United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

General Technical

Report RMRS-GTR-25

April 1999

Small Mammals of the

Bitterroot National Forest:

A Literature Review and

Annotated Bibliography

Dean E. Pearson

This file was created by scanning the printed publication.

Errors identified by the software have been corrected;

however, some errors may remain.
Abstract

Pearson, Dean E. 1999. Small mammals of the Bitterroot National Forest: A literature review and annotated

bibliography. General Technical Report RMRS-GTR-25. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Research Station. 63 p.

Small mammal literature from western Montana and the Northern Rocky Mountains was reviewed to assess the

ecological role of small mammals on the Bitterroot National Forest of western Montana and in the Northern Rocky

Mountains. The goal was to understand how small mammals relate to succession and how proposed ecosystem

management goals would affect small mammals, the predators they support, and the roles they play in forest ecosystem

functions. Small mammals fulfill numerous important roles in forest ecosystems by supporting a wide range of predators,

dispersing seeds and mycorrhizal spores, altering the composition of vegetative communities through herbivory and

seed predation, and preying on insects. Coarse woody debris (CWD) is among the most important habitat components for forest

small mammals. Guidelines are suggested for managing CWD for small mammals with an emphasis on CWD recruitment.

Keywords: small mammals, coarse woody debris, Montana

The Author

Dean E. Pearson is a wildlife biologist with the Wildlife Habitat Relations in the Northern Rocky Mountains Research Work

Unit at the Rocky Mountain Research Station’s Forestry Sciences Laboratory, Missoula, MT. He conducts research on

small mammals and mid-sized carnivores in the Northern Rocky Mountains. He holds a B.S. degree in wildlife biology and

an M.S. degree in zoology from the University of Montana. Since beginning his career with the Forest Service in 1995, he

has conducted research on habitat selection by American marten and small mammal ecology primarily in forest

ecosystems.

Publisher

Rocky Mountain Research Station

April 1999

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Cover: photo of Vagrant shrew (top) is by Kerry R. Forsman

Cover: photos of Northern flying squirell (left), Deer mouse (right), and Southern red-backed vole (bottom) are by Milo Burcham
Small Mammals of the Bitterroot National Forest: A 

Literature Review and Annotated Bibliography 

Dean E. Pearson 

Contents 

PART I -LITERATURE REVIEW ............................................................................... . 

Introduction . .. . . .. . .. . .. . . . . . . . .. . . . .. .. . . .. ... . .. .. .. ..... .. . .. . .. .. . . .. . ... . .. . .. . . .. . . . .. . . .. .. .. .. . .. . ... . . 1 

Region of Literature Search . .. . . .. . . . .. ... . . . .. . . . . . .. .. . .. . . . . . . .. . . . .. . . .. . . .. . .. . ..... 2 

Defining Small Mammals . ... . .. . .. ... . .. . .. . .. . . .. .. .. . .. . . . . . . . .. . . . .. . .. . . . ... . . .. . .. . .. 2 

Characteristics of Small Mammals Affecting Ecological Interactions............. 2 

A-Selected . .. . ...... ..... ..... .. . . .. ... . . . ... .. . . .. . . . .. .. .. ... .. . .. ... . . ... ... .... .. . . ... .. . ..... 4 

Surface-Area-to-Volume Ratios and Winter Survival Strategies....... 4 

Ecological Role of Small Mammals in Forest Ecosystems ........................... . 

Seed Predation ................................................................................ . 

Direct Effects on Trees ..................................................................... . 

5 

5 

6 

Insect Predation . . . . . .. . . . .. . .. . . .. . .. . . .. . .. . . . . .. . . . . . . . . .. .. ... ... . . . .. . . . . . .. .. .. .. ... . . .. .. 6 

Mycophagy and Spore Dispersal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Prey-Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 

Source and Sink Populations .... ...... ............. .............. ................... .... 13 

Rare and Sensitive Small Mammals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13 

Bats................................................................................................... 13 

Pygmy Shrew.................................................................................... 14 

Dwarf Shrew...................................................................................... 14 

Preble's Shrew . . .. . . . .. . .. . .. .. . .. ... . .. . ... . .. .. . . . . . . . . . .. . . . . . . . . . . .. .. . .. . .. . . . . . . .... ... . .. 14 

Northern Bog Lemming .. . . .. . .. . . . . . .. . . .. .. . . . . . . . . . .. . . .. . . . .. . .. . . . . . . .. ... . . . ... . . ... . . 14 

Habitat Associations....................................................................................... 15 

Shrews ............................................................................................. 15 

Bats................................................................................................... 18 

Pika ................................................................................................... 20 

Snowshoe Hare................................................................................. 20 

Chipmunks . . .. . ... . . . . . . . . . .. . . .. .. . . .. . . . . .. . . . . . .. . .. . . . . . .. . . . . . . . . . . . . . . . . . . .. .. .. . . .. . . . . . . . . 20 

Ground Squirrels............................................................................... 21 

Red Squirrel . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . .. . . .. . .. . . .. . 21 

Northern Flying Squirrel .................................................................... 22 

Northern Pocket Gopher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

Deer Mouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

Bushy-Tailed Woodrat ....................................................................... 23 

Northern Bog Lemming . . . . . .. . .. . . . . . . . . . . . . . . . . . .. . . . .. . . . .. . . . . . . . .. .. . . . . . . .. . . . . . .. . . . . 23 

Montane Heather Vole ...................................................................... 24 

Red-Backed Vole . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. .. . . 24 

Voles (Genus Microtus)..................................................................... 24 

Western Jumping Mouse .................................................................. 25 
Response of Small Mammals to Disturbance .. . . .. . . . . . .. . . . . . .. .. . .. . . . . . . . . . . . . . . . . .. . . . . . 26 

Introduction . . . . . . .. .. . . . . . . . . .. . . . . . . . . . . .. . . . .. . . . . . . . . . . . .. . . . . .. . .. . . . . . . . . . . .. . . .. . . . . . . . . . .. . 26 

Review of Disturbance and Succession Literature............................ 27 

Management Recommendations . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 32 

Coarse Woody Debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 32 

The Ecological Role of Douglas-fir Within Ponderosa Pine Communities ..... 37 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

PART II- ANNOTATED BIBLIOGRAPHY.................................................................. 45 

Introduction .................................................................................................... 45 

Annotated Bibliography.................................................................................. 45 

Acknowledgments 

I wish to thank those people who provided critical support in developing this literature review. Jack Lyon, from 

the Rocky Mountain Research Station, provided an integral link to Forest Service resources and 

knowledgeable guidance in directing this review toward its completion. Irene Voit of the Rocky Mountain 

Research Station, Forest Service Information Center in Ogden, Utah enthusiastically and efficiently attacked 

data bases in an effort to provide an extensive collection of literature for this review while filtering out 

unnecessary sources. Her efforts greatly facilitated my task of synthesizing the vast body of literature that 

exists on small mammals. Margaret Beer of the Montana Natural Heritage Program, Helena, Montana was 

extremely helpful in providing information from the Heritage Program's data bases. Kerry Foresman graciously 

provided copies of manuscripts from his book Wild Mammals of Montana, which is currently in preparation for 

publication. I thank Ellen McCullough for valuable editorial comments, and Amanda Stanley and Morris 

Myerowitz for assisting in preparing this document. I would like to thank the following people for taking the 

time to review earlier draft manuscripts: Steve Arno, Clint Carlson, Greg Hayward, Peter Landres, Bob Lee, 

Dave Lockman, L. Jack Lyon, Kevin McKelvey, Kerry McMenus, L. Scott Mills, Yvette Ortega, Len Ruggiero, and 

Dave Spildie. Funding for this literature review was provided by the USDA Forest Service, Rocky Mountain 

Research Station, Bitterroot Ecosystem Management Research Project. 

.---... 

Federal Recycling Program ~ .. , Printed on Recycled Paper 
PART I - LITERATURE REVIEW 

Introduction _________ _ 

The purpose of this literature review is to: 

1) identify the small mammals of the Bitterroot 

National Forest; 

2) determine their habitat associations with regard to moisture, elevation, and successional 

gradients; 

3) outline the ecological importance of the various 

taxa; and 

4) determine the possible outcome of land management practices on composition and abundance of the small mammal communities and 

the potential effects of changes in the small 

mammal communities on the ecosystem as a 

whole. 

To this end, an examination and review of the 

relevant literature on small mammals is presented 

here with an annotated bibliography of the more 

pertinent local and regional research. 

In 1993, the Bitterroot National Forest ,CBNF) 

initiated the Bitterroot Ecosystem Management Research Project (BEMRP). This project applies an 

ecosystem-level multi-disciplinary approach to research and management on the BNF. The primary 

goal of BEMRP is to restore an ecosystem, altered by 

fire suppression and timber harvest, to a n1ore natural state and in so doing reduce the potential for 

catastrophic fire by favoring natural, low-intensity 

ground fires. 

Low- to mid-elevation habitats on the BNF were 

historically dominated by dry seral ponderosa pine 

(Pinus ponderosa) and moist seral ponderosa pinewestern larch (Larix occidental is) stands. Open understories in these fire-dependent, savanna-like forests 

were maintained in presettlement times by frequent, 

low-intensity fires (Arno 1976). One-hundred years 

of fire suppression and timber harvest practices 

have encouraged dense stands of Douglas-fir (Pseudotsuga menziesii) and grand fir (Abies grandis) within 

the under- and midstories and, in some cases, the 

canopy. Overcrowded stand conditions and the ensuing competition for limited resources has increased 

the susceptibility of stands to disease and insect 

infestations. With this buildup in the under- and 

USDA Forest Service Gen, Tech. Rep. RMRS-GTR-25. 1999 

midstory, which contributes to the fuel loads and 

provides a fire ladder to the canopy, the stage is set 

for catastrophic fires. Because low-elevation ecosystems of the BNF are adapted to a low-intensity, highfrequency fire regime (Arno 1976), intense fires 

may deleteriously affect these habitats. Catastrophic 

fires obviously lead to undesirable consequences in 

the urban interface. Recent development adjacent to 

the BNF has pushed the urban interface beyond the 

dry, seral ponderosa pine habitat of the lowest elevations into more heavily forested cover types that are 

more susceptible to intense fires. 

The subalpine zone has been similarly impacted. At 

high elevations, the fire-dependent whitebark pine 

(Pinus albicaulis) community has been weakened by 

encroaching subalpine fir (Abies lasiocarpa), and outbreaks of mountain pine beetle (Dendroctonus ponderosa), and white pine blisterrust(Cronartium ribicola) 

(see Arno and Hoff 1989). Unique plant-animal interactions render this an important community for the 

Clark's nutcracker (Nucifraga columbiana) and the 

grizzly bear (Ursus arctos) (Hutchings and Lanner 

1982; Kendall 1981; Tomback 1981). Furthermore, 

whitebark pine is restricted to high elevation sites and 

so persists only within a narrow range of abiotic and 

biotic conditions (Arno and Hoff 1989). 

By reintroducing periodic, low-intensity fire and 

variously applying knowledgeable thinning and harvesting methods, researchers and managers wish to 

1) re-establish fire-dependent, park-like ponderosa 

pine and ponderosa pine-western larch communities 

to presettlement conditions in mid- and lower elevation sites; 2) stabilize high-elevation, whitebark pine 

communities; and 3) reduce the threat of insect infestation, disease, and catastrophic fire on the BNF. 

Re-establishing historic ecosystem functions to the 

Bitterroot watershed will result in local and landscape-level changes in vegetation that will strongly 

affect existing animal communities. To incorporate 

wildlife into the BEMRP framework, a Faunal Research Group was appointed to study the BNF's wildlife populations. Research has been initiated on bird 

and mammal communities to understand how animals fit into historic dynamics of the BNF ecosystem 

and how they will respond to changes proposed in 

BEMRP management strategies. 
In recognition ofthe importance of small mammals 

in forest ecosystems, the BEMRP Faunal Research 

Group, led by L. Jack Lyon, sponsored an exploratory 

research project to investigate the effects of timber 

harvest and fire on small mammal community 

composition and abundance (Landres et al. 1995). 

After an initial field season in 1994, the group found 

that more extensive long-term research than time and 

funding would permit was necessary to answer the 

questions posed. However, the questions were important enough for a group to begin reviewing the 

current scientific literature in order to assess the role 

· of proposed fire and timber management practices on 

composition and abundance of small mammals on 

the BNF. 

In keeping with the goals of BEMRP, this report 

presents an ecosystem-level review of small mammals by elaborating on their ecological interactions on 

the BNF and within the Northern Rockies. The role 

that mycophagous rodents play as catalysts for mycorrhizal symbiosis is critical to forest ecosystem function and so receives critical attention. The trophic 

importance of small mammals as "prey-base" is similarly developed, though somewhat less so, since this 

aspect of interaction has been addressed to a limited 

extent from the carnivore perspective in other recent 

literature reviews (Ruggiero et al. 1994; Heinemeyer 

and Jones 1994; Weaver 1993; Butts 1992a, 1992b). 

Finally, the central position of coarse woody debris 

(CWD) in linking predator with prey and fungi with 

fungivore is examined in light of an ecosystem management perspective. 

Small mammals and habitats reviewed in this document are present throughout the Northern Rocky 

Mountains, and ecological interactions and habitat 

relations discussed here are generalizable throughout 

most of this region. Additionally, many of the ecosystem management principals being applied within 

the BNF will also be applied to much of the Northern 

Rocky Mountains via the Columbia River Basin Project. 

This information is therefore pertinent to most if not 

all National Forests within Region 1 of the United 

States Forest Service. 

Region of Literature Search 

The intent of this project was to review small mammal studies conducted on the BNF and in areas 

within the Northern Rocky Mountain Region that 

fulfilled the criteria of being similar in habitat and 

physiographic attributes to those habitats found on 

the BNF. The extent of research conducted on small 

mammals within the BNF was found to be extremely 

limited. Therefore, ecological information addressing 

small mammals occurring on the BNF was acquired 

primarily from research in theN orthern Rocky Mountains and secondarily the Pacific Northwest. For 

2 

rare species and species under-represented in the 

ecological literature within these regions, review included pertinent information from regions beyond the 

northwestern United States. 

Defining Small Mammals 

The term small mammals is used to describe a 

variety of taxa that fulfill the criteria of being both 

"small" and mammals. Although the term is widely 

used, it provides little information without clearly 

defining the range of taxa being discussed. Table 1 

presents a species list for small mammals occurring on 

or suspected of occurring on the BNF based on surveys 

conducted within the Bitterroot Valley and review of 

species distributions published in the literature. Information made available by the Montana Nat ural 

Heritage Program substantially augmented this species list. The list in Table 1 serves to identify species 

recognized in this literature review as the small mammals of the BNF. Species not included due to the 

terrestrial focus, as outlined in the criteria set forth for 

this review, include the beaver (Castor canadensis) 

and the muskrat (Ondatra zibethica). Small carnivores (Carnivora) are similarly excluded, except to 

the extent of mention in predator-prey interactions. 

Bats (Chiroptera) and snowshoe hares (Lepus 

american us) are, for ecological reasons, not generally 

recognized as members of the more traditional suite 

of small mammals (see Chew 1976). However, the 

snowshoe hare is included because of its importance as 

prey-base, and in some cases, forest pest. Bats are also 

included because of their ecological importance as 

insect predators and their high degree of sensitivity to 

disturbance. 

Forty-one species are listed in Table 1. The volume 

of literature surrounding these species, even when 

geographically delimited to the northwestern United 

States, is tremendous. Although searches of data bases 

were extensive, as evidenced by the literature cited 

section, they could by no means be exhaustive. However, within the realm of the primary focus of this 

review (the response of small forest mammals to 

timber harvest), the literature presented is virtually 

exhaustive for this region. Many similar studies have 

been conducted in the eastern United States and 

Canada that are, for numerous ecological reasons, not 

included here. Most of these have been reviewed elsewhere (Pearson 1994; Kirkland 1990). 

Characteristics of Small 

Mammals Affecting Ecological 

Interactions 

Small mammals are an extremely diverse group of 

organisms representing a variety of ecological guilds. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
Table 1-Small mammals of the Bitterroot National Forest. Common names and former scientific 

names for species are presented in Appendix 1. Nomenclature follows Jones et al. (1992). 

Global and state ran kings and United States Fish and Wildlife Service and United States Forest 

Service status are given as reported in the Montana Natural Heritage Program Element 

Occurrence database for the spring of 1995 (Montana Natural Heritage Program, Helena, MT). 

Rank Status 

Species Presence Global State USFWS USFS 

Cinereus shrew p G5 S5 

Preble's shrew* p G4 S3 

Vagrant shrew p G5 S4 

Montane shrew p G5 S5 

Water shrew p G5 S5 

Pygmy shrew s G5 S4 

Dwarf shrew* s G4 S3 

Little brown myotis p G5 S5 

Yuma myotis ** p G5 S3 

Long-eared myotis p G5 S4 

Fringed myotis * p G5 S3 

Long-legged myotis p G5 S4 

California myotis p G5 S4 

Eastern small-footed myotis p 

Western small-footed myotis s G5 S4 

Silver-haired bat p G5 S4 

Big brown bat p G5 S4 

Hoary bat s G5 S4 

Spotted bat * s G4 S1 

Townsend's big-eared bat* p G4 S2S3 

Pika p G5 S5 

Snowshoe hare p G5 S5 

Columbian ground squirrel p G5 S5 

Richardson's ground squirrel p G5 S5 

Golden-mantled ground squirrel p G5 S5 

Yellow-pine chipmunk p G5 S5 

Red-tailed chipmunk p G5 S5 

Red squirrel p G5 S5 

Northern flying squirrel p G5 S4 

Northern pocket gopher p G5 S5 

Idaho pocket gopher p G4 S3 

Deer mouse p G5 S5 

Bushy-tailed woodrat p G5 S5 

Northern bog lemming p G4 S2 

Heather vole p G5 S5 

Southern red-backed vole p G5 S5 

Meadow vole p G5 S5 

Montane vole p G5 S5 

Long-tailed vole p G5 S5 

Water vole p G5 S4 

Western jumping mouse p G5 S5 

* species of special concern as determined by the Montana Natural Heritage Program 

** watch list species as determined by the Montana Natural Heritage Program 

C2 

C2 

C2 

C2 

C2 

C2 

C2 

C2 

sen 

sen 

sen 

p: present on BNF; confirmations are based on museum specimens, literature review, review of surveys 

conducted on the BNF, or sightings or trapping conducted by the author. 

s: suspected of residing on BNF, based on distribution records and habitat affiliations. 

G1 or 81: species critically imperiled because of extreme rarity ([5 occurrences). 

G2 or 82: species imperiled at the global or state level, respectively, because of rarity or biological factors 

rendering it very vulnerable to extinction (6-20 occurrences). 

G3 or 83: species very rare or local throughout its range or found locally within a restricted range (21-100 

occurrences). 

G4 or 84: species apparently secure though it may be rare in parts of its range. 

G5 or 85: species demonstrably secure though it may be rare in parts of its range. 

C2: category 2; current information indicates that proposing to list as endangered or threatened is possibly 

appropriate, but insufficient biological information exists to warrant immediate listing. 

sen = sensitive: "sensitive" as outlined by the Endangered Species Act. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 3 
They include insectivores (shrews and bats), fungivores 

(northern flying squirrel), omnivores (deer mice and 

red-backed voles), herbivores (voles, pikas), and 

granivores (chipmunks). Species also represent semiaquatic (water shrews), fossorial (pocket gophers), 

terrestrial (most) and arboreal (tree squirrels) habits. 

The great diversity of the species collectively referred 

to as small mammals poses a challenge in terms of 

reviewing the ecological roles they play in the variety 

of environments they inhabit. However, a few important generalizations can be made about small mammals which, in the gross sense, bind them together 

ecologically and justify a collective review of this 

diverse array of taxa. 

R-Selected 

Most small mammals are r-selected. That is to say 

they produce large litters which mature quickly 

with little parental care (bats are the exception). The 

Muridae, mice and voles, are seasonally polyestrous 

and may produce up to 3 litters in a single year (Krebs 

and Meyers 1974). Several species produce litters 

during the winter when resources and conditions 

permit. In some microtine rodents, the first litter of 

the year matures and produces a litter of its own 

within the same season when conditions are optimal 

(Krebs and Meyers 1974). The result of this productivity is an abundance ofbiomass available for harvest by 

predators. 

Surface-Area-to-Volume Ratios and Winter 

Survival Strategies 

Small mammals have high surface-area-to-volume 

ratios that result in excessive heat loss, leaving them 

inordinately susceptible to hypothermia. This physiological condition greatly affects the ecology of small 

mammals living in the northern temperate zone. 

Physiological adaptations that evolved in response to 

cold include hibernation and torpor. Hibernation is a 

long-term depression of metabolic activity and body 

temperature in response to cold-related stress. In 

hibernation, body temperature approximates that of 

ambient temperature, just above freezing (usually 

within a den or cavity) (Schmidt-Nielsen 1975). Torpor 

also involves a reduction in metabolic activity and 

body temperature, but it usually lasts only a short 

time and body temperature drops only a few degrees, 

down to 10 to 20 oc (Wang 1989; Hudson 1978). Both 

are means of surviving periods of low resource availability and cold temperatures, and both affect activity patterns of temperate zone small mammals. This 

is particularly important with regard to the temporal availability of small mammals to predators (see 

Prey-Base section below). 

4 

Ironically, the smallest mammals, those most affected by high surface-area-to-body ratios, do not hibernate. The exception is the western jumping mouse 

(Zapus princeps) (Luoma 1970). Animals not hibernating must resort to behavioral strategies to survive 

extreme winter conditions. Many temperate zone rodents hoard food in anticipation of resource limitations in the winter. Pikas (Ochotona princeps) produce massive haystacks by drying herbaceous plants 

and flowers collected from the edge of talus slopes 

and caching them beneath boulders (Millar and 

Zwickel 1972). Northern pocket gophers (Thomomys 

talpoides) store foods in hypogeous and subnivian 

chambers (Tryon 194 7). Deer mice (Peromyscus maniculatus), chipmunks (Tamias spp.J, and red squirrels 

(Tamiasciurus hudsonicus) cache seeds (Pierce and 

Vogt 1993; Hatt 1943; Gordon 1943). 

Shrews (Sorex spp.), which are at the theoretical 

lower size limit for homeothermy (Pearson 1948), 

employ a variety of behavioral and morphological 

tactics to survive the cold, including communal nesting (Davis and Joeris 1945), food caching (Martin 

1984), and decreasing body mass over winter to 

reduce energy requirements (Mezhzherin 1964). Communal nesting has also been described for deer mice 

(Millar and Derrickson 1992). Many bats (Chiroptera) 

migrate to warmer climates and are unique among 

mammals in this respect. Other small mammals 

periodically enter torpor during winter, especially 

during inclement weather. 

Winter survival strategies affect ecosystem dynamics by directing small mammal interactions with ecosystem components. Hoarding and caching behaviors 

often result in territoriality, which affects social 

structure and population dynamics of small mammals 

and their dispersion within habitats. These factors, in 

turn, regulate their abundance and temporal and 

spatial availability to predators. Seed predation can 

be heavy in some circumstances, but caching may 

result in seed dispersal when caches are forgotten 

(Abbott and Quink 1970; Radvanyi 1970; West 1968). 

