/N (where N is population size) has been esti- mated for any marten population. Calculating in- breeding requires knowledge of any of several demographic and life-history traits, including popu- lation sex ratio, variation in population size over time, and among-individual variation in lifetime reproduc- tive output (Crow and Kimura 1970; Chesser 1991). Few of these attributes are available for marten popu- lations. Importantly, the effect of trapping-induced sex ratios biased toward females on N /N has not e' been considered for any trapped population. Management Considerations 1. Population densities of martens are low, for their body size, in comparison with mammals or terres- trial carnivores. But, because martens are the small- est-bodied of the forest carnivores reviewed herein, their densities are higher than those of most other forest carnivore species. Assuming habitats of simi- lar quality, marten populations typically will be smaller than those of similar-sized other mammals but larger than those of the other forest carnivores considered in this assessment. 2. Marten populations can undergo fluctuations in size of up to an order of magnitude in response to resource conditions. These responses can be attributed to prey conditions and to loss of physical structure. 3. The reproductive rates of martens are low, and longevity is high, by mammalian standards. This suggests that, for a 1-kg mammal, martens are slow to recover from population-level impacts. 4. Some western states allow martens to be trapped each year, which may limit the ability of these mar- ten populations to respond to resource abundance. The structure of trapped populations is altered by the persistent application of trapping mortality. The result is that marten population size and structure may reflect conditions other than habitat or prey Research! Needs 1. To parameterize a model of population persis- tence, we need to know how the major vital rates vary among individuals, sexes, ages, years, and geo- graphic areas. 2. We need multiple estimates of the size of indi- vidual populations to evaluate the reliability of cur- rently used indices of abundance. 3. To estimate inbreeding N^, it is necessary to know how fitness varies among individuals in a population, and how spatial patterns of mating dif- fer from those based on distances among potential partners. The factors that enter into various estimates of include sex ratio among breeders (Crow and Kimura 1970), mean number of and variance in suc- cessful matings by males, incidence of multiple pa- ternity (Chesser 1991), and pregnancy rates and lit- ter sizes, and variances thereof, of females by age (Chesser 1991). To calculate inbreeding N^, it is also necessary to know how population size varies over time (Crow and Kimura 1970). 4. The genetic attributes of marten populations have been studied little. There is a need to know how population history, including size and degree of iso- lation, affects genetic variability. This will enable us to understand whether any extant populations ex- hibit the loss of genetic variability that theoretically accompanies small population size and insularity (Ralls et al. 1986). 5. We also need to understand the sensitivity of martens to inbreeding — that is, to what extent and at what level inbred martens show loss of fitness. This is important for understanding at what sizes marten populations can be expected to exhibit the behavior of extinction vortices (Gilpin and Soule 1986). REPRODUCTIVE BIOLOGY Phenology Breeding occurs from late June to early August, with most matings in July (Markley and Bassett 1942). During this time, the testes become enlarged and sperm can be found in the epididymides (Jonkel and Weckwerth 1963). Females entering estrus exhibit swelling of the vulva and cytological changes that are typical of mustelids (Enders and Leekley 1941). It is unclear whether females undergo a single long estrus or multiple brief estruses in the wild. Copula- tion occurs on the ground or in trees, and is prolonged (Henry and Raphael 1989; Markley and Bassett 1942). Captive females mate with multiple males (Strickland et al. 1982), and wild females likely do as well, but it is not known whether these multiple matings result in litters of multiple paternity. Ovulation is presumed to be induced by copulation (Mead 1994), but among Martes this has only been shown for the sable. The oocyte is fertilized in the oviduct and moves to the uterine horn, where the conceptus increases in size to that of a blastocyst, which is about 1 mm in diam- eter (Marshall and Enders 1942). 16 Like many other Carnivora, the marten undergoes embryonic diapause. The total gestation period is 260-275 days (Ashbrook and Hansen 1927; Markley and Bassett 1942), but during only the last 27 days is gestation active (Jonkel and Weckwerth 1963). Im- plantation of the blastocyst in the endometrium, which marks the onset of active gestation, is under photoperiodic control (Enders and Pearson 1943). Active gestation is accompanied by development of the mammaries (Mead 1994). Parturition occurs in March and April (Strickland et al. 1982). Newborn kits weigh about 28 g, open their eyes at about 35 days, and eat solid food begin- ning at about 40 days (Ashbrook and Hanson 1927). Weaning occurs at about 42 days (Mead 1994), which is late by mammalian standards. Allometric equa- tions developed for mammals predict ages at wean- ing for a 1-kg mammal of from 28 days (Millar 1977) to 34 days (Blaxter 1971). Young martens emerge from the dens at about 50 days but may be moved among dens by the mother earlier (Hauptman 1979, Henry and Ruggiero, in press). The young leave the com- pany of their mother in late summer but disperse later (Strickland et al. 1982). Den Sites Two types of dens are recognized in the literature: natal dens, in which parturition takes place, and maternal dens, which are occupied by the mother and young but are not whelping sites (Ruggiero, in re- view). A variety of structures are used for dens, with trees, logs, and rocks accounting for 70% of the re- ported den structures (table 2). In virtually all cases involving standing trees, logs, and snags, dens were found in large structures that are characteristic of late- successional forests (Ruggiero, in review). In Wyo- ming, den sites having well-developed characteris- tics of old-growth forest were preferred by martens, and natal den sites had significantly better-developed old-growth characteristics as compared to maternal den sites (Ruggiero, in review). Old growth was de- fined in this study in terms of canopy cover, number of tree species, total canopy cover, number of canopy layers, tree diameters, snag densities and diameters, and log densities and diameters. Given the impor- tance of natal dens to recruitment, the availability of structurally complex sites could have important im- plications for conservation. Mating Systems and Betiavior The marten generally displays a promiscuous breeding system, but the impregnation of multiple females by a single male, or breeding with multiple males in a single year by a female in the wild, has not been proven. As with other polygynous Car- nivora (Sandell 1989), male martens are alleged to Table 2.— Summary of den structures used by American martens (grand total = 116). Den structures Human- Author Location Year Trees Middens Logs made Rocks Ground Snags Rootwad Stump Logpiles Grinnell et al. California 1937 1 Remington Colorado 1952 1 Francis Ontario 1958 1 1 More Northwest Territory 1978 1 Hauptman Wyoming 1979 7 2 O'Neil Montana 1980 1 Simon California 1980 1 Burnett Montana 1981 1 Wynne & Shierburne Maine 1984 4 2 Vernam Alaska 1987 1 Jones & Western Raphael Washington 1991 4 1 Baker British Columbia 1992 1 3 3 Ruggiero Wyoming in review 11 3 23 2 22 1 17 1 Total 27 3 28 2 25 3 19 1 4 4 17 set home range size in part to gain access to multiple female mates (Powell 1994). Modes of Communication Several vocalizations have been described (Belan et al. 1978), ranging from a "chuckle" to a "scream." Martens vocalize during copulation (Henry and Raphael 1989; Ruggiero and Henry 1993) and when frightened by humans (Grinell et al. 1937) but ordi- narily use vocal communication little. The role of specific vocalizations is poorly understood. Martens have a broad range of known and hypothesized means for transmitting chemical signals. These in- clude the products of their anal sacs, abdominal glands (Hall 1926), and plantar foot glands (Buskirk et al. 1986), as well as urine and feces. But, as with vocal- izations, the functions of these specific scent modalities in reproduction or other life functions are not known. Parental Care Maternal care includes finding a suitable natal den, carrying nest material to the den, moving kits to other dens (Henry and Ruggiero, in press; Wynne and Sherburne 1984), post-partum grooming and nurs- ing (Brassard and Bernard 1939; Henry and Ruggiero, in press), and bringing food to the young until they are old enough to forage for themselves. Paternal care of young has not been reported and likely does not occur (Strickland and Douglas 1987), consistent with the pattern for polygynous Carnivora (Ewer 1973). Survival of Young Almost no data are available on survival of young to specified ages. To gather these data, newborn kits would have to be tagged or radiocollared in natal dens and tracked for the time interval of interest. This has not been done, and it is unlikely to be done in the foreseeable future. Thus, estimates of survival for the first six months of life will continue to be inferred from numbers of placental scars, which are taken to represent numbers of neonates. Management Considerations 1 . The phenology of reproductive events is impor- tant in managing harvested populations. Trapping seasons are set in part to avoid periods of breeding and maternal care of young. 2. The mating system has important implications for managing trapped populations. The predisposi- tion of males to be caught in traps results in sex ra- tios favoring females. Males, however, can impreg- nate multiple females, so that sex ratios skewed toward females do not necessarily reduce pregnancy rates. 3. Natal den sites appear to be in very specific habi- tat settings and may represent a special habitat need. The availability of special habitat conditions for na- tal denning may limit reproductive success and population recruitment. Research Needs 1. Obtain more reliable information on reproduc- tive rates and variation in reproductive rates of free- ranging martens. Environmental factors, including habitat type and prey availability, that influence re- production need to be quantitatively understood. We also need to know whether and when skewed sex ratios affect pregnancy rates in trapped populations. 2. Investigate how the loss of genetic variability that results from persistently small population size affects reproduction in martens. Reproductive dys- function is a common correlate of inbreeding in mam- mals generally (Ralls et al. 1988) and in mustelids (Ballou 1989) and needs to be understood better in martens. 3. Determine the natal and maternal den require- ments of martens. Specifically, we require knowledge of how habitat needs for reproduction affect repro- ductive success, and whether these habitat needs are more or less limiting than habitat needs for other life functions. FOOD HABITS AND PREDATOR-PREY RELATIONSHIPS General Foraging Ecology and Behavior About 22 published studies have reported diets of American martens (Martin 1994), and most authors have considered the marten a dietary generalist (Simon 1980; Strickland and Douglas 1987). Martens kill vertebrates smaller and larger than themselves, eat carrion, and forage for bird eggs, insects, and fruits (table 3). Martens are especially fond of hu- man foods but seldom are implicated in depredation on domestic animals or plants (Buskirk 1994). Martens forage by walking or bounding along the ground or snow surface, investigating possible feed- 18 Table 3.— Major food items in the diet of American marten. Values given are percent frequency of occurrence for all seasons sampled. Cricetids Location Number of scats (except muskrat) Shrews Sciurids Snowshoe hares Ungulates Birds Fruits Insects Human foods Maine' 412 -80 7.0 -7 1.7 0.7 18,0 * 8,3 • Northwest Territories^ 499 89 -6 6 5 0 19 -23 -14 * Sierra Nevadas California^ 300 -20 2.2 ft 4.9 1.2 8.8 ~5 8.0 6.0 Northwest Territories" 172 >90 1.2 0 0 • * « 32 * Western Montana^ 1758 73.7 7.6 12.0 2.9 4.7 12.0 29.2 19.0 * Alberta* 200 66.0 1.6 10.2 1.6 <1 4.3 5.2 5.2 » Interior Alaska^ 466 73 0 <1 <1 <1 10 17 0 • Northern Idaho^ 129 -82 1 -12 2 « 5 12 9 » Southeastern Manitoba' 107 18.6 1.9 15,9 58.9 0 17,8 0 0 « South-central Alaska'° 467 88.2 1.7 7.2 1.1 20.5 9.7 20.5 <1 1.3 Colorado" 47 -80 -42 -10 -6 ~7 -9 -15 Vancouver Island'^ 701 -18 2 6 0 20 30 <1 <2 « ' Soutiere (1979), 67% of material from April-September. ^ More (1978), material from all seasons. ^ Zielinski et al. (1983), material from all seasons. " Douglas et al. (1983), scats from Marcti-April and October-November over two-year period. ^ Weckwertti and Hawley (1962), scats from all seasons over a five-year period. * Cov/an and Mackay (1950), season unknown. ^ Lensink et al. (1955), 80% of material from June-August. ^ Koehler and Hornocker (1977), 63% of material from winter " Raine (1981), all winter scats. '° Buskirk and MacDonald (1984), scats from autumn, winter, and spring. " Gordon (1986), all from winter Nagorsen et al. ( 1 989), all Gl tracts from winter * Not mentioned, or cannot be inferred from data given. ing sites by sight and smell. In winter they forage on the snow surface, with forays up trees or into the subnivean space (Raine 1981; Spencer and Zielinski 1983; Zielinski et al. 1983). In the western United States in winter, most prey are captured beneath the snow surface, but squirrels may be caught in trees. In these areas, structure near the ground is impor- tant in providing access to subnivean spaces (Corn and Raphael 1992). In the eastern Canadian prov- inces, snowshoe hares are an important food and are caught on the snow surface or in slight depressions (Bateman 1986; Thompson and Colgan 1987). Seasonal, Supra-annual, Geographic Variation in Diets All data on diets of martens are disaggregated by study area (table 3), with some additional disaggre- gation by year, season, sex, and individual. Yearly variation is common and reflects the dynamics of food sources, especially prey numbers (Martin 1994; Thompson and Colgan 1987) and berry crops (Buskirk 1983). Seasonal variation in marten diets is universal. Diets in summer include a wide range of food types. including mammals, birds and their eggs, fish, in- sects, and carrion. The importance of soft mast, es- pecially the berries of Vaccinium and Rubus, peaks in autumn and declines over winter. As snow covers the ground and deepens, martens turn to mostly mammalian prey, which dominate the winter diet. The most important genera at this time are Clethrionomys, Microtus, Spermophilus, Tamiasciurus, and Lepus. There is a trend in some areas to turn to sciurids, especially Tamiasciurus sp. and Spermophilus lateralis, in late winter and early spring (Buskirk and MacDonald 1984; Zielinski et al. 1983). These seasonal patterns are largely explainable by food availability. Many of the birds and bird eggs (Gordon 1986) and fish (Nagorsen et al. 1989) eaten in summer are mi- gratory and only seasonally present in marten home ranges. Insects that are active in summer burrow into soil or organic debris in winter. Fruits ripen in late summer but fall off plants or are covered with snow by early winter. And small mammals undergo wide seasonal changes in numbers and in physical acces- sibihty (Buskirk and MacDonald 1984; Raine 1981; Zielinski et al. 1983). Mice and voles, which are cap- tured beneath the snow, may decrease in their dietary importance as snow depths increase in late winter. 19 and species that can be caught more easily, especially pine squirrels (Tamiasciurus spp.) and hares, increase in importance correspondingly (Martin 1994; Ziehnski et al. 1983). Geographic patterns reveal striking differences as well as some similarities. For example, snowshoe hares have been consistently more important prey in central and eastern Canada than farther west. But, although prey species vary across study areas, the same prey choices are not available everywhere. Martens often prey similarly on ecological analogues (e.g., Tamiasciurus hudsonicus and T. douglasii) in dif- ferent areas, often under similar circumstances (c.f. Zielinski et al. 1983 with Buskirk and MacDonald 1984). Martin (1994) showed that dietary diversity (Shannon- Weaver H') was lowest for high geographic latitudes (Buskirk and MacDonald 1984; Douglas et al. 1983; Lensink et al. 1955) and sites where martens eat mostly large-bodied prey, especially snowshoe hares (Bateman 1986; Raine 1987). The most diverse marten diets tended to be those from the west temper- ate part of the geographic range, including California. Principal Prey Species The most common prey species taken include red- backed voles (Clethrionomys spp.), voles {Microtus montanus, M. oeconomus, M. pennsylvanicus, M. xan- thognathus and Phenacomys intermedius), pine squir- rels {Tamiasciurus spp.), and ground squirrels {Spermophilus spp.). Of these, red-backed voles are staple, but not preferred, foods in most areas, being taken only in proportion to their availability (Buskirk and MacDonald 1984; Weckwerth and Hawley 1962). Microtus spp. are taken in excess of their availability in most areas. Martens capture them in small herba- ceous or shrub patches (Buskirk and MacDonald 1984), which in many areas are riparian (Zielinski et al. 1983). Deer mice and shrews are generally eaten less than expected based on their numerical abun- dance, but deer mice are the staple food on Vancouver Island, where red-backed voles are absent. Martens appear to have important ecological rela- tionships with red squirrels and Douglas squirrels. The active middens of these species provide resting sites that may be energetically important to martens in winter (Buskirk 1984, Spencer 1987). Middens also provide natal and maternal den sites (Ruggiero, in review). Sherburne and Bissonette (1993) found that martens gained access to the subnivean space via openings that were closer to squirrel middens than were openings not used by martens for subnivean access. The amount of coarse woody debris around access holes used and not used by martens did not differ. Although martens rest in active middens in some areas in winter, red and Douglas squirrels ap- pear to have limited importance in the winter diet of martens in those locations (e.g., Alaska [Buskirk 1983]; Wyoming [Clark and Stromberg 1987]). This indicates that the two species may coexist at resting sites, and it further indicates that an important symbiosis may exist. This relationship may have important implica- tions relative to marten habitat quahty and to marten behaviors at times of energetic stress (Buskirk 1984). Habitat Associations of Principal Prey Red-backed voles are occupants of coniferous for- ests (Clough 1987; Nordyke and Buskirk 1991; Tevis 1956), where they associate closely with large-diam- eter logs (Hayes and Cross 1987) and understory plant cover (Nordyke and Buskirk 1991). Raphael (1989) showed that in the central Rocky Mountains, southern red-backed voles were most abundant in mature, mesic coniferous stands. The attributes with which red-backed voles associated most closely were high basal areas of Engelmann spruce and high old- growth scores. The old-growth attributes that con- tributed to a high score were multiple tree species contributing to the canopy, dense canopy, large-di- ameter trees, dense and large-diameter snags, and dense and large-diameter logs. Microtus pennsylvan- icus, M. montanus, M. oeconomus, and M. longicaudus occupy herbaceous and shrub meadows. Red and Douglas squirrels are mostly restricted to coniferous forests of cone-producing stages, especially late-suc- cessional stages (Flyger and Gates 1982), although they can occur in hardwood stands in the eastern con- terminous United States (Odum 1949). Snowshoe hares occur in a wide range of habitats (Bittner and Rongstad 1982) but generally prefer dense conifer- ous forests, dense early serai shrubs, and swamps interspersed with shrubs or saplings (Bookhout 1965; Richmond and Chien 1976). Dolbeer and Clark (1975) found that snowshoe hares in the central Rocky Mountains preferred mixed stands of spruce, subal- pine fir, and lodgepole pine. Taiga voles, important foods of martens in taiga areas of Alaska and the Yukon, are variously reported to have wide habitat tolerances (Douglass 1977), be restricted to early post- fire seres (West 1979), or be associated with lightly burned forest (Wolff and Lidicker 1980). 20 Management Considerations 1 . The most important prey of martens in the West in winter are forest species {Clethrionomys spp. and Tamiasciurus spp.) and herbaceous meadow or ripar- ian species (Microtus pennsylvanicus, M. montanus, M. xanthognathus, others). Martens avoid deer mice in the sense of having a lower proportion of them in their scats than the proportion of deer mice among small mammals in the area. The same is true for shrews. In the western United States in winter, the distribution and abundance of these species provide some measure of the value of habitats for foraging. 2. Abundance and availability of small mammals in winter are important determinants of fitness in martens. Habitats that provide an abundance of red- backed voles, pine squirrels {Tamiasciurus spp.), and meadow voles generally provide good foraging ar- eas. Habitats with high densities of deer mice gener- ally provide little in the way of foraging habitat. 3. Although major disturbance, including distur- bance such as timber harvest activities, tends to in- crease populations of some small mammal species, especially deer mice, these species are not important prey for martens. Research Needs 1 . Document to what extent foraging habitat asso- ciations of martens are mediated by prey abundances as opposed to prey vulnerability. The latter may be affected by prey behavior, physical structure of habi- tat, and other factors. 2. Elucidate the relationship between pine squir- rels {Tamiasciurus spp.) and martens with special emphasis on squirrels as prey and as builders of middens that are important resting sites and dens for martens. Whether middens are preferable to or an alternative for other structures as resting sites and natal and denning sites needs to be clarified. HABITAT REI^TIONSHIPS General Considerations Habitat quality is defined in terms of the fitness of animal occupants (Fretwell 1972). In the case of mar- tens, fitness or components thereof are difficult to estimate, even by mammalian standards. Therefore, other attributes commonly are used as indicators of habitat quality, and we, like many who have studied marten habitats, accept the validity of this substitu- tion although it is largely untested (Buskirk and Powell 1994; Ruggiero et al. 1988). The two most com- mon attributes from which habitat quality is inferred in research studies are the behavioral choices of indi- vidual martens and population density, including some measure of population structure where possible. The use of behavioral choices to indicate habitat quality assumes that martens recognize and prefer the best of a range of available habitats at some spa- tial scale (Ruggiero et al. 1988). It also requires that research be designed at spatial and temporal scales that will detect the important preferences of martens. Group selection has not been reported for any mem- bers of the genus Martes; therefore, using individual choices to reflect total fitness appears appropriate for this species (Buskirk and Powell 1994). The use of population density to indicate habitat quality in- volves assumptions discussed by Van Horne (1983). Hov/ever, the marten appears to meet the criteria proposed by Van Horne for species in which popu- lation density is coupled to habitat quality. It is a habitat specialist, its reproductive rate is low, and it lacks patterns of social dominance in stable popula- tions in high quality habitats, although there is evi- dence of avoidance by juveniles of high-quality habi- tats occupied by adults. Similarly, martens do not undergo seasonal shifts in home ranges, and only rarely do they migrate in the face of environmental unpredictability. Therefore, the use of population density to indicate habitat quality in the American marten should be valid, but this assumption has not specifically been tested. Use of Major Vegetation Zones Interpretations of studies of habitat use require that the context, sampling approach, and landscape of the study be understood. For example, stands in the Rocky Mountains dominated by lodgepole pine {Pinus contorta) are variously described as preferred (Pager 1991), used in proportion to availability (Buskirk et al. 1989), or avoided (Wilbert 1992) based on the spatial extent of lodgepole types. But this ap- parent discrepancy is largely due to variation in land- scapes studied, rather than habitat plasticity of mar- tens. If a study area contains roughly even propor- tions of a highly preferred mesic forest type, a dry, less preferred forest type, and nonforested habitat, the lodgepole pine is more likely to be used in pro- portion to availability than if the nonforested habi- 21 tat is not considered in the study or not present in the study area. Also, rejection of null hypotheses re- garding habitat selection depends on the power in the statistical tests. Studies involving small numbers of animals or other units of replication are likely to conclude that martens are habitat generalists. Broadly, American martens are limited to conifer- dominated forests and vegetation types nearby. In most studies of habitat use, martens were found to prefer late-successional stands of mesic coniferous forest, especially those with complex physical struc- ture near the ground (Buskirk and Powell 1994). Xe- ric forest types and those with a lack of structure near the ground are used little or not at all. In the north- ern part of its range, xeric coniferous stands are not available to the American marten; therefore, this site moisture preference is not seen here, but the prefer- ence and apparent need for structure near the ground, especially in winter, appears universal. Complex physical structure, especially near the ground, appears to address three important life needs of martens. It provides protection from predators, it provides access to the subnivean space where most prey are captured in winter, and it provides protec- tive thermal microenvironments, especially in win- ter (Buskirk and Powell 1994). Structure near the ground may be contributed in various ways, includ- ing coarse woody debris recruited by gradual tree death and tree fall (Buskirk et al. 1989), coarse woody debris recruited en masse by fire (Harmon et al. 1986), the lower branches of living trees (Buskirk et al. 1989), rock fields in forests (Buskirk et al. 1989), talus fields above treeline (Streeter and Braun 1968), shrubs (Hargis and McCullough 1984), herbaceous plants (Spencer et al. 1983), squirrel middens (Finley 1969), and combinations of these. Preferences for major vegetation types vary across geographic areas and have been reviewed by Bennett and Samson (1984). This variation may seem to con- tradict the habitat specialization of the species, but closer examination shows that the requirement for structure near the ground is constant and that the same tree species show different site and structural attributes across regions. On the west slope of the Cascade Range, Jones and Raphael (1991, unpubl. data) reported that old-growth forests within the Pa- cific silver fir (Abies amabilis) and western hemlock (Tsuga heterophylla) zones were preferred by 14 mar- tens, based on 1,292 telemetry locations. Clearcuts were used less than expected from their availability. and the largest diameter trees available typically were used as resting sites. In Okanogan County, Washing- ton, Koehler et al. (1990) found 10 of 11 marten tracks in stands dominated by Engelmann spruce (Picea engelmannii) — subalpine fir {Abies lasiocarpa) and lodgepole pine >82 years old. These two types rep- resented 51 % of the area sampled. Marten tracks were rare or absent in stands dominated by younger lodge- pole pine and Douglas fir (Pseudotsuga menziesii), larch, and aspen. On Vancouver Island, Baker (1992) found martens in 10- to 40-year-old second-growth Douglas fir more than in old-growth western hem- lock-Pacific silver fir- western redcedar {Thuja plicata). However, structures used by martens for resting gen- j erally were residual components of the pre-existing old-growth stands. In the Sierra Nevadas, martens were shown to prefer lodgepole pine in riparian set- tings and red fir at higher elevations and to avoid Jeffrey pine {Pinus jeffreyi) associations (Simon 1980; Spencer et al. 1983). In interior Alaska martens oc- cupy both of the major forest types available, domi- nated by white spruce {Picea glauca) and black spruce (P. mariana) (Buskirk 1983). In Ontario, martens pre- ferred stands with some conifer component over pure hard wood stands (Francis and Stephenson 1972; Tay- lor and Abrey 1982). Snyder and Bissonette (1987) found that martens on Newfoundland Island oc- curred in stands dominated by balsam fir {Abies balsamea) and black spruce. In various sites in the northern Rocky Mountains, martens have preferred stands dominated by mesic subalpine fir, Douglas fir, and lodgepole pine in some associations, and martens have used stands dominated by xeric sub- alpine fir and lodgepole pine in other associations less than predicted from the spatial availability of these types (Burnett 1981; Fager 1991). In the central and southern Rockies, martens prefer stands domi- nated by spruce {Picea spp.) and subalpine fir, occur in stands dominated by lodgepole pine and limber pine (P. flexilis), and are rare or absent in stands domi- nated by ponderosa pine or pinyon pine (P. edulis) (Buskirk et al. 1989; Wilbert 1992). In no place have American martens been found to prefer hardwood- dominated stands over conifer-dominated stands. Use or selection of riparian zones has been reported by several authors. Buskirk et al. (1989) reported pref- erence for riparian areas for resting, and Spencer and Zielinski (1983) reported foraging in riparian areas. Jones and Raphael (1992, unpubl. data) also reported heavy use of areas close to streams. 22 Habitat Use in Relation to Sex, Age, and Season The selection of natal den habitat by females likely is an example of a gender-specific habitat selection, but it is unclear whether females select den sites that differ from male resting sites. Descriptions of natal dens are scarce. In all cases involving trees, large structures associated with late-seral forest conditions were used, and in Wyoming, martens selected for old- growth characteristics at 14 natal dens (Ruggiero, in review). Baker (1992) showed that female martens were more selective of habitats than were males and hypothesized that this difference was due to more stringent demands for resources placed on females by reproduction. Age-specific habitat associations have been re- ported in some studies that looked for them. For ex- ample, Burnett (1981) concluded that juveniles oc- cupied a wider range of habitat types than did adults. Likewise, Buskirk et al. (1989) showed that although martens >1 year old preferred spruce-fir stands for resting, juveniles were not selective of any stand type. Spruce-fir stands had higher basal areas, larger-di- ameter trees, and higher densities and diameters of logs than did lodgepole stands, and resting sites were presumed to be more common in the former. Juve- niles may fail to recognize, or may be excluded by territorial adults of the same sex, from high-quality habitats (Buskirk et al. 1989). Therefore, habitat choices by juveniles may be constrained by the be- haviors of dominant adults, with important implica- tions for juvenile survival. For example. Baker (1992) reported that two juveniles using early successional habitats in a logged landscape were killed by great- horned owls (Bubo virginianus) . Juveniles may maxi- mize their fitness by choosing from among a set of habitats that exclude the best habitats occupied by conspecifics in the area. This age-dependent habitat selection has important implications for our under- standing of the habitat needs of martens, and possi- bly for the density - habitat quality relationship. If juveniles are less habitat-selective (or more habitat constrained) than adults, which they appear to be, and because juveniles are more likely to be captured, and therefore radio-collared and studied, habitat studies that do not specifically consider the effect of age on habitat selection may characterize martens as far less habitat-specialized than they are as reproduc- ing adults. For this reason, it is vitally important in studies of habitat preference to focus on the fitness of individuals, and persistence of populations, rather than on the mere presence of individuals in particu- lar habitats for brief periods (Ruggiero et al. 1988). Seasonal variation in habitat selection has been reported by most authors who have analyzed their data for it. There is little evidence of shifts of home range boundaries to seasonally encompass different habitat types; therefore, martens seasonally adjust their selection of stands within stable home ranges. Campbell (1979), Soutiere (1979), Steventon and Major (1982), and Wilbert (1992) all reported more selective use of late- successional coniferous stands in winter than in summer. Koehler and Hornocker (1977) reported more selective use of habitats in deep snow than in shallow snow. Buskirk et al. (1989) showed that in winter marten were more likely to use spruce-fir with more old-growth character in cold weather than in warm weather. No studies have shown the converse pattern. Of the studies that have compared summer and winter use of nonforested habitats, all report less use in winter (Koehler and Hornocker 1977; Soutiere 1979) and in some cases no use (Spencer et al. 1983). The possible reasons for this seasonal variation have been reviewed by Buskirk and Powell (1994) and include the greater visibility of martens to potential predators on a snow background, and the greater importance of structure near the ground in providing foraging sites in win- ter. This seasonal variation also has important impli- cations for understanding the results of habitat stud- ies. Habitat studies conducted during winter are more likely than those in summer to conclude that martens strongly prefer late-successional conifers. Winter, therefore, appears to be the season when martens in most areas are limited to the narrowest range of habitats within their home ranges. Special Requirements and Spatial Scales Microtiabitat Use The smallest scale at which habitat use has been investigated involves use of resting sites (e.g., Buskirk et al. 1989; Taylor 1993; Wilbert 1992), natal and ma- ternal dens (Henry and Ruggiero, in press; Ruggiero, in review), and access sites to spaces beneath the snow (Corn and Raphael 1992; Sherburne and Bissonette 1993). Wilbert (1992) found that martens selected boles for resting that were larger than those in surrounding plots, and logs that were in interme- diate stages of decomposition. Taylor (1993) showed that martens could reduce thermoregulatory costs by 23 selecting from among the resting site types available over small areas. Wilbert (1992) also found that struc- tural variability was itself selected for resting. Natal dens were in the largest boles available in Ruggiero's (in review) study area. Corn and Raphael (1992) showed that martens gained access to subnivean spaces via openings created by coarse woody debris at low snow depths, and by lower branches of live trees in deep snow. Compared with marten trails generally, subnivean access points had higher vol- umes of coarse woody debris, more log layers, and fewer logs in advanced states of decay. These find- ings support the view that marten are highly selec- tive of microenvironments for thermal cover, for pro- tection from predators, and for access to subnivean foraging sites. Landscape-Scale Habitat Use Knowledge is almost completely lacking regard- ing behavioral or population responses of martens to such landscape attributes as stand size, stand shape, area of stand interiors, amount of edge, stand insularity, use of corridors, and connectivity (Buskirk 1992). Snyder and Bissonette (1987) reported that marten use of residual forest stands surrounded by clearcuts on Newfoundland Island was a function of stand size. Stands <15 ha in area had lower capture success rates than larger stands. However, the dearth of knowledge in this area makes managing forested landscapes for martens highly conjectural. Effects of Forest Fragmentation Fragmentation includes loss of stand area, loss of stand interior area, changes in relative or absolute amounts of stand edge, and