Historic, Archive Document
Do not assume content reflects current
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(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. However, this
loss of habitat quality may not occur in all areas.
Generally, consistent preference is not shown by
martens until stands reach the "mature" or
"overmature" stage.
8. Changes in patterns of distribution and abun-
dance of martens indicate that this species is not se-
cure throughout its range. In areas where popula-
tions appear to have been isolated by human actions,
or where already isolated populations have had the
carrying capacity of the habitat reduced, immediate
measures to ensure persistence appear prudent.
Given the marten's association with late-successional
29
forests, we believe there is an urgent need to base
further assessments of conservation status on addi-
tional research addressing issues of marten-land-
scape relationships.
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36
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37
Chapter 3
Fisher
Roger A. 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. If fisher
populations are limited by deep snow, however, fish-
ers may never reach high densities in these moun-
tain states.
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Yocum, C.F; McCollum, M.T. 1973. Status of the fisher
in northern California, Oregon and Washington.
California Fish and Game. 59(4): 305-309.
York, E.C.; Fuller, T.K. [In press]. Fisher population
dynamics: in pursuit of lambda. International
Union Game Biologists.
Young, H.C. 1975. Pequam the fisher. Fur-Fish-Game.
71(11): 16-17, 48-50.
Zielinski, W.J. 1986. Relating marten scat contents to
prey consumed. California Fish and Game. 72:
110-116.
73
Chapter 4
Lynx^
Gary M.|Koehler, 6505 Markel Road, Deming, Washington
Keith B(Aubry, USDA Forest Service,
Pacific Northwest Research Station, Olympia, Washington
INTRODUCTION
Natural History
Three species of wild cats (felids) occur in the tem-
perate forests of North America: the cougar {Felis
concolor), bobcat {Lynx rufus), and lynx {Lynx
canadensis). 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.
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Trostel, K.; Sinclair, A.R.E.; Walters, C.J., [et al.]. 1987.
Can predation cause the 10-year cycle? Oecologia.
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Tumlinson, R. 1987. Felis lynx. Mammalian Species.
American Society of Mammalogists. 269: 1-8.
97
Turbak, G. 1991 . The cat survives by a hare. National
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van Zyll de Jong, C.G. 1963. The biology of the lynx,
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van Zyll de Jong, C.G. 1966. Food habits of the lynx
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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