In the case of the red squirrel, middens associated 

with caches and feeding areas function as important 

resting sites, denning sites, and access points to the 

subnivian zone for American marten (Ruggiero et al. 

in prep.; Ruggiero et al. 1998; Sherburne and Bissonette 

1993; Buskirk 1984). Red-backed voles appear to be 

more abundant near squirrel middens suggesting 

that middens may also provide important resources 

for these voles (Ruggiero and Pearson in prep.). Hibernation reduces the number of species and individuals 

and thereby the total biomass available to carnivores 

during periods when environmental stress is greatest. 

These characteristics and their resulting impacts are 

discussed in greater detail later. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
Ecological Role of Small Mammals 

in Forest Ecosystems _____ _ 

Small mammals consume little net primary productivity (NPP) in forest ecosystems. On the Hubbard 

Brook Experimental Forest in New Hampshire the 

three most abundant small mammals, the deer mouse, 

the southern red-backed vole, and the woodland 

jumping mouse, consume 0.3 percent of the 

aboveground NPP (Potter 197 4). Energy utilization by 

small mammals in spruce forests (Picea spp.) has been 

estimated at 1.4 to 2.2 percent NPP (Grodzinski 1971; 

Hansson 1971). In general, NPP ingested by small 

mammals in forest ecosystems is less than 0.5 percent 

(see Potter 1976). Potter (1976) argues that use ofNPP 

does not effectively assess the impact that small mammals have on forest ecosystems since much of the 

primary productivity in forests ends up in woody 

biomass (over 50 percent in Hubbard Brook [Whittaker 

et al. 197 4]) and within the canopy, where it is unavailable to small mammals. 

Although small mammals affect NPP only slightly, 

the specificity of their diets and high reproductive 

rates provide them with a means to greatly impact 

various aspects of ecosystem dynamics. Selective foraging by northern pocket gophers (Thomomys 

talpoides) for preferred forbs can affect species composition of local meadows and grasslands (Laycock and 

Richardson 1975). Pikas can significantly alter the 

composition of vegetation bordering talus slopes by 

selective foraging within a restricted swath surrounding such areas (Huntly 1987; Huntly et al. 1986). 

Shrews may function as keystone predators increasing diversity of insect communities by depredating 

the dominant insect species in the community (Anderson 

and Folk 1993), and deer mice and short-tailed shrews 

can control economically important insect pests 

through functional and numerical responses to prey 

increases (Holling 1959). Early research on forest 

small mammals arose due to concerns over their impact as seed predators (Tevis 1956a, 1956b) but has 

more recently recognized the potentially positive role 

small mammals play in mycorrhizal spore dispersal 

(Maser et al. 1978; Fogel and Trappe 1978). Perhaps 

the most prominent role of small mammals in community ecology is that of prey base supporting many 

carnivore species. 

Seed Predation 

Much of the early research on forest small mammals was conducted because of concerns that rodents 

deleteriously affect conifer regeneration by consuming conifer seeds (Gashwiler 1967, 1965; Tevis 1956a, 

1956b; Squillace 1953; Adams 1950). Rodent seed 

predators in the Northern Rocky Mountains include 

USDA Forest Service Gen. Tech. Rep. RivlRS-GTR-25. 1999 

red squirrels, chipmunks, deer mice, and southern 

red-backed voles (Radvanyi 1973, 1970; Schmidt and 

Shearer 1971; Adams 1950). Of these, red squirrels, 

which specialize in harvesting conifer seeds, are 

the most effective seed predator within forest stands 

(Smith 1970; Hatt 1943; Yaeger 1937). Red squirrels 

have an advantage over terrestrial rodents because 

they harvest cones before seed dispersal occurs. In 

northwest Montana, red squirrels removed as much as 

82 percent of the ponderosa pine seed crop from a 

study site in 1965, but the average for 3 years was 

44 percent (Schmidt and Shearer 1971). Smith (1970) 

contends that selective foraging by red-squirrels 

affects a variety of cone characteristics including 

number of seeds per cone, the time when cones shed 

seeds, the thickness of seed coats, and annual fluctuations in volume of cone crops. He concludes this 

selective pressure has resulted in a co-evolutionary 

relationship between conifers and squirrels. Deer 

mice may be the second most important conifer seed 

predator (Sullivan 1979a; Gashwiler 1979; Radvanyi 

1973; Abbott 1961). They are generally the primary 

small mammal predator of seeds that reach the forest 

floor (Schmidt and Shearer 1971; Adams 1950). Both 

red squirrel and deer mouse population fluctuations 

have been correlated with changes in conifer seed 

crops (Halvorson and Engemen 1983; Gashwiler 1979; 

Schmidt and Shearer 1971). 

When seed predation in forests is presented as a 

percentage of total mast consumed, the percentages 

are generally relatively small (Potter 1976), and when 

the potential population of seeds has been examined, 

seed abortions account for 70 percent of the total seed 

loss, red squirrels 14 percent, and other small mammals and birds 2 percent (Schmidt and Shearer 1971). 

The effect that rodent seed predation may have on 

stand composition is unclear, but evidence may suggest that small mammals do influence tree biology. 

For example, the phenomenon of mast fall may have 

evolved in response to seed predation in an "attempt" 

to saturate predators in space and time so that sufficient seeds would survive to germinate. Such asynchronous fluctuations in populations of seed predators 

and mast are likely to result in many seeds surviving 

predation during years when small mammal populations are low and seed production is high (Potter 1976). 

Seedling survival studies have shown that survival 

was inversely proportional to seed germination (Hett 

1971). Rodent seed predation during mast years 

could therefore function to thin seeds and bring 

about an increase in successful germination due to 

decreased competition for nutrients. Caching behavior exhibited by red squirrels, chipmunks, deer mice, 

and southern red-backed voles can result in seed 

dispersal when unused or forgotten caches germinate 

(Abbott and Quink 1970; West 1968; Tevis 1953). 

5 
These caches sometimes contribute significantly to 

tree recruitment. West (1968) concluded that 15 percent of ponderosa pine regeneration at his central 

Oregon study site originated from rodent caches, and 

Tevis (1953) suggested that the yellow-pine chipmunk (Tamias amoenus) was an important factor 

affecting natural stand regeneration in northeastern 

California. Severity and length of winter are presumably unpredictable. Evolution should therefore favor 

"over-achievement" among hoarding species. Ideally, 

stores will last into the spring, and as new crops 

mature they should be nutritionally and palatably preferable to last year's caches. This phenomenon would 

likely result in unused seed caches except in years of 

severe conditions when all caches are exhausted. 

However, in intensively managed stands where 

manual seeding occurs, chipmunks and deer mice 

may deleteriously affect seeding efforts (Radvanyi 

1973, 1970; Gashwiler 1967). This situation may be 

exacerbated if structure is removed through piling 

and burning of logging slash, since structure may 

provide "hiding'' places for seeds. Radvanyi (1970) 

determined that approximately 50 percent of radiotagged spring-placed white spruce (Picea glauca) 

seeds were consumed within four months of placement. Krauch (1936) suggested that fire after logging 

aided stand regeneration by decimating populations 

of seed eating rodents, but Tevis (1956b) provided 

conclusive evidence that slash burning increased deer 

mice (the primary seed predator) populations on recent clearcuts. Other studies have also demonstrated 

increases in deer mice populations on burned clearcuts (Hooven and Black 1976; Hooven 1969). 

Under these circumstances, timing of seeding is an 

important factor in reducing seed predation. Radvanyi 

(1970) observed that winter-placed radiotagged seeds 

exhibited 19 percent loss to predation whereas 50 

percent loss was reported for spring-placed seeds. 

However, he observed a 5- to 6-fold increase in germination of winter-placed over spring-placed seeds and 

suggested that other factors, such as availability of 

moisture, are at least equally important in increasing germination rates following winter seeding. 

Supplemental feeding is another technique shown to 

reduce seed predation by deer mice in intensively 

managed stands (Sullivan 1979b). 

Though rodents consume large numbers of conifer 

seeds (Sullivan 1979a; Radvanyi 1973, 1970; Schmidt 

and Shearer 1971; Adams 1950), no evidence was 

found that small mammal seed predation negatively 

affects natural forest regeneration. In fact, seed predation may increase seedling survival by reducing site 

competition (Hett 1971). Granivorous rodents may 

greatly reduce the number of manually placed seeds in 

clearcuts, and the more heavily managed a stand, the 

more important rodent seed predation may be, since 

6 

alternative foods will be scarce. Supplemental feeding 

and later-winter seeding reduce seed predation by 

deer mice (1979b). These methods are more effective 

than pest control measures which often fail (see Malloy 

1981; Sullivan 1979a). 

Direct Effects on Trees 

Debarking of trees and destruction of seedlings by 

porcupines (Erithizon dorsatum), snowshoe hares 

(Lepus americanus), red squirrels, and northern 

pocket gophers are also means by which small mammals may alter primary productivity and stand composition in forests (Sullivan and Klenner 1993; Sullivan 

and Sullivan 1988). These activities are more prominent early in stand development in intensively managed systems (for example, Sullivan and Moses 1986). 

Herbicide campaigns (Borrecco 1976) and mechanical habitat destruction (Sullivan and Moses 1986) 

have been carried out to reduce snowshoe hare numbers in young conifer plantations in Washington and 

British Columbia. In the case of mechanical habitat 

destruction, even though populations of snowshoe 

hares were reduced, impact on trees by hares was not. 

However, Sullivan and Sullivan (1988) reported 

snowshoe hare damage to crop trees decreased as did 

hare populations after thinning of lodgepole pine 

stands in British Columbia. For red squirrels, Sullivan 

and Klenner (1993) found that supplemental feeding 

significantly reduced tree damage without increasing resident squirrel populations. They concluded this 

was an effective method of reducing bark damage in 

young lodgepole pine (Pinus contorta) stands. 

Although supplemental feeding and timber treatments can minimize the impact of forest pests, encouraging natural predators such as lynx, fishers, 

martens, weasels, hawks, accipiters, and owls may be 

the most ecologically sound means of reducing the 

impact of these potential pests. 

Insect Predation 

Shrews and deer mice are prominent insect predators (Pearson et al. in review; Pearson in press; Frank 

1967; Buckner 1958) that can control prey populations 

of important forest pests such as the pine sawfly 

(Neodiprion sertifer), at least up to saturation densities (Holling 1959). Platt and Blakley (1973) found 

higher diversity of arthropod prey positively correlated with abundance of the cinereus shrew (Sorex 

cinereus). They postulated that the shrew functioned 

as a keystone predator by suppressing populations of 

otherwise numerically dominant species in the community (but see Mills et al. 1993 for critique of keystone concept). A 2-year exclosure study by Andersen 

and Folk (1993) indicated that shrews and deer mice 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
could reduce survival of acorn weevils (Coleoptera: 

Curculionidae), an important forest pest. 

Field research on deer mouse predation of gall flies 

(Urophora spp.) released as biological control agents 

to reduce the spread of spotted knapweed (Centaurea 

maculosa) in westcentral Montana suggested that 

deer mice consumed between 150 and 250 larvae per 

mouse per night during winter in knapweed-infested 

grasslands (Pearson et al. in review; Pearson in press). 

Estimated numbers of gall fly larvae depredated per 

individual per month was 8058 in 1997 based on the 

nightly foraging potential of this species (Pearson in 

press). However, Pearson et al. (in review) argued 

that these data, based on snap trapping methods, 

underestimated true predation rates by as much as 

five-fold based on results from feeding trials that 

showed mice could consume an average of > 1200 

larvae per mouse per 24 hr interval. Deer mouse 

capture rates increased linearly in response to increasing knapweed cover (which translates to increasing gall fly densities), and mice were able to reduce 

their handling time when depredating seedheads by 

somehow assessing the likelihood that a seedhead 

contained larvae (Pearson et al. in review). Deer mice 

may affect some control over gall fly populations 

through these functional and numerical responses. 

Though the implications of such predation on this 

introduced biological control agent are not yet fully 

understood, the predatory potential of the deer mouse 

on insects is well illustrated by this example. 

Few studies have addressed the potentially critical 

role small mammals may play as natural biological 

controls over forest insect pests, but this may be an 

important aspect of small mammal interactions 

within forest ecosystems. 

Mycophagy and Spore Dispersal 

Most higher plants maintain an obligatory symbiotic relationship with 1 or more species of mycorrhizal 

(root-inhabiting) fungi in order to meet their minimum nutrient requirements for survival (Marks and 

Kozlowski 1973; Sanders et al. 1975). Hypogeous forms 

of mycorrhizal fungi include Ascomycetes (truffles), 

Basidiomycetes (false truffles), and Phycomycetes 

(Endogonaceae); these groups make up a large and 

important component of the mycorrhizal community. 

Sporocarps of hypogeous fungi are below ground and 

so do not have access to wind for spore dispersal as do 

epigeous (aboveground) forms. These fungi are therefore dependent upon animals for spore dispersal, and 

Maser et al. (1978) suggest that small mammals are 

the primary vectors for dissemination of their spores. 

Mycophagy (fungus consumption) has been described 

for numerous species of small mammals throughout 

North America (Maser et al. 1978; Fogel and Trappe 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

1978). In many cases, mycophagy is incidental or 

opportunistic, but several species including the 

northern flying squirrel (Glaucomys sabrinus) and 

western red-backed vole (Clethrionomys californicus) 

consume fungi almost exclusively and show a strong 

preference for hypogeous forms (Maser et al. 1985; 

Maser et al. 1978; Hayes et al. 1986). In consuming 

fungal sporocarps, small mammals also incidentally 

ingest and thereby disperse ecologically important 

microorganisms such as yeast and nitrogen-fixing 

bacteria (Li et al. 1986a). 

Available information suggests a long evolutionary 

relationship exists between small mammal mycophagists and hypogeous mycorrhizal fungi. Hypogeous 

fungi emit distinctive odors that attract small mammals (Fogel and Trappe 1978; Maser et al. 1978). 

These odors may be analogous to odors and coloration 

in flowers that have evolved to lure pollinators. Although many epigeous fungi also emit strong odors, 

hypogeous fungi predominate in samples of small 

mammal digestive tracks (Maser et al. 1978). Howard 

et al. (1968) established that deer mice locate hypogeous sporocarps through olfaction. Species like the 

northern flying squirrel and red-backed voles, which 

specialize on mycorrhizal fungi, are presumably even 

more adept at finding sporocarps using olfactory cues. 

Fogel and Trappe (1978) note that hypogeous sporocarps do not emit an odor until they are mature. This 

would prevent sporocarps from being found and consumed before spores are ready for distribution and is 

arguably a coadapted evolutionary trait. The correlation noted by some investigators (Fogel and Trappe 

1978; Tevis 1953) between rodent size and the size of 

sporocarps ingested suggests that species of fungi 

producing small sporocarps may require smaller animals such as voles, mice, shrews, or insects to disperse their spores, since these are the only species for 

which consumption of these tiny sporocarps is 

nutritionally and energetically beneficial. 

Spores of mycorrhizal fungi, yeast, and nitrogenfixing bacteria are viable after passing through rodent 

digestive tracts (Kotter and Farentinos 1984; Li et al. 

1986a; Trappe and Maser 1976), and the probability 

that spores will reach fertile substrates may increase 

through mycophagy, since mycophagist rodents forage where sporocarps are likely to be found. Li et al. 

(1986b) found the feces of northern flying squirrels 

and Douglas' squirrels (Tamiasciurus douglasii) to be 

as effective a medium as yeast extract in promoting 

growth and nitrogenase activity in nitrogen-fixing 

bacteria collected from the feces. Kotter (1981) determined that tassel-eared squirrels (Sciurus aberti) 

disseminated 200 million to 1 billion fungal spores per 

gram of fecal material in Colorado ponderosa pine 

communities, implying great dispersal potential for 

some mycophagist rodents. 

7 
Table 2 presents information for species on the 

BNF for which mycophagy has been documented. 

Much of the information comes from Maser et al. 

(1978) who give an extensive review of mycophagy 

for rodents in the Pacific Northwest. Fogel and Trappe 

(1978) provide comprehensive lists of fungi consumed 

by fungivores and ofmycophagists that consume fungi 

as reported in the literature. These two papers are 

key works on mycophagy, and both are included in 

the annotated bibliography. 

Although many species of small mammals are 

known to consume hypogeous mycorrhizal fungi, the 

extent that a species relies on fungi is quite variable, 

and some species are probably more important than 

others as disseminators of mycorrhizal spores (Table 2). 

In the northern Rocky Mountain Region, the northern 

flying squirrel and the southern red-backed vole are 

likely the primary and secondary mycophagists, respectively. Chipmunks may also be important, and the 

red squirrel may play a variable though less certain 

role. The deer mouse is best described as an opportunistic mycophagist, but its ability to switch habitats 

may make it a critical bridge for dispersal of spores 

from late successional forests to newly disturbed habitats. The literature is reviewed for the primarymycophagist species below, followed by a discussion and some 

speculation (resulting from gaps in the literature on 

mycophagy for this region) on the probable roles of 

mycophagist rodents in ecosystems on the BNF. 

The northern flying squirrel is possibly the most 

specialized fungivorous rodent in North America and 

is probably the strongest mycophagist in theN orthern 

Rocky Mountain Region. Maser et al. (1978) found 

hypogeous fungi made up 78 percent of the stomach 

contents by volume of 12 individuals captured in 

Oregon coniferous forests. More recently, Maser et al. 

(1985) reported the mean volume of fungi in stomachs 

of 21 individuals collected during the summer in 

northwestern Oregon was 100 percent. Approximately 

80 percent of this volume was hypogeous fungi. The 

remaining portion was unidentified fungi. The stomach contents of an additional 61 individuals caught 

throughout the year in northeastern Oregon resulted 

in 93 percent fungi by volume, of which lichens made 

up 60 percent and hypogeous fungi made up 11 percent, on average; epigeous and unidentified fungi 

made up the remaining contents. In northeastern 

California, for 24 northern flying squirrels captured throughout the year, nearly 100 percent of the 

stomach contents by volume contained fungi 

(McKeever 1960). On average, 51 percent of the volume was sporocarps and 49 percent was lichen. In 

Table 2-Summary of mycophagy information for small mammals occurring on the Bitterroot National Forest. The 

absence of a species from the list indicates no volumetric information was available for that species in 

the Northwest, but absence does not preclude it as a mycophagist. 

Family and species %volume Type n State Author citation 

Ochotonidae 

Pika 8 hyp 10 OR Maser et al. 1978 

Sciuridae 

Yellow-pine chipmunk 50 hyp 11 OR Maser et al. 1978 

38 39 Tevis 1952 

28 170 Tevis 1953 

Red squirrel 77 hyp 5 OR Maser et al. 1978 

Northern flying squirrel 78 hyp 12 OR Maser et al. 1978 

90-100 hyp 82 OR Maser et al. 1985 

Geomyidae 

Northern pocket gopher epi 11 OR Maser et al. 1978 

Muridae 

Deer mouse trace hyp 21 OR/NV Maser et al. 1978 

10 hyp 62 BC/OR Maser et al. 1978 

Bushy-tailed woodrat 10 hyp 34 OR Maser et al. 1978 

Red-backed vole 72 10 OR/CO Maser et al. 1978 

5-100 hyp WY/CO Williams and Finney 1964 

Montane heather vole 60 hyp 1 OR Maser et al. 1978 

11 co Williams and Finney 1964 

Long-tailed vole 28 hyp 4 OR Maser et al. 1978 

Western jumping mouse 100 hyp 1 WY Williams and Finney 1964 

hyp 3 co Williams and Finney 1964 

hyp = hypogeous 

epi = epigeous 

8 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
general, northern flying squirrels rely heavily upon 

hypogeous sporocarps most of the year, but in winter 

and at times when sporocarp production is down, they 

consume lichens (Maser et al. 1985; Maser et al. 1978; 

McKeever 1960). In central Idaho, northern flying 

squirrels consumed predominantly lichens and fungi 

with lichens most abundant in winter diets and 

fungi most abundant in summer (Rosentreter et al. 

1997). The only other item in stomachs was vascular 

plant tissue in 25 percent of 2000 samples. 

In the Pacific Northwest, the western red-backed 

vole vies with the northern flying squirrel for the role 

of primary mycophagist. The southern red-backed 

vole replaces this species in the Rocky Mountain 

states both geographically and in terms of its place 

as a prominent mycophagist rodent. Ure and Maser 

(1982) observed diets of southern red-backed voles to 

contain over 90 percent fungal sporocarps in eastern 

Oregon and approximately 60 percent fungus in western Washington. Gunther et al. (1983) also reported 

high frequencies of fungus and lichen ( = 77 percent 

relative frequency for animals from clearcuts and 

forest) in stomachs of southern red-backed voles in 

the Cascade Mountains of western Washington. 

Food habit studies of the southern red-backed vole 

have been conducted throughout much of North 

America (see Pearson 1994 for review), but research 

on food habits of this vole in the Northern Rocky 

Mountains is limited, and mycophagy is not well 

addressed. Maser and Maser (1988) reported that 27 

Clethrionomys gap peri idahoensis consumed approximately 46 percent fungi by volume of which around 19 

percent was hypogeous sporocarps. They found 16 

stomachs of the subspecies C. g. galei, also from the 

Rocky Mountain region, contained 45 percent fungi 

by volume of which about 18 percent was hypogeous. 

These same 2 subspecies were found by Maser et al. 

(1978) to have consumed 72 percent fungi by volume, 

wherein 75 to 95 percent was hypogeous fungi. Clark 

(1973) examined 25 voles from Grand Teton National 

Park, Wyoming, but did not include a category for 

fungi, although he indicated that 26 percent of the 

volume of stomachs was unidentified. He reported 59 

percent of the contents was plant material. Ten of 

27 individuals from Colorado and Wyoming had consumed hypogeous Endogone, but volumetric and relative frequencies of fungi in stomachs were not determined (Williams and Finney 1964). 

Maser and l\1aser (1988) examined stomach contents of red-backed voles collected across the United 

States and concluded that habitat was a more important factor in determining extent of mycophagy than 

was taxonomic status. In the Northern Rocky Mountains, the southern red-backed vole's diet is approximately 45 percent fungi with around 20 percent being 

hypogeous (Maser and Maser 1988). However, Maser 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

and Maser (1988) is the only good food habit study 

reporting on the volume of fungi found in stomachs of 

the southern red-backed vole in the Northern Rocky 

Mountains, and most information on hypogeous sporocarp production comes from the Pacific Northwest 

(Amaranthus et al. 1994; Luoma 1991; Luoma et al. 

1991; Fogel and Hunt 1979; Fogel1976; but see Harvey 

et al. 1976 for MT). 

Other fungivorous small mammals in the Rocky 

Mountains may be seasonal or opportunistic mycophagists. Tevis (1952, 1953) showed that yellow-pine 

chipmunks in northern California rely heavily on 

hypogeous fungi. In northeastern Oregon; Maser and 

Maser (1987) reported that stomach contents of 135 

individuals consisted of about 13 percent hypogeous 

fungi by volume. 

Beg (1969) did not report fungi in the diets of either 

red-tailed chipmunk or yellow-pine chipmunk in western Montana, but he examined only cheek pouch 

contents of live-captured individuals. It is likely that 

cheek pouches are biased toward cached foods such as 

seeds which Beg found a preponderance of in his 

samples. Hypogeous fungi would probably be consumed upon collection. Beg indicated that on several 

occasions he observed both species feeding on "something" gathered beneath loose bark of old trees and 

stumps. He also often observed them foraging in the 

leaf litter. Both locations are likely spots for fungi. 