changes in insularity (Turner 1989). The term is context-specific but is more commonly used to characterize major retrogressional changes to late-successional forests than successional processes affecting early seres. Again, marten re- sponses to these processes above the stand level are completely unstudied; virtually no knowledge exists that would allow scientific management of fragmen- tation processes to accommodate martens. Brainerd (1990) presented a general hypothesis of the response of Eurasian pine martens (Martes martes) to forest fragmentation, which predicted that marten popu- lations would increase in response to forest fragmen- tation that cut small patches and left 45% of pristine forest intact. The reasoning behind this prediction is that Microtus are abundant in Scandinavian clearcuts. and if these cuts are small enough that martens can forage in them and remain close to trees, then a posi- tive numerical response should result. Brainerd (1990) also predicted that cutting of larger patches should reduce marten densities. Brainerd's model may be relevant to North America; however, the lack of any Microtus or other preferred prey species that responds positively to clearcutting of conifers in the western conterminous United States limits the ap- plicability of this model. Response to IHuman Disturbances The effect of major retrogressional change on | stand-level habitat selection has been studied in sev- eral areas (Bateman 1986; Francis and Stephenson 1972; Soutiere 1979; Spencer et al. 1983; Thompson ' 1994). Among the habitat types included in these studies have been clearcuts and selective ("partial") ' cuts in various stages of regeneration. These studies . have generally shown that martens make little abso- lute or relative use of clearcuts for several decades and that marten populations decline after clearcut logging. Soutiere (1979) showed that marten densi- ties in clearcut areas in Maine were 0.4 /km^ about one-third of those in uncut and partially cut stands. In partially cut stands all balsam fir {Abies balsamae) 15 cm or greater dbh, and all spruce and hardwoods 40 cm or greater dbh had been removed so that, among stands, 57-84% of basal area had been re- moved. Soutiere (1979:850) believed that retention of 20-25 m^/ha basal area of trees in pole and larger trees "provided adequate habitat for marten." The clearcut logging had taken place 1-15 years before the study. But Steventon and Major (1982) found that use of clearcuts in the same study area was limited to summer. Self and Kerns (1992, unpubl.) studied habitat use by three martens in northcentral Califor- nia and suggested that martens did not show strong habitat selection. However, they did not report any | statistical analyses of habitat use upon which infer- ences were based. Thompson and Harestad (1994) I summarized the results of 10 studies of habitat se- ! lection in relation to successional stage. These stud- ies showed consistent use /availability ratios <1 in shrub, sapling, and pole stages. Only when succes- sion reached the "mature" stage did use /availabil- ity ratios begin to exceed one, and only "overmature" stands were consistently preferred. None of the stud- ies found use /availability ratios for "overmature" stands <1 (Thompson and Harestad 1994). Baker 24 (1992) described the most striking exception to this pattern from Vancouver Island. She found preference for 10- to 40-year-old post-cutting Douglas fir over old-growth types. However, her study area was un- usual in that large-diameter coarse woody debris pre- dating the cutting provided structures not ordinarily found in second-growth stands. Almost no other studies specific to western North America show how marten preference for regenerating clearcut stands varies with time. For North America generally, Thompson and Harestad (1994) reviewed literature on the duration of the negative effects of clearcut logging on mar- tens. They concluded that for the first 45 years post- cutting, regenerating clearcuts supported 0-33% of the marten population levels found in nearby uncut forest, and by inference, in the pre-cut forest. Thomp- son (1994) reported that some martens occupied ar- eas that had been clearcut 10-40 years before but that these animals experienced high mortality rates from predation and trapping. The mechanisms by which martens are impacted by timber cutting are the removal of overhead cover, the removal of large-diameter coarse woody debris, and, in the case of clearcutting, the conversion of mesic sites to xeric sites, with associated changes in prey communities (Campbell 1979). Some of these effects, such as loss of canopy cover, can be reversed by succession in the near-term. Others, including the removal of coarse woody debris, can only be reversed by the addition of coarse woody debris or by the growth of new large-diameter boles. Structural Features Relative to Succession The structural features that develop with succes- sional advancement and that are important to mar- tens include overhead cover, especially near the ground; high volumes of coarse woody debris, espe- cially of large diameter; and small-scale horizontal heterogeneity of vegetation, including the intersper- sion of herbaceous patches with patches of large, old trees. Overhead cover is important because it con- fers protection from predators and addresses the be- havioral preference of martens for areas with cover (Hawley and Newby 1957). Some early successional stages provide overhead cover in the form of dense herbaceous or shrubby vegetation (Magoun and Vernam 1986). In later successional stages, this need is met by the lower branches of living trees, by coarse woody debris, and by squirrel middens. One impor- tant change that occurs with succession is the replace- ment of shade-intolerant tree species with shade-tol- erant ones. The latter (e.g., spruce and fir) retain lower branches on the bole in shaded settings, contribut- ing to structure near the ground in forests with dense canopy (Peet 1988). However, the behavioral avoid- ance of openings by martens shows geographic varia- tion, with martens in taiga areas of Alaska and the Yukon apparently showing greater tolerance of sparse canopy than martens farther south (Buskirk 1983; Magoun and Vernam 1986). Some kinds of major retrogressional change also produce structural conditions preferred by martens. Considerable work in Alaska shows that martens attain high local densities in post-fire seres that have complex physical structure in the form of horizontal boles or dense herbaceous vegetation (Johnson and Paragi 1993; Magoun and Vernam 1986). However, Pager (1991) found almost no use of forests burned by the 1988 Yellowstone fires, although martens passed through burns and rested in unburned is- lands. Therefore, marten responses to burns appear to vary regionally, but it is not clear whether behav- iors of martens or site responses to fire produce this variation. Horizontal heterogeneity may be important be- cause it allows martens to fulfill their life needs in small areas, reducing travel distances. Martens may be especially benefitted by the small-scale horizon- tal heterogeneity that results from the natural dynam- ics of old-growth forests (Hunter 1990). For example, the death of large old trees results in tree boles fall- ing to the forest floor. In this position, they are im- portant for overhead cover and for natal dens and maternal dens, and for winter resting sites. At the same time, opening of the canopy by the loss of large old trees admits sunlight to the forest floor, which stimulates herbaceous growth, which may in turn attract or produce small pockets of mice or voles (Hunter 1990), important prey for martens. It is not clear whether selective harvest of trees could mimic these small disturbances. Coarse woody debris, especially in the form of large-diameter tree boles, can address many of the needs that martens have for physical structure: preda- tor avoidance, access to subnivean spaces (Corn and Raphael 1992), and thermal protection (Buskirk et al. 1989). Coarse woody debris accumulates in volume with advancing succession, and logs in old mesic coniferous stands are larger in diameter than those in young ones (Harmon et al. 1986). Also, in 25 unmanaged forests, coarse woody debris accumu- lates more and attains higher diameters in mesic stands that have not been disturbed by fire than in xeric stands that have. Of course, human changes to the dynamics of coarse woody debris alter these re- lationships. The processes of tree death and decay alter the position, shape, internal structure, and physical prop- erties of boles (Harmon et al. 1986) to make them more important features of marten habitats. Patho- gen-induced changes in the growth form of conifers can create important microenvironments ("witch's brooms") for martens (Buskirk et al. 1989). Wind fells rot- weakened boles of old trees to positions near the ground, and the hollows created by decay in logs and stumps are used by martens for resting sites and na- tal dens (see Buskirk et al. [1987] for review). Par- tially decayed wood may have physical properties that affect the microenvironments used by martens. Lastly, other vertebrate occupants of late-successional forests cause structural changes that are important to martens. These include primary cavity-nesting birds, which build cavities in boles, and red and Dou- glas squirrels, which build leaf nests in trees and underground nests in piles of conifer cone bracts (Finley 1969). All of these structures are important to martens for resting (Buskirk 1984; Spencer 1987; Wilbert 1992). Use of Nonforested Habitats Martens generally avoid habitats that lack over- head cover. These habitats include prairies, herba- ceous parklands or meadows, clearcuts, and tundra. In an evaluation of placement of bait stations to avoid nontarget effects, Robinson (1953) found that mar- tens avoided traveling >23 m from forest edges in Colorado. Fager (1991), Koehler and Hornocker (1977), Soutiere (1979), Simon (1980), and Spencer et al. (1983) have reported complete or partial avoid- ance of nonforested habitats. The size of openings that martens have been observed to cross have var- ied from 10 m (Spencer et al. 1983) to 40 m (Simon 1980) to 100 m (Koehler and Hornocker 1977). In most cases, these are the largest openings that the authors observed to be crossed during their respective stud- ies. Buskirk (1983) described a marten crossing a 300- m wide unforested river bar in winter during a home- range shift. Soutiere (1979) reported martens cross- ing clearcuts in winter and stopping to investigate woody debris protruding from the snow. Hargis and McCullough (1984) reported martens crossing mead- ows but not stopping to rest or forage. However, sum- mer use of nonforested habitats above treeline is com- mon in the montane part of the distribution. Streeter and Braun (1968) documented martens in talus fields 0.8-3.2 km from the nearest forest in Colorado, and Grinnell et al. (1937) reported similar use of talus fields in the Sierra Nevadas in summer. Also, mar- tens forage in some herbaceous and low-shrub meadow openings if suitable prey, especially Microtus, are available (Buskirk and Powell 1994; Martin 1994). The Refugium Concept For over 40 years, researchers have emphasized the importance of refugia to the conservation of Ameri- can martens. DeVos (1951) first pointed out that the difficult and inferential nature of population moni- toring for martens required landscape designs that assured population persistence. The refugium con- cept has been advocated often since then (Archibald and Jessup 1984; Strickland 1994; Thompson and Colgan 1987), and the broad outlines of such a con- servation design have been stated (Howe et al. 1991). Clearly, the refugium concept is a nonquantitative application to wildlife management of the principles embodied in source-sink theory (PuUiam 1988). How- ever, many specific features of refugium systems that would assure population persistence of martens have not been stated or involve untested assumptions (Buskirk, in press). These include habitat quality of refugia relative to areas where martens are trapped or timber is cut, and sizes of and permissible dis- tances separating refugia. To implement a system of refugia for conserving American martens, the param- eters of such a system must be derived and tested. Management Considerations 1 . Although American martens at times use other habitats, populations depend on {sensu Ruggiero et al. 1988) coniferous forests. Martens associate closely with mesic, late-successional coniferous forests but occur in other vegetation types. They use treeless areas less than predicted from their spatial availabil- ity, especially in winter. Clearcutting reduces mar- ten densities for several decades. In some areas, un- der conditions that are not well understood, martens may use regenerating clearcuts after a decade or two if sufficient structures useful to martens persist from 26 the clearcutting. The effect of other cutting regimes, including small patch cutting, seed tree cutting, or salvage harvest of dead or damaged timber have not been widely studied. 2. Coarse woody debris, especially in the form of large-diameter boles, is an important feature of mar- ten habitat. Logs are most useful to martens for gain- ing access to subnivean areas and for resting. Re- moval of coarse woody debris from forests or inter- fering with processes that make it available in suit- able sizes and stages of decay may reduce habitat quality for martens. Research Needs 1. To design conservation strategies at stand and landscape scales, we need better understanding of how martens use edges and small, nonforested open- ings. These features are too small to be studied by traditional research techniques. Examples of small nonforested openings include patch cuts, small her- baceous meadows, and breaks in the canopy caused by deaths of individual trees. Pursuing this goal will require gathering data that have measurement error that is small relative to the size of the feature that is being studied. 2. Determine habitat quality gradients affecting the density and fitness of marten populations. There is also a need to test the assumption that the habitats that have the highest marten densities confer the highest fitness on occupants. This information is important for understanding the differences between habitat occupancy and habitat quality. 3. Obtain better knowledge of how landscape at- tributes, including stand size, stand shape, area of stand interiors, amount of edge, stand insularity, cor- ridors, and connectivity affect marten populations. 4. To provide cost-effective means of assessing habitat quality for martens, perform a systematic evaluation of existing models of marten habitat qual- ity (e.g., Allen 1984), such as has been done for fish- ers (Thomasma et al. 1991). 5. In order to understand the meaning of past stud- ies that have examined habitat preferences, investigate how sex, age, and social rank affect habitat choices. 6. To place the habitat use of martens into the con- text of source-sink theory, determine how habitat quality gradients affect juvenile survival rates, dis- persal rates, directions, and distances. This has im- portant implications for understanding population insularity and metapopulation structure. HOME RANGE Variation in IHome Range Attributes Home ranges of American martens, usually in the sense used by Burt (1943), have been described for many study sites, and home range size has been re- ported in over 26 published accounts (Buskirk and McDonald 1989). Home range data usually consist of two-dimensional sizes, with additional informa- tion on shape, use intensity within the home range, and spatial relationships among home ranges. Buskirk and McDonald (1989) analyzed patterns of variation in home-range sizes from nine study sites and found that most variation was unexplained among-site variation. Male home ranges varied sig- nificantly among sites, but those of females did not. The largest home ranges, described by Mech and Rogers (1977) from Minnesota (male mean = 15.7 km^), were about 25 times the size of the smallest ones (male mean = 0.8 km^) reported by Burnett (1981) from Montana. Home range size was not correlated with latitude or with an index of seasonality. Male home range sizes were 1.9 times those of females, but no significant age variation was observed. Marten home ranges are large by mammalian stan- dards. Harestad and Bunnell (1979) and Lindstedt et al. (1986) developed allometric equations for home range size for mammalian carnivores and herbivores. Averaging all study site means reviewed by Buskirk and McDonald (1989), home ranges of American martens are 3-4 times larger than predicted for a 1- kg terrestrial carnivoran, and about 30 times that predicted for an herbivorous mammal of that size. In addition to sex and geographic area, home range size of martens has been shown to vary as a function of prey abundance (Thompson and Colgan 1987) and habitat type (Soutiere 1979; Thompson and Colgan 1987). Soutiere (1979) found home range sizes about 63% larger in clearcut forest than in selectively cut and uncut forest in Maine. Thompson and Colgan (1987) reported even more striking differences from Ontario, with home ranges in clearcut areas 1.5-3.1 times the size of those in uncut areas. Territoriality Intrasexual territory of most or all of the adult home range has been generally inferred, as it has for other Martes species (Powell 1994). This inference is based on the greater overlap of home ranges between 27 than within sexes (Baker 1992; Francis and Stephenson 1972; Hawley and Newby 1957; Simon 1980), on observations of intrasexual strife (Raine 1981; Strickland and Douglas 1987), and on the pat- tern exhibited by other solitary Mustelidae (Powell 1979). Juveniles and transients of both sexes appar- ently occupy neither territories nor true home ranges (Strickland and Douglas 1987). Spatial Relationships Among Cohorts Martens exhibit the pattern of spatial organization that is typical of solitary Carnivora: intrasexual ter- ritoriality among residents (Ewer 1973; Powell 1979). In addition, geographically and temporally variable numbers of transients, as well as predispersal young, occur in the home ranges of adults of both sexes. Because male home ranges are larger, they must be the space-limited cohort under conditions of equal sex ratio. Management Considerations 1 . Marten home ranges are very large, a correlate of low population densities. Martens must assemble home ranges from landscapes, rather than stands. Research Needs 1. We need better knowledge of the relationship between home range size and specific habitat at- tributes, such as forested area in specific successional or structural stages. To manage forested landscapes for martens, we need better knowledge of how home range size varies as a function of landscape attributes, such as those involving forest interior, edge, and stand connectivity. 2. To relate habitat quality to fitness, we need bet- ter knowledge of the amounts of particular habitat types, especially late-successional forest, that must be incorporated into a marten home range in order for a marten to survive and for a female to produce litters. 3. There is a need for more rigorous methods of inferring population density from home range data. We need to identify the assumptions underlying the conversion of home range size to population den- sity. We also need better understanding of the rela- tionship between habitat attributes and the degree to which habitat is saturated with home ranges. MOVEMENTS Movements of martens beyond home range boundaries, including dispersal and migration, have been studied little. This is a result of the technical difficulty and high cost of studying long-distance movements in small-bodied mammals. Reports of long-distance movements, likely representing dis- persal, are largely anecdotal. Archibald and Jessup (1984) reported two periods of dispersal, one from about mid-July to mid-September, and the other over winter. They inferred the onset of dispersal by the arrival of new nonresident animals, mostly juveniles, in their study area. However, the timing of dispersal has not been consistent among studies and ranges from early August to October (Slough 1989). Clark and Campbell (1976) reported a period of shifting during late winter and spring. For most of the year, marten populations may include some animals with- out true home ranges. Migration by martens, involving unidirectional movements by many animals, have been reported by trappers in Alaska (Buskirk 1983:44) and else- where but have not been documented in the scien- tific literature. Management Considerations 1 . The long dispersal distances of martens, to the extent that we understand them, in combination with the sensitivity of martens to overhead cover suggest that connectivity of habitat providing overhead cover is important to population dynamics and colonization. Research Needs 1 . Investigate the relationship between habitat and dispersal attributes if we are to understand natural colonization of habitats and metapopulation structure. COMMUNITY INTERACTIONS DeVos (1952) reported killing of martens by fish- ers, and Raine (1981) found marten remains in fisher scats but acknowledged that the remains could have represented scavenging. Various mammalian preda- tors (Jones and Raphael 1991, unpubl.; Nelson 1973) and raptors and owls (Clark et al. 1987) have been reported to kill martens. Because martens scavenge carcasses of animals killed by other predators (see General Foraging Ecology and Behavior section). 28 they may be considered to be commensal, at least at some times. Other important community interactions not involving predation include the use by martens of cavities built by birds for resting and denning, and of resting structures built by red and Douglas squir- rels (see Habitat Relationships section). Squirrel middens appear to represent an important habitat need in some areas (Buskirk 1984; Ruggiero, in re- view; Sherburne and Bissonette 1993), but this rela- tionship is poorly understood. The greater ability of martens than of fishers to travel across deep, soft snow (Raine 1981) may result in partitioning of habi- tats between martens and fishers along lines of snow attributes. American martens have been hypoth- esized to serve as important dispersal agents of the seeds of fleshy-fruited angiosperms (Willson 1992). This function is enhanced by the high frugivory (table 3) and wide-ranging behaviors of martens. Management Considerations 1 . The abundance of other mammalian predators may affect marten behaviors or populations. |) 2. The close association of martens and pine squir- rels (Tamiasciurus) in many areas suggests that man- agement actions that affect pine squirrel populations I will affect marten populations. Research! Needs 1. Investigate how habitat-generalist predators may affect survival of martens, especially in man- j aged forests. 2. Investigate the symbiotic relationship between martens and red and Douglas squirrels, including predator-prey relationships and use by martens of structures built or modified by squirrels. CONSERVATION STATUS 1. In the western conterminous United States, the marten has undergone major reductions in distribu- tion. These changes are poorly understood for some I areas because of fragmentary or unreliable data. The geographic range has apparently been fragmented, especially in the Pacific Northwest. The reduction and fragmentation of the geographic range of mar- tens has resulted primarily from the loss of habitat due to timber cutting. The only range expansions in the western United States are the result of transplants to islands in southeast Alaska. 2. In the Rocky Mountains and Sierra Nevadas, the marten has a geographic range apparently similar to that in presettlement historical times. Population lev- els are not known reliably enough to compare cur- rent population levels with those at any earlier time. 3. A named subspecies, Martes americana humboldtensis, may be threatened or endangered in northwestern California. The most likely cause of this hypothesized status is loss of habitat due to timber cutting. 4. Several marten populations are known or hy- pothesized to have been isolated by human-caused habitat change. The genetic and stochastic processes that predispose small populations to extinction likely are acting on these remnants. 5. The marten is predisposed by several attributes to impacts from human activities. These attributes include its habitat specialization for mesic, structur- ally complex forests; its low population densities; its low reproductive rate for a mammal of its size; and its vulnerability to trapping. Counteracting these fac- tors, the marten is small-bodied and has more favor- able life history traits, from a conservation stand- point, than some larger-bodied Carnivora. 6. The effects of trapping on marten populations over most of the western conterminous United States likely are local and transient. However, trapping may adversely affect some marten populations and may have contributed to or hastened local extinctions, especially where habitat quality was poor. Also, populations that are kept at artificially low levels by trapping should not be expected to respond to re- source limitations, such as limited prey, except un- der conditions of extreme resource scarcity. 7. Clearcutting, the most common timber harvest- ing practice in the northwestern United States in the last 20 years, is generally deleterious to marten popu- lations. Regenerating clearcuts have little or no value as marten habitat for several decades. 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Icpwell, Department of Zoology, College of Agriculture & Life Science, »^orth Carolina State University, Raleigh, North Caroline^ i William J.,Zielinski, USDA Forest Service, Pacific Southwest Research Station, Areata, California INTRODUCTION Natural History The fisher (Maries penmnti) is a medium-size mam- maUan carnivore and the largest member of the ge- nus Maries (Anderson 1970) of the family Mustelidae in the order Carnivora. The genus Maries includes five or six other extant species. The fisher has the general body build of a stocky weasel and is long, thin, and set low to the ground. A fisher's head is triangular with a pronounced muzzle, its ears are large but rounded, and its eyes face largely forward (Douglas and Strickland 1987). Adult male fishers generally weigh between 3.5 and 5.5 kg and are be- tween 90 and 120 cm long. Adult female fishers weigh between 2.0 and 2.5 kg and are between 75 and 95 cm long. The weights of adult females are more con- stant than those of adult males over the species' range (Powell 1993). From a distance fishers often look uniformly black but they are actually dark brown over much of their bodies. Guard hairs on a fisher's tail, rump, and legs are glossy black while those on the face, neck, and shoulders are brown with hoary gold or silver tips (Coulter 1966). The undersurface of a fisher is uni- formly brown, except for white or cream patches on the chest and around the genitals. These patches might be used to identify individuals (Frost and Krohn, unpubl. data; Powell, unpubl. data). The fur of fishers is very soft and glossy but varies among individuals, sexes, and seasons. Males have coarser coats than females. The single yearly molt may begin during late summer and is finished by No- vember or December (Coulter 1966; Grinnell et al. 1937; PoweU 1985, 1993). During September and October, the guard hairs are noticeably shorter than during the rest of the year, giving fishers a sleek appearance. Fishers have five toes on all four feet. Their claws are retractable but not sheathed. Fishers are planti- grade and their feet are large. There are pads on each toe and four central pads, one each behind digits 1, 2 and 3, 4, and 5, on each foot. From the central pads to the heels of the hindpaws, there are coarse hairs covering tough skin. The small, circular patches of coarse hair on the central pads of the hindpaws are associated with plantar glands and carry an odor distinctly different from other fisher odors (Buskirk at al. 1986; Powell 1977, 1981a, 1993). Because these patches enlarge on both males and females during the breeding season (Frost and Krohn, unpubl. data), as they do in American martens {Maries americana; Buskirk et al. 1986), they are probably involved in communication for reproduction. Fishers leave a characteristic mustelid track pat- tern: two footprints next to each other but slightly out of line. Deep, fluffy snow and thin crusts restrict fishers' movements (Grinnell et al. 1937; Heinemeyer 1993; Leonard 1980b, 1986; Powell 1977; Raine 1983) and, to avoid deep snow, fishers sometimes hunt in habitats in which they can travel most easily rather than in habitats that have most prey (Leonard 1980b; Raine 1983, 1987). Distribution of deep winter snow may limit fisher distribution (Aubry and Houston 1992; Krohn et al., in press) and may affect success of reintroductions (Heinemeyer 1993) and perhaps re- production (Krohn et al., in press). At the time of European settlement, fishers were found throughout the northern forests of North- America and south along the Appalachian and Pa- cific Coast mountains (Graham and Graham 1994). The northern limit to the range is approximately 60°N 38 latitude west of Hudson Bay and the latitude of the southern tip of James Bay to the east. Between 1800 and 1940, fisher populations declined or were extir- pated in most of the United States and in much of Canada due to overtrapping and habitat destruction by logging (Brander and Books 1973; Irvine et al. 1964; Powell 1993). Closed trapping seasons, habitat recovery programs, and reintroduction programs al- lowed fishers to return to some of their former range (Gibilisco 1994; Powell 1993). Populations have never returned to the Southern Appalachians, and popula- tions are extremely low in Oregon and Washington (the Pacific Northwest) and parts of the northern Rocky Mountains (Aubry and Houston 1992; Gibilisco 1994; Powell 1993). In eastern forests, fishers occur predominantly in dense lowland and spruce-fir habitats with high canopy closure (Arthur et al. 1989b; Kelly 1977; Powell, 1994b; Thomasma et al. 1991, 1994). Aside from avoiding areas with little cover (Powell 1993), fishers use most forest types within extensive north- ern-conifer forests (Buck et al. 1983; Coulter 1966; Hamilton and Cook 1955; Jones 1991 ; Raine 1983) and within mixed-conifer and northern-hardwood forests (Clem 1977; Coulter 1966; Johnson 1984; Kelly 1977; Powell, 1994b; Thomasma et al. 1991, 1994). These mustelids occur in extensive, mid-mature, second- growth forests in the Midwest and Northeast (Arthur et al. 1989b; Coulter 1966; Powell 1993) but have been considered obligate late-successional mammals in the Pacific Northwest (Allen 1983; Harris et al. 1982). Later authors (Ruggiero et al. 1991; Thomas et al. 1993) have categorized the species as "closely-asso- ciated" with late-successional forests. Buck et al. (1983), Seglund and Golightly (1994, unpubl.), and Jones (1991) considered riparian areas important for fishers in California and Idaho. Although Strickland et al. (1982) suggested that fishers could inhabit any forested area with a suitable prey base, the distribu- tion of fishers does not include the extensive south- ern forests of the eastern United States or the exten- sive conifer and mixed-conifer forests of the Rockies south of Wyoming (Powell 1993). Buskirk and Powell (1994) hypothesized that tree species composition is less important to fishers than aspects of forest struc- ture which affect prey abundance and vulnerability and provide denning and resting sites. Such forest structure can be characterized by a diversity of tree sizes and shapes; light gaps and associated under- story vegetation; snags; fallen trees and limbs; and limbs close to the ground. Because fishers are generalized predators, their major prey are small- to medium-sized mammals, birds, and carrion (reviewed by Powell 1993). Wher- ever abundant, snowshoe hares {Lepus americana) are common prey. Other common prey include squirrels {Sciurus sp., Tamiasciurus sp., Glaucomys sp.), mice {Clethrionomys gapperi, Microtus sp., Peromyscus sp.), and shrews {Blarina sp., Sorex sp.). The porcupine {Erethizon dorsatum) is the fisher's best known prey but does not occur in fishers' diets at some locations due to low population densities. Carrion is eaten readily and is mostly that of large mammals, such as deer (Odocoileus sp.) and moose {Alces alces). Seasonal changes in diet are minor and sexual differences have not been found (Clem 1977; Coulter 1966; Giuliano et al. 1989; Powell 1993). Newborn fishers weigh 40-50 g and are completely helpless; their eyes and ears are tightly closed (Coulter 1966; Hodgson 1937; LaBarge et al. 1990; Leonard 1986; Powell 1993). When 2 weeks old, kits are covered with light silver-gray hair and by age 3 weeks, kits are brown. By 3.5 weeks of age, white ventral patches may be visible. Their eyes open when 7-8 weeks old and teeth erupt through the gums at about the same age. Kits are completely dependent on milk until 8-10 weeks old. They cannot walk well until 8 weeks of age or older but by 10-12 weeks of age can run with the typical mustelid gait. From ages 10-12 weeks through 5-6 months, young fishers are the same general color as adults but are more uni- form in color. Sexual dimorphism in weight between males and females is first apparent around age 3 months and is pronounced by late autumn (Coulter 1966; Hodgson 1937; Powell 1993). Aggression between fisher kits begins at about 3 months of age (Coulter 1966; Powell 1993) but kits cannot kill prey until about 4 months of age. They do not require parental instruction to learn proper killing techniques (Kelly 1977; Powell 1977). Kits re- main within their mothers' territories into the win- ter (Powell, unpubl. data), but most juveniles have established their own home ranges by age 1 year (Arthur et al. 1993). Current Management Status Fisher populations are formally protected in four western and northwestern states in the United States: Oregon, Utah, Washington and Wyoming (table 1). California and Idaho have closed their trapping sea- sons; California has not had an open season since 39 Table 1 .—Current management status of fishers in thie western United States and Canada. 1 onnth of f jcK^rc 1 lOI 1^1 o Ii iricdi^tion n-1 s 1990 Rritich (^/^li iml^ii^ DIMIoll ^(wJIUI 1 IkjIvJ n-9n Mnnitohn 1972-73^ Nnrthwp^t Tprritnri^^ 1 N \y 1 1 1 1 VV 1 1 ^1 1 1 1 \y\ 19-21 Saskatchewan 17 Yukon 17 California 02 Idaho 02 1962-63 Montana 4-9 1959Hf)0, 1988-91 Oregon Protected i96r Washington Protected Wyoming Protected ' Reinfroducfion failed. 2 Fishers afforded protecfion fhrougli closed trapping season, but fishers are not afforded specific protected status. 1945. Montana has had an open trapping season since 1983-84 with a quota of 20 animals; all trapped fish- ers were to be reported and tagged (table 1). Con- cern has been expressed about the status of fisher populations in Washington, Oregon, and California (Central Sierra Audubon Society et al. 1990; Gibilisco 1994; USFWS 1991) and the fisher is a candidate for "threatened" status in Washington. The fisher is con- sidered a sensitive species by the Forest Service in all Regions where it occurs, with the exception of Region 6 (Appendix C, table 4b). All of the western provinces and territories of Canada have open fisher trapping seasons and Alberta and British Columbia require that all trapped fishers be reported and tagged (table 1). In Ontario, the ratio of the number of juvenile fishers harvested to the number of adult females harvested in a given year is used to project next year's relative popula- tion size and allowable harvest (Strickland 1994). This technique is empirical, however, and therefore may not be applicable to other fisher populations. Fisher populations are found in second-growth forests from northern Ontario and Minnesota east- ward. Available information from the West (Aubry and Houston 1992; Buck et. al 1994; Jones and Carton 1994), however, suggests that fishers are late-succes- sional associates in that region. This difference may reflect a response to forest structure rather than serai stage (Buskirk and Powell 1994; Powell 1993). Krohn et al. (in press) have argued, however, that the distri- bution of deep snow may be an overriding influence on habitat use, even in areas with adequate prey populations. Fishers in different regions may have different ecologies. Until the habitat relationships of fishers have been adequately studied in the West, we should be cautious about applying the results of stud- ies conducted in the East to the conservation of fish- ers in the West. DISTRIBUTION AND TAXONOMY Range Although the genus Martes is Holarctic in distri- bution, fishers are found only in North America. Their present range is reduced from their range be- fore European settlement of the continent (Gibilisco 1994; Graham and Graham 1994; Hagmeier 1956), but most of this reduction has occurred in the United States. During historical times the northern limit to the fisher's range has been approximately 60° N lati- tude in the west and somewhat south of the south- ern tip of James Bay in the east, following the 15.5° C isotherm. Once fishers ranged from what is now northern British Columbia into central California in the Pacific coastal mountains and south into Idaho, Montana and probably Wyoming in the Rocky Mountains. In the western mountains of the United States fishers have been reported in the following ecoprovinces (see Appendix A and B): Georgia-Puget Basin, Thompson-Okanogan Highlands, Columbia Plateau, Shining Mountains, Northern Rocky Moun- tain Forest, Snake River Basins, Pacific Northwest Coast and Mountains, Northern California Coast Ranges, and Sierra Nevada. Within this range fish- ers have occurred most commonly in northwestern California (the Northern California Coast Ranges Ecoprovince), the southern Sierra Nevada Ecoprovince, and in northern Idaho and northwest- ern Montana (the Shining Mountains and Northern Rocky Mountain Forest Ecoprovinces) (Appendix B). In what is now the central United States, fishers may have ranged as far south as southern Illinois I (Gibilisco 1994; Graham and Graham 1990, 1994; i Hagmeier 1956). And in the eastern part of the conti- nent, fishers ranged as far south as what is now North Carolina and Tennessee in the Appalachian Moun- j tains (Gibilisco 1994; Graham and Graham 1994; Hagmeier 1956). Fisher remains from southern Illi- nois to Alabama are probably artifacts created by the trading and travel patterns of American Indians (Barkalow 1961; Graham and Graham 1990). 40 Historical Changes in Populations and Distribution During the last part of the 19th century and the early part of this century fisher populations declined strikingly Fishers were extirpated over much of their former range in the United States and in much of eastern Canada (Bensen 1959; Brander and Books 1973; Coulter 1966; deVos 1951, 1952; Dodds and Martell 1971; Dodge 1977; Hall 1942; Ingram 1973; Rand 1944; Schorger 1942; Weckwerth and Wright 1968). Human activities, especially trapping and logging, con- tributed substantially to these declines. Both are capable of reducing fisher populations today and information available about the past decline is inconclusive as to whether one cause was more important than the other. In addition, trapping and logging are not independent because logging increases access to forests by trappers. Fishers are known by trappers to be easy to trap (Young 1975) and prices paid for fisher pelts, espe- cially the silky, glossy pelts of females, have always been high. Before the 1920's, there were no trapping regulations for fishers and high fur prices provided trappers with strong incentive to trap fishers (Balser 1960; Brander and Books 1973; Hamilton and Cook 1955; Irvine et al. 1964; Petersen et al. 1977). Prices have never been stable, however, and have not been the same throughout the United States and Canada. Peak prices were paid for fisher pelts in 1920 and in the 1970's and 1980's; lowest prices were paid in the 1950's and 1960's (Douglas and Strickland 1987; Obbard 1987). The decrease in fisher populations began first in the East, undoubtedly because of the longer history of European settlement. New York fisher populations had already begun to decrease by 1850 (Hamilton and Cook 1955), but the decrease in Wisconsin was not great before the first part of this century (Schorger 1942; Scott 1939). Wisconsin closed its fisher trapping season in 1921 but by 1932 the fisher was believed extinct in Wisconsin (Hine 1975). Fisher populations persisted in California, Oregon, and Washington (Aubry and Houston 1992; Schempf and White 1977; Yocum and McCollum 1973) but the last reliable re- ports of native fishers in Montana and Idaho came during the 1920's (Dodge 1977; Weckwerth and Wright 1968). Because of warnings from biologists, other states followed the example set by Wisconsin and closed their fisher-trapping seasons. Fisher populations in Canada also showed signifi- cant declines but the declines were somewhat ob- scured by pronounced 10-year population cycles in response to cycles in snowshoe hare populations. The numbers of fishers trapped throughout the country declined by approximately 40% between 1920 and 1940 (deVos 1952; Rand 1944). Between 1920 and 1950 the number of fishers trapped in Ontario declined by 75%, adjusted to the phases of the 10-year popu- lation cycle (deVos 1952; Rand 1944). Fishers were com- pletely exterminated from Nova Scotia before 1922 (Bensen 1959; Dodds and Martell 1971; Rand 1944). At the same time that fishers were heavily trapped, their habitat was being destroyed. By the mid-1 9th century, clearing of forests by loggers and farmers and by frequent forest fires reduced the forested area of much of the northeastern United States to approxi- mately 50%, from 95% 200 years earlier (Brander and Books 1973; Hamilton and Cook 1955; Silver 1957; Wood 1977). Land clearing in the Upper Midwest occurred during the early 20th century (Brander and Books 1973; Irvine et al. 1962, 1964). Either trapping or habitat destruction by itself could have dramati- cally reduced fisher populations; together, their ef- fect was extreme. During the 1930's, remnant fisher populations in the United States could be found only on the Moosehead Plateau of Maine, in the White Mountains in New Hampshire, in the Adirondack Mountains in New York, in the "Big Bog" area of Minnesota, and in the Pacific States (Brander and Books 1973; Coulter 1966; Ingram 1973; Schorger 1942). In eastern Canada, the only remnant popular tion was on the Cumberland Plateau in New Brunswick (Coulter 1966). Concurrent with the closure of trapping seasons during the 1930's, the logging boom came to an end in eastern North America and abandoned farmland began to return to forest. The few remnant fisher populations in these areas recovered (Balser and Longley 1966; Brander and Books 1973). By 1949, wildlife managers in New York felt that the fisher population in that state had recovered sufficiently to reopen a trapping season. Over the following de- cades, trapping seasons were reinitiated in several states and provinces. Following the reduction in fisher populations, por- cupine populations climbed to extremely high den- sities in much of the forested lands in the United States (Cook and Hamilton 1957; Earle 1978). Porcu- pines were blamed for much timber damage (Cook and Hamilton 1957; Curtis 1944), though the dam- age was often exaggerated (Earle 1978). It is difficult to quantify the damage caused by porcupines be- 41 cause porcupines also beneficially prune trees (Curtis 1941). Nonetheless, damage did occur in areas with very high porcupine populations (Krefting et al. 1962). During the 1950's, interest in reestablishing fisher populations began to increase. Concurrent declines in the porcupine populations were noted in those areas of Minnesota, Maine, and New York where fisher populations were increasing (Balser 1960; Coulter 1966; Hamilton and Cook 1955). Cook and Hamilton (1957) suggested using fishers as a bio- logical control for extremely high porcupine popu- lations. Coulter (1966) warned, however, that there was no evidence that fishers could limit porcupine populations for long periods of time. Nonetheless, during the late 1950's and 1960's, many states and provinces reintroduced fishers (table 1, Powell 1993). The purpose of these reintroductions was twofold: to reestablish a native mammal and to reduce high porcupine population densities (Irvine et al. 1962, 1964). Some states or provinces moved fishers within their borders, others released fishers from other jurisdictions. Not all releases succeeded in reestablishing fisher populations, but many did. A few states, for example Vermont and Montana, aug- mented low fisher populations. Massachusetts and Connecticut have reestablished fisher populations largely through population expansion from other states. And fishers have occasionally been sighted in Wyoming, North Dakota, South Dakota, and Maryland. Thus, the range of the fisher in eastern North America has recovered much of the area lost during the first part of this century. The fisher is again liv- ing in areas from northern British Columbia to Idaho and Montana in the West, from northeastern Minne- sota to Upper Michigan and northern Wisconsin in the Midwest, and in the Appalachian Mountains of New York and throughout most of the forested re- gions of the Northeast (Balser 1960; Banci 1989; Berg 1982; Bradle 1957; Coulter 1966; Earle 1978; Gibilisco 1994; Heinemeyer 1993; Irvine et al. 1962, 1964; Kebbe 1961; Kelly 1977; Kelsey 1977; Morse 1961; Penrod 1976; Petersen et al. 1977; Powell 1976, 1977a; Roy 1991; Weckwerth and Wright 1968; Williams 1962; Wood 1977). Many states and provinces have trap- ping seasons for fishers and regulations are adjusted in an attempt to maintain fisher populations at cur- rent levels. In the 1980's and early 1990's, trapping mortality in southcentral Maine exceeded reproduction (Arthur et al. 1989a; Paragi 1990). Fishers have not returned to the southern Appalachians. Illinois, Indiana, and Ohio may never again have forested areas extensive enough to support fisher populations. And in areas where there has been extensive, recent logging that fragments forests extensively, fisher populations have not recovered, perhaps because fishers appear sen- sitive to forest fragmentation (Rosenberg and Raphael 1986). There were only 89 potential sightings of fishers in Washington between 1955 and 1993 and only 3 were supported with solid evidence, such as photographs or carcasses. Fishers may be on the verge of extinction in Washington ( Aubry and Hous- ton 1992; Aubry, unpubl. records). Although no evaluation of their status and distribution in Oregon has been conducted, sightings are extremely rare (Appendix B; Aubry, unpubl. data). Recent work with remote cameras, hov/ever, has detected the presence of fishers just west of the Cascade Crest in southern Oregon (S. Armentrout, pers. comm.). Finally, the fisher population in the southern Sierra Nevada Moun- tains in California (Appendix B) may be doing well, but it appears to be isolated from the population in northwestern California (W. Zielinski, pers. obs.). The latter population has remained stable since the early part of this century (Grinnell et al. 1937; Schempf and White 1977) and may have the highest abundance of all populations in the western United States. It is sometimes necessary to augment isolated fisher populations with fishers captured elsewhere. Fish- ers have been released in eastern North America to reestablish populations where fishers had gone ex- tinct. Releases have generally been unsuccessful in western North America. Roy's (1991) results indicate that many fishers from eastern North America may lack behaviors, and perhaps genetic background, to survive in western ecological settings. If fishers are moved from one population to another, inappropriate genetic background or ecotypic adaptations could have adverse effects on resident populations. Irvine et al. (1962, 1964) recommended winter re- introductions. It has been believed, incorrectly, that females would not travel far as parturition approached (Roy 1991). Fishers reintroduced during winter travel long distances (Proulx et al. 1994; Roy 1991), however, and may be subject to greater risk of predation (Roy 1991) than they were in their capture sites. Only once have fishers not been released during winter. Proulx et al. (1994) released fishers in the parklands of Alberta during both late-winter and summer. Fishers released during winter travelled sig- nificantly longer distances and had significantly higher mortality than the fishers released during 42 summer. Most fishers released in summer established home ranges close to their release sites, whereas this was not the case for the fishers released during win- ter. Proulx et al. recommended more experiments to find optimal release times; in the mean time, sum- mer should be tried when possible. Taxonomy Goldman (1935) recognized three subspecies of fishers: Martes pennanti pennanti, M. p. pacifica, and M. p. Columbiana. Recognition of subspecies, however, may not be valid. Goldman stated that the subspe- cies were difficult to distinguish, and Hagmeier (1959) concluded from an extensive study that rec- ognition of subspecies was not warranted because the subspecies were not separable on the basis of pelage or skull characteristics. The continuous range of fishers across North America, allowing free inter- change of genes, is consistent with a lack of valid subspecies. Anderson (1994) and Hall (1981) retained all three subspecies but failed to address Hagmeier's conclusion. On the basis of Whitaker's (1970) evalu- ation of the subspecies concept, Hagmeier was prob- ably correct, but genetic analyses will be required to resolve this question. Management Considerations 1 . Isolated populations are of special concern and must be monitored. 2. Forest fragmentation may result in the isolation of populations. 3. Reintroductions would be most likely to succeed if translocated animals are from similar habitats in the same ecoprovince (Appendix A). Research Needs 1 . Develop, refine, and standardize survey meth- ods to document the distribution of fishers in west- ern North America. 2. Investigate the dispersal capabilities of fishers and characterize habitats and geographic features that facilitate or inhibit their movements, i.e., corri- dors and barriers. 3. Document genetic diversity within and among fisher populations to reevaluate named subspecies of fisher, to identify isolated populations that may require special management, and to identify similar genetic stocks for reintroduction. 4. Investigate factors that contribute to successful reintroductions and augmentations. POPULATION ECOLOGY Population Densities and Growth Fisher population densities vary with habitat and prey, and density estimates in the northeastern United States have ranged from 1 fisher per 2.6 km^ to 1 fisher per 20.0 km^ (Arthur et al. 1989a; Coulter 1966; Kelly 1977). Coulter (1966) and Kelly (1977) did not believe that fishers could sustain densities of 1 fisher per 2-1 / l-A km^ and Kelly reported a decrease in the number of fishers in New Hampshire and Maine following a period with such densities. Arthur et al. (1989a) calculated a summer density of 1 fisher per 2.8 to 10.5 km^ in Maine and a winter density of 1 fisher per 8.3 to 20.0 km^. The densities reported by Arthur et al. are the best available from the North- east; they include seasonal changes in density caused by the spring birth pulse and they give the ranges of densities possible, showing the uncertainty of their estimates. Information on fisher densities outside the North- east is limited. Buck et al. (1983) estimated a density of 1 fisher per 3.2 per km^ for their northern Califor- nia study area. Fisher population densities in north- ern Wisconsin and Upper Peninsula Michigan have been estimated at 1 fisher per 12-19 km^. (Earle 1978; Johnson 1984; Petersen et al. 1977; Powell 1977). The density estimates for fisher populations vary for many reasons. Fisher populations fluctuate with populations of prey and in some places exhibit 10- year cycles in densities (Bulmer 1974, 1975; deVos 1952; Rand 1944) in response to 10-year cycles in snowshoe hare population densities (Bulmer 1974, 1975). Where fishers were reintroduced (e.g., Michi- gan, Wisconsin, Idaho, Montana), population densi- ties may be low because of insufficient time for popu- lations to build. Trapping in New England has at times been intense, even recently (Krohn et al. 1994; Wood 1977; Young 1975), and overtrapping can re- duce populations in local areas (Kelly 1977; Krohn and Elowe 1993). Finally, it is difficult to estimate fisher population sizes because fishers do not behave according to the assumptions necessary to use most methods of estimating populations (e.g., equal trapability, no learned trap response, sufficient trapability to give adequate sample sizes). Therefore all estimates incorporate considerable sampling error. 43 W, Krohn (pers. comm.) suspects that as fishers colonize new, suitable habitat in Maine their density is initially very low, then rises to levels that probably cannot be maintained, and finally falls to intermedi- ate levels. This pattern is consistent with informa- tion available from Wisconsin as well (C. Pils, pers. comm.). It is the pattern of population growth ex- pected for animals whose density-dependent feed- back comes through changes in adult and juvenile mortality rather than through changes in reproduc- tion. Such a pattern is consistent with changes in fisher population density that track cycles in snow- shoe hare numbers (Bulmer 1974). This pattern of rapid population increase has not been observed in western populations, many of which have failed to recover despite decades of pro- tection from trapping (e.g., northern Sierra Nevada, Olympic Peninsula), reintroductions (e.g., Oregon), or both. Therefore, one or more major life requisites must be missing. Suitable habitat may be limited, colonization of suitable habitat may be limited due to habitat fragmentation, or some other factor or com- bination of factors may be involved. Other popula- tions, most notably the one in northwestern Califor- nia (R. Golightly, pers. comm.; W. Zielinski, pers. obs.), have sustained themselves while nearby popula- tions have apparently declined and failed to recover. York and Fuller (in press) summarized the life his- tory information available for wild and captive fish- ers (all of which came from eastern populations). Using a simple accounting model, they estimated the exponential rates of increase for a number of hypo- thetical populations. Initial values for survival and reproductive parameters were set at the lowest, weighted mean, unweighted mean, and highest val- ues for each of four runs. Only the model run that incorporated the highest values of survival and re- production resulted in lambda values that exceeded 1.0. The authors interpreted this to mean that most fisher populations require immigrants to increase and that only those with high reproductive and survival rates are self-sustaining. Survivorship and Mortality Fishers have lived past ten years of age (Arthur et al. 1992), which may be near the upper limit of life expectancy (Powell 1993). They exhibit low incidence of diseases and parasites (Powell 1993). Few natural causes of fisher mortality are known. Fishers have choked on food (Krohn et al. 1994) and have been debilitated by porcupine quills (Coulter 1966; deVos 1952; Hamilton and Cook 1955). Healthy adult fish- ers appear not to be subject to predation, except fish- ers that have been translocated. A fisher in Maine was trapped on the ice and killed by coyotes (Canis latrans, Krohn et al. 1994) and a fisher was killed by a dog (Canis familiaris) in Ontario (Douglas and Strickland 1987). An adult female fisher in northern California was killed by a large raptor, probably a golden eagle {Aquila chrysaetos) or great horned owl {Bubo virginianus, Buck et al. 1983). Reintroduction of fishers to the Cabinet Mountains of Montana was hindered by predation; of 32 fishers from Wisconsin released in the Cabinet Mountains, at least 9 were killed by other predators (Roy 1991). All appeared to have been in good health. It is possible that the dif- ferences between Wisconsin and Montana in habi- tat, topography, prey, and predators somehow made these fishers vulnerable to predation. Trapping has been one of the two most important factors influencing fisher populations. Management of fisher populations, either to stabilize populations and harvests (Strickland 1994) or to provide recre- ational harvests, replaces natural population fluctua- tions with fluctuations caused by periods of overtrapping followed by recovery when trapping pressure decreases (Berg and Kuehn 1994; Douglas and Strickland 1987; Kelly 1977; Krohn et al. 1994; Parson 1980; Wood 1977; Young 1975; reviewed by Powell 1993). This occurs despite adjustments in trap- ping regulations. Fishers are also easily trapped in sets for other furbearers (Coulter 1966; Douglas and Strickland 1987; Young 1975). Where fishers are scarce, the populations can be seriously affected by fox {Vulpes vulpes, Urocyon cinereoargenteus) and bob- cat (Lynx rufus) trapping (Coulter 1966; Douglas and Strickland 1987). Whether population fluctuations caused by trapping affect social structure of fisher populations in the same manner as natural popula- tion cycles is not known. Mathematical models for the fisher community in Michigan (Powell 1979b) indicated that small in- creases in mortality due to trapping could lead to population extinction. Depending on the model, the increase in mortality needed to lead to extinction was as low as 3% or as high as 98%. This is equivalent to an increase in mortality of 1^ fishers /km^ above natu- ral mortality levels. These models did not incorporate sex or age structure in the model fisher populations. Based on data from radio-collared fishers, Krohn et al. (1994) estimated mean annual mortality rates 44 over a five-year period from a population in Maine where 94% of all mortality was from commercial trap- ping. The sexes did not show significant differences in survivorship for either adults or juveniles outside the trapping season, but adult females had signifi- cantly higher survivorship than adult males during the trapping season. It is not known whether the sexes have similar survivorships in populations that are not harvested. Survivorship during the trapping season for adult females, adult males, juvenile fe- males, and juvenile males was 0.79, 0.57, 0.34, and 0.39, respectively. During the non-trapping season, survivorship rates were 0.87, 0.89, 0.75, and 0.71. Using a model that incorporated differential suscep- tibility to trapping for fishers of different ages and sex, Paragi (1990) found that annual fall recruitment needed to maintain a stable population was approxi- mately 1.5 offspring per adult female (>2 years old). Actual recruitment was 1.3 offspring per adult fe- male, indicating a 2% per year population decline. Age Structure and Sex Ratio Age-specific survivorships for fisher populations appear to fluctuate with prey populations. During periods of high prey availability, juvenile fishers com- prise a higher-than-average proportion of a trapped population; when prey populations are low and fisher populations decline, cohorts of old fishers com- prise higher-than-average proportions of the popu- lation (Douglas and Strickland 1987; Powell 1994a). Harvested populations of Martes species tend to be biased more toward young animals, on the average, compared to unharvested populations (Powell 1994a). Average age structure for the heavily trapped fisher population in Ontario is highly skewed toward young animals (Douglas and Strickland 1987). Our understanding of age structure in fishers and other animals is hampered by biases in population biology and demography research, which have his- torically been oriented to understand population sta- bility (e.g., Lomnicki 1978, 1988; May 1973). Unstable age structure leads to variations in population re- sponses to changes in prey populations. Because fish- ers do not reproduce until age two, populations bi- ased toward young animals may not be able to re- spond to increases in prey populations as rapidly as populations biased toward old individuals. Thus, trapping may affect the abilities of fisher populations to respond to increasing prey populations (Powell 1994a). Natural fisher populations may be character- ized by episodes of local extinction and recolon- ization (Powell 1993), which we have hypothesized to be the norm for weasel populations (Mustela fren- ata, M. erminea, M. nivalis [= rixosa]; Powell and Zielinski 1983). If remnant populations in the Pacific Northwest and Rocky Mountains are reduced in number and sufficiently separated they may not be capable of recolonizing depopulated areas. Sex ratios of unharvested fisher populations are poorly known and true sex ratios (primary, second- ary, or tertiary) are difficult to determine. Live-trap- ping and kill-trapping results for all mustelines ex- hibit a significant bias toward males (Buskirk and Lindstedt 1989; King 1975). Sex ratios for natural fisher populations should be close to 50:50 (Powell 1993, 1994b). This trapping bias toward males might skew harvested populations toward females (Krohn et al. 1994; Powell 1994b). This will not, however, nec- essarily increase reproductive output of the popula- tion. The density of adult males must be sufficient for maximal reproduction and recruitment must ex- ceed mortality Management Considerations 1 . The reproductive rates of fishers are low, rela- tive to other mammals, and low density fisher popu- lations will recover slowly. 2. Population densities of fishers are low, relative to other mammals, and can undergo fluctuations that are related to their prey. These fluctuations make small or isolated populations particularly prone to extirpation. 3. Fishers are easily trapped and can frequently be caught in sets for bobcats, foxes, coyotes, and other furbearers. To protect fisher populations, trapping using land sets may need to be prohibited. Inciden- tal trapping of fishers in sets for other predators may slow or negate population responses to habitat improvement. Research Needs 1 . Obtain demographic data (age structure, sex ra- tio, vital rates) for representative, untrapped popu- lations in ecoprovinces in the West. 2. Develop methods of estimating fisher densities. 3. Use demographic data and density estimates to develop models to estimate viable population sizes. 45 REPRODUCTIVE BIOLOGY Reproductive rates The reproductive biology of female fishers is simi- lar to that of other members of the Mustelinae (wea- sels, martens, and sables) (Mead 1994). Female fish- ers are sexually mature and breed for the first time at 1 year of age (Douglas and Strickland 1987; Eadie and Hamilton 1958; Hall 1942; Wright and Coulter 1967). Ovulation is presumed to be induced by copu- lation and the corpora lutea of actively pregnant fe- male fishers can be readily identified (Douglas and Strickland 1987; Eadie and Hamilton 1958; Wright and Coulter 1967). Implantation is delayed approxi- mately ten months, and, therefore, female fishers can produce their first litters at age two. Females breed again approximately a week following parturition. Pregnancy rates for fishers are generally calculated as the proportion of adult females (>2 yr) harvested whose ovaries contain corpora lutea (Crowley et al. 1990; Douglas and Strickland 1987; Shea et al. 1985). Corpora lutea generally indicate ovulation rates of >95% (Douglas and Strickland 1987; Shea et al. 1985), while placental scars indicate much lower birth rates. Far fewer than 95% of female fishers >2 years old den and produce kits each spring. From 1984 to 1989, 12 radio-collared female fishers in Maine had a den- ning rate of only 63% (Arthur and Krohn 1991; Paragi 1990). Fifty percent (3 of 6) of the adult females in Massachusetts produced litters (York and Fuller, in press). Although an average of 97% of the female fish- ers from Maine, New Hampshire, Ontario and Ver- mont had corpora lutea (range 92 to 100), only 58% had placental scars (range 22-88; Crowley et al. 1990). This indicates that placental scars document birth of kits better than do corpora lutea (Crowley et al. 1990). A controlled study in Maine, however, is currently investigating the retention of placental scars in cap- tive female fishers known to have produced litters (Frost and W. Krohn, pers. comm.). Why some females that have bred fail to produce litters is unknown, but nutritional deficiency related to stressful snow con- ditions is suspected because reproductive indices are higher in areas of low snowfall (Krohn et al., in press). Estimates of average numbers of corpora lutea, unimplanted blastocysts, implanted embryos, pla- cental scars, and kits in a litter range from 2.7 to 3.9 (reviewed by Powell 1993). York and Fuller (in press) summarized the mean litter sizes for fishers from seven studies and discovered that they ranged from 2.00 to 2.90. Paragi (1990) estimated survival rates from six weeks until late October for kits in Maine to be > 0.6 and estimated fall recruitment at 0.7-1 .3 kits/ adult female. Although it is usually assumed that sufficient num- bers of males exist to breed with receptive females, this may not always be the case. Strickland and Dou- glas (1978; Douglas and Strickland 1987) found that trapping during January and February causes dis- proportionately high mortality of adult males, may decrease their numbers below that necessary to in- seminate all females, and may even lead to popula- tion decline. In 1975 the fisher trapping season in the Algonquin region of Ontario was restricted to end on 31 December, reducing the trapping pressure on adult males. Thereafter, both the breeding rate of fe- males and the population increased. Breeding Season and Parturition From mid-March through April, all adult males appear fully sexually active. Testes of fishers have been found with sperm as late as May (M. D. Carlos, Minn. Zool. Soc, unpubl. records; Wright and Coulter 1967). Despite having sperm, 1 -year-old male fish- ers appear not to be effective breeders, probably be- cause baculum development is incomplete. Begin- ning in March, adult male fishers, but not necessar- ily adult females, increase their movement rates and distances traveled (Arthur et al. 1989a; Coulter 1966; Kelly 1977; Leonard 1980b, 1986; Roy 1991). Estab- lished spacing patterns of adult males break down, they trespass onto the territories of other males, and they may fight (Arthur et al. 1989a; Leonard 1986). The first visible sign of estrus in female fishers is the enlargement of the vulva (Laberee 1941; Mead 1994) and females are in estrus for about 6-8 days (Laberee claimed only two days), beginning 3-9 days follow- ing parturition for adult females (Hall 1942; Hodgson 1937; Laberee 1941). Douglas and Strickland (1987) summarized the breeding season for fishers to be from 27 February to 15 April, based on known birth dates of captive litters, but this ignored the 3-9 day delay between parturition and breeding. Implanta- tion can occur as early as January and as late as early April (Coulter 1966; Hall 1942; Hodgson 1937; Laberee 1941; Leonard 1980b, 1986; Paragi 1990; Powell 1977; Wright and Coulter 1967). Parturition dates as early as February and as late as May have been recorded (Coulter 1966; Douglas 1943; Hall 1942; Hamilton and Cook 1955; Hodgson 46 1937; Kline and D. Carlos, Minn. Zool. Soc, unpubl. records; Laberee 1941; Leonard 1980b; Paragi 1990; Powell 1977; Wright and Coulter 1967). The only data from western North America are from fur farms in British Columbia, where parturition occurred dur- ing late March and early April (Hall 1942). Females probably breed within 10 days after giving birth. Thus, an adult female fisher is pregnant almost all the time, except for a brief period following parturi- tion. Healthy females breed for the first time when they are 1 year old, produce their first litters when they are 2 years old, and probably breed every year thereafter as long as they are healthy. Den Sites Female fishers raise their young in protected den sites with no help from males. Almost all known na- tal dens (where parturition occurs) and maternal dens (other dens where kits are raised) have been discov- ered in eastern North America (Arthur 1987; Paragi 1990). Of these, the vast majority were located high in cavities in living or dead trees. This strongly sug- gests that female fishers are highly selective of habi- tat for natal and maternal den sites. Information is available for only two natal dens (California, Buck et al. 1983; Montana, Roy 1991) and one maternal den (California, Schmidt et al. 1993, unpubl.) in the west- ern United States. The den found in Montana was in a hollow log 11m long with a convoluted cavity av- eraging 30 cm in diameter. A natal den in California was in a 89 cm dbh ponderosa pine {Pinus ponderosa) snag. The maternal den was located in a hollow white fir (Abies concolor) log that was 1.5 m in diameter at the den site (Schmidt et al. 1993, unpubl.). Of the 32 natal dens found by Arthur (1987) and Paragi (1990) in Maine, over 90% were in hardwoods and over half were in aspens (Populus spp.). The den site Leonard (1980a, 1986) studied in Manitoba was also in an as- pen. Because female fishers in eastern North America and in the Rocky Mountains are highly selective of habitat for resting sites (Arthur et al. 1989b; Jones and Carton 1994; Kelly 1977; Powell 1994b), they are prob- ably highly selective of habitat for natal and mater- nal den sites as well. Female fishers will use 1-3 dens per litter and are more likely to move litters if disturbed (Paragi 1990). The natal den found by Leonard (1980a, 1986) had no nesting material and was extremely neat after the kits left: no excrement, no regurgitated food, and no food remains. Natal nests of captive fishers are simi- larly spartan (Hodgson 1937; Powell, unpubl. data). A natal den found by Roy (1991), however, contained a dense mat of dried pine needles and moss. Roy also found a pile of 40-50 scats separated from the nest by 20 cm and behind a block in the cavity in the den log. Except during mating, female fishers raised on fur farms spend little time outside natal nest boxes after parturition (Hodgson 1937; Laberee 1941). Although mating may keep a female away from her young for several hours when the young are only a few days old, she returns quickly to her young when she has finished mating. Wild female fishers exhibit indi- vidual variation in activity patterns both before and after weaning their kits. A female followed by Leonard (1980a, 1986) spent very little time away from her kits at first but spent increasingly more time away as they grew. Females followed by Paragi (1990) exhibited no discernable pattern. Kits are often moved from natal to maternal dens at 8 to 10 weeks of age (Leonard 1980b; Paragi 1990). Scent Marking During March fishers scent mark with urine, fe- ces, musk, and black, tar-like marks on elevated ob- jects such as stumps, logs and rocks (Leonard 1980b, 1986; Powell 1977). This March surge in scent mark- ing coincides with the beginning of the breeding sea- son as does the elaboration of plantar glands on the feet (Buskirk et al. 1986; W. Krohn, pers. obs.; Powell 1977, 1981a, 1993). Fishers possess anal glands, or sacs, containing substances that have neither the strong nor offensive odor of weasels and skunks. The precise function of anal gland secretions is unknown. An odor and prob- ably some secretion is discharged when wild fishers are frightened, such as when they are handled by humans (Powell 1993). In other mustelines, the anal gland secretions differ between males and females and change seasonally (Crump 1980a, 1980b). It is presumed that the anal gland secretions of fishers provide infor- mation to other fishers regarding sex, sexual activity, and perhaps maturity and territorial behavior. Fishers lack abdominal glands (Hall 1926; Pitta way 1984), which are found in some but not all other Martes (de Monte and Roeder 1990; Rozhnov 1991). Other Martes have many glands on their cheeks, necks, and flanks (de Monte and Roeder 1990; Petskoi and Kolpovskii 1970). Fishers rub these areas, indi- cating that they may have glands there as well (R. Powell, pers. obs.). 47 Management Considerations 1 . The recovery of fisher populations will be slow because fishers have small litters and do not produce their first litters until two year of age. Reproductive output of populations biased toward young fishers is limited by the inability of yearling males to breed effectively. Over-trapping may also bias the popula- tion toward young animals, further delaying recovery. 2. All natal and maternal dens in the West were found in large diameter logs or snags. These habitat elements may be reduced in stands that have been intensively managed for timber. Research! Needs 1 . Determine characteristics of structures used as natal or maternal dens. Investigate whether den choices vary with the age of the kits and what fac- tors influence a female's choice to change den sites over time. 2. Investigate the reproductive rates of fishers in free-living, non-trapped populations. In addition, study the reproductive rates of females in small populations because these may have suffered loss of genetic variability. 3. Determine the fisher mating system and whether few dominant males do most of the breeding. Deter- mine whether the number of males, and sex ratio, affect the proportion of breeding females. 