No studies of chipmunk mycophagy in this region 

were found, so it is difficult to draw conclusions, but 

chipmunks may consume and disperse spores of 

hypogeous fungi here in important quantities. Fungus 

in the diet of the deer mouse is highly variable, depending presumably on sporocarp availability (which 

is known to be seasonally abundant in spring and fall) 

(Luoma 1991; Luoma et al. 1991). 

The importance of a species as a vector for mycorrhizal spores varies depending on habitat requirements, diet, and the behavior of other mycophagous 

species in the community. Habitat and dietary specialists like the northern flying squirrel and the southern red-backed vole facilitate spore dissemination 

within forest stands. By specializing on mycorrhizal 

fungi and being restricted to later successional stages 

(Pearson 1994; Witt 1992; Nordyke and Buskirk 1991; 

Scrivner and Smith 1984; Andersen et al. 1980), they 

are likely the primary catalysts for mycorrhizal symbiosis within moist forests in the Northern Rocky 

Mountains. 

However, these species rarely enter newly disturbed 

sites, and the hot, dry conditions associated with 

recent clearcuts and stand-replacing fire are believed 

to destroy mycorrhizal fungi (Clarkson and Mills 1994; 

Maser et al. 1978). Yet the obligatory nature of mycorrhizal symbiosis requires that the symbionts be 

present for the survival of newly germinating trees, 

9 
creating an apparent ecological dilemma for non-wind 

dispersed hypogeous species. Habitat and dietary generalists such as deer mice may function as vectors for 

re-introducing spores to early seral conditions. Deer 

mice do not specialize on mycorrhizal fungi, but a 

given individual, having indulged itself in an opportunistic meal of sporocarps, may carry hundreds of 

thousands of spores from the forest into an adjacent 

clearcut or burn, thereby facilitating the reintroduction of critical mycorrhizal fungi into a habitat devoid 

of mycobionts for regenerating trees. Until recently 

the deer mouse had been regarded only as seed predator (Tevis 1956a). Such a limited understanding of the 

ecological role of this species may undermine the 

success of long-term forest ecosystem management. 

Chipmunks may consume larger quantities of sporocarps and do so more often than deer mice. Although 

they are more specialized in their use of habitats 

than deer mice, they may also bridge the ecotone 

separating recently cut or burned sites from mature 

forest. The yellow-pine chipmunk prefers ponderosa 

pine savanna, but it is also found in shrubby habitats 

associated with early seral conditions and forest 

edges (see Habitat Associations). 

The lack of literature on hypogeous fungi and small 

mammal mycophagy in the northern Rocky Mountain 

Region leads to much speculation regarding the relative importance of different mycophagist species in 

different habitats; however, mycophagy, and therefore mycophagist rodents, clearly play an important 

part in forest ecosystem functions within this region. 

Prey-Base 

TheN orthern Rocky Mountains accommodate a rich 

assemblage of predators, most of which occur on the 

BNF. Small mammals are the trophic substrate upon 

which many of these predators depend for survival 

during at least some portion of the year. Red-backed 

voles,Microtus spp., red squirrels, and snowshoe hares 

are particularly important prey within forested environments. The removal of any one of these species 

could significantly alter upper trophic levels. Redbacked voles are the primary food source for American 

marten (Martes americana) (Buskirk and Ruggiero 

1994; Weckwerth and Hawley 1962) and boreal owls 

(Aegoliusfunereus)(Haywardetal.1993)in the Northern Rocky Mountains. Snowshoe hares are a critical 

resource for fisher (Martes pennanti) in the Cabinet 

Mountains, western Montana (Roy 1991). The 10-year 

cycle linking snowshoe hare and lynx (Lynx lynx) 

populations is well documented in northern latitudes 

(Koehler and Aubry 1994; Keith 1963). Keith and Cary 

(1991) have also shown that weasels (Mustela frenata 

andM. erminea) and mink(M. vison) exhibit a 10-year 

cycle that is synchronous with that of lynx in Alberta 

10 

suggesting that they also may take advantage of the 

snowshoe hare resource. Snowshoes are also taken, 

to a lesser extent, by marten and wolverine ( Gulo gulo) 

(see Buskirk and Ruggiero 1994; and Banci 1994). 

Microtus spp. are the primary prey for grassland 

predators (Ryszkowski et al. 1973; Golly 1960), but 

they also occur in restricted habitats in forest environments where they are one of the few species of 

small mammals present in marten diets in greater 

proportions than they occur in surrounding habitats 

(Buskirk and Ruggiero 1994). 

Red squirrels are the primary prey of northern 

goshawks in Wyoming, where they occurred -in 55 

percent of900 goshawk pellets (Squires in prep.). Red 

squirrels occur in the diets of marten but rarely make 

up >10 percent of the diet (see Buskirk and Ruggiero 

1994). Since distribution, abundance, and seasonal 

availability do not greatly affect marten access to red 

squirrels, the under-representation of red squirrels in 

marten diets could indicate that they have difficulty 

securing squirrels due to their larger size. However, 

marten are capable of killing snowshoe hares 

(Weckwerth and Hawley 1962), which are much larger 

than squirrels, and snowshoe hares comprise a large 

proportion of their diets in southeastern Manitoba 

(Raine 1987). 

Buskirk and Ruggiero (1994) suggested a symbiotic 

relationship may exist between red squirrels and 

martens, wherein squirrels provide important resting 

sites, denning sites, and access to the subnivian space 

in the form of middens (Ruggiero et al. in prep.; 

Ruggiero et al. 1998; Sherburne and Bissonette 1993; 

Buskirk 1984). They argued red squirrels may benefit 

marten by creating critical marten habitat, and the 

two species may coexist at midden sites. For example, 

Buskirk (1984) reported that 70 percent ofhis Alaska 

marten rest sites occurred within red squirrel middens 

even though red squirrels occurred in only 5 percent of 

467 scats and colon tracts collected from the same 

area concurrent to the study. Red squirrel middens 

may also be favorable feeding sites for marten, since 

middens appear to have higher numbers of red-backed 

voles than non-midden sites (Ruggiero and Pearson in 

prep.). 

Insights Into Prey Selection-Food habit studies 

of marten indicate that they generally take prey items 

in proportion to their availability (Buskirk and 

Ruggiero 1994; Weckwerth and Hawley 1962). Results 

of an intensive study in Idaho suggests this is also true 

for boreal owls (Hayward et al. 1993). This is likely the 

result of cost effective foraging within the predators' 

primary habitat, as has been described for long-eared 

owls (Asia otus) (Korpimaki 1992). The red-backed 

vole is the most common species encountered by both 

predators throughout the year and is consumed in 

proportion to its availability. This does not negate its 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
importance as a food item, but rather explains its 

importance to forest carnivores in terms of their cohabitation within structurally complex environments. 

Boreal ow Is and marten do exhibit selection for some 

prey. Marten show a "preference" for Microtus spp., 

and boreal owls consume a disproportionate amount of 

northern pocket gophers during years of low redbacked vole abundance. This prey selectivity may 

result from optimal foraging strategies (see Pyke et al. 

1977). Within the moist coniferous forest habitat occupied by both predators, the aforementioned prey are 

habitat-specific and clumped in their distributions. 

Microtus favor grass-forb openings in the forest and 

grass-forb areas along riparian corridors (Kinsella 

1966; see Habitat Associations). Northern pocket gophers occupied a wider range of habitats within 

Hayward et al.'s (1993) study area including sage, 

lodgepole pine, and wet meadows, but this species 

favors microsites with deep, moist soils and leaves 

conspicuous sign indicating its presence. These characteristics allow predators to develop search images 

(Pietrewics and Kamil 1979) for microsites where 

prey are concentrated. Additionally, these species 

weigh more than the "non-selected" red-backed vole. 

Mean adult weights for these three prey items in 

Idaho were: red-backed vole, 27 g; Microtus spp., 30 g; 

northern pocket gopher, 101 g (Hayward et al. 1993). 

Selection for the northern pocket gopher by boreal 

owls and Microtus by marten can probably be explained by the higher probability of success associated 

with foraging for a clumped and predictably located 

resource and the greater energetic returns associated 

with capturing larger prey. 

The underrepresentation of deer mice in marten 

diets (Buskirk and Ruggiero 1994) and their apparent 

underrepresentation in boreal owl diets is also congruent with optimality theory. Deer mice are present 

in essentially all habitats (see Habitat Associations), 

are less predictable in their selection of microhabitats 

(Pearson 1994) and weigh less than red-backed voles, 

24.2 g for adults (Hayward et al. 1993). Predation on 

deer mice is probably opportunistic due to low returns 

and the lack of predictability associated with finding 

them. However, in winter, deer mice are believed to 

undergo prolonged periods of torpor and have been 

shown to reduce activity at this time (Kucera and 

Fuller 1978; Fuller et al. 1969). As a result, their 

availability is reduced in winter and this may not be 

accounted for in some food habits studies. The small 

size of shrews may partly explain their rarity in the 

diets of marten (Buskirk and Ruggiero 1994) and 

other carnivores (Jackson 1961), but these animals 

also have pungent scent glands that may render them 

less than palatable. Shrews are, however, a common 

prey item in boreal owl diets (Hayward et al. 1993). 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

Hibernation and Seasonal Availability of 

Prey-Seasonality of the temperate zone environment affects other aspects of prey availability. Hibernation by chipmunks, ground squirrels, and jumping 

mice greatly reduces their accessibility to predators 

over the winter months as is apparent from winter 

food habit studies of forest carnivores (see Ruggiero et 

al. 1994). Other small mammals such as northern 

pocket gophers become generally unavailable within 

tunnels beneath the snow pack (Hayward et al. 1993). 

This places a heavy burden on small mammals that do 

not hibernate and especially on those that make use of 

the snow surface. Although marten forage beneath the 

snow, they probably depend largely on subnivian spaces 

near woody debris (Sherburne and Bissonette 1994, 

1993). Therefore, use of the subnivian space provides 

some refugia from predation. 

When animals leave the subnivian space, they greatly 

increase their susceptibility to predation. Deer mice, 

red-backed voles,Microtus spp., and shrews are active 

both on the snow and within the subnivian space 

(Kucera and Fuller 1978). These species are correspondinglymore important in the diets offorest carnivores during winter. Shrews are more abundant in 

the diets of fisher than expected (Powell and Zielinski 

1994) given their general absence from most carnivores' diets (Jackson 1961). Fishers may prey upon 

shrews more because fishers are restricted to the 

snow surface by their large size. Shrews make heavy 

use of the snow surface (pers. obs.) and forage more 

frequently during the winter than in the summer 

(Gillihan 1992). Although deer mice also travel across 

the surface, they reduce their activity in the winter 

and are suspected of periodically entering torpor 

(Kucera and Fuller 1978; Fuller et al. 1969). Red 

squirrels and northern flying squirrels remain active 

and accessible all winter (see Foresman in review). 

Red-backed voles and northern flying squirrels increase in the diets ofboreal owls (Hayward et al. 1993) 

in the winter, and red-backed voles and red squirrels 

are often the most important species in diets of 

marten at this time (Buskirk and Ruggiero 1994). 

Most hibernating species are associated with earlysera! stages (ground squirrels, chipmunks, and jumping mice) whereas late-seral stands support species 

that do not hibernate (tree squirrels). Microtus associated with early successional stages are subject to 

radical population fluctuations while their late-seral 

counterpart, the red-backed vole, is much more 

stable from year to year. This condition should result 

in late-seral forests being favored by predators in 

winter due to a greater abundance of accessible food 

and perhaps in general due to greater stability over 

time. However, predators capable of using recent 

clearcuts and grasslands might be expected to shift 

11 
their efforts to these areas in spring when ground 

squirrels appear and in years when Microtus populations peak to provide a superabundant prey. 

Red-backed Voles, American Marten, and the 

Role of CWD-Coarse woody debris is an important 

habitat feature for both predators and prey in forest 

ecosystems. Red-backed voles favor mature and oldgrowth forest in the Northern Rocky Mountains 

(Pearson 1994; Nordyke and Buskirk 1991; Scrivner 

and Smith 1984; Halvorson 1982; Ramirez and 

Hornocker 1981). Pearson (1994) and Nordyke and 

Buskirk (1991) determined that old-growth characteristics and CWD predicted macrohabitat selection (selection at the stand level) of the southern red-backed 

vole. Pearson (1994) also established a direct link 

between southern red-backed voles and the use of 

CWD at the microhabitat level. In comparing data 

collected from red-backed vole trap sites with data 

from randomly selected trap stations, Pearson (1994) 

observed that southern red-backed voles were more 

closely associated with larger diameter logs in some 

stands and younger decay classes in others. Using 

fluorescent pigment tracking to identify exact patterns of movement, Pearson determined that voles 

used logs as travel corridors through the forest. 

Marten are known to associate primarily with mature forest at the macrohabitat scale (Buskirk and 

Ruggiero 1994), and forests exhibiting old-growth 

characteristics may provide optimal habitat (Buskirk 

and Powell 1994). Studies of resting site ecology and 

use of the subnivian space for foraging suggest that 

CWD and snags are important microhabitat components for marten (Sherburne and Bissonette 1994; 

Taylor and Buskirk 1994; Sherburne and Bissonette 

1993; Buskirk et al. 1989; Buskirk 1984). Resting sites 

associated with CWD are critical to marten when 

ambient temperatures drop below a critical threshold 

(Taylor and Buskirk 1994). Squirrel middens may 

serve a similar role to that of CWD in marten resting 

site ecology by providing an insulating surface superior to that afforded by snow alone (Sherburne and 

Bissonette 1993; Buskirk 1984). Access to the subnivian space via CWD is also crucial for foraging 

(Sherburne and Bissonette 1994). 

However, conclusions drawn by Sherburne and 

Bissonette (1994) that marten select subnivian access 

points based upon some assessment of small mammal 

biomass beneath the snow may be premature. Their 

use of spring trapping data to indicate small mammal 

abundance near CWD may be misleading. However, 

small mammals are known to aggregate within the 

subnivian space by shifting away from areas used in 

summer (West 1977), and studies conducted during 

the snow-free period indicate that small mammals 

shift use areas seasonally (for example, Belk et al. 

1988; Vickery 1981). Coarse woody debris likely creates 

12 

a more extensive subnivian space that may afford 

better access to resources and therefore be preferred 

by small mammals (Coulianos and Johnels 1962; as 

cited in Merritt and Merritt 1978). However, use of 

CWD sites has been shown to change between spring 

and summer (Belk et al. 1988) and may change between spring and winter as selection criteria change. 

During snow-free periods, CWD sites may function as 

foraging areas for truffles (Clarkson and Mills 1994), 

or may be chosen for hiding or escape cover. In winter, 

other less well understood aspects of subnivian ecology may drive selection for such sites. The correlation 

observed by Sherburne and Bissonette (1994) is one 

between marten winter access points and spring abundance of small mammals and should not be extrapolated beyond this. 

It remains to be seen whether marten are selecting 

sites for small mammal abundance or for some criteria 

that small mammals are similarly selecting. Unless 

martens tunnel, which is unlikely as a general strategy, they require larger spaces beneath the snow for 

foraging such as those associated with CWD. Larger 

spaces may be favored by small mammals for more 

expansive foraging areas or better ventilation, since 

carbon dioxide is likely to accumulate beneath the 

snow. 

If winter aggregation in small mammals is a cold 

adapted behavior as suggested by West (1977), small 

mammals may aggregate in small inaccessible 

subnivian pockets where moss is abundant. They 

could then be least available to marten, which are 

restricted to larger spaces, when cold-related stress is 

highest. This factor could affect the temporal availability of subnivian small mammals and should be 

considered before drawing conclusions about marten 

selection of access points based upon spring small 

mammal densities. 

Coarse woody debris may play a seasonally dynamic 

role in predator prey relationships in the Northern 

Rocky Mountains. In winter, CWD serves to link 

predator and prey via portals which facilitate interchange between the subnivian space and the snow 

surface. During snow-free seasons, CWD may provide 

prey with refugia in space and time from predators, 

thereby potentially dampening oscillations in predator-prey cycles (see Huffaker 1958 and Gause 1934). 

Wolff (1980) maintains that habitat heterogeneity 

afforded by mosaics of thick, low evergreen and deciduous vegetation provides refugia for snowshoe 

hare populations in Alaska. He argues that reduced 

cyclicity in more southern populations is due to increases in generalist predators and alternative prey 

species that allow prey switching and dampen oscillations. Lee (1995) has shown that vagrant shrews were 

more stable on sites with CWD than on controls 

lacking this structural component. 

Southern red-backed voles exhibit multiannual 

fluctuations in some populations, but not in others. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
Habitat heterogeneity has been implicated in determining population stability within this genus 

(Bondrup-Nielsen and Ims 1988). Bondrup-Nielsen 

and Ims (1988) suggest that habitat heterogeneity 

dampens oscillations by preventing habitat space 

from being filled, thereby precluding social interactions and other intrinsic population control mechanisms that could initiate a crash, but they ignore the 

role of predation in this interaction. However, their 

hypothesis does not exclude predation, and others 

argue that predation is important in dampening prey 

cycles (Erlinge et al. 1983). The habitat heterogeneity 

hypothesis as presented by Bondrup-Nielsen and Ims 

(1988) is more probable when predation is introduced 

into the equation as demonstrated by laboratory studies (Huffaker et al. 1963; Huffaker 1958; Gause 1934). 

That CWD may stabilize ecosystem processes by 

dampening oscillations in red-backed vole populations seems quite possible. If CWD does play such a 

role, whether it does so by means of prey refugia, 

habitat heterogeneity, or both remains to be seen. In 

any case, microhabitat selection by forest carnivores 

and their small mammal prey indicates CWD is an 

important component in the ecology of these species. 

Source and Sink Populations 

An understanding of the nature and dynamics of 

source and sink populations (Pulliam 1988; Van Horne 

1983) is extremely important for managing small 

mammals and for understanding how habitat quality 

for small mammals relates to habitat quality for 

predators and predator-prey interactions. Differences 

in productivity combined with social controls such as 

territoriality result in some habitats giving rise to 

source populations, populations which produce beyond the local carrying capacity, and others functioning as sink populations (unsustainable populations 

where mortality exceeds natality). 

Sink populations have been identified in the Northern Rocky Mountains (Pearson 1994) and possibly in 

the central Rocky Mountains (Nordyke and Buskirk 

1991) for the southern red-backed vole. A lack of oldgrowth attributes such as CWD was associated with 

sink populations in young lodgepole pine stands studied by Nordyke and Buskirk (1991) in Wyoming. In 

Glacier National Park, Pearson ( 1994) similarly determined that young lodgepole pine stands were sinks 

and further suggested that some stands that were 

over 350 years old might also be sinks based on a 

combination of population parameter estimates. 

Populations of southern red-backed voles within 

lodgepole pine stands were identified by Pearson ( 1994) 

as dispersal sinks based on a lack of breeding adults. 

However, other sink populations identified by Pearson 

(1994) and Nordyke and Buskirk (1991) for southern 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

red-backed voles and by Sullivan (1979c) for deer mice 

were associated with moderate to high densities of 

animals, and so required detailed population demographic information to distinguish them as dispersal 

sinks. For species such as the southern red-backed 

vole that function as prey-base for a variety of predators and fulfill other important ecological roles such as 

spore dispersal (see Mycophagy and Spore Dispersal), 

it is important to recognize that abundance is not 

always a good indication ofhabitat quality (Van Horne 

1983) and that superficially similar habitats may not 

be equally productive. Management that supports 

productive small mammal populations will best provide for predator populations and spore dispersal 

activities. · 

Rare and Sensitive Small 

Mammals 

Bats 

Seven of 13 species of bats known to occur or suspected of occurring on the BNF are potential candidates for listing under the Endangered Species 

Act, pending further biological information (Category 2) (Table 1). Townsend's big-eared bat (Plecotus 

tow nsendii) and the spotted bat (Euderma maculatum) 

are recognized as "Sensitive" species by the USDA 

Forest Service. However, the spotted bat may not 

occur on the BNF. Of the species known to occur on 

the BNF, Townsend's big-eared bat is listed as imperiled within the ~tate (S2), and the yumamyotis (Myotis 

yumanensis) and fringed myotis (Myotis thysanodes) 

are listed as very rare in Montana (S3). The eastern 

small-footed myotis (Myotis leibii) is not currently 

recognized as present within the state by the Montana 

Natural Heritage Program, so no status is given. 

However, this species does occur in Montana where it 

is perhaps most abundant in the Bitterroot Valley 

(Hoffinann et al. 1969b) and should probably be listed 

as S3 or S2 at the state level. 

There are several reasons for the precarious status 

of such a large proportion of bats. Understanding 

these will help to understand how bats can be protected on the BNF. In general, bats are extremely 

sensitive to disturbance in hibernation and maternity 

roosts (Genter 1989; HumphreyandKunz 1976). Therefore, when hibernacula and maternity colonies are 

too often disturbed, sites are abandoned and whole 

colonies may perish if individuals are unable to reestablish themselves in available, undisturbed habitat. 

Townsend's big-eared bats are very sensitive to disturbance in maternity colonies, and Humphrey and Kunz 

(1976) conclude that disturbance could threaten the 

survival of colonies. Disturbance of big brown bats 

13 
(Eptesicus fuscus) at maternity roosts in British 

Columbia reduced site fidelity and decreased reproductive success (Brigham and Fenton 1986). Given the 

specificity of site selection for roosts exhibited by 

many species, and the energetic demands of mammalian flight whl.ch further requires that roosting sites 

be located near feeding sites, many bats are probably 

limited by a unique combination of foraging site and 

roosting site conditions. 

Surveys should be conducted on the BNF to identify 

hibernacula and maternity roosts. Once these sites 

are identified, they can be protected from management and recreational disturbance. Because roost 

sites are often point locations such as caves or mine 

adits within other habitats (for many bats), they are 

relatively easy to manage by grating off entrances to 

adits or caves. This also reduces the potential for 

human injury in these locations. 

Large old trees provide important habitat for tree 

roosting bats and maternity colonies for some species 

and so should also be managed with this in mind. 

Thomas and West ( 1991) reported that in Washington 

and Oregon, bat activity in old-growth stands was 2.5 

to 9.8 times greater than in younger stands and concluded that large decayed trees in old growth provided 

critical roosting habitat. Since large ponderosa pine 

snags are recognized as important sites for some 

species in British Columbia (Brigham 1991), proposed 

management of ponderosa pine stands on the BNF as 

outlined in BEMRP reports may favor some bat fauna. 

Nonetheless, additional efforts will be necessary to 

maintain this diverse component of the BNF small 

mammal community. 

Pygmy Shrew 

The pygmy shrew (So rex hoyi) is currently ranked as 

G5 and S4 with the Montana Natural Heritage Program. In Idaho, it is a species of special concern, and in 

Wyoming, it is a Priority 2 species (see Foresman 

1989). The pygmy shrew is rare in the state, and its 

presence on the BNF is not yet confirmed. However, it 

has been captured nearby in Idaho subalpine fir (Abies 

lasiocarpa) and grand fir (Abies grandis) stands 

(Foresman 1986) and is very likely present on the 

BNF. 

The pygmy shrew seems capable of surviving a wide 

range of moisture and seral conditions (see Habitat 

Associations). This species has been collected in 

clearcuts in Montana (Brown 1967a) as well as from 

disturbed floodplains (Key 1979) and so may notrespond deleteriously to timber harvest practices. A 

general lack of know ledge regarding ecology and distribution precludes management recommendations 

for this species. 

14 

Dwarf Shrew 

The dwarf shrew (So rex nan us) is the smallest 

mammal in North America (Foresman 1989). This 

species is found most commonly in rocky habitats at 

high elevations in Montana (see Habitat Associations). The dwarf shrew has not been reported on the 

BNF, but its distribution and habitat associations 

indicate that pitfall trapping may produce specimens 

in high-elevation rocky habitats. Due to its rarity in 

Montana and in North America, this species is listed 

by the Montana Natural Heritage Program as a species of special concern that is globally secure though 

rare (G4) and very rare at the state level (S3) (Table 1). 

Because of its habitat affiliations, the dwarf shrew is 

unlikely to be affected by most management activities 

on the BNF. 

Preble's Shrew 

Preble's shrew is a rare shrew of arid sage (Artemisia spp.) habitats and has been reported only once in 

the Bitterroot Valley in 1910, 8 miles northeast of 

Stevensville (Hoffmann and Fisher 1978). The area 

described has likely changed a great deal since 1910, 

and the population that existed may have been 

extirpated by development. Habitat associations described for Preble's shrew (see Habitat Associations) 

suggest that other populations may exist in sagebrush 

habitats within the foothills on the BNF. Pitfall trapping of the sage community for this species might 

prove fruitful. Snap trapping and Sherman live trapping of this community might also produce other new 

records of rare species known to occur in similar 

habitat in adjacent Beaverhead County (see Hoffmann 

et al. 1969a). Preble's shrew (Sorex preblei) is classified by the Montana Natural Heritage Program as a 

species of special concern that is globally secure though 

rare (G4) and very rare within the state (S3) (Table 1). 

Northern Bog Lemming 

The northern bog lemming (Synaptomys borealis) 

occurs at the southern extent of its range in Montana. 

This species is considered a Pleistocene relict and is 

found in association with bog and fen habitats that 

are themselves relict communities surviving in isolated pockets within the state. The northern bog lemming is more common in northern latitudes, but even 

there its populations are localized, and its avoidance 

of traps has limited ecological information on this 

species to anecdotal accounts and speculation. For 

these reasons, this species is listed by the Montana 

Natural Heritage Program as globally secure though 

rare (G4) and as imperiled at the state level (S2) 

(Table 1). The USDA Forest Service recognizes this 

microtine as a "Sensitive" species within this region. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
The fact that the northern bog lemming has persisted for some 10,000 years since the late Pleistocene 

in isolated habitats is testimony to its long-term 

viability. However, the human factor adds a new 

dynamic to this equation. Reichel and Beckstrom 

(1994) identified threats to this species as cattle grazing and trampling within bog/fen habitats, and timber 

harvest around such habitats where the species is 

present. They provide guidelines for protection or' 

these habitats. 

However, there is reason to question whether bog 

lemmings are actually restricted to bog/fen habitats. 

Pearson has taken 2 specimens in association with 

mesic old-growth stands near streams as a result of 

incidental captures while trapping for other species 

(McDonald Creek, Glacier National Park and Big 

Creek, BNF, unpublished data). Since surveys by 

Reichel and Beckstrom (19941993) and Pearson (1991) 

targeted bog/fen habitats, their results cannot be 

used to infer that bog lemmings favor bog habitats. 

Other potential habitats (such as cedar and spruce 

old-growth near streams) must be trapped with equal 

effort before any such conclusions can be drawn. However, their relative success in capturing bog lemmings 

in bog/fen systems implies some association exists. I 

suggest the assumption that bog lemmings require 

"bog" habitats is reasonable based on current information (Reichel and Beckstrom 1994, 1993; Pearson 

1991). Any management or other activity that might 

alter bog or fen habitats could jeopardize the persistence of this unique species. Bogs and fens are defined 

by their hydrology and associated acidity (see Mitsch 

and Gosselink 1986) and bog/fen plant communities 

and, therefore, possibly bog lemmings are dependent 

upon these hydrological conditions. Any activity likely 

to alter bog/fen hydrology (forestry, grazing, trampling, road or trail building, etc.) may destroy the 

unique flora and fauna associated with these rare 

communities. 

This species has been identified at 2 sites on the 

BNF: Meadow Creek (Reichel and Beckstrom 1993) 

and Big Creek (D. E. Pearson, unpublished data). 

Additional surveys could be conducted at minimal 

expense to determine the distribution of northern bog 

lemmings on the BNF. This would be the first step in 

managing for this rare, sensitive species on the BNF. 

Habitat Associations -----------------

Shrews 

Five species of shrews have been identified on the 

BNF: the cinereus shrew (So rex cinereus ), the montane 

shrew (S. monticolus), the water shrew (S. palustris), 

Preble's shrew (S. preblei) and the vagrant shrew 

(S. vagrans). Preble's shrew is represented by only 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

one specimen within the Bitterroot watershed 

(Hoffmann and Fisher 1978). The pygmy shrew has 

not been identified on the BNF, but one was taken 

nearby in Idaho, and this species is likely present on 

the BNF (Foresman 1986). The dwarf shrew is not 

known from the BNF but has been found in highelevation rocky habitats in the Northern Rocky Mountains including the isolated mountain ranges of the 

Sweetgrass Hills and Bearpaw Mountains, Montana 

(Brown 1967a; Hoffmann and Taber 1960; Thompson 

1977). This shrew may also occur on the BNF, which 

has an abundance of such habitat near the species' 

current range. 

The vagrant shrew and the montane shrew are 

closely related and morphologically very similar. This 

similarity has resulted in some confusion regarding 

the taxonomic status of these shrews. In western 

Montana and the Northern Rocky Mountains, morphology of the two species converges to such an extent 

that mammalogists could not distinguish between 

them (Hennings and Hoffmann 1977), and Findley 

(1955) lumped them together into a single species: 

the vagrant shrew. More recently, Hennings and 

Hoffmann (1977) have reinstated full species status 

and clarified the differences between the 2 species. 

This distinction is important not only for identification of these shrews in the field, but also for interpreting the literature surrounding them. In early papers, 

S. obscurus = S. monticolus. Mter Findley's 1955 

review of the taxonomy, distinctions were no longer 

made between the 2 species except by authors who 

maintained their separation at the subspecies level. In 

such cases, S. vagrans vagrans = S. vagrans, and S. 

vagrans obscurus = S. monticolus. Clothier (1955) 

refers to S. vagrans monticola, which is presumably 

S. monticolus. According to Hennings and Hoffmann 

(1977), shrews identified as S. vagrans by Brown 

(1967a), Spencer and Pettus (1966), Ingles (1961), and 

Hoffmann and Taber (1960) are all S. monticolus. 

Further interpretation of the literature requires careful reading and examination of range maps provided 

for these species by Hennings and Hoffmann (1977). 

Overall, a good deal of data regarding habitat associations of S. vagrans and S. monticolus was lost where 

subspecies were not assigned and confused where 

taxonomy was misused. 

Live vagrant, cinereus, and montane shrews can 

often be identified in the field using a hand lens by 

determining the position of the medial tines on the 

upper front incisors relative to the pigmentation line 

(pers. obs.; Hennings and Hoffmann 1977). Other field 

characteristics reportedly can also be used: tail length, 

pelage color, odor (in breeding males), robustness of 

the rostrum, and number of callosities on the hind toes 

(Van Zyll de Jong 1982; Hawes 1977; Hennings and 

Hoffmann 1977). Collected specimens are generally 

15 
easy to identify in the lab, and the cinereus shrew is 

easily separated from vagrant and montane shrews 

based on relative length of the third unicuspid 

(Hoffmann and Pattie 1968). Field biologists studying 

small mammals need not lump shrews into Sorex spp. 

thereby losing valuable information. The Montana 

mammal key, A Guide to Montana Mammals 

(Hoffmann and Pattie 1968), does not distinguish 

between vagrant and montane shrews. The keys in 

Foresman (in review), Hennings and Hoffmann ( 1977) 

or Jung and Hoffmann (1981) should be consulted to 

distinguish between these species. 

The cine reus shrew, the vagrant shrew, and the 

montane shrew are the most common shrews in western Montana. The cinereus shrew has the widest 

distribution of any North American shrew (Hoffmann 

and Pattie 1968), and the montane shrew is more 

widely distributed than the vagrant shrew, which is 

restricted to areas within the Pacific Northwest and 

the Rocky Mountains (see maps in Hennings and 

Hoffmann 1977). HoffmannandPattie(1968)reported 

that the vagrant shrew was more common than the 

cinereus shrew in western Montana, but since it is 

now evident that they combined vagrant and montane 

shrews, it is unclear how abundance of the three 

species compare for this area. In mature and oldgrowth forests of Glacier National Park, where the 

three species are sympatric, the montane shrew is 

comparatively rare (K. A. Keating, unpublished data). 

In mature grand fir forests on the University of 

Montana Biological Station, Flathead Lake, vagrant 

shrews made up 56 percent, cinereus shrews 35 percent, and montane shrews 9 percent of captures for 

the three species (McCracken 1990). Hoffman (1960) 

similarly found vagrant shrews most abundant followed by cinereus and montane shrews within the 

cedar-hemlock zone of Washington and Idaho. Spildie 

(1994) reported a preponderance of vagrant shrews 

(85 percent of two species) captured in Grand Teton 

National Park. However, shrews identified as vagrant 

shrews were montane shrews (see Hennings and 

Hoffmann 1977; and discussion above). 

Clothier (1955) trapped shrews in Glacier National 

Park, at Yellow Bay on Flathead Lake, and near 

Missoula. He reported extensive overlap between S. 

vagrans monticola (=S. monticolus) andS. cinereus but 

always found S. monticolus four times more abundant. Williams(1955)foundS. cinereus andS. obscurus 

(=S. monticolus) sympatric within moist habitats in 

Colorado as did Smith (1988) in Alberta. In Washington, 

Terry (1981) concluded that S. vagrans inhabited 

alder stands and sites with a high water table, but 

was rare in closed forest. He caught S. monticolus in 

forested habitats in microsites associated with surface debris, but not mineral soil. Hawes (1977) conducted an intensive studyofS. vagrans andS. obscurus 

16 

(=S. monticolus) in 40-year-old western red cedar 

(Thuja plicata) and western hemlock (Tsuga 

heterophylla) stands in British Columbia. Distribution patterns indicated strong habitat separation between the vagrant and montane shrews. The montane 

shrew selected mossy sites beneath hemlock on mor 

soils, and the vagrant shrew favored the more mesic 

habitats under cedar on less acidic modor soils, where 

sword fern (Polystichum munitum) provided understory cover. 

Although habitat separation was distinct over several generations of shrews and was clearly important, 

Hawes (1977) observed that territorial boun~aries 

separating species near habitat interfaces matched 

boundaries of neighboring individuals more closely 

than lines dividing habitats. He concluded that interspecific interactions were important in maintaining 

ecological separation between vagrant and montane 

shrews. He suggested that odors emitted via the dermal glands of reproductively active males, which are 

sufficiently distinct to identify the two species in the 

field, may function as a reproductive isolating mechanism between species (Hawes 1976, 1977). 

Few studies identify habitat or microhabitat 

separation between the vagrans complex, montane, 

and cinereus shrews in the Northern Rocky Mountains, though many variously describe their habitats 

as wet or moist sites (Spencer and Pettus 1966; Clothier 

1955), and as noted above, extensive overlap is reported. 

Spencer and Pettus (1966) observed extensive overlap 

between S. vagrans ( =S. monticolus; see Hennings and 

Hoffmann 1977) and S. cinereus in Colorado. However, they felt they identified an area of separation 

between the two species. They concluded that the 

cinereus shrew was more abundant in a shrubby patch 

of marsh than was the montane shrew and suggested 

that 1) this might result from a founder affect or 2) true 

habitat segregation was observed, but the discriminating variables could not be discerned. Hoffmann 

and Pattie (1968) described the cinereus shrew as the 

more xeric species and suggested that it is excluded 

from wetter sites by vagrant shrews when sympatric. 

However, Brown ( 1967 a) determined that the cinereus 

shrew was found in relatively wetter sites (moist bogs) 

than S. vagrans (=S. monticolus; see Hennings and 

Hoffmann 1977) in the central Rocky Mountains of 

Wyoming, regardless of elevation. The relatively drier 

sites described by Brown (tree and shrub communities, and rock slides) where montane shrews outnumbered cinereus shrews were also structurally more 

complex than the mesic sites. It may have been this 

attribute that montane shrews were selecting for, 

since as Brown (1967a) reported, moisture did not 

vary greatly among sites. 

McCracken (1990) studied habitat use by vagrant, 

montane, and cinereus shrews on two plots, one 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
termed "wet" the other "dry," at the University of 

Montana Biological Station on the east shore of Flathead Lake. Sixty-two percent of 82 vagrant shrews 

inhabited the wet plot, while 78 percent of 51 cinereus 

shrews used the dry plot. Only 13 montane shrews 

were captured. Of these 13, 69 percent were from the dry 

plot and 31 percent from the wet. The vagrant shrew 

was significantly closer to water and was associated 

with greater abundance and density of logs >7.5 em 

diameter than the other species. Cinereus shrews 

were captured in areas higher in woody stem densities 

than vagrant shrews. Montane shrews were captured 

too few times to draw conclusions about habitat use. 

Habitats used by vagrant shrews on the University of 

Montana Biological Station plots were both wetter 

and structurally more complex than those inhabited 

by cinereus shrews. Given its cosmopolitan distribution, the cinereus shrew expresses a wider ecological 

amplitude than the other two shrews and may be 

excluded from more mesic and/or more structurally 

complex habitats by vagrant and montane shrews. 

Hoffman (1960) captured vagrant, cinereus, and montane shrews within drier habitat types of the cedarhemlock zone but caught only the vagrant shrew in the 

wettest habitat types trapped. 

In an attempt to determine the upper elevational 

limit of shrews, Clothier (1955) sampled in the 1800-

to 2000-m zone in Glacier National Park. Having no 

success at this elevation, he inferred that the upper 

elevationallimit for shrews in this area was around 

1800 m based on captures by Bailey (1918) and Jackson 

(1928) within the 1524- to 1829-m zone. However, 

Hoffmann and Taber (1960) caught fourS. uagrans 

(=S. monticolus; see Hennings and Hoffmann 1977) on 

Logan Pass (2012 m), seven on the Beartooth plateau, 

WY (3048 m) and four in the Crazy Mountains, MT 

(3048 m). Brown (1967a) captured S. uagrans (=S. 

monticolus; see Hennings and Hoffmann 1977) and 

S. cinereus at elevations from 2164 to 3231 min the 

Rocky Mountains of southern Wyoming. Clearly, the 

upper elevational limit for these shrews exceeds 

1800 m, but they are much less common above this 

elevation. 

The northern water shrew (Sorex palustris) is a 

unique shrew which, because of its semi-aquatic nature, is found only near mountain streams, ponds, or 

in boggy areas (Brown 1967a; Spencer and Pettus 

1966; Conaway 1952; Jackson 1928). Though usually 

associated with running water, this species has been 

captured n_ear ephemeral streams in Pattie Canyon, 

Missoula, County, during the dry season (Kinsella 

1967). In 1952, C. H. Conaway published the "Life 

History of the Water Shrew" based on 119 specimens 

collected near Missoula, MT. He found that 49 percent 

of 87 stomachs examined contained aquatic insects, 

and that the most productive habitats were overhanging banks along cold, rapid mountain streams. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

The pygmy shrew is predominantly a boreal species 

but is present in the western United States in two 

disjunct populations (Hoffmann and Pattie 1968). 

One encompasses eastem Washington, northern Idaho, 

and western Montana and the other encompasses 

southeastern Wyoming and northcentral Colorado. 

However, both of these "populations" are described by 

incidents of usually one to a few captures sporadically located within the given range that may represent relict populations from the late Pleistocene (see 

Foresman in review). 

Little is known about the habitat preferences or life 

history of the pygmy shrew. Brown (1967a) collected 

six pygmy shrews from Sphagnum mats along the 

periphery of a spruce-fir bog. at 9,620 feet in southcentral Wyoming. Spencer and Pettus (1966) also 

reported taking this species along the edges of a 

spruce-fir bog in Colorado. In Wisconsin and Canada, 

where the pygmy shrew is not a disjunct species, it 

occurs in, though is not restricted to, boggy habitats 

(Buckner 1966; Jackson 1961). 

In Montana, pygmy shrews have been reported from 

a wide variety of habitats, and it is unclear if any 

specific habitat preference exists for the species there. 

Conaway (personal communication in Brown 1967a), 

using trapping data from northwest Montana, described this species' habitat as "dry areas of clearcut 

forest having dense ground cover." In Glacier National 

Park, Key (1979) collected one pygmy shrew from the 

floodplain on the North Fork of the Flathead River. 

Koford (1938) captured an individual in an open ponderosa pine stand 100 feet from the Thompson River, 

northwest Montana. Hoffmann et al. (1969a) report 

that 14 pygmy shrews have been collected from the 

grand-fir habitat type at the University of Montana 

Biological Station, Yellow Bay. Numerous individuals have been captured in the Swan Valley, western 

Montana (K. R. Foresman pers. comm.). Foresman 

(1986) collected two specimens from the South Fork of 

Spruce Creek, Idaho County, Idaho, in stands dominated by subalpine fir (Abies lasiocarpa), grand fir 

(Abies grandis) and Engelmann spruce (Picea engelmannii). Since this site is near the BNF, where similar 

habitat is abundant, it is reasonable to presume that 

this species occurs on the BNF. 

Preble's shrew is unusual in that it is associated 

with dry shrub-step habitats (Hoffmann et al. 1969a). 

This species is represented in Ravalli County by one 

specimen collected in 1910, eight miles northeast of 

Stevensville, MT (Hoffmann and Fisher 1978). No 

habitat description is given, but based on adjacent 

undeveloped habitat, the site was probably dominated 

by big sage (Artemisia tridentata) and bunchgrasses 

(Festuca spp. and Agropyron spicatum) (personal observation). This species is associated with dry sagebrush habitats in Montana as seen by six specimens 

17 
taken near Butte, MT, and one specimen each taken 

from St. Mary's, Glacier County, MT, and the Lamar 

Ranger Station, Yellowstone National Park, WY 

(Hoffmann et al. 1969a). Pitfall trapping in sagebrush habitats along the foot hills of the Saphire 

Range may well produce more specimens of Preble's 

shrew in the Bitterroot Valley. 

Bats 

The inactivity of bats during the day and their 

great mobility make it difficult to determine habitat 

preferences for these particularly secretive small mammals. For these reasons, less information is available 

for this group than others. Ten species of bats are 

confirmed as present in the Bitterroot Valley. Most of 

these probably occur to some extent on the BNF 

(Table 1). An additional three species are included as 

possibly present based on habitat affiliations and 

distributions. 

The little brown myotis (Myotis lucifugus), or little 

brown bat, is the most common bat in Montana. It 

lives in summer colonies that can be found in buildings 

and caves throughout Montana. Other less common 

species ofmyotis such as the yuma (M. yumanensis), 

California (M. californicus), and long-legged myotis 

(M. uolans) often occur in conjunction with colonies of 

little brown bats. Little brown bats may migrate south 

to overwinter (Hoffmann and Pattie 1968), but at least 

some remain (Nagorsen et al. 1993). In Alberta, 75 

percent of 269 maternity colonies of little brown bats 

were found in buildings (Schowalter et al. 1979). This 

bat forages low over water surfaces during the brief 

period after sunset when its chironomid food is most 

abundant (Barclay 1991). 

The yuma myotis is the second most common bat in 

Montana and the Bitterroot Valley (Hoffmann and 

Pattie 1968). This species is commonly found in colonies with the little brown bat (Hoffmann et al. 1969b). 

Brigham (1992) determined that the yuma bat forages 

predominantly in open areas and feeds opportunistically on aquatic insects, taking whatever species are 

abundantly available. This species likely migrates 

south in the fall. 

The long-eared myotis (Myotis euotis) is widespread 

but uncommon as it generally occurs singly or in small 

numbers. In the Bitterroot Valley, it has been collected 

at Stevensville, Victor, Corvallis, Hamilton, West Fork 

Ranger Station, and Sleeping Child (Hoffmann et al. 

1969b). This species is thought to be associated with 

coniferous forests (Hoffmann and Pattie 1968). The 

long-eared myotis is described by Barclay (1991) as a 

moth-eating bat that forages primarily within forests 

and on forest paths on the front range of the Rocky 

Mountains, Alberta. Foresman and Pearson ( unpublished data) collected an individual feeding over a 

18 

small pond in an Engelmann spruce bog in the Flathead Valley. The foraging conditions and behavior at 

this site were similar to those described by Barclay 

(1991) in Alberta. Roemer (1994) captured 16 individuals predominantly in moist forested habitats in 

northwest Montana. 

The fringed myotis is rare, occurring near the northern extent of its range in Montana (Hoffmann and 

Pattie 1968). The first fringed myotis in the state was 

taken at Woodside, Montana, in the Bitterroot Valley 

(Hoffmann et al. 1969b). Few additional records have 

been added, but adult females andjuveniles have been 

among them, suggesting that some breeding occurs 

within the state. 

The California my otis (My otis californicus) is also 

somewhat rare, occurring at the eastern edge and near 

the northern edge of its range in western Montana 

(Hoffmann and Pattie 1968). This species was first 

reported in the state from the Bitterroot where one 

was collected from a house in Hamilton (Hoffmann et 

al. 1969b). Until recently, all but one specimen had 

been taken from Ravalli County. Roemer (1994) captured 19 California myotis while surveying for bats 

on the Kootenai and Lolo National Forests, and 

Foresman and Pearson (unpublished data) collected 

one near a small pond in a spruce bog in the Flathead 

Valley. This species probably migrates south as do 

other myotis, but a number of winter records are 

described for British Columbia (Nagorsen et al. 1993). 

The eastern small-footed myotis has been collected 

only at a few locations in the southern portion of the 

state. Many of the known collections are from the 

Bitterroot Valley: Stevensville, Victor, Corvallis, 

Woodside, Hamilton, Grantsdale, and Sleeping Child 

(Hoffmann et al. 1969b). The eastern small-footed 

myotis is thought to migrate to southern climes to 

overwinter (Hoffmann and Pattie 1968). 

The western small footed myotis (M. ciliolabrum) 

has not been reported in the Bitterroot Valley, but 

eight individuals were captured by Roemer (1994) 

while surveying the Kootenai and Lolo National Forests, and this species may occur on the BNF. This 

species is notincludedin Hoffmann and Pattie's (1968) 

key to Montana mammals and was not reported during intensive surveys in the Bitterroot Valley 

(Hoffmann et al. 1969b). 

The big brown bat maintains a wide distribution in 

the United States but is less common in Montana 

than elsewhere (Hoffmann and Pattie 1968). It occurs 

in a variety of habitats and is known to roost in caves 

and buildings. Brigham (1991) identified eight maternity colonies in hollows of large-diameter (ca. 2-m 

circumference) ponderosa pine snags in southcentral 

British Columbia. This species will also use humanmade structures (Brigham and Fenton 1986) and will 

establish maternity colonies in buildings (Kunz 1982). 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
Hoffmann and Pattie (1968) suggest that most big 

brown bats leave the state during the winter, but 

evidence from British Columbia indicates that at least 

some individuals overwinter in caves, mines, and 

buildings in Canada (Nagorsen et al. 1993). 