4. Test the hypotheses that successful hunting dur- ing winter leads to high implantation rates and that successful hunting during gestation leads to high em- bryo survival. FOOD HABITS AND PREDATOR-PREY RELATIONSHIPS Principal Prey Species and Diet Fishers are generalized predators. They eat any animal they can catch and overpower, generally small- to medium-size mammals and birds, and they readily eat carrion and fruits (table 2). The methods used to quantify the diets of carnivores are at best indices of foods eaten. Food items with relatively large proportions of undigestible parts are overrep- resented in gastrointestinal (GI) tracts and scats; therefore the remains of small mammals are over- represented compared to large food items (Floyd et al. 1978; Lockie 1959; Scott 1941; Zielinski 1986). A list of the foods identified from fecal remains or GI tract contents gives little information about where foods were obtained, when they were obtained, or how they were obtained. Almost all of the GI tracts collected for diet studies were obtained from trap- pers during legal trapping seasons and therefore only provide information on winter diets. Trap bait is com- monly found in GI tracts of trapped animals, mak- ing it difficult to distinguish between kills initiated by fishers and items obtained as carrion. Trap bait, however, is a legitimate component of fishers' diets during the trapping season because fishers readily eat carrion (Kelly 1977; Powell 1993). In the following discussion, we use the term "mice" to refer to all small cricetids, including microtines (voles and lemmings). All studies were predomi- nantly winter diets (table 2). It is unfortunate that the only study of the food habits of fishers from Pa- cific Coast states was limited to the analysis of seven GI tracts from California and appears to have been affected by considerable sampling error due to small sample size. Grenfell and Fasenfest (1979) found a high frequency of "plant" material, a large amount of which was mushroom (false truffles). Black-tailed deer (Odocoileus hemionus), cattle, and mice remains also occurred in this sample. The study of food habits of fishers in the Idaho Rocky Mountains (Jones 1991) has only slightly larger sample sizes: 7 GI tracts and 18 scats. Both GI tracts and scats had high frequencies of occurrence of mam- mal remains (58% and 68%) and low frequency of occurrence of bird remains (3%, 4%). Ungulate re- mains, consumed as carrion, were common in both samples (86%, 56%). Remains of insects and other invertebrates were uncommon and vegetation was consumed commonly but probably incidentally to eating prey or in attempts to escape live traps. For fishers in the Cabinet Mountains of Montana, 50% of the prey remains found in 80 scats were from snowshoe hares (Roy 1991). Mice and other small rodents constituted the next most common prey. Por- cupines constituted 5-10% of the prey items eaten and deer carrion constituted less than 5%. Roy (1991) believed that the importance of carrion was under- estimated by his scat analyses because the fishers he studied used deer carcasses extensively on several occasions but no scats were collected in those areas. Snowshoe hares are the most common prey for fishers and have been reported as prey in virtually 48 Table 2. — Food habits of fishers in five geographic locations. When there are three or more sources of information for a geographic location the range of frequencies of occurrence are provided and when there are only two sources of information commas separate the actual frequencies. The types of samples used are listed under each location. Maine Manitoba New Hampshire Michigan ^ villi VI 1 IIVJ 1 Wl \\J l^tl? W f \J\ IV iviii II icroviu wlllUlll./ rOOU II61TI 01 VI 1 1 wi 1 N^l « owl wl " OV^VI OlwlllUV^II ~ dV^UI Medium-sized orev 0 29, 50 3-28 19-84 19 44 Porouninp 0 0, 6 0-26 0-20 20, 35 Small prey Mice and voles'^ 37 43,39 3-50 3-20 9, 16 01 lltyWo vji \Kji 1 1 ivji^o 19 n n 3-59 n-ft 7 ft 19 1-14 n A Birds 0 14, 17 6-30 0-8 11,23 blue & gray jays 0-7 0 0,2 lUMc?*^ yik-'Uoc? n-19 0-7 4 14 iTlloC oc uiiicj^rii. ri— 1 0 H-O 9 7 Carrion White-tailed/black-tailed deer + moos© + siK zo 00, 00 9-^n n-9fi u zo % 99 0, zz PrA%/ in<^li iHinn tr/^n hnif 1 VIUoKI \Jk 1 n \j 0 0 0-9 0-1 0 1 5 n n u 0 n u Beaver^^ 0 29,6 1-17 0 0,2 Misc. & unident. Mammals^' 100 14, 24 0-30 9-14 2,45 Vertebrates^^ 88 0,6 0-4 3-35 12, 13 Artl-iropods 37 0,22 0-5 0-2 3,21 Plant materia|22 100 39, 21 3-37 6-13 18, 61 Sources 1 2 3,4,5.67.8,9 10,11,12 13,14 ' Grenfell and Fasenfest 1979. 'Jones 1991. ' Coulter 1966. ^ Arthur etal. 1989a. 5 Stevens 1968. " Kelly 1977. ^ Guiliano et al. 1989. ^ Hamilton and Cook 1 955. ^ Brown and Will 1979. '°Ralne 1987. " Powell 1977. '^Kuehn 1989. De Vos 1952. Clem 1977. Clettirlonomys, MIcrotus, Mus, Napeozapus, Peromyscus, Relthrodontomys, Synaptomys, Zapus. Blarina, Scalopus, Sorex. Glaucomys, Sciurus, Tamiasclurus. Includes bait. " Miscellaneous mammals (often bait): moles, cottontail rabbit, mink, red fox, American marten, weasels, otter caribou, fishier, skunk, beaver muskrat, woodchuck, domestic mammals, unidentified. '° Miscellaneous birds: red-breasted nuthatch, thrushes, owls, black-capped chickadee, downy woodpecker, yellow-shafted flicker, sparrows, dark-eyed junco, red-winged blackbird, starling, crow, ducks, grouse eggs, domestic chicken, unidentified. ^' Miscellaneous vertebrates: snakes, toads, fish, unidentified. ^ Plant material: apples, winterberrles, mountain ash berries, blackberries, raspberries, strawberries, cherries, beechnuts, acorns, swamp holly berries, miscellaneous needles and leaves, mosses, club mosses, ferns, unidentified. 49 all diet studies (table 2). The species range of the snowshoe hare is coincident with almost the entire fisher species range and, therefore, snowshoe hares are expected to occur frequently in the diets of fish- ers. The occurrence of snowshoe hare remains in fisher scats ranges from 7% to 84% (table 2), though the California study (Grenfell and Fasenfest 1979) and a study in progress in Connecticut (Rego, pers. comm.) did not discover hare in the diet. Surprisingly, raccoon (Procyon lotor) are common prey in Connecticut. Fisher populations across Canada cycle in density approxi- mately 3 years behind the hare cycle (Bulmer 1974, 1975) and as the snowshoe hare population declines, snow- shoe hares decrease in fishers' diets (Kuehn 1989). Understanding the habitat relationships of fisher prey is an important element of understanding fisher ecology Fishers often hunt in those habitats used by hares (Arthur et al. 1989b; Clem 1977; Coulter 1966; Kelly 1977; Powell 1977, 1978; Powell and Brander 1977) and may direct their travel toward those habi- tats (Coulter 1966; Kelly 1977; Powell 1977). Hares use a variety of habitat types (Keith and Windberg 1978) , but areas with sparse cover appear to be poor hare habitat (Keith 1966). Hares tend to concentrate in conifer and dense lowland vegetation during the winter and to avoid open hardwood forests (Litvaitis et al. 1985). On the Olympic Peninsula of Washing- ton hares appear common in both early and late suc- cessional Douglas-fir forests stands, but not mid-suc- cessional stands (Powell 1991, unpubl.). The fisher-porcupine predator-prey relationship has been the subject of considerable study The im- portance of porcupines as prey for fishers is reflected in the evolution of the unique hunting and killing behaviors used by fishers to prey on porcupines. Their low build, relatively large body, great agility, and arboreal adaptations make them uniquely adapted for killing porcupines. As a result of these adaptations, fishers have a prey item for which they have little competition. The importance of this should not be underemphasized, even though fishers are found in areas with no porcupines. Porcupines are important prey for fishers in many places and the frequency of porcupines in diet samples can reach 35% (table 2). Porcupines, how- ever, are seldom as common in fisher diets as snow- shoe hares and sometimes they are completely ab- sent. Hares are preferred over porcupines (Powell 1977), presumably because hares are easier and less dangerous to catch. Nonetheless, where porcupines and fishers co-occur, fishers eat porcupines. Collectively, mice appear in fishers' GI tracts and scats almost as frequently as snowshoe hares. White- footed mice {Peromyscus leucopus), deer mice (P. maniculatus) , red-backed voles {Clethrionomys gap-peri), and meadow voles {Microtus pennsylvanicus) are the most common mice found in fishers' diets and are generally the most common mice in fisher habitat. Mice are probably not as important to fish- ers as their occurrence in the diet samples indicates. Because they are small, have a relatively large amount of fur and bones, and are eaten whole, mice are over- represented in the GI tracts and scats of fishers. Mice are often active on the surface of the snow during the winter, especially white-footed mice, deer mice, and red -backed voles (Coulter 1966; Powell 1977, 1978), where fishers presumably catch them more frequently than under the snow. Shrews are found with unexpectedly high frequen- cies in GI tracts and scats of fishers, since carnivores are usually reluctant to prey on them (Jackson 1961). Shrews are often active during periods of extreme cold (Getz 1961) and, therefore, may sometimes be relatively abundant locally. Squirrels are common mammals throughout the fisher's range but are eaten less frequently than mice. Red squirrels {Tamiasciurus hudsonicus), Douglas squirrels (T. douglasii), and flying squirrels (Glaucomys spp.) are found over more of the fisher's range and are, therefore, eaten more often than grey and fox squirrels {Sciurus spp.). Red squirrels are difficult to catch (Jackson 1961) and fishers probably catch them most often when they sleep in their cone caches. Fish- ers capture flying squirrels on the ground (Powell 1977) and in nest holes in trees (Coulter 1966). Be- cause most food habits studies are conducted in win- ter, chipmunks (Tamias spp.) and other hibernating ground squirrels {Spermophilus spp., Marmota spp., and others) are probably underrepresented in the sample. The remains of deer and other large ungulates have been found in all diet studies of fishers, but in most studies the total volume of deer remains was small in comparison to its incidence (Clem 1977; Coulter 1966; deVos 1952; Powell 1977). Fishers often return to carcasses long after all edible parts are gone and only tufts of hair and skin are left. Some fishers may have deer hair in their digestive tracts and scats al- most all winter and still have eaten few meals of veni- son (Coulter 1966). Kuehn (1989) reported, however, that the amount of fat carried by fishers in Minne- sota increased when the number of white-tailed deer {Odocoileus virginianus) harvested by hunters in- 50 creased. Fishers apparently scavenged viscera and other deer parts left by hunters. Kelly (1977), Roy (1991) and Zielinski (unpub. data) documented ma- ternal or natal dens in close proximity to deer carcasses suggesting that females may select dens near carrion. Some captive fishers eat berries (W. Krohn, pers. comm.) but others generally refuse to eat any kind of fruit or nut (Davison 1975). However, plant mate- rial has been found in all diet studies of fishers. Apples are eaten by fishers in New England, where orchards have regrown to forests, but apparently only when other foods are unavailable (W. Krohn, pers. comm.). Diet Analyses by Age, Season, and Sex Juvenile fishers eat more fruits than do yearlings or adults (Guiliano et al. 1989). Because juveniles are learning to hunt, they may often go hungry (Raine 1979) and turn to apples and other fruits to ward off starvation. Analyses of diet by season have found little change in diet through the winter (Clem 1977; Coulter 1966) but significant increases in plant ma- terial, especially fruits and nuts, in summer (Stevens 1968). No consistent differences in diet exist between the sexes (Clem 1977; Coulter 1966; Guiliano et al. 1989; Kelly 1977; Kuehn 1989; Stevens 1968; reviewed by Powell 1993). Anatomical analyses demonstrating that the skulls, jaws, and teeth are less dimorphic than their skeletons (Holmes 1980, 1987; Holmes and Powell 1994a) suggest that dietary specialization of the sexes is unlikely. Foraging and Killing Behavior Fishers studied in eastern North America have two distinct components to foraging behavior: search for patches of abundant or vulnerable prey, and search within patches for prey to kill (Powell 1993). Typical of members of the subfamily Mustelinae, fishers hunting within patches of concentrated prey fre- quently change direction and zigzag. This pattern has been used in dense, lowland-conifer forests where snowshoe hares are found in high densities and in other habitats with high densities of prey (Powell 1977). Between patches of dense prey, fishers travel nearly in straight lines, searching for and heading to new prey patches. Within habitat patches with high densities of prey, fishers hunt by investigating places where prey are likely to be found (Arthur et al. 1989b; Brander and Books 1973; Coulter 1966; Powell 1976, 1977a, 1978, 1993; Powell and Brander 1977). Fishers will run along hare runs (Powell 1977, 1978; Powell and Brander 1977; Raine 1987) and kill hares where they are found resting or after a short rush attack (Powell 1978). Fishers seeking porcupine dens in upland hardwood forests travel long distances with almost no changes in direction (Clem 1977; Powell 1977, 1978; Powell and Brander 1977). These long upland travels often pass one or more porcupine dens, which fishers locate presumably using olfaction and memory (Powell 1993). The hunting success rates for fishers are difficult to quantify but appear to be low. There were 14 kills and scavenges along 123 km of fisher tracks in Up- per Peninsula Michigan, representing approximately 21 fisher days of hunting (Powell 1993). Seven scav- enges were only bits of hide and hair having little food value and 2 kills were of mice (Powell 1993). Thus, the remaining porcupine kill, hare kill, 2 squir- rel kills, and scavenging deer were the major results of 21 days of foraging. Fishers kill small prey such as mice and shrews with the capture bite, by shaking them, or by eating them. They kill squirrels, snowshoe hares, and rab- bits with a bite to the back of the neck or head (Coulter 1966; Kelly 1977; Powell 1977, 1978), but a fisher may use its feet to assist with a kill (Powell 1977, 1978). Porcupines are killed with repeated attacks on the face (Coulter 1966; Powell 1977a, 1993; Powell and Brander 1977). Porcupines deliver quills to fishers but they sel- dom cause infections or other complications (Coulter 1966; deVos 1952; Hamilton and Cook 1955; Morse 1961; Pringle 1964). All mammals appear to react in the same manner to porcupine quills. Quills carry no poison or irritant and have no characteristics that should cause infection. They are, in fact, covered with a thin layer of fatty acids, which have antibacterial action (Roze 1989; Roze et al. 1990). Porcupines may have evolved antibiotic coated quills to minimize infections from self-quilling when they fall from trees (Roze 1989) or to train individual predators to avoid them and thus to minimize predation (G. Whittler, pers. comm.). Rabbits, hares, and smaller prey are usually con- sumed in one meal. Fisher have been observed to cache prey they cannot eat, sometimes in the tempo- rary sleeping dens (Powell 1977). Fishers usually sleep close to large items, such as a deer carcass or a 51 porcupine, or will pull a porcupine into a hollow log sleeping den (Coulter 1966; deVos 1952; Jones 1991; Kelly 1977; Powell 1977, 1993; Roy 1991). Management Considerations 1. Snowshoe hares are a major prey item almost ever3rwhere fishers have been studied, including the Rocky Mountains. If this is confirmed from studies elsewhere in the West, managing for hare habitat might benefit fishers if it is not at the expense of den- ning and resting habitat. 2. In late-successional coniferous forests the pres- ence of high densities of snowshoe hares or porcu- pines indicates the potential for a fisher population. Research Needs 1. Determine the seasonal diets of fishers in repre- sentative ecoprovinces (Appendix A) in the western United States. In particular, study whether snowshoe hares and porcupines are important fisher prey in the West. 2. Investigate the habitat associations of species found to be common fisher prey and determine how vulnerable they are to fishers in those habitats. 3. Determine whether the management of habitat for primary prey species will increase or decrease habitat suitability for fishers. 4. Investigate whether natal or maternal den choices are influenced by the availability of carrion. HABITAT RELATIONSHIPS General Patterns and Spatial Scales Fishers occur most commonly in landscapes domi- nated by mature forest cover and they prefer late- seral forests over other habitats (Arthur et al. 1989b; Clem 1977; Coulter 1966; deVos 1952; Johnson 1984; Jones and Carton 1994; Kelly 1977; Powell 1977; Raine 1983; Thomasma et al. 1991, 1994). In the Pacific states and in the Rocky Mountains, they appear to prefer late-successional coniferous forests (Buck et al. 1983; Jones 1991; Jones and Carton 1994; Raphael 1984, 1988; Rosenberg and Raphael 1986) and use riparian areas disproportionately more than their occurrence (Aubry and Houston 1992; Buck et al. 1983; Heinemeyer 1993; Higley 1993, unpubl.; Jones 1991; Jones and Carton 1994; Seglund and Colightly 1994, unpubl.; Self and Kerns 1992, unpubl.). However, in two studies, both in the Rocky Mountains, there were times of the year where young to medium-age stands of conifers were preferred (Jones 1991; Roy 1991). In eastern North America fishers occur in conifer (Cook and Hamilton 1957; Coulter 1966; Hamilton and Cook 1955; Kelly 1977), mixed-conifer, and northern- hardwood forests (Clem 1977; Coulter 1966; Kelly 1977; Powell 1977, 1978). Everywhere, they exhibit a strong preference for habitats with overhead tree cover (Arthur et al. 1989b; Buck et al. 1983; Clem 1977; Coulter 1966; deVos 1952; Johnson 1984; Jones 1991; Jones and Carton 1994; Kelly 1977; Powell 1977, in press; Raine 1983; Raphael 1984, 1988; Rosenberg and Raphael 1986; Thomasma et al. 1991, 1994). Throughout most of the fisher's range, conifers constitute the dominant late-successional forest types. In the Northeast and Upper Midwest, fishers successfully recolonized and were successfully rein- troduced into forests that are predominantly mid- successional, second-growth, mixed-conifer, and hardwood forests. This does not mean that all mid- successional, second-growth forests meet the require- ments to support fisher populations. In the Idaho Rocky Mountains, fishers use predominantly old- growth forests of grand and subalpine fir (Jones and Carton 1994). In the Coast Ranges and west-side Cascade forests, fishers are associated with low to mid-elevational forests dominated by late-succes- sional and old-growth Douglas-fir and western hem- lock (Aubry and Houston 1992; Buck et al. 1983, 1994; Raphael 1984, 1988; Rosenberg and Raphael 1986). However, in east-side Cascade forests and in the Si- erra Nevada fisher occur at higher elevations in as- sociation with true fir {Abies sp.) and mixed-conifer forests (Aubry and Houston 1992; Schempf and White 1977). Fishers do not appear to occur as frequently in early successional forests as they do in late-succes- sional forests in the Pacific Northwest (Aubry and Houston 1992; Buck et al. 1983, 1994; Raphael 1984, 1988; Rosenberg and Raphael 1986). While some re- cent work in northern California indicates that fish- ers are detected in second-growth forests and in ar- eas with sparse overhead canopy (Higley 1993, unpub.; R. Klug, pers. comm.; S. Self, pers. comm.), it is not known whether these habitats are used tran- siently or are the basis of stable home ranges. It is unlikely that early and mid-successional forests, es- pecially those that have resulted from timber harvest, will provide the same prey resources, rest sites, and den sites as more mature forests. 52 Studies of fisher habitat have introduced a prob- lem of scale that has not been resolved. Fishers oc- cupy several regional biomes but have been studied most intensively in the forests in the eastern half of North America. Each population studied has been found within one large-scale habitat, such as mixed conifer and northern-hardwood forest or boreal for- est. Studies have then investigated selection on the next smaller habitat scale: What stands within the major regional habitat do fishers use? On this scale it has been impossible to parcel portions of population survivorship and fecundity into different stand types. Researchers have therefore assumed that relative time or distance spent in stand types is a measure of habitat preference which, in turn, is a measure of fit- ness. However, this assumption may not always be true (Buskirk and Powell 1994). For example, fishers may find vulnerable, preferred prey more quickly in some habitats than others and thus may spend more time in habitats in which they find vulnerable prey more slowly (Powell 1994b). No studies have investigated large-scale habitat preferences, as might be found across the pronounced elevational gradients in the western mountains, yet fishers may have critical preferences on this large scale (Aubry and Houston 1992). There is no universally appropriate scale for ana- lyzing habitat because the scale used must match the questions being asked. Kelly (1977) found that the composition of forests used by a fisher population in New Hampshire was different from the selections made by individual fishers for forest types within their home ranges. Individual fishers appear to use different scales in choosing where to perform differ- ent behaviors (Powell 1994b). Where to establish a home range is decided on a landscape scale; where to hunt is decided on a scale of habitat patches; where to rest is decided on a scale of both habitat patches and habitat characteristics within patches. Habitat analyses can be done on several scales but confusing scales can lead to incorrect conclusions (Rahel 1990). Forest Structure Habitat requirements of fishers may not always coincide with habitat variables measured, such as predominant tree species and forest types. Buskirk and Powell (1994) hypothesized that physical struc- ture of the forest and prey associated with forest structures are the critical features that explain fisher habitat use, not specific forest types. Structure in- cludes vertical and horizontal complexity created by a diversity of tree sizes and shapes, light gaps, dead and downed wood, and layers of overhead cover. Forest structure should have three functions impor- tant for fishers: structure that leads to high diversity of dense prey populations, structure that leads to high vulnerability of prey to fishers, and structure that provides natal and maternal dens and resting sites. Examining fisher habitat use at this level may recon- cile the apparently different habitat choices made by eastern and western fishers. Forest structure may also be important to fishers through effects on snow depth, snow compaction, and other snow character- istics (Aubry and Houston 1992; Heinemeyer 1993; Krohn et al., in press). All habitats used disproportionately by fishers have high canopy closure, and fishers avoid areas with low canopy closure (Arthur et al. 1989b; Coulter 1966; Jones and Carton 1994; Kelly 1977; Powell 1977, 1978; Raphael 1984; Rosenberg and Raphael 1986; Thomasma et al. 1991, 1994). Fishers also appear to select areas with a low canopy layer that occur in lowland habitat with dense overall canopy cover (Kelly 1977). Late-successional Douglas fir forests of the Pacific Northwest are characterized by multiple layers of cover that create closed-canopy conditions (Franklin and Spies 1991). The studies conducted in this region have concluded that fishers use late-suc- cessional forest more frequently than the early to mid- successional forests that result from timber harvest (Aubry and Houston 1992; Buck et al. 1994; Rosen- berg and Raphael 1986). Similarly, fishers in the Rocky Mountain study preferred late-successional forests with complex physical structure, especially during the summer (Jones and Carton 1994). How- ever, in areas where late-successional forests are char- acterized by more open conditions (e.g., ponderosa pine forests maintained by frequent light fires in the Sierra Nevada, McKelvey and Johnson 1992), it is uncertain if fishers will still prefer the closed canopy conditions typical of more mesic ecoregions. Open, hardwood-dominated forests are frequently avoided throughout the fisher's range (Arthur et al. 1989b; Buck et al. 1983; Clem 1977; Kelly 1977) and, depending on the other available habitats, mixed hardwood-conifer forest types may be avoided (Buck et al. 1983, 1994; Coulter 1966). Habitat and Prey In western North America, our ability to charac- terize fisher foraging habitat on the basis of the habi- 53 tat of their prey is hampered by the absence of any significant food habitats studies. However, in the Upper Midwest and Northeast, dense lowland for- ests are preferred by snowshoe hares, and these habi- tats are selected by fishers. In the Pacific Northwest, the range of the snowshoe hare coincides with the original distribution of Douglas fir forests, where fishers appear to occur most frequently. On the Olym- pic Peninsula, snowshoe hare sign appears to be as- sociated with late-successional, old-growth Douglas fir/ western hemlock stands and with stands of Dou- glas fir and western hemlock regenerating from log- ging or from fire and having dense, low branches (Powell 1991, unpubl.). However, others have char- acterized the habitat of hares on the Olympic penin- sula as "semi-open country with brush" (Scheffer 1949). The importance of snowshoe hare in the fisher diet and the habitat relationships of hare, in this re- gion and elsewhere in the West, will need to be de- termined before the role of hare in fisher habitat choice can be understood. In eastern North America hunting fishers use both open, hardwood and dense, conifer forest types (Arthur et al. 1989b; Coulter 1966; deVos 1952; Kelly 1977; Powell 1977, 1978; Powell and Brander 1977), but foraging strategies appear to be different in each habitat (Clem 1977; Powell 1977, 1978, 1981b, 1994b; Powell and Brander 1977). Fishers hunting in open, hardwood forests during the winter sometimes alter their directions of travel for small conifer stands where snowshoe hares are abundant (Coulter 1966; Kelly 1977; Powell 1977). Even though fishers may use certain habitats less than expected from their availabilities, those habitats may still have prey im- portant for fishers. In Michigan, fishers used open, hardwood forest significantly less than expected by chance, yet porcupines were found exclusively in those forests. Fishers foraged in a manner that mini- mized the time and distance traveled in open, hard- wood forests while maximizing their chances of find- ing vulnerable porcupines (Powell 1994b). Kelly (1977) found that fishers in New Hampshire selected habitats with the greatest small mammal (squirrels, shrews, mice) diversity but not the greatest small mammal populations, which are often found in open habitats avoided by fishers. Fishers are opportunis- tic predators and the availability of vulnerable prey may be more important than high populations of particular prey species. Because fishers have relatively general diets their potential prey can occur in a variety of forest types and serai stages. However, fishers may forage in dif- ferent habitats from the ones they use for resting and denning so a complete description of habitat require- ments should consider both foraging and resting habi- tat needs. Resting and denning tend to occur in struc- tures associated with late-successional conifer forests (see below), whereas prey can be distributed among a variety of successional stages. Because the types of forests that contain resting and denning sites may be more limiting, these habitats should be given more weight than foraging habitats when planning habi- tat management. Snow and Habitat Selection Fishers appear to be restricted to areas with rela- tively low snow accumulation. Deep, fluffy snow affects habitat use by fishers (Leonard 1980b; Raine 1983) and may affect distribution, population expan- sion, and colonization of unoccupied habitat (Arthur et al. 1989b; Aubry and Houston 1992; Heinemeyer 1993; Krohn et al. 1994). When snow is deep and fluffy, causing fishers to leave body drags, fishers move less but travel disproportionately often on snowshoe hare trails and on their own trails (R. Powell, pers. obs.). Fishers will even travel on fro- zen waterways, which they otherwise avoid, where the snow has been blown and packed by wind (Raine 1983). Where snow is deep, fishers may forage for hares on packed, snowplow drifts along roads that bisect hare habitat (Johnson and Todd 1985). Snow appears to limit fisher distribution in Wash- ington (Aubry and Houston 1992). On the Olympic Peninsula, and on the west slope of the Cascade Range (primarily the Pacific Northwest Coast and Mountains Ecoprovince, Appendix A), where snow- fall is greatest at high elevations, fisher sightings in the past 40 years have been confined to low eleva- tions. On the east slope of the Cascades, where snow is less deep, fisher sightings have been recorded at higher elevations. Krohn et al. (in press), using fisher harvest data, found that indices of fisher recruitment were lower in regions of Maine with deep and fre- quent snows compared to other areas. Data from the Rocky Mountains are consistent with avoidance of deep, fluffy snow. Fishers in Idaho and Montana select flat areas and bottoms and avoid mid- slopes (Heinemeyer 1993; Jones 1991). However, fish- ers do not show detectable selection or avoidance of ridgetops and steep slopes (Heinemeyer 1993; Jones 1991), although the "selectivity indices" calculated 54 by Heinemeyer (1993) appear to confuse effects of small sample size with selection. The fishers in all three Rocky Mountain studies (Heinemeyer 1993; Jones 1991; Roy 1991) selected riparian areas, which have relatively gentle slopes, dense canopy, and per- haps protection from snow. Raines' (1983) research indicates that slopes with deep snow should provide poor footing for fishers and should be avoided. The effect of snow on fisher populations and dis- tribution may also help explain why fisher habitat appears so variable across the species' range. Where snow is deep and frequent, fishers should be expected to be either absent or occur where dense overhead cover intercepts the snowfall (Krohn et al., in press). This hypothesis may explain why fishers in the west- ern United States and the Great Lakes region, where snow tends to be deep, are thought to occur most frequently in late-successional forests (Buck et al. 1994; Harris et al. 1982; Jones 1991; Thomasma et al. 1991) whereas second growth forests are more com- monly used by fishers in the northeastern United States in areas where snowfall is relatively low (Arthur et al. 1989b; Coulter 1960). This effect, how- ever, does not explain distribution among habitats during the summer. Additional work is necessary before we can understand how snow, and the inter- action between snow and forest structure, influences fisher distribution and habitat choice. Elevation In the Pacific States, fishers were originally most common in low to mid-elevational forests up to 2500 m (Aubry and Houston 1992; Grinnell et al. 1937; Schempf and White 1977). In the past 40 years, most sightings of fishers on the Olympic Peninsula and the west slope of the Cascade Range in Washington have been at elevations less than 1000 m but sightings on the east slope of the Cascades where snow is less deep have generally been between 1800 and 2200 m (Aubry and Houston 1992). The highest elevation recorded for an observation of a fisher in California was 3475 m, in the Sierra Nevada (Schempf and White 1977), but most observations in northern Cali- fornia forests have been below 1000 m (Grinnell et al. 1937; Schempf and White 1977; Seglund and Golightly 1994, unpubl.; Self and Kerns 1992, unpubl.). In Montana, fishers released from Wiscon- sin avoided high elevations (1200-1600 m) and se- lected low elevations (600-1000 m) after they became established (Heinemeyer 1993). Use of Openings and Nonforested Habitats Fishers avoid nonforested areas (Arthur et al. 1989b; Buck et al. 1983, 1994; Coulter 1966; Jones 1991; Jones and Carton 1994; Kelly 1977; Powell 1977, 1978; Roy 1991). Fishers have avoided open areas 25 m across and less in the Midwest (Powell 1977). Large forest openings, open hardwood forests, recent clearcuts, grasslands, and areas above timberline are infrequently used in the West. Existing data are in- adequate to assess the use of forest areas with inter- mediate forest cover resulting from either natural or human-caused disturbances. Fishers are occasionally found in managed forests with little overhead tree cover, especially in north- ern California (R. Golightly, pers. comm.; M. Higley, pers. comm.; S. Self, pers. comm.), but the residency, age and reproductive status of these animals is un- known. It is possible that some of these observations may be of foraging animals, given that prey typically associated with nonforested habitats occur in the fisher diet (Jones and Carton 1994). Recently clearcut areas in the Northeast may be used during the sum- mer, when they provide some low overhead cover from brush and saplings, but they are avoided dur- ing the winter (Kelly 1977). Rosenberg and Raphael (1986) listed fishers as an "area sensitive" species in northwestern California on the basis of a positive relationship in the frequency of their occurrence and the size of late-successional forest stands. This rela- tionship suggests that, at least for northwestern Cali- fornia, as forested landscapes become more frag- mented with openings fishers are less prevalent. Aversion to open areas has affected local distribu- tions and can limit population expansion and colo- nization of unoccupied range (Coulter 1966; Earle 1978). An area of farmland in Upper Peninsula Michi- gan delayed expansion of the population to the north by at least 15 years (R. Powell, pers. obs.) and the Pennobscot River delayed expansion of fishers to eastern Maine for over a decade (Coulter 1966). Habitat Use by Sex, Age, and Season There are few seasonal or sexual variations noted in the literature on habitat preferences of fishers. Fe- male fishers in the Northeast may be less selective in their use of habitats during summer than during winter, especially for resting habitat (Arthur et al. 1989b; Kelly 1977). Male fishers in the mountains of 55 northern California may restrict access of females to preferred habitat that lack hardwoods (Buck et al. 1983). In Idaho, both sexes select late-successional conifer forests during summer but preferred young forests during the winter (Jones and Garton 1994). This was more likely due to a change in prey used during these seasons than to the influence of snow. Some change in habitat preference is caused by avoid- ance of open habitats that exist in winter but not in summer. Open habitat vegetated with young, decidu- ous trees and shrubs (typical of recently harvested areas in the East) can be used by fishers in summer (Kelly 1977) but are completely open with no over- head cover in winter. Resting Sites Fishers use a variety of resting sites. Most resting sites are used for only one sleeping or resting bout, but a fisher often will rest in the same site for many days, especially when it is close to a large food item, like carrion (R. Powell, pers. obs.), or during severe weather (Coulter 1966; deVos 1952; Powell 1977). Occasionally, individuals may use a site more than once (e.g., Jones 1991; Reynolds and Self 1994, unpubl.) and sometimes more than one individual will use the same resting site (Reynolds and Self 1994, unpubl.). Fishers often approach resting sites very directly, indicating that sites are remembered (deVos 1952; Powell 1993). Live trees with hollows, snags, logs, stumps, "witches' brooms," squirrel and rap- tor nests, brush piles, rockfalls, holes in the ground, and even abandoned beaver lodges have been re- ported as rest sites during various seasons (Arthur et al. 1989b; Coulter 1966; deVos 1952; Grinnell et al. 1937; Hamilton and Cook 1955; Powell 1977, 1993; Pringle 1964). The canopies of, or cavities within, live trees are the most commonly used rest sites reported in eastern and western studies (Arthur et al. 1989b; Buck et al. 1983; R. Golightly, pers. comm; Jones 1991; Krohn et al. 1994; Reynolds and Self 1994, unpubl.). In the published western studies, logs were of sec- ondary importance, followed by snags (Buck et al. 1983; Jones 1991). The average diameters of trees used as resting sites were 55.8 cm in Idaho (Jones 1991), and 114.3 cm in northwestern California (Buck et al. 1983). Arthur et al. (1989b) located 180 rest sites of 22 fishers in Maine. Tree "nests" in balsam firs (resting sites on top of branches or in witches' brooms) were commonly used all year. Burrows, especially those of woodchucks {Marmota monax), were used most commonly in winter, and cavities in trees were used most commonly in spring and fall. This pattern of rest site use suggests that temperature affects rest- ing site choice and that sites are chosen for warmth and insulation in winter and perhaps to prevent over- heating in summer. This conclusion is also supported by the observation that fisher use of logs increases significantly during the winter in Idaho (Jones 1991). During the winter, fishers sometimes use burrows under the snow with one or more tunnels leading 0.5 to 2.0 m to a larger, hollowed space under the surface of the snow (Coulter 1966; deVos 1952; Powell 1977). Arthur et al. (1989b) reported no use of snow dens by fishers in southcentral Maine, where snow is generally not deep. They did find that fishers tun- neled up to 1.5 m through snow to get to ground burrows and they suggested that use of these snow dens may be exaggerated in the literature. Snow dens excavated in Upper Peninsula Michigan were not connected to ground burrows (Powell 1993). Resting sites reported in studies in the western United States tend to occur predominantly in closed canopy stands. Jones (1991) analyzed canopy closure at 172 rest sites in Idaho and found that fishers pre- ferred to rest in stands that exceeded 61 percent canopy closure during summer and winter, and avoided stands with less than 40 percent closure. Canopy closure at 34 rest sites in northcentral Califor- nia averaged 82% (Reynolds and Self 1994, unpubl). Fishers are more selective of habitat for resting sites than of habitat for foraging. Researchers working in the Rocky Mountains, the Upper Midwest, and the Northeast in the United States have all found that fishers choose lowland-conifer forest types for rest- ing significantly more often than for traveling or for- aging (Arthur et al. 1989b; Jones and Garton 1994; Kelly 1977; Powell 1994b). As noted above, fisher prey may be found in a variety of forest types and serai stages. However, resting and denning tends to occur in large trees, snags and logs that are normally asso- ciated with late-successional conifer forests. Fishers in the eastern United States find these structures within some second-growth forests (Arthur et al. 1989b), but with the exception of a few observations of fishers using residual snags in early successional forest in California (S. Self, pers. comm.), there are no data in the West to determine how these compo- nents are used when they occur in other than late- successional stands. Because the types of forests that normally contain resting and denning sites may be more limiting than foraging habitat within the fisher 56 range in the West, they should receive special con- sideration when planning habitat management. Management Considerations 1. In the western mountains, fishers prefer late- successional forests (especially for resting and den- ning) and occur most frequently where these forests include the fewest large nonforested openings. Avoidance of open areas may restrict the movements of fishers between patches of habitat and reduce colo- nization of unoccupied but suitable habitat. Further reduction of late-successional forests, especially frag- mentation of contiguous areas through clearcutting, could be detrimental to fisher conservation. 