Townsend's big-eared bat ranges across Montana 

but is uncommon and localized within the state. Only 

a few maternal colonies and hibernacula have been 

identified in Montana. One maternal colony near the 

National Bison Range is set in a mine adit bordering 

an open ponderosa pine community (K. R. Foresman, 

pers. comm.). The habitat is similar to ponderosa pine 

stands found in lower elevations throughout the Bitterroot Valley. This species has been collected from 

several locations within the Bitterroot Valley including the Curlew Mine near the mouth of Big Creek, 

Hamilton, and Lake Como (Hoffmann et al. 1969b). 

Townsend's big-eared bat hibernates in caves in 

Montana and British Columbia (N agorsen et al. 1993; 

Hoffmann and Pattie 1968). 

The largest Montana bat is the hoary bat (Lasiurus 

cinereus) (Hoffmann and Pattie 1968). Because this 

species roosts individually in trees, it is difficult to 

locate and has been captured uncommonly in the 

state. Roemer (1994) captured only one hoary bat in 

42 nights of mist netting in northwestern Montana. 

No record of hoary bats from the Bitterroot Valley 

was uncovered, but it very likely occurs on the BNF. 

The hoary bat migrates to more southern latitudes to 

overwinter (Perkins and Cross 1988; Findley and 

Jones 1964). Perkins and Cross (1988) found hoary 

bats significantly more abundant in Douglas-fir stands 

>200 years old. They suggested that structural diversity of older trees provided roosting habitat necessary 

for this species. 

The silver-haired bat (Lasionycteris noctiuagans) 

roosts in trees and snags and is thought to be associated with mature and old-growth coniferous forests 

(Campbell1993; Hoffmann and Pattie 1968). In Oregon, 

the silver-haired bat selects Douglas-fir stands >100 

years old but does not select ponderosa pine of the 

same age class (Perkins and Cross 1988). Ponderosa 

pine may not provide the appropriate roost sites for 

this species, or the habitat may be too dry. Silverhaired bats probably forage within openings in mature forests. Nine individuals were captured by 

Roemer (1994), primarily in moist forests in northwest Montana. Evidence from British Columbia indicates some overwintering of silver-haired bats occurs 

in trees and beneath the bark of older trees. A small 

colony has resided in a building in West Glacier at 

least since 1990 (pers. obs.). 

The spotted bat (Euderma maculatum) is rare 

within its range across the western United States 

and parts of Canada (Watkins 1977; Hoffmann and 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

Pattie 1968). This species is known from only two 

sites in Montana, Billings, and the Prior Mountains 

(Worthington 1991; Hoffmann and Pattie 1968). However, based on its current distribution and its use of 

open ponderosa pine habitat in British Columbia 

(Leonard and Fenton 1983; Woodsworth et al. 1981), 

this species could occur in ponderosa pine communities at the southern end of the Bitterroot Valley. In 

British Columbia, the spotted bat is extremely faithful to roosts in rock crevices (Wai-Ping and Fenton 

1989 ), a habitat component also prevalent on the BNF. 

In general, spotted bats exist in arid habitats across 

the western United States (Watkins 1977). This species consumes moths and tends to fly about 10m above 

the ground (Navo et al. 1992; Woodsworth et al. 1981). 

It may trapline and seems to be territorial (W oodsworth 

et al. 1981). Spotted bats are believed to migrate 

south to overwinter (Genter 1989). 

Feeding and Habitat-Many species of bats forage over ponds, rivers, and streams where insects are 

abundant. Some forest species feed in natural openings and over roads and trails (Roemer 1994; Barclay 

1991). Foraging height varies as does size, species of 

prey, and foraging time. These factors may be important in separating potential competitors. Fenton et al. 

(1983) found hoary bats almost exclusively associated 

with lights in British Columbia. In Ontario, the big 

brown bat was similarly drawn to lights both in towns 

and in urban areas (Furlonger et al. 1987). It may be 

that lights, which draw in noctuid moths, provide 

ideal foraging conditions for the energy requirements 

of these large bats. Other myotis were also encountered near lights, but they were found away from 

lights as well. Small pools in western red-cedar 

stands were busy drinking areas for bats in British 

Columbia, whereas pools with high vegetation around 

the edges were not used, suggesting that an open 

flight path for access is important (Furlonger et al. 

1987). Calm water may be preferable to turbulent 

streams for drinking because it is less hazardous. 

It is difficult to identify specific habitat relationships for bats beyond their requirements for hibernacula and day roosts and their rather general use of 

foraging areas with high concentrations of insects and 

sufficiently open flight paths for hunting. Many species seem to optimize foraging from a central roost site. 

Under this scenario, the best habitats are those that 

provide day roosts or hibernacula within close proximity to water or other concentrations of food (Brigham 

1991; Furlonger et al. 1987; Barclay 1991). Furlonger 

et al. (1987) found "no unique associations between 

different species of foraging bats and specific habitats." However, radiotelemetry studies are now providing more detailed information on habitat use by 

bats. 

19 
Pika 

The pika is a small, unusual member of the 

Lagomorpha. This herbivorous animal resides almost 

exclusively in talus slopes (Wiseley 1973). In lieu of 

storing brown fat for hibernation, the pika dries and 

caches herbaceous vegetation in "hay piles" beneath 

boulders to carry it through the winter months (Millar 

and Zwickel 1972). To protect this energetic investment, pikas are extremely territorial (Barash 1973b). 

Because they are also central place foragers, further 

intraspecific competition occurs for sites near the 

edges of talus slopes that provide optimal foraging 

areas (Kawamichi 1976). Numerous researchers 

(Southwick et al. 1986; Krear 1965; Kilham 1958) 

argue that this intense territoriality explains the lack 

of fluctuations observed within pika populations. 

Pikas are herbivorous and so must feed in vegetation bordering talus slopes (Elliot 1980). When foraging, they remain near the protective cover of the rocks 

and usually stay within 5 or 10m of the border (Tyser 

1980, 1978; Barash 1973a). As a result, pikas can 

heavily impact abundance and composition of herbaceous plants near talus slopes (Huntly 1987; Huntly 

et al. 1986). An examination of 11 hay piles in a pika 

colony iri central Idaho revealed that, although 26 

plant species were present, three species (Smilacina 

stellata, Apocynum androsaemilifolium, Fragaria 

virginiana) made up 88 percent of the total dry weight 

of the hay piles (Elliot 1980). 

Not all talus slopes provide optimal pika habitat. 

Pikas favor conditions where rocks are 10 to 12 inches 

in diameter (Roper 1956). Roper (1956) suggests that 

rocks of this size class provide ideal conditions for 

mazes that allow movement beneath the cover of 

rocks. Larger rocks may not provide sufficient protection from predation, and small ones would not allow 

enough space for passages beneath. Stability and 

aspect are also thought to be important habitat 

components. Steep slopes tend to be too unstable and 

shaded slopes may not remain snow-free long enough 

during the growing season (Roper 1956). Tyser (1980) 

found that pikas near Logan Pass, Glacier National 

Park, were also selective in the types of rock promontories used for surveillance activities, preferring 

medium-sized boulders from 0.20 to 0.99 m diameter. 

Snowshoe Hare 

The snowshoe hare is the common "rabbit" of western Montana forests. It is an extremely important prey 

species for forest carnivores such as fishers (Martes 

americana) and lynx (Lynx lynx), which consume primarily snowshoe hares (Powell and Zielinski 1994; 

Koehler and Aubry 1994; Roy 1991; Koehler 1990; 

Koehler et al. 1979). They also support many other 

20 

carnivores, though less exclusively (see Ruggiero et al. 

1994; Keith and Cary 1991; Adams 1959). Snowshoes 

reach their greatest numbers in mature lodgepole pine 

stands [ 25 years old (Koehler 1990) but may inhabit 

late seral forest as well (Powell1991, unpublished, as 

cited in Powell and Zielinski 1994). Optimal habitat 

for snowshoe hares is consistently described as dense 

cover from 1.0 to 2.5 m above the ground (Wolfe et al. 

1982) in the form of shrubs or dense stands of young 

trees (Fuller and Heisey 1986; Litvaitis et al. 1985; 

Wolfe et al. 1982; Adams 1959). 

In western Montana and Washington, conifers are 

important foods for snowshoe hares (Koehler 1990; 

Adams 1959). This is problematic as hare populations 

at peak densities can become forest pests in some 

lodgepole pine forests (Sullivan and Moses 1986). 

However, hares at this latitude do not exhibit the 

radical 10-year cycles observed farther north where 

vegetation sustains heavy damage from snowshoe 

hare foraging in peak years (Wolff1980). Wolff(1980) 

hypothesized that dampened amplitudes in hare 

cycles at this latitude result from a greater diversity of 

generalist predators and alternative prey. These predators, through prey switching, may more effectively 

control populations by culling hares from suboptimal 

habitats. A recent review of the ecology of snowshoe 

hares in southern montane forests can be found in 

Murray (in prep.). 

Chipmunks 

Two species of chipmunks occur on the BNF: the 

red-tailed chipmunk (Tamias ruficaudus) and the 

yellow-pine chipmunk (Tamias amoenus). The redtailed chipmunk is most commonly associated with 

gaps and small openings in moist forests where shrubs 

occur (Foresman in review). The yellow-pine chipmunk inhabits ponderosa pine and drier, more open 

Douglas-fir forests. Beg (1969) found that red-tailed 

chipmunks dominated stands within the subalpine 

zone in westcentral Montana, while the yellow-pine 

chipmunk primarily inhabited ponderosa pine forests 

was present within the Douglas-fir zone where it was 

restricted to dry aspects where ponderosa pine dominated the canopy. In mid-slope locations where habitats integrated, the species were restricted to their 

respective habitats and only overlapped where sharp 

ecotones occurred. 

Both species are associated with shrubs, which they 

actively climb to obtain fruits and seeds. The yellowpine chipmunk tends to do well in early seral habitats, 

especially after shrubs have become established (Medin 

and Booth 1989; Medin 1986; Walters 1991). In 

westcentral Montana, Ruggiero and Pearson (unpublished data) found that the two species were sympatric 

in three of five moist seral ponderosa pine stands 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
where Douglas-fir encroachment was high, and they 

found only yellow-pine chipmunks in two stands with 

low levels of Douglas-fir that had a recent history of 

prescribed fire. For the red-tailed chipmunk, there is 

conflicting data regarding its use of early seral stages. 

This point is discussed in detail later (see section on 

Disturbance). Elevationally, the two species are separated by the ranges of their corresponding habitats, 

though overlap does occur. The red-tailed chipmunk 

does well in higher-elevation, closed canopy forests, 

whereas the dry savanna-like habitat of yellow-pine 

chipmunk is most common at lower elevations. 

Ground Squirrels 

The columbian ground squirrel (Spermophilus 

columbianus), common in grasslands, pastures, and 

agricultural lands in western Montana, occurs within 

a limited range in the northwestern United States and 

western British Columbia (Hoffmann et al. 1969a). In 

addition to the more familiar, dry, low-elevation habitats, columbian ground squirrels inhabit moist highelevation subalpine and alpine meadows (Hoffmann 

and Pattie 1968; Manville 1959). This species is also 

commonly found in talus slopes at higher elevations 

where it is sympatric with marmots (Marmota spp.) 

and pikas (for example, Tyser 1980, 1978). Though 

the columbian ground squirrel can inhabit more open 

forests, it is not present in closed canopy forests 

associated with mid- to late-seral stands. 

Columbian ground squirrels develop extensive burrow systems. Through these earth moving activities, 

they provide a service to annuals and forbs which 

favor the disturbed patches. They also affect soil 

characteristics through aeration and nutrification by 

means of earth moving processes and the introduction 

of feces to these sites. Digging and burrowing activities may further alter plant communities by facilitating the invasion of non-native weeds that readily 

colonize such disturbed sites. 

In agricultural areas and pasture lands, this species 

is commonly referred to by locals as a "gopher" and 

considered an agricultural pest. To control it, poisoning programs have been implemented. A study in the 

Blackfoot Valley indicated that 1080-laced bait was 

ineffective in controlling columbian ground squirrel 

populations (Malloy 1981). Although populations initially declined to zero, they returned to 20 percent of 

the original population size by the follow_ing year. A 

number of non-target species were also killed by baiting, including most small mammals on site and 

scavengers that consumed poisoned carcasses. Ecologically, such practices do more harm than good. 

The golden-mantled ground squirrel (Spermophilus 

lateralis) is often erroneously described as a giant 

chipmunk by budding naturalists and visitors to 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

national parks, but its similarity to the chipmunks 

extends beyond superficial morphological likeness to 

food habits and, to some extent, habitat. This species 

tends to be more omnivorous in its diet than the 

columbian ground squirrel, taking seeds, flowers, and 

fungi (Foresman in review). Like chipmunks, it favors 

brushy habitats and rocky outcrops. The goldenmantled ground squirrel also differs from the columbian 

ground squirrel in that it is asocial (Ferron 1985). It 

has a wider distribution in the western United States 

than does the columbian ground squirrel and inhabits 

a wider range of habitats including open areas 

within dry seral forests (ponderosa pine, lodgepole 

pine, Douglas-fir), moist high elevation stands (spruce 

and subalpine fir), disturbed·sites, clearcuts, and alpine rock slopes (Foresman in review). This species 

can persist on mountain tops in patches of alpine 

habitat (pers. obs.). 

Trapping in old-growth ponderosa pine stands in 

westcentral Montana and on the BNF indicates that 

this species is an important member of the ponderosa 

pine small mammal community (Ruggiero and Pearson 

unpublished data). Golden-mantled ground squirrels 

were captured in association with rocky outcrops in 

five of five ponderosa pine stands where they were the 

second most abundant species after the deer mouse. 

Red Squirrel 

The red squirrel seems to be restricted in habitat 

only by its arboreal nature and preference for conifer 

seeds. In the Northern Rocky Mountains, this species 

occurs wherever coniferous forests exist. It ranges 

from lower treeline in ponderosa pine communities to 

near upper treeline in subalpine fir forests (Foresman 

in review). 

The red squirrel is omnivorous (Foresman in review) 

and will prey upon birds and small mammals (Callahan 

1993). However, the red squirrel is a highly skilled 

pine-cone farmer that spends most of its time harvesting cone crops from the tops of conifers and caching 

cones for winter (Brink and Dean 1966). Its dependence on cone crops is apparent in its demographic 

response to years of high and low cone productivity. 

Halvorson and Engeman (1983) demonstrated that 

red squirrels born during years of high seed production on Cedar Island, Flathead Lake, had a significantly higher probability of surviving the first year 

than squirrels born at other times. These squirrels 

also lived an average of five months longer the second 

year, though the difference was not significant. 

One result of hoarding behavior is often territoriality. The red squirrel maintains several middens where 

it feeds, removes seeds from cones, and caches seeds 

for later use. These sites are aggressively defended 

against conspecifics and are easily identified by great 

21 
mounds of pine cone debris. Middens may be built up 

over many years by a single individual (which can live 

seven years; Halvorson and Engeman 1983). Later 

generations add further to such structures as territories change owners (Hatt 1943). Because of this 

strong dependence on cone crops and aggressive territoriality, red squirrels are probably subject to source/ 

sink dynamics. Red squirrel populations found in postharvest treatments may be sinks. 

Middens are ecologically important sites not only 

for the red squirrel, but also for the American marten 

which uses squirrel middens as resting sites, denning 

sites, and access points for entering the subnivian 

zone in winter (Ruggiero et al. in prep.; Ruggiero et al. 

1998; Sherburne and Bissonette 1993; Buskirk 1984). 

Middens may also function as supplemental feeding 

sites for deer mice and southern red-backed voles, 

which may visit these sites to pilfer seeds from caches 

or simply clean up scraps left by squirrels. Because 

deer mice are nocturnal and red squirrels are diurnal 

(see Foresman and Pearson 1995 for data on red 

squirrel activity patterns), deer mice would have free 

reign to pilfer caches at night. If such pilfering does 

occur, marten could take advantage of middens as 

baiting stations for small rodents. 

Northern Flying Squirrel 

The northern flying squirrel was identified by the 

Scientific Assessment Team as an old-growth associated species that requires old-growth components in 

the Pacific Northwest (Thomas et al. 1993). This 

species is a cavity nester that primarily nests in natural 

openings and woodpecker holes (Wells-Gosling and 

Heaney 1984; Cowan 1936). Although it has also been 

observed using external dray-type nests (Rust 1946; 

Cowan 1936), Cowan (1936) believed such nests were 

mostly used in summer. Because of its cavity nesting 

habit, the northern flying squirrel requires snags of 

sufficient diameter to provide for nesting habitat. This 

species is also primarily a fungivore, satisfying most of 

its dietary needs by consuming hypogeous mycorrhizal fungi (see Mycophagy) that are most abundant 

in mature and old-growth forests (Amaranthus et al. 

1994; Clarkson and Mills 1994). 

However, northern flying squirrels can exist in a 

variety of forest types provided that these habitat 

requirements are met. They have been trapped in 

ponderosa pine, lodgepole pine, Douglas-fir, and mixed 

conifer forests in the northwestern United States 

(Maser et al. 1985; McKeever 1960; Cowan 1936). 

Andersen etal. (1980) found northern flying squirrels 

in several forest types but recorded the highest densities in spruce-dominated forests. Witt (1992) compared populations of northern flying squirrels between old-growth and second-growth stands in the 

22 

western Oregon western hemlock zone and found 

that northern flying squirrels were six times more 

abundant in old-growth forest sites. He attributed 

his findings to greater availability of den sites and 

higher productivity of hypogeous sporocarps associated with the old-growth stands. Rosenberg and 

Anthony (1992) also observed greater numbers of 

northern flying squirrels in old growth than secondgrowth stands in western Oregon. However, because 

they found higher proportions of females than males 

in second-growth compared to old-growth stands, and 

because densities were not correlated with habitat 

characteristics, the authors concluded that the northern flying squirrel was a habitat generalist rather 

than an old-growth associated species. 

This species occurs on the BNF in late seral ponderosa pine and western larch-Douglas-fir stands 

(Ruggiero and Pearson unpublished data; Halvorson 

1982), and in northwest Montana in late-seral western hemlock-western red cedar (K. A. Keating and 

D. E. Pearson unpublished data). For many years, a 

population has persisted on the University ofMontana 

Biological Station on the east shore of Flathead Lake 

in association with large cottonwoods (Populus 

trichocarpa) within a late-seral grand fir stand (K. R. 

Foresman pers. comm.). 

Northern Pocket Gopher 

Two species of pocket gophers, the northern pocket 

gopher and the Idaho pocket gopher (Thomomys 

idahoensis), exist in the Bitterroot Valley. However, 

the latter is only present in an isolated population in 

the valley bottom (P. L. Wright, pers. comm.) and may 

not occur on the BNF. Foresman (in review) indicates 

that there is very limited data on the ecology of the 

Idaho pocket gopher, which has only been recognized 

as a distinct species for the last 20 years, but suggests 

that it is ecologically similar to the northern pocket 

gopher. 

The northern pocket gopher is fossorial, inhabiting 

extensive underground burrows. It is therefore restricted to locations where deep soft soil is present, 

such as open meadows, but ranges from valley bottoms 

to high-elevation alpine habitats where appropriate 

soil conditions occur (Andersen and McMahon 1981; 

Tryon 194 7). Pocket gophers produce mounds that are 

highly visible and a good indication of the species' 

presence. Scrivner and Smith (1981) have shown that 

indices of pocket gopher sign (mounds and earth plugs) 

can be used in place of trapping data to estimate 

pocket gopher density. 

The digging activities of the northern pocket gopher 

can affect the local environment by increasing soil 

porosity and introducing nitrogen, phosphorous, and 

organic materials into the soil (see Bonar 1997 for 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
review; Laycock and Richardson, 1975). Pocket gophers also affect community composition by favoring 

annuals and reducing forbs, especially dandelions 

(Taraxacum officional). On healthy rangelands, this 

species is thought to improve soil conditions. However, 

under conditions of overgrazing, pocket gophers may 

increase dramatically possibly due to an increase in 

preferred species associated with disturbance. The 

addition of pocket gopher disturbance then makes it 

difficult to restore the range even after livestock grazing has been removed (Laycock and Richardson 197 5). 

In northern Utah, Andersen and McMahon (1981) 

documented a decline in northern pocket gophers 

with advancing succession from alpine meadow to 

aspen-subalpine fir and spruce forest. They estimated 

northern pocket gopher densities ranged from 62 individuals/ha in alpine meadow to two individualslha in 

spruce forest. Bioenergetic analyses indicated that 

the climax spruce forest was food limited and that 

additional energy costs associated with reproduction 

in females may exceed the below ground available food. 

supply within mid-seral aspen and subalpine fir. However, in northern Idaho spruce-fir forests, Scrivner 

and Smith (1981) found no difference between numbers 

of northern pocket gopher in early seral (1 to 10 yr) and 

late seral (80+ yr) stands, but observed significantly 

higher abundance in early seral (1 to 10 yr) and late 

seral (80+ yr) stands than in mid-seral stands (11 to 

39, 40 to 79 yr). 

Deer Mouse 

The deer mouse is the most ubiquitous small mammal in North America due to its broad ecological 

tolerance. It exists in Montana at all elevations and in 

numerous habitats (Hoffmann and Pattie 1968; Pattie 

and Verbeek 1967). Some evidence suggests that deer 

mice avoid habitats at the wettest end of the hydrosere: bogs, fens, wet meadows, and marshes (Hayward 

and Hayward 1995; Clark 1975, 1971). Reichel and 

Beckstrom (1994, 1993) and Pearson (1991) trapped 

these habitats extensively in western Montana and 

captured very few deer mice. 

The deer mouse is the paradigm habitat generalist, 

thriving in such a wide variety of environments that 

it is difficult to determine habitat affiliations. Although in forest habitats, the deer mouse seems to 

favor early seral stages (Walters 1991; Morrison and 

Anthony 1989; Ramirez and Hornocker 1981; Sullivan 

and Krebs 1981; Campbell and Clark 1980; Gashwiler 

1970) and drier forest habitats (Foresman in review; 

Raphael1988), it also inhabits mesic old-growth forest 

(Pearson 1994; Raphael1988; Halvorson 1982). It has 

been reported to increase in abundance with increasing stand age (Pearson 1994; West 1991; Scrivner and 

Smith 1984), to have similar population densities 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

between cutting treatments and uncut stands (Medin 

1986), and to exhibit greater numbers in uncut versus 

selectively harvested stands (Medin and Booth 1989). 

Deer mice often associate with shrubby habitats 

(Belk et al. 1988) and shrubby microhabitats within 

forest stands (pers. obs.). 

Pearson (1994) found deer mice to increase along a 

successional gradient in Glacier National Park. He 

reported that the deer mouse displayed stronger microhabitat selection than the southern red-backed vole, a 

habitat specialist, in four seral stages (65, 138, 256, 

457 yr) of cedar-hemlock forest. He suggested that 

deer mice may exhibit "habitat switching'' and respond to local site conditions by developing search 

images that manifest thems~lves as distinctive foraging patterns at the microhabitat scale. Such behavior would render the deer mouse a formidable 

competitor for resources and explain its tenacity for a 

wide variety of habitats. 

Bushy-Tailed Wood rat 

The bushy-tailed woodrat nests in rocky habitats 

such as caves, talus slopes, boulder fields, and cliff 

faces (Topping and Millar 1996; Finley 1958), but may 

also use snags and CWD in forest environments. 

Woodrats construct nests of sticks, dried vegetation, 

and debris used by later generations, which continue 

to add to their volume. Fidelity to perch sites used for 

feeding sites and latrines by individuals and lineages 

over time results in an accumulation of plant material 

and bones that, along with nest structures, provide 

storehouses of information for paleontologists (see 

VanDevender 1986). Middens can persist for thousands of years if they remain dry (Spaulding et al. 

1983). 

The social structure and finite nesting sites limit 

population sizes of bushy-tailed woodrats. Foraging 

is likely to occur in rocky areas immediately near the 

den, but most probably occurs in habitats bordering 

rocky areas (Topping and Millar 1996). The diet consists mostly of vegetation including forbs, conifer 

needles, fruits, seeds, and fungi (Finley 1958). Use of 

restricted den sites by the bushy-tailed woodrat (Moses 

and Miller 1992) has led to philopatry in female 

offspring. W oodrats exhibit strong agonistic behavior 

toward distantly related and unrelated individuals, 

while maintaining congenial relationships with 

closely related kin (mother-offspring). 

Northern Bog Lemming 

The northern bog lemming is a boreal species that 

occurs as a Pleistocene relict in Montana (see Foresman 

in review; and Pearson 1991). It was first discovered in 

the Camas Creek drainage of Glacier National Park 

23 
(Wright 1950). Later Weckwerth and Hawley (1962) 

trapped northern bog lemmings and found their remains in marten scats collected in Anaconda Creek 

not far from the Camas Creek location. A study of 

small mammals in the Rattlesnake Creek drainage 

produced another incidental capture in the bog-like 

habitat of Shoofly Meadows (Adelman 1979). Recent 

surveys conducted for this species have reconfirmed 

its presence in Shoofly Meadows (Pearson 1991) and 

uncovered numerous new populations of northern 

bog lemmings in western Montana (Reichel and 

Beckstrom 1994, 1993; Pearson 1991). Two bog lemmings have been captured on the BNF. One was taken 

in a snap trap at Meadow Creek in 1992 (Reichel and 

Beckstrom 1993). Another was captured in 1996 within 

an old-growth ponderosa pine stand in Big Creek, but 

this individual probably came from the adjacent oldgrowth mixed conifer bottom (Ruggiero and Pearson 

unpublished data). 

Habitat of the northern bog lemming consists primarily of fens and bogs or bog-like environments that 

are themselves relict communities from the Pleistocene (Reichel and Beckstrom 1994, 1993; Pearson 

1991; Layser and Burke 1973; Shaw 1930). However, 

this species has also been taken in wet meadows in 

Camas and Anaconda Creeks, Glacier National Park 

(Weckwerth and Hawley 1962; Wright 1950); oldgrowth hemlock (Tsuga heterophylla) forest, McDonald 

Valley, Glacier National Park (see Pearson 1991); 

subalpine-fir (Abis lasiocarpa) forest, Sunday Creek, 

northwest Montana (Reichel and Beckstrom 1993); 

and alpine habitat in Washington (Wilson et al. 1980). 

Reichel and Beckstrom (1994, 1993) and Pearson 

(1991) suggest that the presence of mat-forming 

Sphagnum spp. is a good, though not definitive, indicator for this rare lemming-mouse. 

Montane Heather Vole 

The heather vole is not common in western Montana 

but can be found in a variety ofhabitats (Hayward and 

Hayward 1995; Millar et al. 1985; Kinsella 1966; 

Negus 1950). In the Northern Rockies, it most often 

occurs within higher-elevation moist forests such as 

spruce-fir associations, and wet meadows, fens, and 

bog-likehabitats(HaywardandHayward1995;Reichel 

and Beckstrom 1994, 1993; Pearson 1991; Hoffmann 

and Pattie 1968). Heather voles have been captured in 

abundance in flooded old-growth spruce-fir near the 

Canadian boarder along the North Fork of the Flathead River, MT (D. E. Pearson unpublished data). 

Reichel and Beckstrom (1994, 1993) caught 72 heather 

voles in fen and bog-like habitats throughout western 

Montana while surveying for northern bog lemmings. 

Although they did not survey other habitats, their 

success suggests that such habitats are important for 

heather voles. 

24 

Red-Backed Vole 

The southern red-backed vole is a wide-ranging 

boreal species found in forested habitats throughout 

most of Canada and the northern United States 

(Hoffmann and Pattie 1968). Due to its broad distribution and community dominance in moist forests, an 

extensive literature has developed around this species, particularly with regard to its habitat associations (see Pearson 1994). In the central Rocky Mountains, this vole is an indicator species for the old -growth 

condition (USDA Forest Service 1985), and in the 

Pacific Northwest it is recognized by the Scientific 

Assessment Team as a species requiring old-growth 

components (Thomas et al. 1993).1t is also listed as an 

old-growth dependent species by Lumen and Nietro 

(1980). 

The southern red-backed vole is found in moist 

forests in much of the Rocky Mountains but disappears soon after stands are cut (Pearson 1994; 

Shepherd 1994; Raphael1988; Medin 1986; Scrivner 

and Smith 1984; Halvorson 1982; Ramirez and 

Hornocker 1981), and young stands are thought to be 

habitat sinks for this species (Pearson 1994; Nordyke 

and Buskirk 1991). 

Gunderson (1959) concluded that southern redbacked voles were associated with logs and therefore 

restricted to forests where logs were abundant. Other 

authors suggested this was also true of the congeneric 

California red-backed vole in the Pacific Northwest 

(Tevis 1956a), and Tallmon and Mills (1994) provide 

some evidence in support of this hypothesis. In Glacier National Park, Pearson (1994) determined that 

southern red-backed voles selected stands containing 

abundant large-diameter logs and further observed 

that when the distribution of these logs was heterogeneous within a stand, the voles selected those microhabitats containing large-diameter logs. 

Voles (Genus Microtus) 

Voles of the genus Microtus dominate grasslands, 

savannas, and grassy areas within forests in western 

Montana. These voles are herbivores, specializing in 

the consumption of grasses and forbs, but they also 

occasionally take seeds, fruits, and insects (see 

Foresman in review). The genus is represented by 

four species on the BNF: the meadow vole (M. pennsylvanicus), the montane vole (M. montanus), the longtailed vole (M. longicaudus ), and the water vole (M. 

richardsoni). 

The meadow vole and the montane vole are often 

sympatric in grassland environments (Hodgson 1972; 

Findley 1951). Within these habitats, the two species 

segregate along a moisture gradient (Hodgson 1972). 

The meadow vole prefers moist meadows and wet, 

grassy areas near water and may exclude the montane 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
vole from these habitats where the two species overlap (Koplin and Hoffmann 1968). The montane vole 

exhibits the greater ecological tolerance of the two 

(Douglas 1976; Clark 1973; Hodgson 1972; Findley 

1951). Although it is most abundant in moist grassy 

conditions where the meadow vole is absent, it does 

well in dry conditions and is the more common species 

in dry grasslands and sagebrush (Clark 1973; Hodgson 

1972). The meadow vole is absent from wet meadows 

in the alpine and subalpine zones, and montane voles 

occupy these grassy habitats in its absence (Hoffmann 

et al. 1969a). 

It seems likely that competitive interactions play 

some part in the habitat segregation of these voles. 

When Koplin and Hoffmann (1968) removed meadow 

voles from wet meadows on theN ational Bison Range, 

Montana, montane voles began to move in from the 

drier surrounding areas. A reciprocal study conducted 

by Stoecker (1972) produced complementary results. 

Removal of montane voles from a xeric grassland 

resulted in the encroachment of meadow voles not 

previously captured there. Enclosure studies conducted 

by Douglas (1976) indicated that montane voles 

maintained larger home ranges and selected different 

vegetation in the presence of meadow voles. Murie 

(1971) concluded that the meadow vole was dominant 

over the montane vole in aggression experiments. 

Hodgson (1972) trapped 59 sites around Bozeman, 

MT, to determine habitat associations of meadow and 

montana voles. Hodgson reported that numbers of 

meadow voles increased as graminoid cover (r = 0. 79) 

and soil moisture (r = 0.77) increased. While the 

montane vole was weakly correlated with increased 

graminoid cover (r = 0.27), it exhibited a strong negative correlation with soil moisture (r = 0.94). He 

determined that montane voles were associated with 

drier habitats dominated by Festuca idahoensis and 

Bromus inermis. Rickard similarly (1960) found 

montane voles in association with habitats dominated 

by Festuca idahoensis in eastern Washington and 

northern Idaho. Hodgson (1972) reported both species 

were rare on plots where shrubs provided significant 

canopy cover (Hodgson 1972) except when the shrub 

was big sage which favored montane voles. 

The long-tailed vole is generally less abundant 

than the other grassland voles (Clark 1973; Hoffmann 

and Pattie 1968) but has been captured in a great 

variety ofhabitats ranging from moist riparian areas, 

spruce-fir forests, and sub-alpine meadows to dry 

sagebrush (see Foresman in review; Clark 1973). Clark 

(1973) described the habitat of long-tailed voles as 

wetter and more structurally complex than that of 

other sympatric microtines. Halvorson (1982) captured long-tailed voles on recently burned Douglas-firwestern larch clearcuts in or near moist pockets of 

heavy cover in western Montana. He did not find this 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

species in a similar burn on the drier south face nor 

did he find it on old-growth control plots on either 

aspect. He concluded that this vole requires moist 

sites with heavy cover and avoids old-growth stands. 

Long-tailed voles have been captured in grass-forb 

microhabitats within old-growth western red-cedarwestern hemlock stands in Glacier National Park 

(pers. obs.) and often occur in forests where these 

microhabitat exist, such as along riparian corridors. 

In Pattie Canyon near Missoula, MT, Kinsella (1966) 

commonly trapped long-tailed voles along streams in 

forested habitat, and in 1964 he captured long-tailed 

voles in greater numbers than southern red-backed 

voles in the Douglas-fir-ponderosa pine forest. Clearly, 

this vole includes forests among its range of acceptable habitats. 

The water vole is the most specialized of the voles. 

This vole has abnormally extended incisors and is the 

largest vole in the state. Its range is limited to the 

Northern Rocky Mountains and the Cascade Range. 

The water vole is a habitat specialist restricted to 

grass, sedge, and shrubby habitats associated with 

riparian areas in the alpine and subalpine zones 

(Foresman in review; Hoffmann and Pattie 1968). 

In western Oregon, Doyle (1987) trapped water 

voles in mature and old-growth forests, but captures 

were always along the riparian area. Findley (1951) 

captured water voles in dry alpine meadows in 

Wyoming but indicated that they were most abundant 

near running water. In southern Alberta, Anderson 

et al. (1976) describe water vole habitat as mossy 

seeps and cold running streams and suggest that 

saturated soils and cool temperatures are important 

habitat features. Hoffmann et al. (1969a) reported 

collecting water voles from Bass Creek, lf2 mile below 

Bass Lake in the Bitterroot Mountains, but did not 

specifically identify the habitat. Water voles have also 

been captured in lower Big Creek (D. E. Pearson, 

unpub. data) and in Sweathouse Creek drainages 

(Landres et al. 1994) on the BNF and probably occur 

in many drainages in the Bitterroot Range. Water 

voles occupy lush herbaceous vegetation near streams 

and wet alpine meadows in Glacier National Park 

(pers. obs.). Pattie (1967) captured water voles next to 

water in the alpine zone on the Beartooth plateau. 

Western Jumping Mouse 

The western jumping mouse prefers grassy areas, 

especially near water (Belk et al. 1988; Cranford 1983; 

Clark 1971; Negus and Findley 1959). However, this 

species has been captured in a variety of habitats 

and appears unrestricted elevationally (Hayward and 

Hayward 1995; Hoffmann and Pattie 1968; Brown 

1967b). Negus and Findley (1959) found western 

jumping mice in meadows and willow-alder thickets 

25 
along a stream but reported they were most abundant in aspen stands. Raphael (1988) reported that 

jumping mice were most abundant in spruce-subalpine fir and mature lodgepole pine stands. Pearson 

(unpub. data) captured this species in mature and oldgrowth cedar-hemlock and spruce-subalpine fir forests as well as in stream -side grassy meadows in 

western Montana. 

Response of Small Mammals to 

Disturbance ---------------------------

Introduction 

Many species of forest dwelling small mammals 

are poorly adapted to the dramatic habitat changes 

associated with stand replacing fires. Even a relatively small fire can encompass an entire local population of small mammals, thereby forcing survivors to 

disperse or perish on site. Thus, stand replacing fires 

restructure small mammal communities. Clearcutting 

and other associated timber harvest treatments 

similarly affect small mammals. 

Numerous studies have addressed the effects of 

clearcutting and stand-replacing fire as major disturbance forces (Landres et al. 1995; Spildie 1994; Walters 

1991; Ramirez and Hornocker 1981; Campbell and 

Clark 1980; Halvorson 1982; Stout et al. 1971), but 

fewer studies have targeted more moderate timber 

harvest practices (Shepherd 1994; Foresman and 

Henderson 1991; Medin and Booth 1989; Medin 1986), 

and only one was found that specifically addressed the 

effects of low-intensity underburning in ponderosa 

pine communities (Bock and Bock 1983). The lack of 

studies addressing the effects ofless intensive natural 

fires can probably be attributed, in part, to the effective suppression of such fires in forest communities 

for the last century (Arno 1976). 

Most studies conducted within the Northern Rocky 

Mountains are natural experiments or natural ex periments involving treatment, and few include replication in their designs (Table 3). Shepherd (1994) used 

four replicate plots for each of three treatments, 

Pearson (1994) had three replicates for each of four 

stand ages, and Foresman and Henderson (1991) 

included four replicates in their study design. 

Halvorson (1982) did not replicate, but his study 

provides a unique design that presents both north and 

south aspect, paired treatments, and controls on the 

same ridge. Halvorson (1982) also follows four post 

treatment years, though he presents no pre-treatment 

data. Although this timeframe covers only a single 

microtine population cycle, few disturbance studies 

are this long-term. Designs used by Medin (1986) and 

Medin and Booth (1989) included control plots with 

pre-treatment and post-treatment data, as did Shepherd (1994). The Medin studies both contained two 

years of pre-treatment and three years of post-treatment data, while the Shepherd study captured one 

year of pre-treatment and presented only the first year 

of post treatment data from an ongoing project. 

In reviewing this literature, I lean most heavily on 

results presented by Shepherd (1994), Pearson (1994), 

Foresman and Henderson (1991), Medin and Booth 

(1989), and Medin (1986) due to their proximity to the 

BNF and use of replication in their study designs. 

Table 3-Primary small-mammal disturbance papers reviewed. Locations of studies, treatments examined, and major 

habitat types are indexed by author to provide a reference to local disturbance studies reviewed in this 

document. 

26 

Author(s) 

Landres et al. 1994 

Pearson 1994 

Shepherd 1994 

Foresman and Henderson 1991 

Halvorson 1982 

Ramirez and Hornocker 1981 

Medin and Booth 1989 

Medin 1986 

Scrivner and Smith 1984 

Scrivner and Smith 1981 

Stout et al. 1971 

Nordyke and Buskirk 1991 

Campbell and Clark 1980 

Spildie 1994 

Walters 1991 

Loc. 

MT 

MT 

MT 

MT 

MT 

MT 

ID 

ID 

ID 

ID 

ID 

WY 

WY 

WY 

BC 

Treatment 

Clearcut/fire 

Sere 

Partial cut 

Partial cut 

Clearcut/burn 

Clearcut 

Partial cut 

Partial cut 

Sere 

Sere 

Fire 

Sere 

Clearcut/part.cut 

Fire 

Clearcut/burn 

Major habitat 

Douglas-fir(?) 

western hemlock-western redcedar 

Douglas-fir 

Douglas-fir-western larch 

Douglas-fir-western larch 

subalpine fir 

ponderosa pine-Douglas-fir 

ponderosa pine-Douglas-fir 

Engelmann spruce-subalpine fir 

Engelmann spruce-subalpine fir 

western redcedar through subalpine fir 

lodgepole pine through subalpine fir 

Engelmann spruce-subalpine fir 

Engelmann spruce-subalpine fir 

pacific silver fir (Abies amabi/is)-hemlock 

(Tsuga heterophylla, T. mertensiana) 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
Three studies, Landres et al. (1994), Foresman and 

Henderson (1991), and Halvorson (1982), were conducted within or near the BNF and represent the 

moist, seral ponderosa pine and Douglas-fir communities of primary interest in this review. Among these 

studies, moderate and extreme harvest treatments 

and fire are addressed. 

Review of Disturbance and Succession 

Literature 

Small mammal communities of western Montana 

can vary in richness and complexity from simple 

systems of one or two species to complex associations with representatives from several ecological 

guilds. Many small mammal communities of western 

Montana are dominated by one or two species, while 

other species add more to the richness of an ass emblage than to numbers and biomass (pers. obs.). As a 

result, the body of literature generated by studies of 

small mammal responses to disturbance focuses primarily on only a handful of species: southern redbacked voles, deer mice, yellow-pine chipmunks, redtailed chipmunks, and generally one of three species of 

Microtus. These species are the most common small 

mammals associated with late successional forests 

and post-disturbance conditions. Other species have 

received variable attention depending on their local 

abundance at study sites. 

Shrews-Shrews are seldom addressed in disturbance literature because of their poor representation 

in many trapping studies. Generally, only cinereus 

and vagrant shrews are reported on. Their response to 

disturbance is not clear from the information currently available. This is partly due to their low capture 

rates in many trapping data sets. 

Spencer and Pettus (1966) captured vagrant and 

cinereus shrews in both clearcut and uncut subalpine 

fir forests in Colorado. They determined that the 

vagrant shrew was more common in the clearcut than 

the cinereus shrew, but that both species selected the 

moist forest and wet, marshy habitat over the clearcut. 

In British Columbia, Walters (1991) captured shrews 

in burned and unburned clearcuts, but most were 

caught in adjacent old-growth coniferous forest. When 

trapping a burned stand, a 22-year-old clearcut, and 

uncut mature forest stand, Landres et al. (1994) captured shrews only in the uncut stand. However, the 

uncut stand was probably influenced by the presence 

of open water absent from other sites. 

Ramirez and Hornocker (1981) caught cinereus 

shrews in both cut and uncut stands. In some stands, 

shrews were more abundant in the forest while in 

others, they were more abundant in clearcuts. The 

vagrant shrew was absent from clearcut subalpine 

fir-Luzula hitchcockii habitat while abundant in 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

forested stands of this habitat type. In the subalpine 

fir-clintonia (Clintonia uniflora) habitat type, the vagrant shrew was more abundant in clearcuts. Medin 

and Booth (1989) found that shrews significantly 

declined after low-intensity, single-tree selection logging of Douglas-fir. However, in similar habitat, more 

intensive diameter-cut logging had no apparent affect 

on shrews (Medin 1986). Seventy-seven percent of 

the shrews captured on a burn chronosequence in 

Grand Teton National Park were found in forest controls (Spildie 1994). Hayward and Hayward (1995) 

found that vagrant and cinereus shrews increased 

with increased forest complexity, number of canopy 

layers, and stand age. The authors did not separate 

the two shrews for their habitat use analysis. 

It seems that shrews are more affected by a moisture 

gradient than a successional gradient (see Habitat 

Associations). Shrews may select older forests, but it 

is unclear as to whether this selection reflects an 

association with wetter microhabitats found within 

such forests or some other feature such as the greater 

structural complexity these forests provide. On sites 

where cutting results in greatly increased temperatures and desiccation, shrews are likely to decline or 

disappear after treatment. 

Bats-Little data exist to address responses of 

bats to disturbance, and none could be found for the 

Northern Rockies. Most data from the Pacific Northwest indicate that many species of bats require the 

structural diversity of roost sites associated with mature to old-growth forests, and therefore decline in 

response to cutting (Thomas and West 1991; Thomas 

1988; Perkins and Cross 1988). Thomas (1988) and 

Thomas and West (1991) reported that bat activity 

was 2;5 to 9.8 times higher in old-growth Douglas-fir 

forests than in younger stands and concluded from 

observed activity patterns that bats were using older 

stands for roosting. 

Perkins and Cross (1988) determined from mist net 

studies that hoary and silver-haired bats were more 

abundant in stands > 100 yrs old, but that silverhaired bats selected Douglas-fir over ponderosa pine 

within the 100+ age class. They concluded that the 

structural components of the older stands may better 

provide roosting habitat for these tree-roosting bats 

and suggested that different tree species will develop 

quality roosting characteristics at different rates. 

Chipmunks-The yellow-pine chipmunk's range 

broadly encompasses much of the northwestern 

United States, whereas the red-tailed chipmunk is 

limited to isolated pockets mostly within the 

former's range (Hoffmann and Pattie 1968). In western Montana, where the two species are sympatric, 

habitat segregation is observed along an altitudinal 

and a moisture gradient. Beg (1969) described strong 

habitat separation between the red-tailed and the 

27 
yellow-pine chipmunk in western Montana. He consistently found the red-tailed chipmunk in more 

mesic, higher elevation forests than the yellow-pine 

chipmunk, which remained in dry ponderosa pine 

and Douglas-fir habitats. Based on this habitat separation, the yellow-pine chipmunk could be expected to 

dominate in the hotter, drier conditions of early 

succession. 

Medin (1986) reported that yellow-pine chipmunk 

densities in Douglas-fir-ponderosa pine forests of 

Idaho doubled after diameter-cut logging and were 

significantly higher than on the unlogged control. 

Medin and Booth (1989) noted a similar response by 

yellow-pine chipmunks to less intensive, single-tree 

selection logging within the same habitat in a nearby 

drainage. In British Columbia, Walters (1991) observed even greater increases in abundance of yellowpine chipmunks in response to clearcutting of a hemlock forest. In a clearcut treatment followed by no 

burning, chipmunks increased 2.75 times more than 

they did in the forested control, where as in an adjacent 

clearcut treatment that was followed by burning, 

populations increased 3. 75 times more than the forest 

population. These results suggest that yellow-pine 

chipmunks are favored by disturbance and that the 

more severe the disturbance, the greater the numerical response. 

The red-tailed chipmunk also increases in response 

to cutting, but the findings are less consistent. Results presented by Ramirez and Hornocker (1981) 

for northwestern Montana showed numbers of redtailed chipmunks were similar between uncut forest 

and 11-to 15-year-oldclearcuts, while 5-year-oldclearcuts contained only half as many animals as the uncut 

stand for the subalpine fir-Clintonia uniflora habitat 

type. However, in the subalpine fir-Luzula hitchcockii 

habitat type, chipmunks were much more abundant in 

clearcut than in the uncut stand where no chipmunks 

were caught. 

Landres et al. (1994) observed an increase of approximately 50 to 66 percent in red-tailed chipmunks 

on a 6-year-old burn compared to an adjacent uncut 

stand and an uncut wilderness control. This increase 

apparently continues into the early pole stage as 

they found numbers of red-tailed chipmunks in a 

26-year-old clearcut were more than double those on 

the same controls. An examination of Scrivner and 

Smith's (1984) data for spruce-fir stands in Idaho also 

reveals that red-tailed chipmunks were more abundant in 1- to 10-year-old stands than in 80+ year-old 

stands, and that they were most abundant in midsera! communities. Foresman and Henderson (1991) 

reported that red-tailed chipmunks were five times 

more abundant on selectively cut sites than on forested controls. 