2. Large physical structures (live trees, snags, and logs) are the most frequent fisher rest sites, and these structures occur most commonly in late-successional forests. Until it is understood how these structures are used and can be managed outside their natural ecological context, the maintenance of late-succes- sional forests will be important for the conservation of fishers. Research Needs 1 . Replicate studies of habitat relationships within ecoprovinces (Appendix A) of the mountainous west- ern United States. 2. Investigate the interaction between snow char- acteristics (depth, density, and frequency), elevation, and forest age/ structure on distribution and habitat associations. 3. Determine whether resting and denning is lim- ited to structures in late-successional forest stands. 4. Explore the importance of riparian areas to fisher habitat use in representative ecoprovinces. 5. After food habits studies are conducted, deter- mine the habitat relationships of primary prey within ecoprovinces. Also, determine how forest structure mediates prey availability. HOME RANGE Fishers are solitary (Arthur et al. 1989a; Coulter 1966; deVos 1952; Powell 1977; Quick 1953) and ap- pear to avoid close proximity to other individuals (Arthur et al. 1989a; Powell 1977). They probably maintain knowledge of the location of other individu- als primarily via scent marking; however, direct con- tact and overt aggression has been documented (Arthur et al. 1989a; Coulter 1966; Kelly 1977; Leonard 1986; Powell 1977). The criteria fishers use when es- tablishing a home range are unknown, but the den- sity of vulnerable prey probably play an important role. Tracking data indicate that fishers use most in- tensively those parts of their home ranges that have high prey densities, and that these areas change (Arthur et al. 1989a; Coulter 1966; Powell 1977). IHome Range Size Early estimates of fishers' home ranges from track- ing data were substantially larger and less accurate than estimates derived more recently from radio-te- lemetry data (table 3). There is considerable varia- tion in estimates of home range sizes, due in part to different researchers using different methods and treating data differently, in part to most methods of quantifying home ranges being inadequate, and in part to true variation. Recently developed fixed-ker- nel estimators quantify better than any other avail- able methods both the outlines of home ranges and the distributions of use within home ranges (Seaman 1993; Silverman 1990). Despite the limits of convex polygon and harmonic mean home range estimators, they have provided most of the information available about fishers' home ranges. There are no apparent geographical patterns in home range sizes, but male home ranges are larger than female home ranges (table 3). In table 3, we have calculated a mean home range area for each sex. Be- cause methods were not consistent between studies, this figure can only be used for general comparisons and therefore includes no measure of variation. The mean home range size for adult male fishers is 40 km^ (range 19-79), nearly three times that for females (15 km-; range 4-32). This difference in size between male and female home ranges is greater than that expected from differences betw^een the sexes in en- ergy requirements, or food requirements, calculated from body size. Energy requirements are propor- tional to W where W is a mammal's weight (McNab 1992). Because male fishers average slightly less than twice as heavy as females (Powell 1993), their energy requirements should be approximately 1.5-1.7 times greater than the energy requirements of females. Because the territories of male fishers are large, hundreds of square kilometers of suitable habitat may be necessary to maintain sufficient numbers of males to have viable populations. Modeling popula- 57 tion viability is premature at this point. However, if a viable population has an effective size as small as 50 (Shaffer 1981), half of which is male fishers all of whom breed, then managed areas in the West may need to be at least 600 km^ in California (based on Buck et al. 1983) to 2000 km^ in the Rocky Mountains (based on Jones 1991) of contiguous, or intercon- nected, suitable habitat. Not all males and females breed, and minimal viable population size may be larger than 50. Therefore, managed areas likely need to be larger than these estimates. It is unknown whether the habitat is best distributed in an unbro- ken block, or, a dendritic pattern of wide and con- nected riparian areas. There are several potential explanations (not mu- tually exclusive) for the disproportionate sizes of male and female home ranges. First, males may have energy requirements greater than expected from Table 3.— Home range sizes (in km^) estimated for fishers. Figures given are means ± standard deviations. Ttie overall mean was calcu- lated by using only one figure for eacti sex in each study (modified from Powell 1993). Male N Female N Location Method and comments Source 20 ± 12 3 4.2 1 California Convex polygons adults with >20 locations males within the breeding season Buck et al. 1983 A ft O.O 0 v^uiivfcjx pcjiyyuiic) adults + juveniles females all year males within the breeding season DUL-K t;l Ul. 1 YOO 16±6 2 California Convex polygon biased to underestimate Self and Kerns 1992 A U A TU 10 \ 1*— 11 1 1 \\J\ \\\^ 1 1 IC?LJI 1 adults + juveniles lr,n(^<; 1991 33± 25 7 19+ 12 6 Maine Convex polygon - Vwivjui 1 o \j\ iiy May-December Arthur etal. 1989a 27 ±24 7 16± 12 6 Maine 90% harmonic mean UvJUl 1 o vji iiy May-December Arthur et al. 1989a 50 + 40 7 31 ±23 6 Maine 99% harmonic mean uuuiib Ul Iiy May-December Arthur et al, 1989a 35 1 15 1 Michigan Convex polygon adults only winter Powell 1977 85 2 17 7 Montana Adaptive kernel non-breeding Heinemeyer 1993 19± 17 3 15+ 3 2 New Hampshire Convex polygon adults only oil year Kelly 1977 26± 17 3 15± 6 3 New Hampshire Convex polygon subodults only all year Kelly 1977 23 ± 16 6 15± 5 5 New Hampshire Convex polygon adults + subodults all year Kelly 1977 49 + 37 2 8± 4 5 Wisconsin Convex polygon adults with >25 locations all year Johnson 1984 39± 27 4 8+ 4 7 Wisconsin Convex polygon adults + juveniles all year Johnson 1984 40 57 15 55 Mean 58 body size and therefore need disproportionately larger home ranges. There is no support, however, for this hypothesis from laboratory research or field estimates of metabolic rates for fishers or other mem- bers of the subfamily Mustelinae (Buskirk et al. 1988; Casey and Casey 1979; Moors 1977; Powell 1979a, 1981b; Worthen and Kilgore 1981). Second, the ac- tual areas used by males and females may be pro- portional to body size, though areas within home range outlines are not. Home ranges of male and fe- male fishers do overlap extensively. In other mustelines, however, males spend minimal time within the home ranges of females encompassed within their own ranges (Erlinge 1977; Gerell 1970). No published data quantify the intensity of home range use by fishers. Third, males and females may space themselves to gain access to different resources: female priority is access to food whereas male prior- ity is access to females. This has been shown to be the case for other mammals, including other mustelines (Erlinge and Sandell 1986; Ims 1987, 1988a, 1988b, 1990; Sandell 1986), and Sandell (1989) has hypothesized this to be the case for solitary car- nivores, such as fishers. Fourth, males wander widely during the breeding season (Arthur et al. 1989a) and some of the data used to calculate the mean value for males includes these extra-territorial forays. Monthly home range of males are greatly enlarged during the breeding season but home ranges of females are not (Arthur et al. 1989a; Johnson 1984). Because male fishers travel so widely during the breeding season, Arthur et al. (1989a) and Buck et al. (1983) excluded estimated locations made during the breeding season when they estimated home range sizes (table 3). Seaman (1993) hypothesized that male and female mammals have equal lifetime reproductive costs. For male fishers, large body and home range sizes are reproductive costs. If these costs for males were equal to the high reproductive costs for females of raising litters, then home ranges sizes for males and females should be equal. Males, therefore, may forage less in- tensively throughout their home ranges. Monthly home ranges for fishers are significantly smaller than yearly home ranges and monthly home ranges of females tend to be smaller than those of males (Kelly 1977). Territoriality In most populations studied, including popula- tions in California and Montana, fishers appear to exhibit intrasexual territoriality: home ranges over- lap little between members of the same sex but over- lap is extensive between members of opposite sexes (Arthur et al. 1989a; Buck et al. 1983; Heinemeyer 1993; Johnson 1984; Kelly 1977; Powell 1977, 1979a). Because territories of males are large, a male's terri- tory may overlap territories of more than one female. How territories are maintained is not known. Little overt aggression has been documented between in- dividuals and fishers undoubtedly communicate by scent marking. During the winter, fishers often walk along the tops of logs and large stumps and some- times walk over and apparently drag their bellies and urinate on small stumps or mounds of snow (Leonard 1986; Powell 1977, 1993). Sometimes, during the breeding season, fishers leave black, tarry marks. These marks resemble feces resulting from rich meals of meat with little fur and bones but do not smell like feces. Fishers also urine mark at the entrances to resting sites and on large carcasses they are scaveng- ing (Pittaway 1978, 1984; Powell, unpubl. data). When logs are moved from one individual's cage to another, the recipient will often rub its abdomen on the log (W. Krohn per. comm.). Directed agonistic behavior has been observed between a captive adult female fisher and her young, among the young within captive litters five months old and older, and between two captive adult female fishers (Coulter 1966; Kelly 1977; PoweU 1977). Arthur et al. (1989a) found male fishers with wounds, and Leonard (1986) examined the carcass of a male fisher with the canine of another fisher in its back. Some researchers have suggested that intrasexual territoriality in carnivores occurs when large sexual dimorphism permits the two sexes to have different diets. However, this hypothesis has consistently been refuted for fishers, martens, and other mustelines (Clem 1977; Coulter 1966; Eriinge 1975; Holmes 1987; Holmes and Powell 1994; Kelly 1977; King 1989; Tap- per 1976, 1979; reviewed by Powell 1994a). Patchily distributed prey is predicted to lead to low costs of sharing a territory with a member of the opposite sex (Powell 1994a). This cost is balanced by reduced chances of reproductive failure for males. Territorial behavior may not be a species-specific characteris- tic. From very low to very high prey population den- sities, the following pattern of change in fisher spac- ing is predicted (Powell 1994a): transient -> individual territories, decreasing in size intrasexual territories, decreasing in size extensive home range overlap. 59 Management Considerations 1 . Fishers, especially males, have extremely large home ranges and the largest ranges may occur in the poorest quality habitat. The management of areas large enough to include many contiguous home ranges will probably have the best chance of conserv- ing fisher populations. Research Needs 1 . Use fixed or adaptive kernel methods to deter- mine home range sizes, and describe use areas therein, for males and females in representative ecoprovinces. 2. Evaluate the effects of prey densities and forest composition on home range size, shape, and compo- sition. 3. Determine whether landscape features (i.e., to- pographic position, elevation within watershed) in- fluence home range locations. IVIOVEIVIENTS Activity Patterns Typical of mustelines, fishers have small numbers of activity periods (1 to 3) during a 24-hour period (Powell 1993). They are active day or night, when they are hungry or when their predominant prey is active (Powell 1993), but they often have peaks in activity around sunrise and sunset (Arthur and Krohn 1991) or during the night (deVos 1952). Dur- ing all seasons, fishers are least active during mid- day and in winter fishers are often inactive in the middle of the night (Arthur and Krohn 1991; Johnson 1984; Kelly 1977). Fishers are most active during all daylight hours during summer and least active dur- ing winter (Johnson 1984; Kelly 1977). No significant difference in activity patterns has been noted between the sexes. Movement Patterns Fishers can travel long distances during short pe- riods of time but travel, about 5-6 km per day on the average (Arthur and Krohn 1991; Johnson 1984; Jones 1991; Kelly 1977; Powell 1993; Roy 1991). Adult males are the most mobile, adult females are least mobile and subadults (<21 months old) of each sex are in- termediate. All fishers travel longer distances dur- ing active periods in winter than in summer. Mobil- ity of adult females appears to peak prior to parturi- tion (Kelly 1977; Roy 1991) and then declines through the autumn months. The restricted mobility of fe- males during summer may be caused by having de- pendent young and may explain why subadult fe- males are more mobile than adult females. All Mattes species have clear adaptations for arboreality (Holmes 1980; Leach 1977a, 1977b; Sokolov and Sokolov 1971), partially due to their rela- tively unspecialized limb anatomy (Holmes 1980; Leach 1977a, 1977b). Fishers climb high into trees to reach holes and possibly to reach prey (Coulter 1966; Grinnell et al. 1937; Leonard 1980a; Powell 1977). Fishers in California were observed to travel from tree to tree to avoid dogs and hunters, sometimes leaping great distances from the branches of one tree to the branches of the next (Grinnell et al. 1937). Nonetheless, fishers are less arboreal than the popu- lar literature claims (Coulter 1966; deVos 1952; Holmes 1980; Powell 1977, 1980; Raine 1987). In the Midwest and Northeast, almost all activity is terres- trial, and in boreal forests fishers may never climb trees while foraging (Raine 1987). Male fishers, who are significantly larger than females, are less adept at cUmbing (Pittaway 1978; Powell 1977). Dispersal Though independent from their mothers starting in the fall, young fishers do not disperse from their mothers' home ranges until mid to late winter (Arthur 1987; Arthur et al. 1993). At age 9 months, few juveniles have established their own home ranges but by age one year, most have (W. Krohn, pers. comm.). In most mammals, males disperse far- ther than do females and females may remain in or near their mothers' home ranges for their entire lives (Greenwood 1980). The data of Arthur (1987) and Paragi (1990) are not entirely consistent with this pattern because both males and females dispersed similar distances. Juveniles dispersed 10-16 km from their mother's range in Maine (Paragi 1990). In Idaho, two, 1 -year-old males established ranges after mov- ing 26 and 42 km, respectively. Because movements occur frequently along forested riparian areas (Buck et al. 1983; Heinemeyer 1993; Jones 1991), it is likely that dispersal occurs in these areas as well. Buck et al. (1983) thought that forested saddles between drainages were important linkages for fisher move- ments, although habitat selection during dispersal 60 has not been studied. Large open areas retard popu- lation expansion (Coulter 1966; Earle 1978), perhaps because dispersing individuals are inhibited from entering nonforested areas. Movements and Reintroduction Movements of reintroduced animals may provide an indication of the maximum distances that fishers from extant populations may move. In West Virginia (Pack and Cromer 1981), fishers moved an average of 43.7 km (90 km maximum) from the release site and movements as far as 98 km were noted in a Wis- consin reintroduction (Olsen 1966). In Montana, males and females moved up to 102 and 56 km (Weckwerth and Wright 1966) and up to 71 and 163 km (Roy 1991) from their release sites. All fisher reintroductions except one were done during winter. Irvine et al. (1962, 1964) recommended winter reintroductions. Fishers can be trapped eas- ily during winter and it was believed that females would not travel far as parturition approached. Nonetheless, fishers reintroduced during winter travel long distances (Proulx et al. 1994; Roy 1991) and may be subject to predation (Roy 1991). Proulx et al. (1994) released fishers in the parklands of Alberta during both late winter and summer. Fish- ers released during winter traveled significantly longer distances and had significantly higher mor- tality than the fishers released during summer. Most fishers released in summer established home ranges close to their release sites, whereas this was not the case for the fishers released during winter. Proulx et al. recommended that more experiments be con- ducted to find optimal release times but that, in the mean time, fishers should be released in June when possible. Management Considerations 1. Fishers are capable of moving long distances, but movements may be restricted in landscapes with large nonforested openings. The maintenance of con- tact between individuals and subpopulations and the recolonization of unoccupied habitat may be facili- tated by reducing the size of openings. 2. Where reintroductions are necessary, conduct them during the summer until additional research dictates otherwise. 3. Fishers probably prey on snowshoe hares in the West. Where fishers are translocated to areas with cyclic snowshoe hare populations, release them dur- ing the increase phase of the hare cycle. Research Needs 1. Investigate the seasonal movement patterns by adults of both sexes in representative ecoprovinces in the West. 2. Study the dispersal behavior of juvenile fishers. Evaluate the dispersal distances, the habitat charac- teristics (landscape and stand scales), and topo- graphic features used and avoided during dispersal. 3. Test the hypothesis that dispersing juveniles are less selective of habitat than adults. 4. Investigate movements of fishers following translocation to understand how and where fishers establish home ranges. COMMUNITY INTERACTIONS Food Webs and Competition The fisher, as a predator, is predominantly a sec- ondary consumer. Occasionally, however, fishers eat berries and eat other carnivores making them both primary and tertiary consumers as well. In the com- munity of organisms living in the northern forests of North America, fishers most clearly take the role of predators on small- to medium-size mammals and birds. Depending on the specific community, fishers may potentially compete with coyotes, foxes, bob- cats, lynx (Lynx canadensis), American martens, wol- verines {Gulo gulo), and weasels. Although this com- petition has not been documented and there is no direct evidence for its occurrence, the competitive interactions between fishers and American martens, in particular, have been the subject of some discussion. Fishers and American martens are the only me- dium-sized, northern predators that are agile in trees and also are elongate and are able to explore hollow logs, brush piles and holes in the ground for prey. The geographic distributions of these species over- lap considerably (Douglas and Strickland 1987; Strickland and Douglas 1978), but in the West mar- tens tend to occur at higher elevations than fishers (Buskirk and Ruggiero, Chapter 2; J. Jones, pers. obs.; Schempf and White 1977). However, martens and fishers are sympatric in areas in the southern Sierra Nevada (W. Zielinski, pers. comm.) in northern Idaho (J. Jones pers. comm.), and undoubtedly in other ar- eas as well. Fishers are larger than martens and are able to kill a larger range of prey. Whenever two gen- 61 eralized predators differ predominantly in size and lack specializations, the larger predator can prey upon the entire range of prey available to the smaller plus it can prey on larger prey. Thus, in periods of severe competition, the larger predator will prevail (Wilson 1975). However, where fishers and marten coexist it may be via niche partitioning (Rosenzweig 1966) because marten are small enough to be able to specialize on hunting voles, especially Clethrionomys sp., under snow (Buskirk 1983; Martin 1994). Clem (1977) found dietary overlap between fishers and martens in Ontario to be most profound during the winter but concluded that competition for food did not likely result in competitive exclusion. In the northeastern United States, Krohn et al. (1994) hy- pothesize that the inverse relationship between cap- tures of fishers and martens by commercial trappers may result from an interaction between competitive displacement of marten by fisher and the avoidance of areas with deep and frequent snowfalls by fishers but not martens. Fishers may compete with bobcats and especially lynx, because snowshoe hares are the fishers' pre- dominant prey in many places. Presumably the for- aging patterns used by fishers differ greatly enough from those used by the felids that competition is mini- mized. Fisher populations in Canada cycle in re- sponse to and about 3 years out of phase from snow- shoe hare populations (Bulmer 1974, 1975). Fishers cycle 1-2 years out of phase from lynx (Bulmer 1974, 1975), because low hare populations affect fisher populations through increased juvenile and adult mortality but affect lynx populations primarily through increased juvenile mortality and decreased reproduction. However, these effects will be mini- mized in the United States where hare populations do not cycle (Dolbeer and Clark 1975; Koehler 1990). Fishers have been reestablished in areas inhabited by foxes, coyotes, bobcats, and lynx, which suggests that competition with these other predators is not lim- iting to fisher populations. Where fishers and porcupines occur together, fish- ers have little competition with other predators for porcupines. Other predators do kill porcupines oc- casionally (Roze 1989) and mountain lions {Puma concolor) may kill porcupines more than occasionally (Maser and Rohweder 1983). Fishers, however, have unique adaptations for killing porcupines and no other predators have been implicated as regulators of porcupine populations (Powell 1977, 1993; Powell and Brander 1977; Roze 1989). Predation on Fishers As far as is known, adult fishers are not regularly subject to predation. The occasional fishers reported as killed by other predators were probably ill, old, otherwise in poor health, or lacking in appropriate behavior, making them easy and not dangerous to kill. Four of 20 radio-collared fishers in California died of wounds inflicted by predators or other fish- ers (Buck et al. 1983). Two fishers were killed by mountain lions in California (Grinnell et al. 1937) and 3 of 21 animals studied by Jones (1991) were killed by predators. Heinemeyer (1993) and Roy (1991) re- ported high predation rates on fishers translocated from Minnesota and Wisconsin to northwestern Montana. Predators there included bears {Ursus spp.), coyotes, golden eagles, lynx, mountain lions, and wolverines. The introduced fishers may have been at risk due to their unfamiliarity with the predators, forests, topography, snow conditions, and prey in the western mountains. Although Heinemeyer's and Roy's results may give little insight into predation on fishers under natural conditions, their results give significant in- sight into design of reintroductions. Special steps may be necessary when fishers are released into habitat very different from that in which they were captured, especially when the new habitat supports several predators not known to the fishers in their original habitat. If fishers are released in summer, as sug- gested by Proulx et al. (1994), they may not travel long distances exposing themselves to other preda- tors. When movements are reduced, fishers establish home ranges promptly and probably learn impor- tant local landscape features quickly. Fishers can be released into holding cages where they are housed for an habituation period, but Heinemeyer (1993) found that such "soft" releases in early winter did not affect subsequent movements and activity by re- leased fishers. Alternatively, fishers might be released into areas with low populations of other predators, especially mountain lions and golden eagles. It is possible that forest fragmentation may affect pre- dation on fishers by other predators. If fragmentation causes fishers to travel long distances through unf anul- iar habitat (especially unpreferred habitat) in search of mates, the fishers might be subject to predation. Management Considerations 1 . Animals reintroduced from the same, or nearby, ecoprovinces and into areas with low populations of 62 potential fisher predators have the best chance of survival. 2. Until the importance of competition between fisher and American marten is determined, it appears that management for both species on the same areas may not be as successful as exclusive areas for each species. Research Needs 1 . Test the hypothesis that the fragmentation of late- successional forest habitat changes competitive in- teractions between fishers and their potential preda- tors and competitors. 2. Investigate the niche relationships of marten and fisher where they co-occur and test the hypothesis that snow depth and forest structure mediates com- petitive interactions. 3. Snowshoe hares may constitute a large propor- tion of the diet of fishers and lynx. Study the food habits of fishers and lynx where they occur together to assess the potential for direct competition. CONSERVATION STATUS Human Effects on Fishers Humans and fishers interact in a number of ways. First, since before European colonization of North America, fishers have been valued for their pelts (Barkalow 1961; Graham and Graham 1990). Fishers have been trapped for fur and, to a lesser extent, farmed for fur. Second, humans affect fisher popula- tions through forestry practices and other activities that alter the fishers' habitat. Fishers lose resting, denning, and foraging habitat through logging of late-successional forests, clearing of forests for agri- culture, and clearing of forests for development. Third, fishers have been used to manage porcupine populations. And, fourth, the fisher is unique to North America and is valued by native and nonna- tive people as an important member of the complex natural communities that comprise the continent's northern forests. Fishers are an important component of the diversity of organisms found in North America, and the mere knowledge of the fisher's existence in natural forest communities is valued by many Ameri- cans. Fishers and their pelts are an important element of some American Indian cultures. For example, on the Hoopa Reservation in northwestern California skins are used to fashion quivers and skirts that are important ceremonial regalia, and the needs of fisher are considered in forest management (M. Higley, pers. comm.). The fisher's reaction to humans in all of these in- teractions is usually one of avoidance. Even though mustelids appear to be curious by nature and in some instances fishers may associate with humans (W. Zielinski, pers. obs.), they seldom linger when they become aware of the immediate presence of a hu- man. In this regard, fishers generally are more com- mon where the density of humans is low and hu- man disturbance is reduced. Although perhaps not as associated with "wilderness" as the wolverine (V. Banci, Chapter 5), the fisher is usually characterized as a species that avoids humans (Douglas and Strickland 1987; Powell 1993). Trapping Trapping, with logging, has had a major impact on fisher populations. Fishers are easily trapped and the value of fisher pelts in the past created trapping pressure great enough to exterminate fishers com- pletely from huge geographic areas. Wherever fish- ers are trapped, populations must be monitored closely to prevent population decrease. In addition to the clear evidence from past population declines, there is evidence from more recent changes in popu- lations in eastern states and provinces (Douglas and Strickland 1987; Kelly 1977; Krohn et. al. 1994; Par- son 1980; Strickland and Douglas 1978; Wood 1977; Young 1975) and theoretical evidence (Powell 1979b) that small changes in mortality due to trapping can greatly affect fisher populations. Because fishers are easily trapped, where fisher populations are low they can be jeopardized by the trapping of coyote, fox, bobcat, and marten (Coulter 1966; Douglas and Strickland 1987; Jones 1991; Powell 1993) . Wisconsin designated fisher wildlife manage- ment areas in the Nicolet and Chequamegon National Forest (approximately 550 km^ and 1,000 km^) where land sets for all furbearers were prohibited (Petersen et. al. 1977). During the two years that British Co- lumbia closed the fisher season the incidental cap- ture of fishers exceeded the legal capture the preced- ing year (V. Banci pers. comm.). The closure of all commercial marten trapping where their range over- laps that of the fisher in Washington and Oregon has been recommended by the Forest Ecosystem Man- agement Assessment Team in a recent EIS (USDA 1994) until the rate of incidental take is considered 63 to be insignificant. Idaho and Montana each provide modest financial incentive for information about in- cidentally captured fishers (B. Giddings, pers. comm.; G. Will, pers. comm.). Where commercial trapping of terrestrial carnivores occurs, the threat exists that fish- ers will be trapped and that their populations could be negatively affected (Powell 1979b). Forest Management The extensive, clearcut logging done during the 1800's and early 1900's, together with trapping, deci- mated fisher populations all over the continent. Be- cause fishers are associated most frequently with rela- tively unfragmented, late-successional forests, recent clearcut logging continues to affect fisher populations today through its profound effects on forest land- scapes. Large nonforested areas are avoided by fish- ers, especially during the winter, and the fact that extensive areas of the Pacific Northwest have been recently clearcut (e.g., Morrison 1988) may be the reason fisher populations have not recovered in some parts of this region (Aubry and Houston 1992). The problem for fishers is not with forest open- ings per se. Fishers evolved in forests where windthrow and fire were common. Small patch cuts, group selection harvests, and small clearcuts can su- perficially resemble both these disturbances in form and in the pattern of succession that follows. Fishers have been reported to use recently clearcut areas during the summer, when the cover formed by ground vegetation and young trees is dense, and, in the East, they also use young, second-growth forests. Presumably, fishers experience habitat loss when tim- ber harvest removes overstory canopy from areas larger and more extensive than natural windthrow and fire would. Provided there are large patches of late-successional conifer habitat nearby, fisher popu- lations should be able tolerate incidents of stand-re- placing disturbances. Small patch cuts interspersed with large, connected, uncut areas should not seri- ously affect fisher populations. In fact, these small- scale disturbances may increase the abundance and availability of some fisher prey. Large clearcuts and numerous, adjacent, small clearcuts of similar age should seriously limit resting and foraging habitat for fishers during the winter. This, in turn, may limit fisher population size. The effect of uneven-aged tim- ber management practices on fisher habitat have not been studied but are likely to have less effect on fisher habitat than even-aged management. Forestry prac- tices aimed at maximizing wood production and minimizing rotation times will probably have detri- mental effects on fisher populations. For many species, including the fisher, much still needs to be known about how natural populations function. Differences in forest habitats between the Pacific States, the Rocky Mountains, and the forest of the Upper Midwest and Northeast are profound enough to prevent simplistic extrapolations about fisher-habitat relationships. We must learn how fish- ers use the forests of the western mountains before we can fully understand the components of these forests that are important to fishers. Conservation Status in the Western United States The primary reason for concern about the fishers in the western mountains of the United States is the utter lack of data on the ecology of the species. Only two intensive, radio-telemetry based habitat studies have been published on fishers, one in northwestern California (Buck et. al. 1983) and the other in Idaho (Jones 1991) (table 4). Two additional studies have been completed at about the same locations in Mon- tana (Heinemeyer 1993; Roy 1991) but both individu- als studied fishers that were introduced from Wis- consin and Minnesota. Inferences from these studies to extant populations elsewhere in the West may be limited. Only two natal dens and one maternal den have been discovered and described in the West (two of the three were in northwestern California). Only about 100 scats and gastrointestinal tracts have been examined to describe food habits, the majority of which may be unrepresentative of native fisher diets because they came from transplanted individuals in Montana (table 4). Thus, the quantity of data on the ecology of fishers in the West is extremely low. A size- able amount of unpublished data exist (noted throughout the text above and in Appendix C) but the quality of this information is hard to verify and thus its usefulness is limited. Neither of the studies of native populations have been replicated within their ecoprovinces and entire ecoprovinces (see Ap- pendix A) are without a single representative study (e.g., Georgia-Puget Basin, Pacific Northwest Coast and Mountains, Sierra Nevada, Columbia Plateau, Northern Rocky Mountain Forest). New research is underway in northern California (Reynolds and Self 1994, unpubl.; Seglund and Golightly 1994, unpubl.; Schmidt et al. 1993, unpubl.) and the southern Sierra 64 Table 4.