Halvorson (1982) followed numbers of chipmunks 

for four years after clearcutting and burning of 180- to 

28 

200-year-old Douglas-fir-western larch stands in 

western Montana. His design included a treatment 

and control on the north and the south aspect of 

Newman Ridge. Red-tailed chipmunks on the hotter, 

drier south aspect exhibited extremely high numbers 

in the forest but did not appear on the burn until the 

third fall when three individuals showed up. In the 

fourth year numbers increased to 15 animals, but 

this may have been overflow from the forest population that had doubled to 34 animals over the same 

period in response to a mast year. The south-aspect 

clearcut population quickly declined to four individuals in the final year of the study. On the north aspect, 

the forest population exhibited lower numbers than 

on the south, although this population also more than 

doubled in response to high seed fall. The north-aspect 

burn produced animals sooner (the second year) than 

the south burn did and quickly increased to populations that exceeded those in the forest by more than 

two-fold in the final year. The rather different results 

described for the two aspects suggest that the variables differentiating the two study sites may be important in predicting the response of red-tailed chipmunks to disturbance. 

Although the design employed by Halvorson does 

not allow a determination of causal forces, it serves to 

identify important variables for future study. The 

major differences between north and south aspect 

were moisture, burn intensity, and the remaining 

cover resulting from the differing burn intensities. 

The initial slow response of chipmunks to the higher 

intensity south burn may be due to the greater reduction of vegetation and woody structure there. Better 

cover left on the north burn may have provided greater 

security for foraging, while vegetation may have supplied cover and more abundant food in the form of 

berries and seeds. However, the forest controls differed as well with regard to chipmunk populations. It 

may be that red-tailed chipmunks, which generally 

occur in more mesic forests at higher elevations, find 

a clearcut on a south-facing slope too hot and dry, 

while the closed forest on the north aspect may offer 

insufficient shrubby habitat, with the optimal conditions lying somewhere in between (in other words, the 

more mesic clearcut and the drier, more open forest 

stand). 

The only disturbance study reporting on sympatric 

populations of yellow-pine and red-tailed chipmunks 

is that of Shepherd (1994) in the Swan Valley, western 

Montana. Shepherd found that yellow-pine chipmunks decreased on control grids after cutting while 

increasing on the overstory-removal treatments. Although increases on treatments were not statistically 

significant, the response was consistent with outcomes observed in other studies and the chipmunks 

similarly appeared to respond to the treatment in 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
proportion to the degree of cutting. The greatest increase in yellow-pine chipmunks took place where 

the greatest disturbance occurred. Red-tailed chipmunks, in contrast, exhibited the reciprocal response; 

they increased on the control grid, while decreasing on 

the treatments in proportion to disturbance. This 

unusual response of the red-tailed chipmunk in the 

context of the results reviewed above suggests that 

there may be a competitive interaction between these 

two species that affects the red-tailed chipmunk's 

reaction to disturbance. In all the allopatric studies 

reviewed, the red-tailed chipmunk exhibited marginal 

to dramatic increases in abundance in response to 

disturbance. The only apparent decrease was on the 

south slopes in Halvorson's (1982) study. Careful examination of Halvorson's and Shepherd's data might 

suggest an appropriate experimental design to determine the degree to which competition versus vegetation and topographic variables may affect the response of the red-tailed chipmunk to disturbance. 

Ground Squirrels-The columbian ground 

squirrel tends to increase after disturbance. Information about this species is seldom reported in small 

mammal-disturbance studies, but it is known to increase after cutting and after fire in response to the 

increase in the grasses and forbs that it feeds on. 

Ramirez and Hornocker (1981) reported that the 

columbian ground squirrel was abundant in alpine 

meadows adjacent to their study sites, and even more 

abundant in 5- to 15-year-old clearcuts. Columbian 

ground squirrels were at least three times more abundant in clearcuts versus forest plots that served as 

controls. 

Golden-mantled ground squirrels were reported in 

onlyonestudy.Medin(1986)foundthatgolden-mantled 

ground squirrels increased in response to diametercut logging in ponderosa pine-Douglas-fir forests in 

Idaho. Where present, the golden-mantled ground 

squirrel and columbian ground squirrel are likely to 

increase in response to disturbance, as their habitat 

needs are favored by such changes. 

Red Squirrel-Red squirrels are tree squirrels, 

and their local and regional distributions are defined 

primarily by the distributions of conifers (Hoffmann 

and Pattie 1968). Although this species is known to 

consume a variety of substances (Callahan 1993), its 

life history is intertwined with the forest environment with which it evolved (Smith 1970). Halvorson 

and Engeman (1983) demonstrated red squirrel dependence on cone crops by showing that offspring survival 

is significantly correlated with cone production in 

island populations in ponderosa pine-Douglas-fir communities on Flathead Lake. They showed that high 

cone yields greatly increased the probability of survival. The extent to which low-intensity management, 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

thinning, etc., and low-intensity fire affect habitat 

quality for this species will largely depend on its 

effect on cone crops and conifer diversity. 

Data for red squirrels is seldom reported in disturbance literature because they tend to avoid traps 

traditionally used in small mammal research (pers. 

obs.). However, Medin and Booth (1989), Medin 

(1986), and Halvorson (1982) provide some information about the effects of timber harvest on this species. 

Halvorson (1982) reported capturing red squirrels, 

but only in forested controls, reinforcing the notion 

that red squirrels respond qualitatively to canopy 

removal by disappearing from recent clearcuts. Medin 

and Booth (1989) noted that numbers of red squirrels 

were high on both treatments and controls after 

single-tree selection logging but did not attempt to 

quantify their numbers. Medin (1986) observed a 

decline in numbers of red squirrels after more intensive diameter cut logging within the same watershed 

but concluded that methods employed in his study 

were insufficient to effectively determine quantitative 

changes in red squirrel populations. These results 

suggest that red squirrels decline in response to tree 

removal, and selective cutting may generate sink 

habitats if reduced tree densities and/or removal of 

dominant trees decreases cone production below some 

minimum threshold necessary to maintain population 

growth rates ~1. 

Northern Flying Squirrel-Northern flying 

squirrels are nocturnal and generally not captured 

unless they are targeted with squirrel traps. Less is 

known about this species than other squirrels because 

of its nocturnal nature. Although the northern flying 

squirrel is widely distributed within forested regions 

of the United States (Hoffmann and Pattie 1968), it 

is thought to be an old-growth associated species 

(Thomas et al. 1993) due to its requirements for 

nesting cavities in medium- to large-diameter snags 

(Cowan 1936) and its dependence on hypogeous mycorrhizal fungi (Rosentreter et al. 1997; Maser et al. 1978; 

Maser et al. 1985; McKeever 1960; see Mycophagy), 

which are most abundant in mature and old-growth 

forests (Amaranthus et al. 1994). 

Rosenberg and Anthony (1992) compared northern 

flying squirrel populations between second-growth 

and old -growth Douglas-fir stands in Oregon and 

found that, although numbers were slightly higher in 

old-growth stands in both years, they did not differ 

significantly. They determined that squirrel densities 

were not correlated with habitat characteristics 

and concluded that "flying squirrels may be habitat 

generalists." In northern Utah, Andersen et al. (1980) 

observed higher densities of flying squirrels in sprucedominated forests (1.2 to 2.5 squirrels/ha) than in 

earlier seral aspen-dominated (Populus tremuloides) 

stands (0.2 to 1.8 squirrels/ha), but squirrels were 

29 
only slightly more abundant in spruce-dominated 

forests than in aspen stands (0.2 to 2.1 squirrelslha). 

In western Montana, Halvorson ( 1982) captured northern flying squirrels on forested control plots, but not 

on burned clearcuts, and reported that 77 percent of 

his captures were on the south-facing as opposed to 

the more mesic north-facing 180- to 200-year-old 

Douglas-fir-western larch stands. 

Witt (1992) trapped 165 northern flying squirrels 

1,023 times over five years in old-growth and secondgrowth forests in western Oregon. Density estimates 

indicated that flying squirrels were six times more 

abundant in old-growth than in second-growth forests. These results were supported by a catch-per-unit 

effort index. Witt (1992) complemented trapping data 

with radiotelemetry data and found that three of five 

squirrels had den sites located outside their estimated 

home ranges. He suggested that trapping results may 

bias toward foraging habitat, thereby ignoring the 

critical denning aspect of habitat use. 

In light of Witt's findings, which .are supported by 

those of Andersen et al. (1980) and Halvorson (1982), 

results presented by Rosenberg and Anthony (1992) 

do not contradict a conclusion that northern flying 

squirrels are old-growth associated species. It is, 

rather, their conclusions that are contradictory, as 

the lack of selection for habitat features may have 

been due to trap bias (Witt 1992) or trap insensitivity 

to the scale of variables being measured (see discussion in Pearson 1994). Foraging in second-growth 

stands by squirrels living in the adjacent old growth 

could easily account for the results observed by 

Rosenberg and Anthony (1992), and the higher numbers of squirrels that they reported in old growth 

suggest that this may have been the case. Although in 

all studies reviewed northern flying squirrels consistently avoided clearcuts, their use of second-growth 

stands suggests that, although second-growth may 

not fulfill all requirements of flying squirrels, it may 

contribute to their resource base when occurring in 

conjunction with mature and old-growth forest in a 

habitat mosaic. 

Northern Pocket Gopher-The northern pocket 

gopher is not generally included in studies of small 

mammal succession, but a few studies in the West 

have reported on this species. Scrivner and Smith 

(1981) found that northern pocket gophers were 

most abundant in the youngest (1 to 10 yr) and 

oldest (80+ yr) stands of spruce-subalpine fir forests 

that they studied in Idaho, although the authors found 

no difference in abundance between these two categories. Stands between these age classes contained similar numbers of pocket gophers when compared to each 

other. Andersen and McMahon (1981) determined 

that food was a limiting factor in later seral stages for 

northern pocket gophers living in forests along a 

30 

spruce-subalpine fir sere in Utah. Their capture data 

supported their bioenergetic analysis. Densities 

ranged from 62 individuals/ha in the meadow to two 

individuals/ha in the spruce forest. In general, pocket 

gophers prefer soft deep soils that facilitate movement beneath the ground (see Habitat Associations). 

Southern Red-Backed Vole-In the Northern 

Rocky Mountains, the red-backed vole ( Clethrionomys 

gap peri) and the deer mouse (Peromyscus maniculatus) 

are the most commonly reported species in disturbance studies. The southern red-backed vole is considered an old-growth associated species (Thomas et al. 

1993). It is typically abundant in mature to old-growth 

forests and reported to crash or to decrease to very low 

numbers after clearcutting and fire (Sullivan and 

Boateng 1996; Landres et al. 1994; Spildie 1994; 

Ramirez and Hornocker 1981; Medin 1986; Halvorson 

1982, 1981; Campbell and Clark 1980). This species 

can be found in early serallodgepole pine stands, but 

such habitat is believed to be a dispersal sink (Pearson 

1994; Nordyke and Buskirk 1991). Under some less 

intensive harvest treatments, southern red-backed 

vole populations may persist after cutting, at least 

for a few years (Shepherd 1994; Foresman and 

Henderson 1991; Medin and Booth 1989; Ramirez 

and Hornocker 1981; Campbell and Clark 1980), but it 

is not known whether such sites function as sink 

populations. 

A number of factors may prevent southern redbacked voles from expanding beyond late seral forests. Getz (1962) and Odum (1944) argued that the 

southern red-backed vole's inefficient use of water 

restricted it to moist habitats. Other authors have 

suggested that a dependence on hypogeous sporocarps 

for food restricts the congeneric California red-backed 

vole to mature forest where this food is present (Mills 

1995; Martell1981; Maser et al. 1978). Although the 

southern red-backed vole depends on fungi for food, it 

is a less strict mycophagist than the California redbacked vole (see Mycophagy). Harvey et al. (1976) 

demonstrated that decomposed woody debris in the 

organic layer was an important substrate for fruiting 

of hypogeous fungi in western Montana, so it is possible that the southern red-backed vole forages for 

sporocarps near decaying logs in this area. Current 

data on habitat associations of southern red-backed 

voles in the Northern Rocky Mountains indicate that 

large-diameter logs are important habitat components for this species (Pearson 1994; Nordyke and 

Buskirk 1991). The primary role of logs and other 

CWD is likely that of hiding and escape cover; however, sporocarp productivity in these microhabitats 

probably also plays a role. 

Nordyke and Buskirk(1991) determined that southern red-backed voles might function as an indicator 

species for the old-growth condition. They found that 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
this species increased in abundance with an increase in old-growth condition rating in a relationship 

that could be described using a second degree polynomial model. Scrivner and Smith (1984) also found a 

general correlation between southern red-backed vole 

abundance and stand age. 

Pearson (1994) reported a strong, positive, linear 

correlation between abundance of southern red -backed 

voles and stand age, and concluded that weaker correlations seen elsewhere may be due to: 1) the incorporation of measurements of old -growth attributes > 1 m 

high in old-growth indices; 2) the use of too few seral 

stages in regression analyses; or 3) inclusion of less 

distinct seral stages which might incorporate ecotones 

between plateaus along the successional gradient or 

include more than one sampling point within a plateau. He suggested that, within the Northern Rocky 

Mountains, southern red-backed voles may be an 

excellent indicator of old-growth conditions at or near 

ground level, and, if used in conjunction with other oldgrowth associated species from different ecological 

guilds, an indicator guild might be developed that 

would allow assessment and monitoring of old-growth 

quality for multiple strata within a stand. 

Deer Mouse-The deer mouse is the paradigm 

habitat generalist, and can be found in any successional stage (Landres et al. 1994; Spildie 1994; Ramirez 

and Hornocker 1981; Walters 1991; Medin 1986; 

Scrivner and Smith 1984; Campbell and Clark 1980; 

Halvorson 1982; Stout et al. 1971). In general, this 

species has been reported to increase in response to 

disturbance (Landres et al. 1994; Spildie 1994; Bock 

and Bock 1983; Ramirez and Hornocker 1981; Walters 

1991; Halvorson 1982; Stout et al. 1971), but Medin 

and Booth (1989) reported a decline for this species 

after single-tree selection logging. Pearson ( 1994) found 

that deer mice increased in abundance with increasing stand age for stands 65, 150, 350, and 450 years 

old, and Scrivner and Smith (1984) obtained similar 

results. Sullivan (1979c) concluded that a clearcut in 

British Columbia was a dispersal sink for deer mice. 

The response of this species to disturbance may depend on ecotypic variation between populations and 

the effects of the disturbance on local food availability. 

Microtus-Three species of voles are affected by the 

type of disturbance defined in this review: meadow 

voles, long-tailed voles, and montane voles. In general, 

voles increase qualitatively in response to disturbance. The species that comes to dominate a site will 

depend on moisture, elevation, and possibly founder 

effect given the nature of interspecific interactions 

noted between montane voles and meadow voles 

(see Habitat Associations). 

Halvorson (1982) observed long-tailed voles in 

abundance on the moist, north-aspect, burned clearcut, 

but found them to be rare on the south burn and absent 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

on both forest controls. Long-tailed voles were also the 

dominant vole taken by Foresman and Henderson 

(1991) in partial cut treatments of Douglas-fir-ponderosa pine stands. Although they were not captured 

in the forest, they were moderate to abundant in the 

treatments. On the BNF, montane voles dominated a 

26-year-old clearcut and were present on a 6-year-old 

burn but were absent from forest controls (Landres 

et al. 1994). Except for a few water voles caught near 

water, this was the only vole reported from this study 

site. Ramirez and Hornocker (1981) observed meadow 

voles and long-tailed voles in low to moderate numbers 

on some, but not all, clearcuts ranging from 5 to 11 

years in northwest Montana; but they trapped none of 

either species within forest c9ntrols. 

Community Response to Disturbance Richness and Diversity-No single small mammal disturbance study in the Northern Rocky Mountains 

examines changes in diversity, species composition, 

and/or biomass along a complete successional gradient that includes grass/forb, shrub, sapling, young 

forest, mature forest, and old-growth forest seral stages. 

Most studies compare recent clearcuts in grass/forb, 

shrub, or sapling stages with mature or old-growth 

forest and few of these studies present data for changes 

in abundance, diversity, or total biomass between 

controls and treatments. 

In comparing young clearcuts (5-15 years) with 

uncut forest, Ramirez and Hornocker (1981) observed 

greater total small mammal abundance and much 

greater biomass in young clearcuts than in uncut 

forests. This was primarily due to the abundance of 

columbian ground squirrels in the uncut stands. However, red squirrels, which were likely common in the 

uncut forests, were not sampled. So these data are 

probably biased in this respect. Landres et al. (1994) 

trapped a young stand in a 26-year-old clearcut, an 

adjacent, uncut, wet forest, and an adjacent uncut 

dry forest. They captured 50 individuals representing four species in the young stand compared to 132 

individuals from six species in the adjacent wet forest 

and 84 individuals representing four species in the 

adjacent dry forest. Medin and Booth (1989) showed a 

slight increase in biomass and species richness following single-tree selection logging (removal of about 

22 trees/ha >23-cm diameter) of ponderosa pineDouglas-fir dominated stands in Idaho. The increase 

in biomass was probably due to a dramatic increase in 

the yellow-pine chipmunk, one of the largest communitymembers captured, in the logged stands. Cary and 

Johnson (1995) found that old-growth stands on the 

Olympic Peninsula produced 1.6 times more small 

mammals and 1.5 times more small mammal biomass 

than managed stands. 

It is unclear how diversity and biomass change in 

response to clearcutting or moderate timber harvest 

31 
within Northern Rocky Mountain forest ecosystems. 

Abundance may increase in the initial grass/forb and 

shrub stages due to increases in early seral small 

mammals such as Microtus, columbian ground squirrels, 

and chipmunks. This increase phase is probably followed by a rapid decline as grasses and shrubs give 

way to young trees and early seral small mammal 

species decline with the loss of their newly acquired 

habitat. Small mammal abundance probably does not 

begin to increase again until forests mature and the 

canopy opens up allowing the understory to develop. 

Diversity may follow a similar coarse reaching its 

peak in the old-growth condition when gap dynamics 

come into play providing a diversity of understory 

vegetation including grass/forb and shrub patches as 

well as greater structural complexity on the forest 

floor that can provide for early- and late-seral small 

mammal species. An important factor that should be 

considered when assessing diversity in relation to 

disturbance and succession is seasonality. Many earlysera! species described here hibernate (columbian 

ground squirrels, golden-mantled ground squirrels, 

and yellow-pine chipmunks) whereas most late seral 

species do not. For example, the tree squirrels remain 

active year-round. Additionally,Microtus exhibit more 

radical population fluctuations than do red-backed 

voles, their late-seral ecological equivalents. Therefore, late-seral forests could be expected to maintain 

more constant diversity and biomass both seasonally 

and annually than sites that have recently been disturbed. More comprehensive research will be necessary to better understand changes in small mammal 

communities such as diversity, abundance, biomass, 

and species composition as they relate to the entire 

successional gradient. 

Management Recommendations _ 

Habitat requirements of small mammals are as 

diverse as the taxonomic groups presented in this 

review. Fortunately, most small mammals are resilient to natural disturbances due to their high reproductive potential, excellent dispersal capabilities, 

and ability to persist in relatively small patches of 

habitat. Some habitat specialists reviewed here are 

unlikely to be affected by forest management practices 

because of their unique habitat affiliations. For example, pikas and dwarf shrews are associated with 

talus slopes and rocky outcrops. Numerous other species benefit from processes that reinitiate succession 

and open forest canopies. These include meadow voles, 

long-tailed voles, golden-mantled ground squirrels, 

columbian ground squirrels, yellow-pine chipmunks, 

and others. Clearcuts, seed tree cuts, shelterwood 

cuts, and under burning favor these species. The deer 

mouse seems impervious to nearly any management 

32 

practice. Although it responds with changes in abundance and demography, this species can exist in most 

altered habitats. Many small mammal species require 

no special management considerations for their survival due to unique habitat affiliations or associations 

with early seral stages. 

However, several old-growth associated species 

such as northern flying squirrels, red-backed voles, 

and tree-roosting bats respond negatively to timber 

harvest, and other habitat specialists like bog lemmings and water shrews may be negatively affected by 

logging if bog hydrology is altered or water quality is 

degraded. Moreover, although mere existence of a 

complement of small mammal species may fulfill mandates for diversity, it may not provide the conditions 

necessary for maintenance of many small-mammaldriven ecological processes. For instance, the mere 

presence of red-backed voles does not ensure that 

martens and boreal owls will have a sufficient prey 

base to persist in an area that otherwise meets their 

needs, nor does it ensure that dispersal of spores of 

hypogeous mycorrhizal fungi will occur above some 

minimum threshold necessary for maintenance of 

fungal or host populations. Thus, I focus management 

guidelines and the discussion of maintaining healthy 

small mammal populations in forest ecosystems on 

the subset of species that are most affected by timber 

harvest. 

Coarse Woody Debris 

Wildlife management is in large part habitat management. Arguably, the single most important habitat 

feature for forest-dwelling small mammals is coarse 

woody debris. Whereas generalist species, such as 

deer mice, use CWD opportunistically for hiding cover 

(Barnum et al. 1992; Platz and Kirkland 1992), habitat specialists such as red-backed voles may require 

CWD for persistence. Coarse woody debris facilitates 

predator/prey interactions in winter by providing 

predators like martens and weasels access to subnivian 

small mammals (Sherburne and Bissonette 1994; Corn 

and Raphael1992). At other times, CWD functions to 

mediate predator/prey interactions by providing 

small mammals with hiding and escape cover, thereby 

potentially dampening small mammal population 

cycles, and stabilizing small mammal and predator 

communities. Red squirrels often construct middens 

in association with CWD, possibly to take advantage 

of the escape cover and feeding promontories offered 

by these structures. In addition to their obvious importance to the squirrels, middens provide critical den 

sites (Ruggiero et al. 1998) and resting sites for marten 

(Ruggiero et al. in prep.; Buskirk 1984) and can support higher densities of red-backed voles than surrounding forest (Ruggiero and Pearson in prep.). Coarse 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
woody debris functions more directly in nutrient cycling (Maser and Trappe 1984), as nurse logs in moist 

forest systems (Harmon and Franklin 1989), and possibly as fruiting sites for hypogeous mycorrhizal 

fungi (Waters et al. 1996; Amaranthus et al. 1994; 

Harvey et al. 1976). Therefore, management favoring 

CWD supports not only small mammal communities, 

but processes integral to forest ecosystems. To maintain long-term forest ecosystem integrity, ecosystem 

management must recognize the importance of CWD 

to wildlife in forest ecosystems and manage for this 

component accordingly. 

Historical Coarse Woody Debris-In most managed forest stands, the largest-diameter CWD has 

been burned and removed since harvesting began, 

leaving us with little evidence of presettlement conditions (Harmon et al. 1986). Additionally, we have 

greatly reduced CWD recruitment through timber 

harvest. These practices have carried us to the brink 

of a CWD bottleneck for many stands especially in 

drier cover types such as ponderosa pine and dry 

western larch-associations. Although decadence is 

occurring within Douglas-fir on these sites, it is not 

large-diameter material and will likely be removed in 

the process of treatment (D. Lockman, Biologist, Bitterroot National Forest, pers. comm. ). Even with careful management, CWD within such stands will not 

regain natural age- and size-class distributions for 

many years. Therefore, while CWD reductions may be 

in order in some cover types such as white-bark pine 

where white pine blister rust has resulted in high 

mortality of large-diameter trees, active recruitment 

will be necessary in many stands entering their 

second rotation and probably all stands entering 

their third rotation. However, restoring historic conditions is made difficult due to our lack of knowledge of 

presettlement CWD. 