— The knowledge base for the fisher in the western United States, excluding Alaska, by subject. This includes studies for which the subject was a specific objective of the study; incidental observations are not included. Sample size is number of animals studied, or for food habits, number of scats or gastrointestinal tract contents, unless stated otherwise. Sample sizes for dispersal include only juveniles. Theses and dissertations are not considered separately from reports and publications that report the same data. A total of four studies (*) are represented in this table. Duration Sample Topic, author Location Method (years) size Home range & habitat use •Bucketal. 1994 *Heinemeyer 1993^ * Jones 1991 *Roy 1991' Demography Roy 1991' Food habits Grenfell & Fasenfest 1979^ Jones 1991 Roy 1991' Dispersal Natal dens Roy 1991' Buck etal. 1983* California IVIontana/ldalno^ Idaho Montana^ Montana California Idaho Montana Montana California Telemetry — convex polygon Telemetry — adaptive kernel Telemetry — harmonic mean Telemetry — habit use primarily Mortality and reproduction of transplanted animals Gl tracts Gl tracts + scats Scats Telemetry Incidental to study 1.5 2 4 2 6 9/10^ 10 32 8 25 80 ' Data collected from transplanted individuals. ^ Adaptive kernel home range calculated from Jones' (1991) data included. ^ Same locations as Heinemeyer (1993). " From fishers that died during the course of the study by Buck et al. (1983). ^ No data for western fishers. * Buck et al. (1983) same as Buck et al (1994). Nevada (W. Zielinski, pers. comm.), but a tremen- dous amount of additional research is necessary before a responsible conservation strategy can be assembled. A second reason for concern comes from interpret- ing the results of the two published studies on na- tive populations in the West. In each case, fishers prefer late-successional coniferous forests: through- out the year in California (Buck et al. 1983) and espe- cially in summer in Idaho (Jones 1991). Late-succes- sional forests provide important benefits for fishers, especially resting and denning habitat. The reduc- tion in this habitat and its increasing fragmentation is part of the reason fishers in the Pacific States are considered by many to be threatened with extirpa- tion and why some have petitioned the U.S. Fish and Wildlife Service to list the fisher under the Endan- gered Species Act (Central Sierra Audubon Society et al. 1991). Reintroductions appear not to have augmented populations in western Oregon and recent records of fishers in Washington are uncommon. Since the late 1950's, only one sighting of a fisher has been sub- stantiated on the Olympic Peninsula in Washington, and that was a fisher killed in a trap in 1969. A fisher killed in the 1990-91 trapping season and a fisher trapped and photographed in 1993 in the Cascade Range are the only other substantiated reports (Aubry and Houston 1992; Aubry, unpub. records). Fishers are probably extirpated on the Olympic Pen- insula and are either extirpated or very patchily dis- tributed in meager populations in the rest of west- ern Washington and Oregon. It is our opinion that the precarious status of the fisher population in Washington and Oregon is re- lated to the extensive cutting of late-successional for- ests and the fragmented nature of these forests that still remain. Fishers appear sensitive to loss of con- tiguous, late-successional Douglas fir forests in the Pacific Coast Ranges, west slope of the Cascade Range, and west slope of the Sierra Nevada (Aubry and Houston 1992; Gibilisco 1994; Raphael 1984, 1988; Rosenberg and Raphael 1986), but their habitat asso- ciations in more xeric forest types in the Pacific States (e.g., east slope of the Cascades, ponderosa pine for- ests in the Sierra Nevada) are unknown. We suspect that in Douglas fir forests, late-seral conditions pro- vide the physical structure that allows fishers to hunt 65 successfully and to find suitable resting and denning sites. Young, second-growth forests may be unable to provide these requirements. Establishing the reasons for the precarious status of the fisher populations in the Pacific Northwest may not be as important in the short term as making people aware of the status and providing federal pro- tection for the populations. That the populations appear dangerously low should be sufficient to gen- erate protection; discussions and research into the reasons should occur after protection. In our opin- ion, protection by the states of Washington, Oregon, and California has not been sufficient to improve population status. The status of fishers in the northern and central Sierra Nevada is unknown but the absence of recent observations suggests they are declining or barely holding steady (Gibilisco 1994). Fisher populations in the northern Rocky Mountains of the United States do not appear to be in as critical condition as those in the Pacific Northwest. Although fishers have not recolonized all of their former range in this region, some healthy fisher populations exist. Fishers were never found much farther south than the Yellowstone region. If trapping seasons are regulated carefully in Montana to prevent overtrapping, fisher populations may slowly expand in Montana and Idaho. 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The cougar is found in both temperate and tropical forests from the mountains of southern British Columbia to the southern tip of South America, whereas the bobcat and lynx are restricted to the temperate zone of North America. Bobcats are common throughout a variety of habitats in the con- terminous United States, southernmost Canada, and northern Mexico. The lynx, in contrast, occurs pri- marily in the boreal forests of Alaska and Canada, but its range extends south into the northern por- tions of the western mountains, where environmen- tal conditions at high elevations support boreal forest habitats similar to those found in northern regions. The bobcat and lynx are both short-tailed cats, but the bobcat is smaller than the lynx and has relatively shorter legs and smaller paws. The lynx's short tail is completely tipped with black, whereas the bobcat's tail is generally longer and is barred with black only on the upper surface (Nowak and Paradiso 1983). The bobcat looks much like a house cat {Felis catus) in body form but is about two or three times larger. The lynx differs in body proportions, however, having relatively long legs and hind legs that are longer than the forelegs, giving it a stooped appearance (Quinn and Parker 1987). The winter pelage of the lynx is dense and has a grizzled appearance with grayish-brown mixed with buff or pale brown fur on the back, and grayish- white or buff -white fur on the belly, legs, and feet. Its sum- mer pelage is more reddish to gray-brown. Male lynx are slightly larger than females, with total length averaging 85 cm compared to 82 cm, and weight av- eraging 10 kg for males and 8.5 kg for females (Quinn and Parker 1987). Both sexes have prominent ear tufts and a flared facial ruff. The paws of the lynx have twice the surface area of those of the bobcat (Quinn and Parker 1987). The lynx's long legs and broad paws enable it to negotiate the deep snows of the boreal forests and effectively hunt its principal prey, the snowshoe hare {Lepus americanus). The bobcat, lacking these features, is largely restricted to habi- tats where deep snows do not accumulate (Koehler and Hornocker 1991). Despite physiological and be- havioral differences that may permit lynx and bob- cats to exploit different niches (Parker et al. 1983), lynx apparently do not compete well with bobcats (Parker et al. 1983; Turbak 1991). Thus, habitat alter- ations that favor a northward range expansion by bobcats may not bode well for lynx, particularly in suboptimal habitats. The distribution and abundance of the lynx ap- pears to be tied to that of the snowshoe hare. Both species are confined to northern forest environments (Hall 1981). Hares seek dense conifer thickets to feed on woody seedlings and saplings and to escape predators and extreme cold; lynx frequent these habi- tats in search of prey. When foraging, lynx select for- ested habitats where hares are plentiful and use this cover to stalk or wait for hares to appear. From the forested peninsulas of western Alaska to the eastern islands of Canada and in the mountains of the west- ern United States, hares comprise 35-97% of the lynx diet (table 1). Although snowshoe hares are the primary food for lynx throughout its range, they also feed on mice, squirrels, grouse, and ptarmigan, especially dur- ing the summer months (McCord and Cardoza 1982). Hares not only determine where lynx are found but also influence how many lynx may occupy an area. This is dramatically illustrated in Alaska and central Canada, where hare populations cycle in abundance at varying amplitudes, with population 74 Table 1.— Percent occurrence of prey items in ttie winter diet of lynx deternnined from anolysis of scats (ST) or digestive tracts (DT). Sample size in parenthieses. Percent of sample Season, location Hares Tree squirrels Mice Ungulates Grouse Winter diets Alaska' (ST= 161) 64 10 9 5 7 Alberta^ (DT = 879) 35-90 9-12 4-28 22-3 2-6 (ST = 260) 61 5 10 3 4 Alberta & NWT^ (DT = 52) 79 2 10 6 10 Newfoundland'' (ST.DT= 152) 85 5 >13 Nova Scotia^ (DT = 75) 97 1 3 5 3 (ST = 55) 93 7 5 4 Summer diets Alaska' (ST = 42) 38 28 15 7 Alberta^ (ST = 38) 71 2 87 5 5 Alberta & NWT^ (DT = 23) 52 9 ZZ NevA/foundland" (ST,DT = 92) 65 30 >3 Nova Scotia^ (ST = 441) 70 4 4 9 1 Annual diets Washington'^ (ST = 29) 79 24 3 3 ' staples and Bailey 1993, unpubl. 2 Brand and Keith 1979: Brand et al. 1976. ^ van Zyll de Jong 1966. ^Saunders 1963a. ^ Parker etal. 1983. 'Koehler 1990. densities changing 2-200 fold within a 5-year period. As this phenomenon is repeated, periods of hare scar- city occur approximately every 10 years (Brand and Keith 1979). In areas where snowshoe hare popula- tions exhibit this cycle, lynx also undergo dramatic population fluctuations. As part of a predator-prey oscillation, lynx populations lag several years behind hares, going from near extinction to densities of 10 to 20 lynx /1 00 km^ during their population peaks (Bailey et al. 1986; Brand and Keith 1979; Parker et al. 1983). At the southern limits of its distribution, however, snowshoe hare populations do not undergo dramatic cycles due apparently to the presence of predators and competitors that do not occur in north- ern regions and to the patchiness of suitable habitat (Dolbeer and Clark 1975; Wolff 1980, 1982). Conse- quently, lynx populations appear also not to cycle in abundance at southern latitudes (Koehler 1990). In general, lynx and snowshoe hares in the western mountains of the United States exhibit life history characteristics similar to those occurring during hare population lows in the northern boreal forests (Brittell et al. 1989, unpubl; Koehler 1990; Dolbeer and Clark 1975; Wolff 1980, 1982). This difference in the popu- lation dynamics of lynx and snowshoe hares in the southern portions of their ranges has strong impli- cations for the management and conservation of lynx in the western mountains. Several excellent literature reviews have recently been produced that describe lynx and snowshoe hare 75 biology in northern areas where populations are cy- clic (Butts 1992, unpubL; Washington Dept. of Wild- life 1993, unpubL; Weaver 1993, unpubl.). The em- phasis of this chapter, however, will be on the popu- lation dynamics and habitat relationships of lynx in either the western mountains or in northern boreal forests during times of low hare densities. This in- formation provides the most meaningful conceptual framework for management and conservation of lynx in the western mountains. During periods of hare and lynx abundance in northern regions, when competition for prey is keen and available territories are occupied or, during pe- riods of prey scarcity after hare numbers have crashed, lynx may undergo dramatic movements in search of adequate prey (Poole 1993, unpubl.). Dur- ing these times, lynx have been known to travel as far as 1,100 km (Mech 1980; Poole 1993, unpubl.; Slough and Mowat 1993, unpubl.) and are found in atypical habitats, such as agricultural areas or geo- graphic areas far south of their normal range (Mech 1980). Although speculative, this process may be important for the persistence of lynx populations in marginally suitable habitats at the periphery of their range. In addition, these extensive movements pre- sumably facilitate gene flow among populations, which may explain why the lynx appears to be ge- netically homogeneous throughout its range; all lynx populations, with the exception of those occurring in insular Newfoundland, are classified as a single subspecies (Hall 1981). Current Management Status As with most felids of the world, except for those that are classified as threatened or endangered with extinction, the lynx is listed on Appendix II of the Convention on International Trade of Endangered Species. This listing requires the exporting country to provide evidence that trade will not threaten or endanger the species and that items of trade, such as pelts, be regulated and monitored. Lynx populations in Alaska and most of Canada are generally considered stable (table 2), although few reliable population estimates have been made (Anonymous 1986, unpubl; Quinn and Parker 1987). Large populations are found in southern Quebec, northern British Columbia, Yukon, and Northwest Territories (lUCN, in press). In Canada, lynx are con- sidered endangered only in New Brunswick; how- ever, they are believed to have been extirpated from Table 2.— Current management status of lynx In states and prov- inces of Northi America and lands of federal jurisdiction within ttie United States (Anonymous 1986, unpubl.; Butts 1992, unpubl.; lUCN, In press; Washilngton Dept. of Wildlife 1993, unpubl.). Status or Seasons or Jijfi^Hif^tion nuiiiiriy ui iiuppiriy Fur animal permit required, harvest Mlllll Z, bfcJUbOl 1 1 lO 4.5 months. P rv /H r\ o r o Ci ivJvJI lyt^it^vj Pi irhonr^r ocUoOii, iiuriiiiiy or trapping permit required. IVIvJII It? P r + o r 1 U 1 1 1 Vil^i ll^kJI 1 r 1 w 1 ^o 1 vz^ Minnesota Furbearer Closed season since K ^ r*» + iVICI \ \\J\ lU Pi irh^o/^ror r 1 c 1 1 Npw York Prntppfprl North Dokoto 1 'I \^ till \Jt T\ V_/ 1 Furhpnrpr 1 VO 1 . t?y LJi 1 VC7kJ} 1 It? Ofw't^V^lt^O \-^lvJot?LJ ot;^oL/i 1. ith Dnkntn n n PI rn o 1 nL^I ly ^I I 1^ IVIwI IIIV_^l O[^t?0lt?o Utah Thrpntpnprl \/cirrri(^r~\t V 1 1 \\J\ II r 1 W 1 1 t7V-J Wn^hinntnn VVViJOl III I^IWI 1 Thrpntpnprl V V lO^ W 1 lOI 1 1 Fnrlnnnprpri i_i i^^t ly \A/\/orninn V V y '^i iiii ly r I 1 C^v^ 1 t?\J AAlL/wl 1 \J nvji vt^oi ot^^-JoL^i lo. Rriti<^h Oolumhin Hnrvpst ^pn^^nn^ 1 \\Jl \ 1 1 Wt?Ol Torrit(^rioc 1 t?l 1 1 1 vJI It^o l-l/^r\/oct Ci^nc/^riC ntjivt^oi ot7^Joijno. 1 Nt^W Dl ui low 1 OK P n /H r\ o r o CI iVwiLJi iyt?it7vj Nova Scotia Extirpated on peninsula Closed since 1980. Ontario Harvest seasons. Prince Edward Island Endangered Quebec Harvest seasons. Saskatchewan Harvest seasons. Yukon Harvest seasons. USDA Forest Service Sensitive Region 1,2,4,6. Prince Edward Island and mainland Nova Scotia. Lynx are considerably more rare in the conterminous United States. The largest populations in the United States outside of Alaska occur in the northern por- tions of Washington and Montana. A petition was submitted to the U.S. Fish and Wild- Hfe Service (USFWS) in August 1991 to list the lynx as endangered in the northern Cascade Range of Washington. In February 1992, the USFWS denied the petition because substantial scientific or commer- 76 cial evidence was not available indicating that the lynx population in the north Cascades should be listed as endangered (Federal Register 1992). In April 1992, the USFWS agreed to reevaluate its 90-day find- ing on the petition in light of new information sub- mitted by the petitioners. The USFWS found that there was no substantial new evidence indicating that the requested action was warranted and concluded that the north Cascades lynx population is not listable because it is not isolated from lynx populations else- where (Federal Register 1993). The USFWS also found, however, that a status review should be con- ducted throughout lynx range in the conterminous United States; this review is currently underway. The lynx was classified as endangered in Colorado in 1973 (Halfpenny and Miller 1980, unpubl.) and Washington listed the lynx as threatened in October 1993 (Washington Dept. of WildHfe 1993, unpubl). The lynx is protected or is considered to be a species of special concern in Wyoming and Utah, but it is still trapped during a restricted season in Idaho and Montana (table 2). The USD A Forest Service, which administers the majority of lands where lynx occur in the conterminous United States, considers the lynx to be a sensitive species in all Regions containing lynx populations (Regions 1, 2, 4, and 6; see Appendix C). This designation refers to species for which popula- tion viability is of concern as evidenced by signifi- cant current or predicted downward trends in popula- tion numbers, population density, or habitat capability. Lynx are relatively common throughout forested areas of Alaska and most of Canada, although inten- sive trapping in the past has eliminated or tempo- rarily reduced numbers in localized areas within that region (Bailey et al. 1986; Todd 1985). The conserva- tion of lynx populations is of greatest concern in the western mountains of the conterminous United States at the southern periphery of the species' range. Be- cause recruitment is low in this region and many lynx populations, especially those in Utah, Wyoming, and Colorado, are geographically isolated, trapping and forest management activities may pose significant threats to the persistence of these populations. DISTRIBUTION, TAXONOMY, AND ZOOGEOGRAPHY Distribution in North America Lynx occupy regions in North America of arctic or boreal influence. They are restricted to forested habi- tats within this region and are found from western Alaska to the eastern edge of Newfoundland. The northern boundary of this range coincides with the northern extension of the boreal forests; lynx are ab- sent north of the Ungava Peninsula in Quebec and in the northern regions of the Northwest Territories (Anonymous 1986, unpubl.). The lynx's historic range also included the northern portions of the contermi- nous United States in the Cascade Range of Wash- ington and Oregon, south in the Rocky Mountains to Utah and Colorado, and east along the Canadian border to the Lake States (McCord and Cardoza 1982; Quinn and Parker 1987). Except for the southern boundary of its range, the distribution of lynx in North America probably has not changed much during historical times (Quinn and Parker 1987). Destruction of forests for timber and incursions of agriculture and settlements, how- ever, may have displaced lynx occurring in the Lake States (Jackson 1961) and southern regions of Manitoba to Alberta (Anonymous 1986, unpubl.; (^uinn and Parker 1987). Lynx have probably been extirpated from Prince Edward Island and the mainland of Nova Scotia (Anonymous 1986, unpubl.), and their range appears to have retracted on Cape Breton Island after the introduction of bobcats (Parker et al. 1983). Taxonomy The taxonomic status of the lynx is an issue of con- troversy among authorities. The debate concerns both the generic status of lynx throughout the world and the specific status of lynx in North America. It is un- clear whether lynx throughout the world should be classified within a separate genus Lynx, or whether they should be placed within the more inclusive ge- nus Felis. In either case, there is also confusion about whether the Canadian lynx should be considered a separate species from the Eurasian lynx. Thus, some authorities (McCord and Cardoza 1982; Tumlinson 1987) consider the Canadian lynx to belong to the Holarctic species Felis lynx. Others (Jones et al. 1992) agree that lynx represent a Holarctic species but con- sider lynx to be generically distinct from other cats and place the Canadian lynx within the species Lynx lynx. Others (Hall 1981; Wozencraft 1989, 1993), how- ever, believe that Eurasian and Canadian lynx repre- sent distinct species and place the Canadian lynx in the species Lynx canadensis. Lynx and bobcat are believed to have evolved from Eurasian lynx that immigrated to North America 77 from Asia via the Bering land bridge during the Pleis- tocene (Quinn and Parker 1987; Tumlinson 1987). It is speculated that the bobcat and the Canadian lynx represent the descendants of two separate coloniza- tions of North America by the Eurasian lynx. The first immigrants became established in the southern por- tions of the continent about 20,000 years ago, when glaciers covered the northern regions. These popu- lations, that were isolated in ice-free areas in the southern portions of the continent, evolved into the bobcat. Some time later, the North American conti- nent was invaded by Eurasian lynx a second time. These populations established themselves in north- ern boreal forests in areas that were occupied previ- ously by glaciers, and evolved into the Canadian lynx (Quinn and Parker 1987). Zoogeography of Lynx in the Western Mountains The boreal forests of Canada and Alaska are the primary habitat of lynx in North America. Popula- tions occurring in the western mountains of the con- terminous United States occupy peninsular exten- sions of this distribution. Lynx distribution at south- ern latitudes represents the occupation of margin- ally suitable habitat that decreases in quality and availability as one moves southward. Ecoprovinces where lynx populations occur in the western moun- tains include the Thompson-Okanogan Highlands of northeastern Washington, the Shining Mountains of northern Idaho and northwestern Montana, the Northern Rocky Mountain Forest of southwestern Montana and northwestern Wyoming, and the Colo- rado Rocky Mountains of west-central Colorado (see Appendices A and B). A brief review of the histori- cal zoogeography and current population status and ecology of lynx and snowshoe hares in the western mountains will illustrate the marginal nature of bo- real habitats in that region. Lynx have apparently never occupied the Sierra Nevada of California in historic times (Grinnell et al. 1937; Ingles 1965). Although the lynx has been found in Oregon, historical records indicate that it has al- ways been rare; only a few specimen records are known from high elevations of the Cascade Range and the Wallowa Mountains in the northeast (Bailey 1936). A lynx shot in northeastern Oregon in 1964 was the first record of a lynx being taken in Oregon since 1935 (Coggins 1969). Oregon clearly represents the southern margin of suitable lynx habitat along the Pacific Coast. Lynx are now considered to be ex- tirpated from the state (Ingles 1965; McCord and Cardoza 1982), although several sightings have been reported recently (Zielinski, pers. comm.). Appar- ently, populations have always been so low in Or- egon that they were unable to persist with the onset of human settlement of that region. The lynx still occurs in Washington, but its range has retracted northward. Taylor and Shaw (1927) reported the lynx to be a component of the fauna occurring in the higher elevations of Mount Rainier National Park in the central Washington Cascades, and Dalquest (1948) showed its range extending south in the Cas- cades to near the Oregon border on Mount Adams, and in the Blue Mountains in the southeastern cor- ner of the state; there are no historic records of lynx in either the Olympic Mountains or Coast Range of Washington. A current description of lynx distribu- tion in Washington (Washington Dept. of Wildlife 1993, unpubl.) indicates that lynx are now restricted to the northeastern Cascade Range and several iso- lated areas in the Okanogan Highlands of northeast- ern Washington. The Okanogan population was stud- ied with radiotelemetry in the 1980's (Brittell et al. 1989, unpubl.; Koehler 1990) and most of the infor- mation available on the ecology, population dynam- ics, and management of lynx in the western moun- tains of the United States comes from these studies. This pattern of decreasing habitat suitability with decreasing latitude is also evident in the Rocky Mountains. Lynx populations are also present in northern Idaho and western Montana. Historical records are relatively numerous in the panhandle of Idaho; Davis (1939) reported lynx occurring in the mountainous regions north and east of the Snake River in Idaho, and Rust (1946) claimed that they were fairly well distributed in wooded areas of the northern counties with 25 or 30 lynx being taken an- nually by trappers and hunters. Historical reports from western Montana also indicate that the lynx was fairly numerous in recent times. Bailey (1918) lists the lynx as being more or less common throughout Glacier National Park, and the Montana Fish and Game reports that from 1959-1967, a total of 990 lynx were taken by trappers statewide (Hoffman et al. 1969). According to Hoffman et al. (1969), lynx are most common in the northwestern areas of the state, and they decrease in abundance south and east. Populations in western Montana are large enough for scientific study; two radiotelemetry studies of 78 lynx movements in western Montana were con- ducted in the early 1980's (Brainerd 1985; Smith 1984). Although early trappers had apparently reported taking lynx from northern Nevada (Bailey 1936), Hall (1946) includes the lynx on a list of hypothetical spe- cies for Nevada based on a lack of museum speci- mens. Further investigation by Schantz (1947), how- ever, revealed the existence of a single specimen of lynx taken from north-central Nevada in 1916. Records of lynx are scarce in Wyoming, Utah, and Colorado. A review of existing records of lynx in Wyoming by Long (1965) shows that 15 museum specimens exist, and all are from the northwestern corner of the state. According to Long (1965) the lynx was "confined to high, inaccessible (to man) ranges of northwestern Wyoming, if not extirpated at the time of this writing." Later authors (Clark and Stromberg 1987; Clark et al. 1989) agree that the lynx remains extremely rare in Wyoming. Reports by trappers in 1915 and 1916 (Barnes 1927) suggest that lynx were relatively common in Utah at that time; however, Durrant (1952) questions the va- lidity of these reports. He believes that many of these records are actually of bobcats because the feet and tail are often removed from pelts, and also because large bobcats are commonly referred to as lynx cats in the fur trade. Durrant (1952) reports that only two lynx from Utah exist in museum collections, and he is of the opinion that "if L. c. canadensis occurs at all in Utah at present, there are only a few animals in the Uinta Mountains" in north-central Utah. Al- though seven lynx specimens were collected from the Uinta Mountains in Utah from 1957-1972, since that time only sightings and tracks have been reported (McKay 1991, unpubl.). Nine museum specimens of lynx exist from eight counties in Colorado (Halfpenny and Miller 1980, unpubl.), but it is generally agreed that lynx were never numerous in the state and are presently ex- tremely rare (Lechleitner 1969; Halfpenny and Miller j 1980, unpubl.). Four of these specimens were col- lected from 1969-1972, and all were from a relatively small area in the west-central portion of the state (Halfpenny and Miller 1980, unpubl.). Records from this state represent the southernmost extension of current lynx distribution in North America. Existing records clearly show that lynx are rare at j the southernmost extensions of its range in Wyoming, Utah, and Colorado, both historically and at present, and that any populations that occur in this area are disjunct and isolated in distribution. It seems doubt- ful, therefore, that gene flow is occurring among these populations. Because boreal habitat is found at higher and higher elevations as one moves southward in the western mountains, suitable habitat for lynx even- tually becomes scattered on isolated mountain peaks (Findley and Anderson 1956). Museum records of lynx in Wyoming, Utah, and Colorado overlap pre- cisely with the range of boreal forest habitat depicted by Findley and Anderson (1956). Given the rarity of records and the dispersal capabilities of lynx, it is possible that existing records represent short-term residents or individuals wandering and dispersing, rather than reproductively stable populations; viable lynx populations may never have occurred in his- toric times in the southern Rocky Mountains. Thus, lynx conservation efforts may best be directed at populations occurring in northeastern Washington, northern Idaho, and western Montana. Because they are contiguous with lynx populations that undergo periodic dramatic increases in numbers, populations near the Canadian border may have benefitted from periodic incursions of lynx as popu- lations peaked in northern latitudes (Hoffman et al. 1969; Mech 1980; Quinn and Parker 1987). For ex- ample, there were dramatic increases in lynx harvests in western Montana and the northern Great Plains in 1962-1963 and 1971-1972 (Adams 1963; Hoffman et al. 1969; Mech 1973). However, after a population irruption of lynx in Minnesota following a cyclic high in Canada in 1972, trappers reported capturing 215 lynx in 1972, 691 in 1973, 88 in 1974, and 0 in 1975 (Mech 1980). Mech (1980) also showed that immigrat- ing lynx occupied very large home ranges, exhibited little reproductive productivity, and were susceptible to human-caused mortality. Thus, immigration of lynx into marginal habitats during population highs in the north may ultimately have little effect on their population persistence at lower latitudes. Management Considerations 1 . Because of the peninsular and disjunct distribu- tion of suitable lynx habitat in the western moun- tains of the conterminous United States, populations in that region are likely to be of greatest conserva- tion concern. 2. Both historical and recent lynx records are scarce from the western mountains, which makes identify- ing range reductions and determining the historical distribution of reproductively stable populations in that region difficult, if not impossible. 79 Research Needs 1 . Reliable information on the current distribution and abundance of lynx populations throughout the western United States is urgently needed. POPULATION ECOLOGY Population Dynamics of Snowshoe Hares and Lynx in the Western Mountains The 10-year cycle of dramatic increases in popula- tion densities for both snowshoe hares and lynx in the boreal forests of Canada and Alaska is well- known (Keith 1963; Brand and Keith 1979; Brand et al. 1976; Nellis et al. 1972; and others). Although this phenomenon is of critical importance for the conser- vation and management of lynx populations in north- ern boreal forests, neither lynx (Brittell et al. 1989, unpubl.; Koehler 1990) nor snowshoe hare (Chitty 1950; Dolbeer and Clark 1975; Wolff 1980; Koehler 1990) populations in the western mountains of the United States exhibit such cycles. It appears, rather, that both species occur in that region at relatively stable densities comparable to those occurring during population lows in the northern boreal forests (Brittell et al. 1989, unpubl; Koehler 1990; Wolff 1980, 1982). A compelling hypothesis has recently been pro- posed by Wolff (1982) to explain this latitudinal varia- tion in the population dynamics of hares and lynx. Wolff speculates that the presence of additional predators and competitors of hares at lower latitudes largely accounts for this pattern. Apparently, during hare population lows in Alaska, hares occupy less than 10% of suitable hare habitat, which appears to be comparable to the normal dispersion of hares in the western mountains. As population density in- creases in northern regions, hares begin dispersing into suboptimal and marginal habitats. When preda- tor populations have crashed and competitors are few, hares moving into such habitats are able to es- tablish themselves and reproduce, and the popula- tion slowly builds again in numbers. In contrast, hares dispersing into low-quality habitat in Colorado suffer increased mortality from predation and are not able to establish themselves in such habitats (Dolbeer and Clark 1975). The reproductive rates of hares in Colorado did not differ significantly from those in northern regions, indicating that limitations in the intrinsic rate of increase do not explain the latitudi- nal gradient in population cycles (Dolbeer and Clark 1975). Rather, the apparent lack of hare population cycles in the western mountains is best explained as resulting from the presence of more stable popula- tions of predators, lower-quality suboptimal habitats, and, possibly, from the presence of fewer competi- tors at southern latitudes. In addition, a regional mosaic of early successional habitats created by fre- I quent large-scale wildfires in northern forest ecosys- tems may contribute to higher quality lynx and hare habitats in that region (T. Bailey, pers. comm.). The major predators of hares in the north are the lynx, goshawk (Accipiter gentilis), red fox {Vulpes vulpes), and great-horned owl {Bubo virginianus) . In that region, lynx, goshawk, and great-horned owl are obligate, migratory predators that all exhibit a de- | layed density-dependent cycle with snowshoe hares, j resulting in a relaxation of predation pressure after snowshoe hare populations have crashed. In contrast, i the major predators of snowshoe hares in the west- i ern mountains are the coyote (Canis latrans), bobcat, red fox, and several species of hawks and owls. These predators are facultative and resident, and their | populations do not cycle in response to hare num- bers. The presence of predators at stable densities prevents snowshoe hares from becoming established ; in suboptimal habitats. Boreal forest habitat in north- j ern regions tends to be relatively continuous in dis- tribution. The insular nature of preferred habitats in the south, however, whereby adjacent habitats can ! be of very low quality, may hinder the occupation of suboptimal habitats by snowshoe hares. No other species of leporid occupies the northern boreal for- | ests; thus, the presence of potential competitors such as jackrabbits (Lepus spp.) and cottontails (Sylvilagus spp.) in the western mountains may also limit snow- shoe hare populations. Reproductive Biology Lynx have a high potential for population growth but, as with other life history parameters, recruitment is influenced by the abundance of its principal prey, the snowshoe hare (Bailey et al. 1986; Brand and Keith 1979; Brand et al. 1976; Nellis et al. 1972; O'Conner 1986; Parker et al. 1983; Slough and Mowat 1993, unpubl.). Recruitment is high during periods of hare abundance primarily because of increased kitten sur- vival. However, periods of high hare numbers are also accompanied by increased reproductive rates for yearlings and increased litter sizes among females in all age classes (Brand and Keith 1979; Brand et al. 1976; O'Conner 1986; Parker et al. 1983). 80 From examination of necropsied carcasses from Alaska, O'Conner (1986) found lynx to ovulate from late March to early April and give birth in late May after a gestation period of 60-65 days. This breeding i| schedule has also been reported for Ontario (Quinn ' and Thompson 1987), Alberta (NelHs et al. 1972) and Newfoundland (Saunders 1964). Kittens observed in north-central Washington in early July (Koehler 1990, unpubl. data) appeared to have been born in late May or early June, suggesting that conception occurs in I March and April at southern latitudes as well. In Alaska, the mean number of corpora lutea and pla- cental scars, the age of first breeding, the proportion of females breeding, the proportion of kittens breed- ing, and the percentage of juveniles present in the t population all reached highest levels the first spring after hare numbers peaked (O'Conner 1986). This time lag may differ in other regions depending on the density of predators other than l3mx, weather fac- tors, and availability of alternate prey (O'Conner 1986). Brand et al. (1976) found that females were capable of becoming pregnant at 10 months of age under II optimal conditions, based on the presence of corpora lutea, but Parker et al. (1983) concluded that most females reach reproductive maturity at 22 months. Age of first ovulation can be influenced by hare abun- dance, however; 61-99% of lynx ovulate as kittens during periods of hare abundance compared to only 10-49% as hare numbers decrease (O'Conner 1986, van Zyll de Jong 1963, Brand et al. 1976, Brand and Keith 1979). Quinn and Thompson (1987) found that 96% of yearlings, 99% of 2-year-olds, and 100% of females >3 years old ovulated during a period of hare abundance in Ontario. O'Conner (1986) also demon- strated a difference in ovulation rates between peri- ods of hare scarcity and abundance. During times of hare abundance, counts of corpora lutea averaged 6.2 ± 0.3 (95% CI) to 6.4 ±1.1 for yearlings (indicat- ing they ovulated as kittens) and 16.5 ± 1.3 to 15.4 ± 2.3 for adults, compared to periods of hare scarcity when counts were 0.5 ± 0.7 for yearlings and 8.6 ± 1.3 for adults. Counts of placental scars have been used to esti- mate pregnancy rates and in utero litter sizes, al- though such counts may not accurately reflect actual I litter size because some implanted embryos may not survive (Quinn and Thompson 1987). Pregnancy I rates range from 33-79% for yearlings and 73-92% for adults during periods of hare abundance, com- pared to rates of only 0-10% for yearlings and 33- 64% for adult females when hares were scarce (Brand and Keith 1979; O'Conner 1986; Quinn and Thomp- son 1987). During a period of hare abundance, Quinn and Thompson (1987) found that although 96% of yearlings ovulated, only 33% became pregnant, whereas 80% of 2-year-olds and 92% of females >3 years old became pregnant. Brainerd (1985) exam- ined 20 female carcasses from western Montana and found pregnancy rates of 44.4% for juveniles and 100% for adults. Among lynx that had colonized ar- eas of low prey density in Minnesota, only 1 of 14 live-captured females showed signs of nursing and only 2 of 22 female carcasses examined showed evi- dence of implantation (Mech 1980). The number of placental scars averaged 3.5-3.9 for yearlings and 4.4- 4.8 for adults during periods of hare abundance, which decreased significantly to 0.2 for yearlings and 1.4-3.4 for adults when hares were scarce (Brand and Keith 1979; O'Conner 1986; Parker et al. 1983; Quinn and Thompson 1987). Average litter size (based on placental scars) in western Montana was 2.75, with a range of 1-5; litter size for yearlings was 1.75 and for adults, 3.25 (Brainerd 1985). During hare population declines, there is increased kitten mortality prior to winter. Brand et al. (1976) found no kittens present on their Alberta study area during a low in hare numbers. Kitten production and survival in north-central Washington during 5 1/2 years of a 7-year period (1980-1983, 1985-1987) was comparable to a 5-year period of low productivity measured at northern latitudes when hares were scarce (Brittell et al. 1989, unpubl.; Koehler 1990; Brand et al. 1976). In Alberta, recruitment of kittens to the winter population decreased dramatically 2 years after the peak, and was near zero for 3-4 years during peri- ods of hare scarcity (Brand and Keith 1979). No lit- ters were produced during 5 winters when hare den- sities were lower than 1.4 hares /ha, and mean litter size increased from 1.3-3.5 as hare density increased from 1.8-5 hares/ha (Brand et al. 1976). In north-cen- tral Washington where hare numbers were believed to be low, Koehler (1990) found only 1 kitten surviv- ing to the winter from 8 kittens present among 3 lit- ters in July, indicating that kitten mortality is high during the snow-free season. A disparity in the ratio of females with corpora lutea compared to those ob- served nursing from August to October, and the few kittens present in fall harvest figures, led Nellis et al. (1972) and Parker et al. (1983) to speculate that sev- eral factors result in lower reproductive rates during periods of hare scarcity, including preimplantation 81 losses, intrauterine losses, and mortality of kittens during summer. Mortality As with reproductive parameters, mortality is also influenced by the relative abundance of hares. Al- though data are scarce, natural mortality rates for adult lynx average < 27% per year (Koehler 1990; Slough and Mowat 1993, unpubl). Bailey et al. (1986) observed no mortality from predation or disease be- tween 1977 and 1984 on their study area in Alaska. In the Yukon, Ward and Krebs (1985) found only 1 of 11 radio-collared animals dying from natural causes. Brand and Keith (1979) calculated natural mortality rates from May to November in Alberta of 34—68% during a snow- shoe hare decline. In the Northwest Territories, annual mortality for radio-collared lynx increased from 0.10- 0.79 as hares declined (Poole 1993, unpubl.). Although starvation appears to be the most significant cause of natural mortality, predation also occurs (Koehler 1990; Koehler et al. 1979; Poole 1993, unpubl.). During periods of decreasing hare numbers, mor- tality rates for kittens may be three times that for adults (Brand and Keith 1979). The cause of postpar- tum mortality of kittens is most likely related to star- vation, as females are more likely to feed themselves first (Brand and Keith 1979). Thus, it appears there may be a minimum density of hares at which females are no longer able to successfully rear kittens (Nellis et al. 1972). Koehler (1990) observed a kitten mortal- ity rate of 88% during summer-fall seasons for 8 kit- tens from 3 litters in Washington, which is similar to mortality rates of 65-95% for kittens in Alberta dur- ing a 3-year period of hare scarcity (Brand and Keith 1979). Mortality for kittens of juvenile females is higher (80-100%) than that for kittens of older females (30- 95%), indicating that juveniles contribute little to recruit- ment (Slough and Mowat 1993, unpubl.). Trapping can be a significant source of mortality for lynx (Bailey et al 1986; Carbyn and Patriquin 1983; Mech 1980; Nellis et al. 1972; Parker et al. 1983; Ward and Krebs 1985). During a period of high recruitment in Ontario, Quinn and Thompson (1987) estimated overall trap mortality for lynx at 38%. Where exploi- tation is intense and recruitment is low, trapping can significantly depress lynx populations. In the inten- sively trapped Kenai National Wildlife Refuge in Alaska, Bailey et al. (1986) found that trapping ac- counted for 44-86% of annual mortality and esti- mated that trappers may have removed as much as 80% of the lynx population in their study area. Parker et al. (1983) estimated that trappers removed 65% of their study population in Nova Scotia. Among 14 radio-collared animals in Minnesota, at least 7 were killed by humans (Mech 1980), and all 5 study ani- mals in Manitoba and 8 of 11 in the Yukon were taken by trappers (Carbyn and Patriquin 1983; Ward and Krebs 1985). On the Kenai Peninsula, juveniles were 5 times more vulnerable to trapping than adults, a phenomenon that may be associated with family co- hesiveness, since several juvenile siblings can easily be trapped from a small area (Bailey et al. 1986). Trapping females that are accompanied by kittens often results in the death of those kittens (Bailey et al. 1986; Carbyn and Patriquin 1983; Parker et al. 1983). Bailey et al. (1986) reported that 2 of 3 kittens starved to death after their mothers were trapped. Apparently kittens are unable to obtain sufficient prey by themselves during the winter (Bailey et al. 1986) . Yearlings also appear to be dependent upon their mothers for survival. Parker et al. (1983) ob- served an increase in numbers of yearlings trapped as the harvest season progressed, presumably be- cause more yearlings were orphaned. In addition, kittens of yearling females have higher mortality rates (80-100%) than kittens from adult females (30- 95%) (Slough and Mowat 1993, unpubl.). Emigrating or nomadic lynx can suffer high trap- ping mortality In the Yukon, during a period of low hare numbers. Ward and Krebs (1985) reported that all radio-collared lynx that emigrated from their study area were subsequently trapped. Slough and Mowat (1993, unpubl.) found that 10-20% of lynx that emigrated from or that occupied areas peripheral to their untrapped study area were harvested by trappers. Fur harvest returns for lynx also indicate a differential rate of mortality among the sexes, whereby males are more vulnerable than females to trapping mortality (Mech 1980; Parker et al. 1983; Quinn and Thompson 1987) , presumably because of their greater mobility and larger home ranges. This pattern has been demonstrated for other furbearers, as well (Buskirk and Lindstedt 1989). Assuming an even sex ratio at birth, Quinn and Thompson (1987) showed from fur harvest records that the annual rate of trap mortality for males was 0.46 ± 0.26 (90% CI) compared to 0.28 ± 0.17 for females, and that increased male vulnerability begins at the age of 1 .5 years. Bailey et al. (1 986) also found males to be twice i as vulnerable to trap mortality as females. ; Trapping mortality appears to be additive, since most natural mortality occurs during summer 82 months prior to the winter trapping season. In their Alberta study area, where lynx trapping did not oc- cur. Brand and Keith (1979) observ^ed no change in the population over the winter, although populations declined elsewhere where trapping occurred. The importance of trapping as a source of mortality is correlated to the price of lynx furs (Todd 1985). Brand and Keith (1979)' estimated that only 107c of the fall population was trapped when pelt prices averaged $44 /pelt, whereas 17-29% were trapped when prices increased to $101 /pelt. Age and Sex Structure Fur harvest data can provide an indication of the direction and amplitude of population changes (O'Conner 1986), although caution must be applied when using these data to interpret population pa- rameters. For example, Brand and Keith (1979) found only a 4.3-fold increase in lynx numbers on their Alberta study area when harvest data for the Prov- ince indicated a 20-fold increase. Caution should also be applied when using harvest statistics to estimate population sex ratios. In Ontario, 58% of trapped lynjc were males (Quinn and Thompson 1987), whereas in Alberta, 71% were males (Brand and Keith 1979). As the density of hares declines, the proportion of kittens in harvest samples decreases. O'Conner (1986) examined trapper-killed carcasses and found that during periods of hare abundance in 1963-1964 (N=745) and 1970-1971 (N=114), 40% and 32% of lynx trapped were kittens and 40% and 55% were year- lings, respectively. Harvest percentages dropped to 0-3% for kittens and 8-17% for yearlings, however, when hare numbers were low. In Alberta, as hare numbers dropped, the proportion of kittens went from 31-7% (Brand and Keith 1979), and Parker et al. (1983) doam:\ented a decHne from 29-2% for kittens and 52- 39% for yearlings during a hare decline in Nova Scotia. Brand and Keith (1979) found only 1 kitten among 518 lynx trapped during a 3-year period of hare scar- city in Alberta. During the first year of decline in hare numbers, yearling and 2-year-old lynx comprised 85% of the harvest; during the second year, 2- and 3- year-olds made up 78% of the harvest; and by the third year, the harvest contained 78% 3- and 4-year- olds. As hare numbers declined dramatically from 1971-1976, the mean age of trapped lynx rose from 1.6-3.6 years (Brand and Keith 1979). At southern latitudes, where hare densities are typically low (Dolbeer and Clark 1975), older age individuals ap- pear to predominate in lynx populations. Brittell et al. (1989, unpubl.) reported an average age of 4.5 years for 14 lynx harvested in Washington from 1976-1981. Density In northern regions, where hare populations cycle, lynx populations respond with a 1- to 2-year lag (Breitenmoser et al. 1993; Brand et al. 1976; O'Conner 1986). Increases in prey numbers result in higher densities of lynx from increased reproduction and decreased mortality. Although social intolerance may separate lynx in time and space (Brand et al. 1976), it does not appear to be a major factor limiting their densities (Breitenmoser et al. 1993; Bergerud 1971). During periods of hare scarcity, lynx congregate around pockets of hare activity, which may result in inflated density estimates for lynx if extrapolated to other habitats (Bergerud 1971; Carbyn and Patriquin 1983; Todd 1985; Ward and Krebs 1985). On the Kenai National Wildlife Refuge, where overall lynx densi- ties were 1/100 km-, densities were 2.3/100 km' in an area that burned in 1947 where hare numbers were high (Bailey et al. 1986). Carbyn and Patriquin (1983) reported trappers removing 16 lynx from 3 km^ of high-quality habitat during mid-winter. Such focal areas of lynx activity and localized densities may lead to erroneous population estimates when based on trapper interviews or fur harvest returns. Snow-tracking studies in Alberta showed that lynx densities increased from 2.1-7.5/100 km' as hare numbers increased (Nellis et al. 1972). In the same study area, later workers (Brand and Keith 1979; Brand et al. 1976) observed a 4.3-fold change in lynx densities from 1966-1972, with the highest density of lynx occurring 1 year after the peak in hare num- bers. Bergerud (1971) reported a lynx density of 7.7/ 100 km- on caribou {Rangife?' spp.) calving grounds during June. In Alaska, Bailey et al. (1986) estimated that lynx trappers removed 10-17/100 km', suggest- ing that peak densities may have been greater than 20/100 km-, a value equivalent to those reported on Cape Breton Island in Nova Scotia (Parker et al. 1983). Using radiotelemetry and snow-tracking to study lynx in Washington, Koehler (1990) estimated lynx densities of 2.3 adults /1 00 km- and 2.6 adults and kittens /1 00 km-. Radiotelemetry studies also docu- ment changing lynx densities in response to chang- ing hare numbers. In the Yukon, Slough and Mowat (1993, unpubl.) found that densities increased from 2.8/100 km^ in 1987 to 37.2/100 km^ in 1991 as hare 83 numbers increased, and then decreased to < 5/100 km^ as hare numbers declined. Poole (1993, unpubl.) observed decreases in lynx densities from 35-2/100 km^ in the Northwest Territories during the same period. Changes in lynx densities may also be a function of intensity of exploitation. Densities were only 1 / 100 km^ on the Kenai National Wildlife Refuge where populations were depleted from heavy trapping pres- sure (Bailey et al. 1986). After trapping was closed on the refuge, lynx densities increased 4-fold (1.6-6.8/ 100 km^) during a period when hare densities were rela- tively stable (Kesterson 1988). During hare population declines, lynx become increasingly vulnerable to trap- pers as they expand their movements in search of alter- nate sources of prey (Brand and Keith 1979). Management Considerations 1. The lack of dramatic fluctuations in lynx and snowshoe hare populations at southern latitudes will require management approaches that are different from those applied in northern boreal forests where populations are cyclic. 2. In the western mountains, the management of habitat for snowshoe hares is likely to be an impor- tant component of lynx conservation efforts due to the relatively low hare densities typical of boreal habitats in the western mountains, and because of the impor- tance of hare availabiUty for successful reproduction. 3. Due to its additive nature, trapping mortality can have significant short-term effects on lynx popu- lations in the western mountains. Research Needs 1. Implement monitoring and intensive research on lynx and snowshoe hare populations in the west- ern mountains to determine the nature of their popu- lation dynamics and to understand why they do not exhibit dramatic fluctuations in numbers over time. 2. Where lynx are harvested in the western moun- tains, carcasses should be collected and age, sex, and reproductive data gathered. FOOD HABITS AND PREDATOR-PREY RELATIONSHIPS Foraging Ecology Lynx occur in habitats where snowshoe hares are most abundant (Bailey et al. 1986; Bergerud 1971; Koehler 1990; Koehler et al. 1979; Parker et al. 1983; Ward and Krebs 1985). During periods of hare scar- city, lynx concentrate their activities in pockets of hare abundance (Bergerud 1971; Todd 1985; Ward and Krebs 1985), which are typically dense, brushy sites where hares seek refuge (Wolff 1980). Carbyn and Patriquin (1983) reported 16 lynx being trapped in an area 3 km^ in extent. Lynx apparently invest a great deal in learning to hunt, since kittens typically remain with their mother until they are 9-10 months of age (Bailey et al. 1986; Brand et al. 1976; Carbyn and Patriquin 1983; Koehler 1990; Koehler et al. 1979; Parker et al. 1983; Saunders 1963b). Their proficiency at hunting during their first 2 years is critical. When female lynx with kittens are trapped, the kittens are particularly vulnerable to starvation (Carbyn and Patriquin 1983). When lynx are traveling, most of the time they are searching for food (Brand et al. 1976). Saunders (1963b) reported lynx to be most active from evening until early morning, although Parker et al. (1983) found that radio-collared lynx traveled during both day and night. The distance traveled during hunts, as determined by distances traveled between day- time beds, can vary from 8.8 km when hares are scarce to 4.7 km when hares are plentiful (Brand et al. 1976; Nellis and Keith 1968). Ward and Krebs (1985), how- ever, found no significant difference in distances trav- eled per day until hare densities dropped below 1.0/ ha. Parker et al. (1983) calculated daily cruising dis- tances of 6.5-8.8 km in winter and 7.3-10.1 km dur- ing summer in Nova Scotia. In north-central Wash- ington, females foraged up to 6-7 km from their den sites (Koehler 1990). Cover is important for lynx to stalk prey. From snow-tracking. Brand et al. (1976) determined that lynx encountered and captured hares by following well-used hare runways, concentrating their move- ments in small areas of hare activity, or using short term "waiting-beds" (typically depressions in the snow) that were usually located near areas of hare activity When numbers were declining. Brand et al. (1976) found lynx using waiting beds as a hunting strategy more frequently, and Saunders (1963b) re- ported that this strategy accounted for 61 % of hares killed by lynx. Prey Requirements and Hunting Success Lynx are specialized predators of snowshoe hares, but they also forage opportunistically, preying on a variety of species as availability of resources change. 84 Most snow-tracking studies show the importance of hares to the lynx diet, even when hares are scarce and capture rates decrease (table 1). In Nova Scotia, Parker et al. (1983) found that 198 of 200 chases and 34 of 36 kills were of snowshoe hares, whereas in the Yukon, lynx were successful at capturing hares on 32 of 52 occasions (Murray and Boutin 1991). Among 361 attempts to kill prey in central Alberta, 73% were hares and 15% were ruffed grouse {Bonasa umbellus) (Brand et al. 1976). Hunting success did not differ among years as hare densities varied, averaging 24% during winters when hares were abundant, and 24- 36% when hare numbers were low; capture rates for tree squirrels, however, varied from 0-67% (Brand et al. 1976; Nellis and Keith 1968). Snow-tracking lynx for 20.5 km in north-central Washington, Koehler (1990) detected 2 captures of hares in 6 attempts, and 2 unsuccessful attempts to capture red squirrels. Nellis and Keith (1968) believed that success in cap- turing hares was a function of snow conditions, ex- perience, and familiarity with the area. Hunting suc- cess has also been shown to increase from 14-55% as the size of groups (usually a female and her kittens) increases from 1 to 4 (Parker et al. 1983). Snow- tracking lynx in Alberta for 416 km, Nellis and Keith (1968) found lynx made 0.42 kills per day, less than half that reported by Parker et al. (1983) for lynx in Nova Scotia. Nellis et al. (1972) calculated a consumption rate of 593 g/ day, which is similar to the 600 g/day calculated by Saunders (1963a). Dur- ing a decline in hare numbers, the mean daily con- sumption rate of individual lynx may decrease by 37% (Brand et al. 1976). Nellis et al. (1972) found that a captive juvenile required about 370 gm/day of hares, tree squirrels, and birds to increase its body weight from 4.9 to 5.6 kg. This captive juvenile was smaller than recaptured wild littermates, suggesting that wild juveniles may require at least 400 g/day to meet requirements for growth. Because the biomass of a grouse is equal to 0.5 hares and that of a tree squirrel to 0.2 hares (Nellis and Keith 1968), a shift to alternate food sources as hare populations decline may not com- pensate for the decrease in biomass of hares kiQed. Lynx will occasionally prey on ungulates (Bergerud 1971; Koehler 1990; Stephenson et al. 1991), but the importance of ungulates in the diet appears to be insignificant. Bergerud (1971) found caribou calves to be more vulnerable to lynx predation dur- ing July and August when newborn calves are led by cows from open habitats to forested sites. Of 33 lynx scats collected on calving grounds, 13 contained caribou hair (Bergerud 1971). Saunders (1963a) and Bailey (pers. comm.) observed lynx scavenging moose {Alces alces) carcasses, and remains of deer {Odocoileus spp.) were infrequently found in lynx scats in Washington (Koehler 1990) and Nova Scotia (Parker et al. 1983). Whether the presence of deer hair in scats was from predation or scavenging is unknown. Temporal and Spatial Variations in Diet Studies in Alberta (Brand et al. 1976; Brand and Keith 1979; Nellis and Keith 1968, Nellis et al. 1972) have shown that although snowshoe hares make up the greatest biomass of prey consumed throughout the year, lynx use alternate prey during periods of hare scarcity and during the summer and fall sea- sons. Staples and Bailey (1993, unpubl.) and Saunders (1963a) also found a greater incidence of voles in lynx diets during summer (15-30%) than in winter (5-9%). Brand et al. (1976) reported that snowshoe hares rep- resented only 27 of 71 food items during the sum- mer, compared to 112 of 140 items in winter. In con- trast, mice and voles represented 33 of 71 food items during summer, but only 22 of 140 during winter. Despite increased consumption of mice and voles during summer and fall, however, hares still com- prised 91% of biomass consumed. Brand and Keith (1979) observed a decline from 90 to 35% in the frequency of occurrence of hare re- mains in the diet as hares became scarce. However, the percent biomass of hares remained high, com- prising 97% of the total biomass consumed when hares were abundant, and 65% when hares were scarce. During a decline in hare numbers, the fre- quency of voles and mice shifted from 4 to 28% of the diet and occurrence of tree squirrels increased from 9 to 12%. However, the percent biomass con- sumed of these species did not change much during the hare decline, remaining 3% for squirrels and 1% for mice and voles. In the only food habits study of lynx conducted in the western mountains, Koehler (1990) found that tree squirrels represented 24% of the food items found in 29 scats in his study area in north-central Washington; remains of tree squirrels were also found at den sites. Staples and Bailey (1993, unpubl.) found a similarly high percentage of squir- rels in the diet of lynx in Alaska (28%) during a hare population low (table 1), providing additional evi- dence that lynx ecology in the western mountains is similar to that occurring in northern latitudes dur- ing lows in the snowshoe hare cycle. 85 Management Considerations 1. In the western mountains, prey species other than snowshoe hares, including tree squirrels, voles, and mice, appear to provide important alternate food sources for lynx. Research Needs 1 . Intensive studies of the food habits of lynx dur- ing all seasons of the year in the western mountains are urgently needed. 2. Determine the composition and structure of habitats in the western mountains that provide both sufficient food and cover for hares and adequate stalking cover for lynx. HABITAT RELATIONSHIPS Components of Lynx Habitat From the coast of western Alaska to the eastern islands of Canada and the mountains of the western United States, the distribution of lynx is tied to bo- real forests. Lynx occupy habitats at 122 m elevation dominated with white {Picea glauca) and black spruce (P. mariana), paper birch {Betula papyrifera), willow {Salix spp.), and quaking aspen {Populus tremuloides) on the Kenai Peninsula of Alaska (Bailey et al. 1986); white spruce-dominated forests in southwestern Yukon (Ward and Krebs 1985); aspen, poplar (P. balsamifera) , and spruce stands in central Alberta (Brand et al. 1976); aspen forests in Manitoba (Carbyn and Patriquin 1983); balsam fir {A. balsamea), white spruce, black spruce, and paper birch forests to 390 m elevation on Cape Breton Island, Nova Scotia (Parker et al. 1983); jack pine (Pinus banksiana), bal- sam fir, black spruce, aspen, and paper birch forests in northern Minnesota (Mech 1980); Engelmann spruce (P. engelmannii) , subalpine fir {Abies lasiocarpa), lodgepole pine (P. contorta), and aspen forests above 1,463 m in north-central Washington (Koehler 1990); and similar forest communities in western Montana (Koehler et al. 1979). They occur in the Rocky Moun- tains above 1,900 m elevation in Wyoming and above 2,400 m in Colorado and Utah (Koehler and Brittell 1990). In these habitats, lynx typically occur where low topographic relief creates continuous forest commu- nities of varying stand ages. These features are most prevalent at northern latitudes but they also appear to be important components of lynx habitat in the mountains of the western United States. In both ar- eas, such conditions are important for maintaining hare populations needed to support stable lynx popu- lations. Habitat continuity, or the degree of habitat fragmentation, may also influence lynx population dynamics. Vast expanses of successional forests at northern latitudes support periodic population booms and crashes in numbers of hares. At southern latitudes, however, habitats are more fragmented and discontinuous resulting in lower, but more stable, hare populations (Chitty 1950; Dolbeer and Clark 1975; Koehler 1990; Sievert and Keith 1985; Windberg and Keith 1978; Wolfe et al. 1982; Wolff 1980). Lynx habitat in the western mountains consists primarily of two structurally different forest types occurring at opposite ends of the stand age gradient. Lynx require early successional forests that contain high numbers of prey (especially snowshoe hares) for foraging and late-successional forests that con- tain cover for kittens (especially deadfalls) and for denning (Brittell et al. 1989, unpubl.; Koehler and Brittell 1990). Intermediate successional stages may serve as travel cover for lynx but function primarily to provide connectivity within a forest landscape. Al- though such habitats are not required by lynx, they "fill in the gaps" between foraging and denning habi- tat within a landscape mosaic of forest successional stages. Foraging Habitat Stand Age Early successional forests where snowshoe hares are plentiful are the habitats that lynx favor for hunt- ing. Such forests may result from fires (Bailey et al. 1986; Fox 1978; Keith and Surrendi 1971; Koehler 1990, 1991), timber harvesting (Conroy et al. 1979; Koehler 1990, 1991; Litvaitis et al. 1985; Monthey 1986; Parker et al. 1983; Wolfe et al. 1982), or windthrow and disease (Koehler and Brittell 1990). Based on hare pellet counts in Washington, Koehler (1990) found that hares were more abundant in younger-aged stands of lodgepole pine than in any other forest type. Hares were 4-5 times more abun- dant in 20-year-old lodgepole pine stands than in 43- and 80-year-old stands, and 9 times more abundant than in stands >100 years old. In Newfoundland, hares began to use cutover areas when stands reached 10 years of age, but frequency of use peaked when the stands were 22 years old (Dodds 1960). In Nova 86 Scotia, Parker et al. (1983) estimated hare densities at 10/ha in mid-successional habitats (16-30 years old), compared to 5.8/ha in mature conifer habitats. In Maine, hare activity was greater in 12- to 15-year- old clearcuts than in younger stages (Monthey 1986). On the Kenai National Wildlife Refuge in Alaska, hares used areas burned in 1947 more intensively than alder-dominated stands, an area burned in 1969, or mature forests, presumably because the latter habi- tats lacked adequate food and cover (Bailey et al. 1986). Stand structure appears to strongly influence recolonization by hares. One year after a wildfire in Alberta, where prefire cover density was 86%, hares recolonized an intensively burned site after seedling and shrub cover approached 61 % (Keith and Surrendi 1971). In this study, aspen and balsam poplar recov- ered quickly by sprouting. This contrasts to findings in Maine where clearcut areas initially experienced a decline in hares, and it wasn't until 6-7 years after spruce and fir became reestablished that hares recolo- nized the area, peaking in numbers 20-25 years later (Litvaitis et al. 1985). Litvaitis et al. (1985) found that clearcutting improved habitat quality for hares in mature forest stands where understory stem density was low. The capacity of burned areas to support high den- sities of hares, and therefore lynx, undoubtedly de- clines over time (Fox 1978). Because succession progresses slowly at northern latitudes, older-aged (-40 years old) stands there may provide optimal conditions for hares, whereas at southern latitudes, younger-aged stands (15-30 years old) appear to pro- vide the best habitat for hares. Tree Species Composition Conifer stands provide greater concealment from predators, lighter snowpacks, and warmer tempera- tures during winter than hardwood stands (Fuller and Heisey 1986). In Minnesota, hares used habitats with a conifer overstory and a low-growing under- story, a pattern that was particularly evident during periods of hare scarcity (Fuller and Heisey 1986). Conifer cover proved to be an important habitat com- ponent for hares during a decline in Nova Scotia as well (Parker et al. 1983). In Alaska, thickets that served as refugia during periods of hare scarcity were dominated by black spruce, whereas burned areas dominated by herbaceous woody plants were occu- pied only during periods of hare abundance (Wolff 1980). In Maine, Monthey (1986) observed hares se- lecting conifer stands and Litvaitis et al. (1985) found that individual conifer stems provided about 3 times more cover than leafless hardwood stems. They also documented a strong positive correlation between the number of hares live-captured in the spring and the density of conifer stems; there was no statistical correlation with the density of hardwoods or with total stem density. Wolfe et al. (1982) concluded that dense stands of aspen in the Rocky Mountains rep- resented marginal habitat for hares because such stands do not provide adequate cover. These studies strongly indicate that conifer cover is critical for hares during the winter. Litvaitis et al. (1985), however, found that in coastal locations in Maine, hares preferred low-density hard- wood stands where lateral foliage density was greater than in conifer stands, and that hares avoided mixed stands with an open understory. In the mountainous inland region of the state, however, hares preferred conifer stands with higher stem densities than those found in hardwood stands. Even at southern latitudes, where hare population cycles may not occur, conifer cover is an important habitat component (Dolbeer and Clark 1975; Koehler 1990; Pietz and Tester 1983). In Colorado and Utah, dense stands of subalpine fir and Engelmann spruce and Douglas-fir were used most frequently by hares (Dolbeer and Clark 1975; Wolfe et al. 1982); in Mon- tana, dense stands of Douglas-fir were selected (Adams 1959); and in Washington, dense stands of lodgepole pine were used most often (Koehler 1990, 1991), indicating that stem density is more impor- tant to hares than species of conifer. Stem Density In Washington, Koehler (1990) found a significant correlation between hare densities and stands with tree and shrub stems that were less than 2.5 cm in diameter at breast height (DBH); intensively used 20- year-old stands had 15,840 stems/ha (1.6 stems/ m^). In Alaska, Wolff (1980) found that hares preferred stands with tree and shrub densities of 22,027 stems/ ha, and in Nova Scotia, hares frequented stands with stem densities of 9,000 conifers/ha {0.9 /m^) and 7,000 hardwoods/ha (0.7 /m^) (Parker et al. 1983). In Maine, hares preferred stands dominated with stems > 0.5 m tall and < 7.5 cm DBH at densities > 16,000 stems/ ha (1.6/m2), with an understory visual obstruction > 60% (Litvaitis et al. 1985). Monthey (1986) also found hares to be common in densely stocked stands (stems < 8.9 cm DBH and > 0.6 m tall with 6,000-31,667 stems/ha [0.6-3.2 stems/m^]) in Maine. In Utah, hares 87 seldom used stands with understories having < 40% visual obstruction during winter (Wolfe et al. 1982). Stem Height Because snow depths typically exceed 1 m in bo- real forests, the height of stems is also an important component of winter habitat. In Minnesota, Pietz and Tester (1983) found a positive correlation between the percentage of shrub cover > 1 m tall and numbers of winter hare pellets. In Nova Scotia, habitats with stem heights between 2-3 m were important for hares, whereas mature forests with stem heights of 6-8 m and browse height < 1.0 m provided inadequate win- ter habitat (Parker et al. 1983). In the Rocky Moun- tains, where snow depths may exceed 1.5 m, Dolbeer and Clark (1975) found that sparsely stocked stands provided little food or cover, and Wolfe et al. (1982) reported that 85% of habitats used by hares had a horizontal cover density of 40% at a height of 1.0-2.5 m above the ground. In central Wisconsin, however, where snow depths may be less, Sievert and Keith (1985) concluded that stands with a dense cover of stems < 1.5-m tall provided good habitat for hares. During snow-free periods, thermal cover is not a critical factor and alternate sources of food are avail- able. During these times, hares will occupy habitats that are more open and where hardwoods and her- baceous vegetation are more prevalent (Dodds 1960; Litvaitis et al. 1985; Parker et al. 1983; Wolfe et al. 1982). During snow-free months, Parker et al. (1983) and Adams (1959) reported that hares avoided very dense stands where shade created by a dense canopy reduces the growth of herbaceous understory vegetation. Denning Habitat For denning, females select dense, mature forest habitats that contain large woody debris, such as fallen trees or upturned stumps, to provide security and thermal cover for kittens (Berrie 1973; Koehler 1990; Koehler and Brittell 1990; Kesterton 1988; Murie 1963). In north-central Washington, lynx denned in stands > 200 years old with Engelmann spruce-sub- alpine fir-lodgepole pine overstories having N-NE aspects; these sites also had a high density (> 1/m) of downed trees supported 0.3-1.2 m above the ground, which provided both vertical and horizon- tal structural diversity (Brittell et al. 1989, unpubl.; Koehler 1990). Other important features of denning sites are minimal human disturbance, proximity to foraging habitat (early successional forests), and stands that are at least 1 ha in size (Koehler and Brittell 1990). Travel corridors between den sites are important to permit females to move kittens to areas where prey are more abundant or to avoid distur- bance (Koehler and Brittell 1990). In areas where denning habitat is abundant, female lynx often change denning sites during and between seasons (Washington Dept. of Wildlife 1993, unpubl.). Where high-quality denning habitat is scarce, how- ever, lynx may re-use the same denning site (pers. comms. by Brittell and Slough cited in Washington Dept. of Wildlife 1993, unpubl.). The availability of alternate den sites may be an important determinant of habitat quality. In low-quality habitat, the inability of females to move kittens to alternate dens when dan- ger threatens may increase mortality rates for kittens. According to Brittell et al. (1989, unpubl.), den sites con- sisting of mature forest habitat are also important for lynx as refugia from inclement winter weather or drought. Travel Cover Like most wild felids, lynx require cover for secu- rity and for stalking prey; they avoid large, open ar- eas. Although lynx will cross openings < 100 m in width, they do not hunt in these areas (Koehler 1990; Koehler and Brittell 1990). Travel cover allows for movement of lynx within their home ranges and pro- vides access to denning sites and foraging habitats (Brittell et al. 1989, unpubl.). In general, suitable travel cover consists of coniferous or deciduous vegetation > 2 m in height with a closed canopy that is adjacent to foraging habitats (Brittell et al. 1989, unpubl.). Lynx are known to move long distances but open areas, whether human-made or natural, will discourage use by lynx and disrupt their movements. Thus, main- taining travel corridors between populations may be important to ensure the long-term viability of periph- eral or isolated populations in the western mountains (Koehler 1990; Koehler and Brittell 1990). Roads constructed for forest management, mining, or recreational purposes may increase the vulnerabil- ity of lynx to hunters and trappers (Bailey et al. 1986; Todd 1985) and increase opportunities for acciden- tal road deaths (Brocke et al. 1992). During winter and summer, lynx frequently travel along roadways with < 15 m right-of-ways, where adequate cover is present on both sides of the road (Koehler and Brittell 1990). Although forbs, grasses, and shrubs that grow along edges of roads can benefit hares and attract 88 lynx, increased access and use of roadways by people may pose a threat to lynx populations, particularly during times of high pelt prices and low recruitment (Bailey et al. 1986). Although sparsely stocked stands are poor habi- tat for hares, they may benefit lynx by serving as dis- persal sinks in which juvenile hares are more vulner- able to predation (Dolbeer and Clark 1975; Sievert and Keith 1985; Windberg and Keith 1978). For these rea- sons, an interspersion of dense stands that provide refu- gia for hares, and sparsely stocked stands where hares are more vulnerable, may be more beneficial to lynx than a continuous distribution of optimal hare habitat. Because plant succession progresses more rapidly at southern latitudes, small-scale disturbances at fre- quent intervals may be necessary to provide for a temporal continuum of stand ages. Fires, epidemics of forest disease, and logging may have negative short-term effects by eliminating cover for snowshoe hares and lynx, but will have long-term benefits as succession progresses, cover is restored, and snow- shoe hares become abundant (Koehler and Brittell 1990; Parker et al. 1983). Management Considerations 1. High-quality lynx habitat in the western moun- tains consists of a mosaic of early successional habi- tats with high hare densities, and late-successional stands with downed woody debris for thermal and security cover and for denning. 2. Clearcuts >100 m wide may create barriers to lynx movements. 3. Hares may not begin to recolonize clearcuts un- til 6-7 years after cutting, thus it may take 20-25 years at southern latitudes for snowshoe hare densities to reach highest levels. 4. Thinning stands early to maximize tree-growth potential can be compatible with snowshoe hare and lynx habitat needs provided that stands are thinned before snowshoe hares recolonize the area. Other- wise, thinning may be most effective when stands are older than 30-40 years and are used little by hares. Both early and late thinning strategies may be re- quired when integrating timber management objec- tives with lynx habitat needs. 5. Small-sized parcels (1-2 ha) of late-successional forest appear to be adequate for den sites, but these H parcels must be connected by corridors of cover to permit females to move kittens to alternate den sites providing suitable access to prey. 6. Approximating the natural disturbance fre- quency and spatial patterns present on the landscape is expected to provide the best habitat for lynx. Fre- quent, small-scale disturbances is expected to pro- vide the best lynx habitat at southern latitudes. 7. Although disease and insect attacks may increase fuel loads and the risk of large, high-intensity fires, they also provide dead and downed trees used for denning cover. Thus, the role that disease and insects play in the dynamics of forests being manipulated must be carefully considered when managing stands for timber and lynx. 8. Road management is an important component of lynx habitat management. Although construction and maintenance of roads both destroys and creates habitat for prey, lynx use roads for hunting and travel which may make them more vulnerable to human- caused mortality. Researchi Needs 1. Studies of lynx distribution and habitat use in the western mountains are urgently needed. Gather- ing this information will require winter surveying of remote areas in winter where lynx are believed to occur and evaluating patterns of occurrence with geographic information systems (GIS). GIS can then be used to inventory available habitats on a regional scale. Once this is achieved, more intensive field inves- tigations of habitat use, spatial patterns, and reproduc- tive ecology using radiotelemetry will be appropriate. 2. Forest management activities, timber harvest- ing, and prescribed and wild fires can be either det- rimental or beneficial to lynx, depending upon their scale and dispersion on the landscape. Although guidelines exist, it will require some experimenta- tion to determine prescriptions that provide an opti- mal range and pattern of habitat patchiness to ben- efit both hares and lynx. Such experimentation will require long-term research and monitoring of both lynx and snowshoe hare populations. HOME RANGE AND MOVEMENTS Home Range Lynx partition resources both spatially and tem- porally, but determining the social and spatial orga- nization of solitary f elids is difficult. Most studies do not encompass a long enough time period nor do they include an adequate sample of individuals. These 89 limitations result from the difficulties involved in (1) capturing and marking individuals occupying adja- cent home ranges, and (2) obtaining representative samples of sex and age classes. However, certain patterns can be detected from the studies that have been conducted. Although lynx are considered to be solitary, they frequently travel in groups, such as fe- males with kittens, two adult females with their lit- ters, or females traveling with males during the breeding season (Carbyn and Patriquin 1983; Parker et al. 1983; Saunders 1963b). Snow-tracking and radiotelemetry studies have been used to delineate spatial requirements of lynx and to assess spatial partitioning between and within sexes. Nellis et al. (1972) identified areas used by lynx as activity centers that were separated in time and space. Radiotracking studies by Parker et al. (1983) support the concept of lynx using activity centers during winter. They documented both males and fe- males concentrating 75% of their activity in core ar- eas, which ranged from 35-63% of winter home ranges. Although in Alaska, Kesterson (1988) found that lynx in Alaska occupied intrasexually exclusive areas, spatial overlap among individuals is common (Bergerud 1971; Brand and Keith 1979; Koehler 1990; Saunders 1963b; Ward and Krebs 1985), and it is gen- erally believed that lynx occupy home range areas rather than exclusive territories. Factors that influence the size and shape of home ranges are not fully understood, but it is generally believed to be related to the availability of prey and the density of lynx. Other factors that may contrib- ute to the size and configuration of home range ar- eas include geographic and physiographic features. Saunders (1963b) found that home range boundaries coincided with habitat features, and Koehler (unpubl. data) observed home range areas in a mountainous region of Washington to correspond to drainage pat- terns, with home range boundaries generally occur- ring along ridges and major streams. Therefore, physiographic features and variation in the distribu- tion of habitats may partially account for differences in home range sizes between geographic areas. Ward and Krebs (1985) demonstrated a correlation between prey density and lynx home range sizes in the Yukon by using radiotelemetry. As numbers of hares decreased from 14.7 to < 1 /ha, the mean home range size for lynx increased from 13.2 to 39.2 km^ a 3-fold increase in home range size in response to a 14-fold decrease in hare abundance. Similarly, Poole (1993, unpubl.) found lynx home ranges increased from 17 km^ to 25-84 km^ as hare numbers dropped, with the majority of lynx becoming nomadic or emi- grating at that time. Such observations of lynx chang- ing their use of space in response to declining num- bers of hares is in contrast to findings by Breitenmoser et al. (1993), however, which showed no change in the size of home ranges between periods of high and low hare numbers. In addition, snow-tracking stud- ies by Brand et al. (1976) indicated that lynx did not modify their home range sizes in response to chang- ing numbers of hares. However, during a period of low hare densities in interior Alaska, Perham et al. (1993, unpubl.) observed some lynx hunting in iso- lated pockets of hare activity and occupying small home ranges, whereas others became nomadic or emigrated. Slough and Mowat (1993, unpubl.) found that mean annual home range sizes varied from 8.3 to 18.2 km^ for females and from 17.3 to 51.0 km^ for males as hare numbers increased from 1982 to 1992. They hypothesized that lynx maintained intrasexual territories during hare lows, but that this intolerance broke down as hare numbers increased. A variety of techniques has been used to calculate the size of home range areas, and each technique can result in different estimates. For example, snow- track- ing generally results in smaller home ranges from those calculated from radiotelemetry studies. Fur- thermore, the number of locations used generally differs between studies and can affect area determi- nation (Mech 1980; White and Garrott 1990). For these reasons, caution must be applied when comparing home range sizes between different studies. Studies using radiotelemetry have estimated home ranges for lynx varying in size from 8 to 783 km^ (Berrie 1973; Bailey et al. 1986; Brainerd 1985; Brittell et al. 1989, unpubl.; Carbyn and Patriquin 1983; Kesterson 1988; Koehler 1990; Koehler et al. 1979; Parker et al. 1983; Perham et al. 1993, unpubl.; Poole 1993, unpubl.; Slough and Mowat 1993, unpubl; Smith 1984; Ward and Krebs 1985). Based on snow- tracking, lynx occupy areas from 15.4 to 20.5 km^ in Newfoundland (Saunders 1963b), and 18 to 49 (av- erage 38.4) km2 in Alberta (NeUis et al. 1972). On the same study area in Alberta, Brand et al. (1976) esti- mated that home range size varied from 11.1 to 49.5 km^ (average 28.0 km^). Although large home ranges are generally associ- ated with low numbers of prey, they may also occur in areas into which lynx have recently immigrated (Mech 1980) or that are heavily trapped (Bailey et al. 1986; Carbyn and Patriquin 1983). In Manitoba, home 90 ranges used by two females during winter averaged 156 km^ while that for a male was 221 km^ in an area that was intensively trapped (Carbyn and Patriquin 1983) . Their study area of 2,144 km^ was an isolated |j refuge surrounded by agricultural land that was only occasionally colonized by immigrating lynx. On the Kenai Peninsula in Alaska, where lynx were heavily exploited. Bailey et al. (1986) found home ranges for two females to be 51 and 89 km^ and that for one male to be 783 km^. As lynx densities increased after || the trapping season was closed, sizes of lynx seasonal home ranges decreased 54.7% for resident males and 36.9% for nondenning, resident females (Kesterson 1988). During a period of increasing hare numbers in Nova Scotia, an adult female used an area of 32.3 km^ and an adult male, 25.6 km^ (Parker et al. (1983). Lynx that had immigrated into Minnesota where hares were scarce occupied areas of 51-122 km^ for females and 145-243 km^ for males (Mech 1980). Lynx translocated to an area of low hare density (mean of ij 0.5 hares/ha) in New York also had large home ' ranges, with harmonic mean estimates of 1,760 km^ , for 21 males and 421 km^ for 29 females (Brocke et al. 1992). In this area, 73% of known mortalities were human-caused. This high level of mortality was be- lieved to have resulted from fragmented property |l ownership and many access roads. In Washington, where hares were relatively scarce and suitable habi- tats scattered, home range sizes averaged 39 km^ for 2 females and 69 km^ for 5 males (Koehler 1990). In western Montana, the mean home range size for 4 lynx (2 males and 2 females) was 133 km^ (Smith 1984) . In a subsequent study in the same area, Brainerd (1985) radio-collared 7 lynx and measured mean annual home ranges of 122 km^ for males and 43.1 km^ for females. Lynx will maintain home ranges for several years. In Washington, site fidelity was observed for more than 2 years (Koehler 1990) and in the Yukon, a male was observed using the same area for at least 10 years (Breitenmoser et al. 1993). Radiotelemetry studies show that home range sizes vary by season. In Alaska, females occupied smaller areas in summer 1 (25 km^) than in winter (49 km^) (Bailey et al. 1986). The opposite relationship was documented in Nova Scotia, however, where an adult female expanded her home range from 18.6 km^ in winter to 32.3 km^ in I summer, and an adult male from 12.3 km^ in winter to 25.6 km^ in summer; there was little seasonal change for a juvenile (10.1 km^ in winter and 7.9 km^ in summer) (Parker et al. 1983). Prior to dispersing. a juvenile male occupied a home range in Alaska of 8.3 km^ in an area providing high-quality hare habi- tat (Bailey et al. 1986). In one of the few studies con- ducted in mountainous terrain, Koehler (1990) found that lynx in north-central Washington used signifi- cantly higher elevations during summer (range 1,463-2,133 m) than in winter (range 1,556-2,024 m). The extent of home range overlap for lynx is vari- able. Ward and Krebs (1985) found male home ranges to overlap those of other males by 10.5%, among fe- males by 24.5%, and between males and females by 22.0%. However, in Washington, Koehler (1990) found home ranges of males and females to overlap completely, particularly during March and April when breeding occurred (Koehler, unpubl. data). Parker et al. (1983) also documented complete over- lap in home ranges of radio-collared males and fe- males, and Mech (1980) found complete overlap among radio-collared females but not among males, although there may have been overlap with uncollared males. Kesterson (1988), however, ob- served little overlap in home range use among fe- males (mean overlap, 5.0%) or among males (3.8%); however, male ranges overlapped those of 1-3 females. Movements and Dispersal When hares are scarce, several lynx may congre- gate around pockets of dense vegetation or on cari- bou calving grounds where prey resources are more plentiful (Bergerud 1971; Ward and Krebs 1985). During such times, the spatial and temporal segre- gation of lynx may cease to exist, and some lynx may abandon their home range areas and become no- madic or emigrate in search of prey (Poole 1993, unpubl.; Ward and Krebs 1985). Records indicate long-distance movements by lynx of 1,100 km (Slough and Mowat 1993, unpubl.) and 700 km (Ward and Krebs 1985) in the Yukon, 930 km in the North- west Territories (Poole 1993, unpubl.), 616 km in Washington (Brittell et al. 1989, unpubl), 325 km in western Montana (Brainerd 1985), 483 km in Minne- sota (Mech 1977), 164 km in Alberta (Nellis et al. 1972), and 103 km in Newfoundland (Saunders 1963b). Translocated lynx in New York used areas exceeding 1,000 km^ (Brocke et al. 1992). Ward and Krebs (1985) considered the abandon- ment of home range areas and nomadic behavior to be related to decreased hare densities, especially when hare densities dropped below 0.5 /ha. In the Yukon, Slough and Mowat (1993, unpubl.) found 91 annual immigration and emigration rates to be rela- tively constant at 10-15%, with most juvenile males dispersing and juvenile females tending to remain on their natal ranges, although emigration increased to 65% with no apparent immigration as hare num- bers crashed. In the Northwest Territories, kittens and yearlings began dispersing during the peak in hare numbers, while emigration of adults didn't occur until after the crash in hare numbers (Poole 1993, unpubl.). These long-range movements may serve to re- populate vacated areas or to augment depauperate populations along the southern edge of the lynx's range. After a long period of heavy trapping pres- sure, lynx populations increased during the 1960's in Alberta (Todd 1985) and in eastern Montana (Hoffmann et al. 1969). As is indicated by the failure of lynx to establish themselves in Minnesota after immigrating there in large numbers in the early 1970's (Mech 1980), however, such movements are unlikely to result in stable lynx populations unless available habitats are capable of supporting both snowshoe hares and lynx in sufficient numbers for population persistence. During the 1970's, heavy trapping pressure prob- ably resulted in overexploitation of lynx populations in Ferry County, Washington, yet only recently does it appear that lynx have recolonized that area (Wash- ington Dept. of Wildlife 1993, unpubl.; Koehler, pers. obs.). Lynx habitat in Ferry County is separated from suitable habitat in British Columbia by the Kettle River drainage and xeric non-lynx habitats that may act as barriers to lynx dispersal and recolonization. Extensive fires, logged areas, and forest disease con- trol programs may also act to inhibit immigration of lynx into suitable habitat (Koehler 1990; Koehler and Brittell 1990). Translocation may be a viable alternative for rees- tablishing lynx populations into areas where they occurred historically, but reintroductions are prob- lematic. Of 50 lynx translocated from Yukon Terri- tory to the Adirondack Mountains of New York, 6 animals were killed on roads, 2 were shot, and 3 young lynx died from natural causes (Brocke et al. 1992). The home range sizes of translocated animals were very large, averaging 1,760 km^ for males and 421 km^ for females, suggesting that they exhibited the unsettled behavior of recently translocated ani- mals, which may make them more vulnerable to both human-related and natural mortality (Brocke et al. 1992). The authors suggest that large, continuous blocks of public land, with minimal development or roads providing vehicular access, will be critical for the survival of reintroduced lynx. Management Considerations 1. Differences in the home range requirements and social organization of lynx in different areas indicate that management is best considered at regional lev- els, rather than provincial or state levels. Consider- ing the role that emigration may play in population dynamics at a regional scale, it is also important to recognize that management activities in one area may affect populations in neighboring and outlying regions. 2. Habitat management for lynx would benefit from a consideration of local home range sizes and distributions, and vegetative and physiographic fea- tures which may serve as home range boundaries. Researcti Needs 1. Many authors have suggested that periodic ir- ruptions of lynx in Canada, resulting in the emigra- tion of lynx to peripheral areas outside of their core range, are an essential factor in the maintenance of marginal populations. Although they will be ex- tremely difficult to conduct, studies are needed to assess the importance of immigration on the demo- graphics and persistence of peripheral populations. COIVIMUNITY INTERACTIONS The lynx is a specialized predator of snowshoe hares; its geographic distribution, the habitats it se- lects, its foraging behavior, reproductive capacity, and population density are all affected by the distribu- tion and abundance of the snowshoe hare. The snow- shoe hare is also an important part of the diet of sev- eral other predators in boreal forests of North America. In central Canada, hares may comprise 20.4-51.8% of the winter diet of marten {Martes americana) (Bateman 1986; Thompson and Colgan 1987) and hares are also potentially important in the diets of fishers {Martes pennanti) and, to a lesser ex- tent, wolverines {Gulo gulo). Their different foraging strategies and use of habitats, however, may mini- mize opportunities for competition for prey between these species and lynx (see chapters on marten, fisher, and wolverine). At northern latitudes, coyotes, red foxes, and several species of raptors also prey on 92 hares, and at southern latitudes, bobcats may also be significant competitors. Other mammalian predators and raptors that prey on hares may contribute to increased mortality and depressed populations of hares, which could affect the availability of prey for lynx (Boutin et al. 1986; Dolbeer and Clark 1975; Keith et al. 1984; Sievert and Keith 1985; Trostel et al. 1987; Wolff 1980). In south- west Yukon, hares comprised 86.2 and 77.0% of coy- ote and red fox diets, respectively (Theberge and Wedeles 1989). Coyotes also preyed on hares in Alaska during winter, where hares occurred in 16% of coyote scats and 64% of lynx scats examined (Staples and Bailey 1993, unpubl.). Keith et al. (1984) found lynx to kill 0.8 hares/ day, coyotes 0.6/ day, and great horned owls 0.35 /day; half of the mortality of radio-collared hares was attributed to coyote kills. At southern latitudes, Litvaitis and Harrison (1989) found snowshoe hare remains in 64.7-84.0% of bob- cat diets and 29.3-66.7% of coyote diets. Although their diets may overlap, differences in habitat selection may minimize competition for prey resources by lynx and other predators, especially during winter. Measurements show the relative sup- port capacity of lynx paws to be twice that for bob- cat paws (Parker et al. 1983) and 4.1-8.8 times that of coyote paws (Murray and Boutin 1991), enabling lynx to exploit high-elevation areas where deep snow would exclude coyotes and bobcats (Brocke et al. 1992; Koehler and Hornocker 1991; Murray and Boutin 1991; Parker et al. 1983). However, opportu- nities for resource overlap among these species may increase during winter due to increased access to high-elevation habitats via snowmobile trails and roads maintained for winter recreation or forest man- agement activities. Increased competition from other predators may be particularly detrimental to lynx during late winter when hare numbers are lowest and lynx are nutritionally stressed. Management Considerations 1. Because the ranges of lynx, bobcats, and coy- otes overlap in the western mountains, competition for snowshoe hares and other prey species may be of significant management concern. Research Needs 1 . Determine the extent to which lynx compete with other predators for prey, and under what conditions competition may adversely affect lynx populations. CONSERVATION STATUS IN THE WESTERN MOUNTAINS Lynx populations in the western mountains of the United States occur at the periphery of the species' range in North America. At high elevations, climatic conditions similar to those occurring at higher lati- tudes support boreal forests, snowshoe hares, and lynx. Populations in this region, particularly those found in Wyoming, Utah, and Colorado, exist at low densities in fragmented and disjunct distributions. Although habitats at high elevations in the western mountains are sufficient to support this boreal com- munity, ecological conditions there vary in signifi- cant ways from those in boreal regions of Canada and Alaska. Because of the fragmented nature of habi- tat and the presence of facultative predators and po- tential competitors in the western mountains, snow- shoe hare populations and, consequently, lynx popu- lations do not exhibit dramatic population cycles (Koehler 1990). In the western mountains, popula- tions of both species occur at densities comparable to those found during hare population lows in Canada and Alaska. Additionally, available evidence indicates that lynx food habits, natality and mortal- ity rates, habitat use, and spatial patterns in the west- ern mountains are comparable to those occurring in the north when hare populations are at low densities. Lynx are vulnerable to trapping, and the effect of trapping mortality on population numbers appears to be largely additive, not compensatory. Brand and Keith (1979) speculated that during hare population lows when recruitment in lynx populations is low, intensive trapping of lynx could result in local ex- tinctions. These authors recommended that trapping of lynx in northern boreal forests should cease dur- ing the 3-4 years when hare populations are at their lowest levels. Because hare populations are always at generally low levels in the western mountains, this line of reasoning suggests that complete protection of lynx populations in the western states may be ap- propriate to ensure their population persistence. Lynx are protected in Wyoming, Utah, and Colo- rado, and Washington closed the lynx harvest in 1991 when the north Cascades lynx population was peti- tioned for federal listing as endangered. The petition was denied (Federal Register 1992, 1993), but Washing- ton State classified the lynx as threatened in October 1993 (Washington Dept. of Wildlife 1993, unpubl.). Lynx are still classified as furbearers in Idaho and Montana, although strict harvest quotas are imposed (table 2). 93 The range of lynx in the western mountains has diminished over the last century, suggesting that lynx may be negatively impacted by development. Be- cause suitable habitats are more fragmented and re- stricted in extent in the western mountains, lynx may be less tolerant of human activities there than in Canada and Alaska, where refuge habitats are more prevalent. Thus, providing protected areas within optimal lynx habitat in the western mountains may be important for the persistence of lynx populations. Landscape-level research using radio-telemetry and GIS analyses are needed to study the effects of hu- man activity on lynx populations. It is of critical importance to the conservation of lynx in the western mountains to evaluate the extent to which these populations are tied to source popu- lations in Canada. Emigrating lynx appear to have very low survival rates. Are southern populations augmented periodically by lynx moving in from the north, or are they simply maintained at low levels by habitat limitations and unaffected by such immi- gration? Will international cooperation involving lynx population management be required, or should efforts be directed at habitat management at the lo- cal or regional level? Answers to these questions will be essential to the design of management strategies for lynx, especially in Washington, Idaho, and Montana. Only five lynx studies have ever been conducted in the western mountains of the United States, in- cluding two in Washington and three in Montana (table 3). These studies have been concerned mainly with home range characteristics and habitat use; in- formation on demography, food habits, dispersal, and denning sites is almost totally lacking. Additional research on lynx in the western mountains, especially studies of their foraging ecology, den site character- istics, and habitat relationships at the landscape scale, are urgently needed. The conservation of such a wide-ranging and specialized predator will require a significant commitment of resources to obtain the information needed to maintain viable populations in the western United States. LITERATURE CITED Adams, L. 1959. An analysis of a population of snow- shoe hares in northwestern Montana. Ecological Monographs. 29: 141-170. Adams, A.W. 1963. The lynx explosion. North Da- kota Outdoors. 26: 20-24. Anonymous. 1986. Lynx. [Unpubl. rep.L Committee on International Trade in Endangered Species. Canadian Status Report. 31 p. Bailey T.N.; Bangs, E.E.; Portner, M.R, [et al.]. 1986. An apparent overexploited lynx population on the Kenai Peninsula, Alaska. Journal of Wildlife Man- agement. 50: 279-290. Table 3.— Studies of lynx in the western mountains of the United States, excluding Alaska, by subject. Only studies for which the subject was an objective of the study are listed; incidental observations are not included. Sample size is number of animals or carcasses studied or, for food habits, number of scats or gastrointestinal tract contents examined. Dispersal refers only to movements away from the mother's home range by juveniles; data on emigration by adults are not included. Separate studies are indicated with an asterisk (*). Topic, author Location Method Duration Sample size Home range and habitat use *Brittell etal, 1989, unpubl. *Koehler 1990 *Koehler et al. 1979 •Smith 1984 •Brainerd 1985 Demography Brainerd 1985 Food habits Koehler 1990 Dispersal None NE Waslnington NE Washington NW Montana W Montana W Montana W Montana NE Washington Telemetry (hr)' Telemetry (hr) Telemetry (hr) Telemetry (hr) Telemetry (hr) Carcasses Scats 34 months 25 months 8 months 23 months 25 months 4 trapping seasons 25 months 15 7 2 4 7 20 29 Natal dens Koehler 1990 NE Washington Telemetry 25 months 4 dens; 2 females ' (hr) - home range size reported. 94 Bailey, V. 1918. Wild animals of Glacier National Park. Washington, DC: Government Printing Office. 210 p. Bailey, V. 1936. The mammals and life zones of Or- egon. North American Fauna. 55: 1-416. Barnes, C.T. 1927. Utah mammals. Salt Lake City, UT: University of Utah; Bulletin. 183 p. Bateman, M.C. 1986. 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Bougy, Swit- zerland: Cat Specialist Group, Cat News. 18: 24. 98 Chapter 5 Wolverine Vivian ^nci,(Minlstry of Environment, Lands and Paries, Wildlife Branch, Victoria, British Columbia^ INTRODUCTION The wolverine {GuXo gulo) is the largest-bodied ter- restrial mustelid. Its distribution is circumpolar; it occupies the tundra, taiga, and forest zones of North America and Eurasia (Wilson 1982). North Ameri- can wolverines are considered the same species as those in Eurasia. They are usually thought of as crea- tures of northern wilderness and remote mountain ranges. In fact, wolverines extend as far south as California and Colorado and as far east as the coast of Labrador, although low densities are characteris- tic of the species. Relative to smaller mustelids, the wolverine has a robust appearance, rather like a small bear. Its head is broad and rounded, with small eyes and short, rounded ears. The legs are short, with five toes on each foot. The claws are curved and semi-retractile and are used for climbing and digging. The skull and teeth are robust and the musculature, especially of the head, neck and shoulders, is well developed. These adaptations allow the wolverine to feed on fro- zen flesh and bone (Haglund 1966). Typical weights for adult males are 12-18 kg and for adult females, 8-12 kg. Adult males are 8-10% larger in measure- ments and 30-40% larger in weight than females. The coat is typically a rich, glossy, dark brown. Two pale buff stripes sweep from the nape of the neck along the flanks to the base of the long, bushy tail. The fur on the abdomen is dark brown. White or or- ange patches are common on the chest or throat. Occasionally the toes, forepaws or legs are marked with white. Color can vary strikingly, even within the same geographical area, from a pale brown or buff with well defined lateral stripes to a dark brown or black with faint or no lateral stripes. Very blond or "white" wolverine are rare. Because of the exten- sive within-site color variation, geographical differ- ences in color do not seem to be apparent, except for possibly greater incidence of white markings in some areas. Color does not vary markedly with season. A single visible moult extends from spring or early summer to autumn (Obbard 1987). Age and sex dif- ferences are seldom described, but Holbrow (1976) suggested that younger animals may be darker. The wolverine has been characterized as one of North America's rarest mammals and least known large carnivores (table 1). Only four North Ameri- can field studies have been completed: two in Alaska (Gardner 1985; Magoun 1985) and one each in the Yukon (Banci 1987) and Montana (Hornocker and Hash 1981). Additional studies, including one in Idaho, Alaska, and the Yukon are in progress (table 1). Reproduction and food habits of northern wol- verine have been described from analyses of carcasses (table 1). Information on the habitat and population ecology of wolverines in the forests of western North America is mainly anecdotal or not available. Because of reductions in numbers and in distributions, in- creasing emphasis is being given in some western North American areas such as California, Colorado, and Vancouver Island, British Columbia, as to whether wolverine still occur. The paucity of infor- mation is largely due to the difficulty and expense of studying a solitary, secretive animal that is rare com- pared to other carnivores, and is usually found in remote places. The wolverine's importance to humans began with the fur trade. Wolverine fur is renowned for its frost- resistant qualities (Quick 1952) and is sought for use as trim on parkas, especially by the Inuit of Canada and Alaska. Although wolverine fur typically is not used for making coats, it is commonly used in rugs and taxidermic mounts. The names by which wol- verine are known are colorful and descriptive. The Cree names ommeethatsees, "one who likes to steal" and ogaymotatowagu, "one who steals fur" (Holbrow 1976), refer to wolverine raiding traplines, cabins and caches, and removing animals from traps. They are called "skunk-bears" because they mark the food they kill or claim, including the contents of cabins, with musk and urine. "Glutton" refers to its mytho- 99 Table 1.— The knowledge base for the wolverine in North America by subject. This Includes studies for which the subject was a specific objective of the study; incidental observations are not Included. Sample size is number of animals studied, or for food habits, number of scats or gastrointestinal tract contents, unless stated othenvise. Sample sizes for dispersal Include only juveniles. Theses and dissertations are not considered separately from reports and publications that report the same data. Individual studies are represented by (*) dis- counting redundancies. Duration Sample Topic, author Location Method (years) size Note Home range & habitat use *Hornocker and Hash 1981 NW Montana Telemetry 1 24 'Gardner 1985 SO Alaska' Telemetry A A 1 z *Magoun 1985 NW Alaska Telemetry A 4 19 *Banci 1987 SW Yukon Telemetry 4 ID Demography 'Wright & Rausch 1955 Alaska Carcasses 4 33 *Rausch & Pearson 1972 Alaska & Yukon Carcasses 5 697 Liskop et al. 1981 N British Columbia Carcasses Z on vU Gardner 1985 A 1 ^ 1 . ^ 1 SC Alaska' Carcasses o 0 / 1 Magoun 1985 NW Alaska Carcasses 4 /. "7 o/ Banci & Harestad 1988 Yukon Carcasses 3 413 Food Habits kausch 1959 Alaska Gut analysis 4 (winter) on ZU Stomachs Rausch & Pearson 1972 Alaska Carcasses 5 (winter) 192 G.I. tracts Hornocker & Hash 1981 NW Montana Scats 6 (Dec-Apr) 56 # individuals unknown Gardner 1985 SC Alaska' Carcasses 4 (Dec-Mar) 35 Colons Gardner 1985 SC Alaska' Observations 3 (Apr-Oct) 9 Of 70 telemetry flights Magoun 1985 NW Alaska Scats 2 (Nov, Feb, Mar) 82 # individuals unknown Magoun 1985 NW Alaska Observations 4 (May-Aug) 48 Of 362 5-min. periods Banci 1987 Yukon Gut analysis 4 (Nov-Mar) 411 G.I. tracts Dispersal Gardner 1985 SC Alaska' Telemetry 4 2 2 moles Magoun 1985 NW Alaska Telemetry 4 7 4 males Banci 1987 SW Yukon Telemetry 4 3 1 mole Natal Dens Magoun 1985 NW Alaska Observations 4 4 3 females ' Three field studies are currently in progress: Golden et al. 1 993, south-central Alaska: Cooley, pers. comm. . northern Yul! ueeriouge V Y M IN Y M In V Y M IN D r M IN riaTneau V Y V Y V Y M IN V Y M IN v Y M IN >c7aiiaTin V Y M IN M IN M / A IN/ A v Y Nl IN v Y M In neiena V Y IN D r M In V Y Nl IN v Y M In luano runrianaie V Y Y V Y M IN V Y Nl IN V Y M In l//^ 4" /'-\ r~\ 1 KOOTenai V Y M IN v Y M IN v Y Nl IN Y M IN Lewis ana v^iarK V Y M IN V Y M IN Y V Y Y v Y LOIO V Y M IN V Y M IN V Y Nl IN v Y Nl IN iNez rerc© V Y V Y V Y v Y V Y Nl IN Y Nl IN Arapaho-Roosevelt Y Y N 1 N N/A N N/A N 1 N N t / A N/A Bighorn \ / Y Y Y N 1 N N N/A N N/A □lack Hills Y Nl N M N M / A N/A N 1 N 1 / A N/A N 1 N N 1 / A N/A Grand Mesa Y Y N N/A N N/A N N/A Gunnison Y Y N N/A N N/A N N/A ivieaicine dow V Y V Y M In M / A IN/ A M IN M / A IN/ A Nl IN M / A In/ A Pike Y Y N N/A N N/A N N/A Rio Grande Y Y N N/A N N/A N N/A Routt V Y N 1 N N/A 1 N / / A N 1 N N/A 1 N / / \ N 1 N N/A 1 N / AA \J\J\ i lOkJk^t?! Y T Y N 1 N N/A 1 N / / \ N IN N/A 1 N/ AA N IN N/A 1 N / AA Qnn li inn Y 1 Y T N N/A N IN N/A N IN N/A 1 N / AA Ol lUol Iv^l it^ Y T Y T IN N /A M IN M / A In/ M In M / A IN/ AA Y T Y T N 1 N N/A M IN M/ A 1 N/ M N In M / A 1 N/ AA VV 1 III t7 Kl V t?l Y T N 1 N Y T N IN M IN M / A IN/ M IN M / A IN/ AA Corson Y M IN M IN M / A IN/A Nl N M / A N/A Nl M / A N/A oania re V Y M IN M In M / A In/ A IN M / A IN/A Nl M / A In/ A Ashely Y N N/A N N/A N N/A Boise Y N N/A N N/A Y N Bridger-Teton Y N 1 N N/A N N/A Y N Caribou Y N N/A Y Y Y N Challis Y N N/A N N/A Y N Dixie N N/A N N/A N N/A N N/A Fishlake N N/A N N/A N N/A N N/A HumuoidT N M / A IN/A M In N! / A N/A Nl N N/A K 1 N N/A ManTi-Laoai M In M / A IN/ A M In M / A IN /A IN M / A N/A Nl N M / A N/A Payette \/ Y Y Nl N N/A Y N Salmon Y v Y M In M / A N/A \/ Y Y Y N bawtooth Y M M / A N/A Nl N N 1 / A N/A Y N Targhee Y Y N 1 N N 1 / A N/A Y N Toiyobe Y N N/A N N/A Y N Uinta N N/A N N/A N N/A N N/A Wasatch-Cache Y N N/A Y N Y N Eldorado Y N Y N N N/A N N/A Inyo Y N N N/A N N/A Y N Klamath Y N Y N N N/A Y N Lk Tahoe Basin MU Y N N N/A N N/A Y N Lassen Y Y N N/A N N/A Y N Mendocino Y N Y N N N/A N N/A (continued) 177 Table 1 .—(continued) MARTEN FISHER LYNX WOLVERINE Region National Forest Presence MIS? Presence MIS? Presence MIS? Presence MIS? Modoc Y Y N N/A N N/A N N/A Plumas Y Y N N/A N N/A N N/A Sequoia Y N Y N N N/A Y N Shasta-Trinity Y N Y N N N/A Y N Sierra Y N Y N N N/A Y N Six Rivers Y N Y N N N/A Y N Stanislaus Y N Y N N N/A Y N Tahoe Y Y Y N N N/A Y Y 6 Colville Y MR N K 1 / A N/A Y N Y N Deschutes Y MR N N/A N N/A Y N Fremont Y MR N N/A N IV 1 / A N/A N N/A Gifford Pinchot Y MR Y N Y N Y N Mt.Baker/SnoqualmIe Y MR U N Y N P N Mt. Hood Y MR N N/A Y N Y N Maiheur Y MR U N Y N Y N Ochoco Y N N N/A N N/A Y N Ol