For drier cover types on the BNF, low-intensity fires 

occurring at frequent intervals (Arno 1976) would 

function to reduce and recycle fine fuels and smaller 

woody debris (_6 inch dia.). Larger debris are more 

resistant to low-intensity fires (Reinhardt et al. 1994, 

1991; Robichaud e( al. 1994), and stand-replacing 

fires would increase CWD due to the transfer of standing biomass to the CWD layer (see Brown and See 

1981). Therefore, fire ecology in fire-dependent communities probably favors larger diameter CWD while 

minimizing finer woody materials and fine fuels by 

frequently recycling these. Larger diameter material 

would often be left only partially burned (see Reinhardt 

et al. 1994), and low intensity fires would select for 

larger trees (due to thicker bark and deeper roots) 

that would ultimately become large-diameter CWD. 

Small Mammal use of Coarse Woody DebrisDeveloping guidelines for CWD management requires 

some understanding of how small mammals interact 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

with CWD and what attributes appear to be limiting. 

Diameter and volume of CWD appear to be the most 

important factors for red-backed voles, with larger 

diameters and greater volumes being favored 

(Tallmon and Mills 1994; Pearson 1994; Nordyke and 

Buskirk 1991; Hayes and Cross 1987). Though stage of 

decay may also be important, it is unclear whether 

earlier stages of decay or later stages are preferred 

(Tallmon and Mills 1994; Pearson 1994; Nordyke and 

Buskirk 1991; Hayes and Cross 1987; Doyle 1987). 

The answer may depend on whether the structure is 

being used more for feeding sites or for hiding and 

escape cover, and the relationship may change seasonally depending on phenology of vegetative cover 

and fruiting of truffles. 

No data exist to assess how iength oflogs affects use 

by small mammals, but fluorescent pigment tracking 

shows that logs are used as travel routes by southern 

red-backed voles (Pearson 1994), shrews (McCracken 

1990), white-footed mice (Peromyscus leucopq,s) 

(Barnum et al. 1992; Planz and Kirkland 1992), deer 

mice, and long-tailed voles (D. E. Pearson unpublished 

data). Longer logs provide secure travel routes over 

greater distances within an animal's home range and 

may be more valuable. Pearson (1994) suggested that 

the spatial distribution of CWD may also affect use 

patterns by small mammals. He concluded that redbacked voles selected more for microhabitats having 

CWD when logs were patchily distributed. 

Coarse Woody Debris Management Guidelines-Though many studies have concluded that 

CWD is an important habitat component for small 

mammals (Tallmon and Mills 1995; Pearson 1994; 

Nordyke and Buskirk 1991; Hayes and Cross 1987; 

Gunderson 1959), guidelines for managing CWD (logs 

primarily) for wildlife have been poorly developed. For 

instance, Harmon et al. (1986) gave the most extensive review of CWD in the United States to date, but 

they did not address the issue of CWD management. 

Hunter (1990) emphasized the importance of CWD 

but did not provide sufficient guidelines for its management. Carey and Johnson (1995) suggested that 

"15 to 20 percent cover ofCWD, well distributed across 

a site, would be adequate for most small mammals." 

However, they did not adequately address the issue of 

recruitment of CWD. 

The BNF Forest Plan currently has no provisions 

for management ofCWD for wildlife (BNF Forest Plan 

1987). It does, however, incorporate CWD guidelines 

proposed by Harvey et al. (1987) for management of 

mycorrhizal fungi in Northwest Montana. These 

guidelines recommend managers retain 10 to 15 tons/ 

acre (2.2 to 3.4 kg/m2 ) of CWD greater than 6 inches 

(15 em) in diameter. The question then arises: If implemented, would CWD guidelines designed to manage for the needs of mycorrhizal fungi be sufficient to 

33 
also fulfill the needs of small mammals? Not enough 

research has been conducted to answer this question 

definitively. Certainly small mammals would benefit 

from the hiding and escape cover provided by following 

these guidelines. Additionally, if these guidelines 

succeeded in maintaining healthy hypogeous fungi 

populations, small mammals would benefit from the 

food resource offered by the resulting truffles. Nonetheless, such an approach may be too simplistic to 

address the more complex needs of small mammals 

such as large-diameter logs, range of decay classes, 

logs elevated aboveground, etc. For example, a "boardwalk" of 15-cm diameter lodgepole stems from blowdown provides high CWD cover woody debris for 

truffles, but does not provide appropriate habitat. 

Mean diameter of CWD probably better predicts 

small mammal species composition and abundance 

than does number of CWD stems, but generic guidelines that simply assign a minimum value (Carey and 

Johnson 1995; Brown and See 1981; Harvey et al. 

1987), even based on a mean, will not likely adequately 

fulfill CWD requirements for small mammals. Furthermore, recruitment of CWD must be addressed if 

CWD is to be maintained on a site in conjunction 

with timber harvest. 

Brown and See (1981) defined CWD management as 

a trade off between its beneficial and detrimental 

effects. They concluded that volumes ofCWD up to 15 

tons/acre (3.4 kg/m2

) would not result in an excessive 

fire hazard, but felt that volumes in the range of 15 to 

20 tons/acre (3.4 to 4.5 kg/m2

) could "diminish fire 

protection efficiency." They also recommended that 

hard logs could be removed for economic values, while 

soft wood (material in late decay stages) could be left 

to fulfill the ecological role ofCWD for ectomycorrhizal 

activity. However, more recently Reinhardtetal. (1991) 

suggested that CWD volumes up to 50 tons/acre 

(11.2 kg/m2

) for fuels >15-cm diameter did not result 

in excessive fire hazards. Given the importance of 

logs in earlier stages of decay for wildlife (Pearson 

1994; Hayes and Cross 1987) and for recruitment of 

CWD into later decay classes, removal of this component would deleteriously affect small mammal communities and ecological processes. 

CWD management should focus on recruitment of 

logs of all size classes. However, past management 

practices have resulted in a bottleneck in recruitment 

of large-diameter CWD, which research to date has 

shown to be the most important for wildlife habitat. 

Therefore, large-diameter CWD should be a recruitment target until the system is brought back into 

balance. Large-diameter CWD at volumes <50 tons/ 

acre (11.2 kg/m2

) should not pose undue fire risk 

(Reinhardt et al. 1991). 

Coarse Woody Debris Guidelines for CavityNesting Birds-Because logs, branches, upturned 

roots, and stumps come from trees, and logs often 

34 

develop from snags, CWD management is integrally 

linked to tree and snag management. Furthermore, 

snags provide den sites and roosting sites for many 

small mammals including tree-roosting bats, redsquirrels, flying squirrels, woodrats, and chipmunks. 

It is therefore reasonable to examine snag management guidelines for cavity-nesting birds to determine 

whether CWD needs on the forest floor can be met 

through snag management. 

Given that snags are by definition more decayed 

than live trees, recruiting CWD only from snags will 

result in a decay class distribution skewed toward 

more advanced decay classes. This is problematic 

because later decay classes lack many CWD attributes 

important to small mammals. For .instance, rotten 

logs tend to lie flat on the ground so that animals 

cannot travel underneath them or pass from side to 

side beneath them. They also tend to lack the overhanging ledge formed by earlier decay classes and 

branches of freshly fallen trees. These are important 

aspects of hiding and escape cover provided by early 

decay classes of CWD (Pearson 1994; Hayes and 

Cross 1987). Additionally, snag densities recommended for cavity-nesting birds of 5 to 10 snags/ha 

(see Hunter 1990: 171; Zarnowitz and Manuwal1985; 

Thomas et al. 1979) are probably not sufficient to 

generate meaningful CWD densities on the ground. 

Overall, snag management guidelines designed to 

meet minimum requirements for cavity-nesting birds 

are unlikely to satisfy the CWD requirements for 

healthy, forest floor, small mammal populations. 

Nonetheless, snag management guidelines developed for cavity-nesting birds provide insight into the 

complexity of this "intensive" management approach 

to maintaining forest structure while harvesting timber. Research on snag requirements of cavity-nesting 

birds has shown that diameter, height, decay class, 

density, context, cover type association, and species 

are important characteristics of snags, and different 

species of birds require these features to differing 

degrees (Raphael and White 1984; Bull1978; Thomas 

et al. 1976). This has resulted in complex snag management guidelines that are based on minimum requirements identified for individual cavity-nesting 

birds (see Thomas et al. 1979). However, perhaps 

because of the complexity of these guidelines, implementation is often simplified to a general rule-ofthumb that specifies a snag density (for example, 5 to 

10 snags!ha) but ignores other important snag attributes (see Hunter 1990:171). Characteristics of 

CWD important to small mammals are equally complex, and less information is available to guide management recommendations. Because small mammals 

are difficult to observe, studying their relationships to 

CWD attributes is costly and time-consuming. In the 

end, management guidelines would likely be too 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
complex for reasonable implementation in the field. 

Although such research is important, a more parsimonious solution is required for effective management of 

CWD for small mammals. 

Recommendations for Managing Snags and 

Coarse Woody Debris for Small Mammals-The 

CWD guidelines described so far are subject to the 

following criticisms: 1) they do not address long-term 

CWD recruitment; 2) they do not take into account 

CWD productivity based on the cover type, aspect, 

temperature, moisture, and other site-specific CWD 

determinants; and 3) they do not provide for a diverse 

array of CWD size classes, decay classes, and other 

attributes important to small mammals and other 

CWD-associated wildlife. Yet the importance of CWD 

to small mammals, their predators, and related ecological processes integral to forest ecosystems argues 

that CWD management for wildlife not be ignored. 

A simple "within-treatment" (defined by the manager as the stand or other treatment area) Coarse 

Filter Approach (after Hunter 1990) could be developed to manage for CWD on the BNF and in the 

Northern Rockies based on an understanding of the 

site-specific nature of CWD recruitment. In natural 

systems, trees that are not entirely consumed by fire 

become CWD. Many become snags first. The amount 

of CWD on a site is determined in a very exacting 

manner by the number and size of trees produced 

there which in turn is a function of temperature, 

moisture, soils, and other factors specific to that site. 

A ponderosa pine savanna will have fewer stems, but 

of larger diameter than a dry-site lodgepole pine 

stand (Harris in press). Moist-site lodgepole pine will 

produce more stems that are of larger diameter, than 

dry-site lodgepole, but logs may decay faster. Production of CWD is cover-type and site-specific (Harris in 

press; Brown and See 1981). Rates of transfer from 

trees to snags and CWD are also site-specific, being a 

function of probabilities of mortality events on a site. 

For instance, a site may be more prone to wind-throw 

due to its exposure to periodic harsh winds. Other sites 

may be more susceptible to fire due to their position 

near a ridgetop where lightning-caused ignition is 

more frequent. Disease outbreaks may occur on a site 

at a higher frequency because local conditions favor 

the pest species. 

Determining a target CWD density for small mammal habitat by cover type would be very difficult based 

on our current understanding of natural CWD recruitment processes (Harris in press; Brown and See 1981). 

Applying such a target within a cover type across a 

landscape would not address site-specific factors and 

would be an affront to managers in the- sense that 

they would be asked to produce CWD targets on some 

sites that simply could not generate the target volumes. For instance, an average CWD tonnage for 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

ponderosa pine might not be achievable on a dry site 

near the lower moisture limit for trees. Similarly, 

highly productive sites, which tend to be of greatest 

importance to the largest number of CWD-associated 

wildlife species, would not be allowed to achieve their 

true potential. 

An effective long-term management strategy 

should generate CWD based on cover type and local 

conditions. Furthermore, distributions for CWD attributes such as length, diameter, decay, degree of 

branching, etc. should reflect natural distributions. 

These goals could be achieved by randomly assigning 

a portion of each tree species/cohort combination in a 

treatment unit to CWD recruitment. Proportions 

could reflect current tree composition or future tree 

composition based on long-term goals. For instance, in 

a seral ponderosa pine community, the saw timber 

in a stand might consist of 30 ponderosa pine and 70 

Douglas-fir trees. If the proportional recruitment of 

CWD is to be 20 percent, then 20 trees will be assigned 

to CWD recruitment based on this scenario. These 20 

trees could be assigned to ponderosa pine and Douglasfir based on their proportional occurrence in the 

overstory (in other words, 30 percent ponderosa pine, 

70 percent Douglas-fir) or all 20 could be assigned to 

ponderosa pine if the long-term objective is to reestablish a ponderosa pine-dominant overstory. In 

this manner, species composition ofCWD would more 

quickly come to reflect that of the overstory species. 

Coarse woody debris recruitment must be applied to 

each cohort in multistory stands to provide for continuous recruitment as occurs in natural systems. 

Dispersion ofCWD within a stand is also important 

and should also reflect a random rather than uniform 

distribution to more closely approximate natural conditions. Trees should, therefore, be randomly assigned 

to CWD recruitment. Since periodic under-burning of 

ponderosa pine- and larch-associated cover types will 

likely result in some tree damage and mortality, and 

since this damage/mortality should be either roughly 

random or emulate natural fire-caused mortality, fire 

damaged/killed trees could contribute to CWD recruitment within fire-treated stands exhibiting such mortality. Landscapes should similarly reflect these ideas 

with some stands being cut while others are left as 

natural escapes from disturbance. Again, a random 

assignment of stands to harvest and non-harvest categories may best reflect natural disturbance patterns. 

The idea of management priority areas could also be 

built into this model. For example, an area that will be 

managed primarily for timber harvest might be assigned 15 percent CWD recruitment, whereas an area 

designated for wildlife priorities could be assigned 

CWD recruitment at a rate of 75 percent per cohort. 

For intensive management areas, this essentially 

means that seed trees in seed tree cuts and some of 

the overstory in shelterwood cuts would remain on site 

rather than be harvested at a later date. 

35 
Assigning proportions of trees within a treatment 

area to CWD recruitment allows CWD to vary by cover 

type and local conditions that affect site productivity 

and decay rates. This is preferable to fixing some 

minimum value and forcing it onto all sites regardless 

of site conditions. Furthermore, natural distributions ofCWD attributes should be emulated based on 

natural processes occurring at the treatment area. 

Thus, without extensive knowledge of small mammalCWD interactions, CWD could be managed for healthy 

small mammal communities. Managing CWD for small 

mammals in this manner is preferable to setting 

minimum values that may not reflect the site potential or small mammal needs, given the limited knowledge of CWD-small mammal interactions. Conner 

(1979) noted that managing for averages instead of 

minimums is preferable for ecological and evolutionary reasons. I argue that the approach outlined here is 

ideal since it results in management for distributions 

that reflect natural means and variances rather than 

simple averages or minimums. Additionally, because 

ofthe natural linkage between CWD recruitment and 

snag recruitment, these guidelines can provide snags 

as well as logs, stumps, and root wads for a wide range 

of species including rare and sensitive bats, northern 

flying squirrels, red-backed voles, martens, fishers, 

salamanders, cavity-nesting birds, and mycorrhizal 

fungi (Bull et al. 1997). 

Any successful management strategy should be 

founded on principles of adaptive management. The 

implementation of the above CWD management strategy should be monitored to assess CWD recruitment 

rates in different cover types. This could easily be 

done by permanently marking trees assigned to CWD 

recruitment and tracking their death and decay processes. Important questions include: 1) What percentage of trees become snags before reaching the forest 

floor? 2) What are the distributions of age, size, length, 

hardness, species, etc. of snags and CWD resulting 

from this approach, and how do these compare with 

unmanaged stands? 3) Do wildlife use these components as they do in natural stands? 4) Does the random 

assignment of CWD reasonably reflect natural distributions or is there a more appropriate distribution? 5) Does the CWD management strategy result in 

healthy forest small mammal populations? Such research would necessarily be long-term, but some of 

these questions would not require extensive resources 

once trees were marked, and long-term data collection 

could be built intoNational Forest System Monitoring 

programs. Proportions assigned to CWD recruitment 

could then be altered to adapt to new information. 

Slash Treatment and Site Preparation Versus 

Coarse Woody Debris Retention-Minimizing the 

risk of fire and the negative visual impacts of logging 

debris through slash reduction is an important aspect 

36 

of timber harvest operations. Large volumes of slash 

are generated through limbing, removal of tops, butts, 

etc. Much of this material does not qualify as CWD in 

terms of small mammal habitat. However, larger 

diameter materials (> 15-cm diameter) can contribute 

to CWD, and material >30-cm diameter should be 

preserved unless volumes exceed safe fuel volumes 

(Reinhardt et al. 1994, 1991; Robichaud et al. 1994). 

Slash piling with heavy equipment is unlikely to 

distinguish important CWD from slash. These methods can reduce habitat for some small mammal species 

(Martell 1983a, 1983b ). Hand piling can be used in a 

discriminating manner to reduce slash while maintaining CWD if crews are directed to cut and pile only 

materials <15-cm diameter. Broadcast burning may 

be the best means of reducing slash while maintaining CWD. In most cases, large diameter materials will 

not be removed through broadcast burning because of 

the time of year when such burning is done (Reinhardt 

et al. 1994, 1991; Robichaud et al. 1994). Slash treatments such as lop-and-scatter segment large diameter materials into short pieces. This may also have a 

negative impact on small mammals. Broadcast burning and piling and burning of slash <15.24 em dia 

should address the negative visual effects of harvest 

and reduce fine fuels that serve as ignition sources 

while maintaining CWD. 

Scarification is a commonly used technique for preparing seedbeds for larch (Arno and Fischer 1995) and 

ponderosa pine (D. Lockman, Biologist, Bitterroot 

National Forest, pers. comm.). Mechanical scarification destroys small mammal habitat (see Martell1983a, 

1983b) and deleteriously affects soils by removing 

woody residue (Jugensen et al. 1992). Historically, 

larch regenerated on burned soils, and research has 

shown that controlled burning works extremely well 

for creating larch seed beds in clearcuts, partial cuts, 

and even in uncut stands in western larch-Douglas-fir 

cover types (see Arno and Fischer 1995). Prescribed 

fire has less deleterious effects on small mammals 

than mechanical scarification and preserves organic 

matter for soils in larch stands (Schmidt and Shearer 

1990). Prescribed fire is therefore preferable to mechanical scarification and fuels treatments. However, 

burned logs may not provide the same functions for 

small mammals as unburned logs. No research has 

addressed this question, but it is reasonable to assume 

that removal of bark, moss, branches, and fungi resulting from fire may reduce the value ofCWD to small 

mammals for uses other than hiding and escape cover. 

Hand scarification practices (BNF Forest Plan 1987) 

are likely to impact small mammal communities and 

the forest floor less than mechanical scarification. 

Aside from timber harvest, firewood gathering is 

probably the greatest threat to CWD on National 

Forest lands. Firewood gatherers will remove solid 

logs and snags from roadsides for some distance into 

the forest on the uphill side. The greater the road 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
access to an area, the more critical this problem 

becomes. Firewood gathering restrictions must apply 

not only to removal of wildlife trees, but also to the 

removal ofwildlife logs, ifCWD management is to be 

successful. 

Some economic impact will result from managing 

for CWD and snags since some harvestable trees will 

go uncut. However, long-term ecological gains are 

substantial. The CWD management guidelines proposed here provide large trees for seed sources, CWD 

for maintenance of mycorrhizal fungi and soil integrity, and visual aesthetics that will result in long-term 

financial gains in addition to helping achieve the longterm goals of forest health. The bottom line is, there is 

no other way to produce CWD and snags than to give 

up merchantable fiber since it is precisely this fiber 

that is required by wildlife, but ecosystem-level gains 

from managing for CWD are significant. 

The Ecological Role of Douglas-fir 

Within Ponderosa Pine 

Communities _________ _ 

An important ecosystem management restoration 

goal proposed for seral ponderosa pine stands on the 

BNF and other Forest Service lands includes removal 

of Douglas-fir through harvest and controlled burning. Before such a strategy is imposed on the landscape, we should try to understand the natural ecological role of Douglas-fir within seral ponderosa pine. 

The presence of old Douglas-fir trees (>300 yrs) that 

substantially predate the period of effective fire exclusion in ponderosa pine stands demonstrates that 

individual Douglas-fir trees and pockets of Douglas-fir 

trees escaped fire in some stands (Arno et al. 1995). 

Additionally, our current understanding of fire intervals in these dry forest types originates from fire scar 

techniques that are necessarily applied to old-growth 

stands (Arno and Sneck 1977). These data, therefore, 

represent fire intervals that present a biased sample 

of the range of stand age classes that would have 

existed on the presettlement landscape. That is to say, 

they represent the within-stand fire interval for stands 

that obviously have persisted under a low intensity 

fire regime, in other words, natural escapes. These 

stands likely do not represent the full range of stands 

that existed on the landscape and so these data do not 

provide a complete understanding of presettlement 

fire processes at the landscape scale. Stands subjected 

to longer fire intervals that resulted in more intense, 

possibly stand-replacing fires, would not be available 

for sampling at the present time. 

There is, therefore, little data to help explain the 

natural presettlement ecological role of Douglas-fir in 

ponderosa pine and western larch communities. 

However, it is reasonable to assume that even in 

stands that clearly underwent a fire interval of, for 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

example, 10 to 15 years, Douglas-fir encroachment 

might have occurred in the form of small regenerative 

patches of trees somewhat younger than the average 

fire frequency interval, and mature Douglas-fir trees 

would also occur where wet sites and cool drainages 

within ponderosa pine stands favored escape from 

frequent, low-intensity fires. On the landscape scale, 

there were also undoubtedly entire stands that escaped fire, allowing Douglas-fir to mature and become 

established. 

A recent study in westcentral Montana (Ruggiero 

and Pearson unpublished data) suggests that small 

mammal communities in old-growth ponderosa pine 

have greater species richness and evenness in stands 

heavily invaded by Douglas-fir than in those with very 

little Douglas-fir that have been treated by understory 

burning. Moist-site, late-seral species such as redbacked voles, red-tailed chipmunks, and vagrant 

shrews were found in the stands where Douglas-fir 

had become established in association with ephemeral 

drainages, adding to the diversity of small mammals 

present in ponderosa pine communities. Therefore, 

removal of encroaching fir may reduce small mammal 

diversity within moist ponderosa pine cover types. 

Some such reduction in diversity should not be a 

concern since it is compatible with managing for the 

presettlement ponderosa pine community. However, 

the historic role of Douglas-fir in seral ponderosa pine 

should be considered in light of its effect on small 

mammal diversity. 

Small ephemeral drainages and seeps associated 

with some ponderosa pine stands may provide natural 

refugia from low-intensity fire and offer favorable 

habitat for Douglas-fir within ponderosa pine cover 

types. Red-squirrel middens are much larger and 

better developed in these seeps and ravines (pers. 

obs.), indicating the importance of these sites for this 

species and other small mammals that may associate 

with red-squirrel middens (Ruggiero and Pearson in 

prep.). Mesic Douglas-fir microhabitats also appeared 

to favor red-tailed chipmunks, red-backed voles, and 

shrews, which did not occur in ponderosa pine stands 

treated with fire and lacking in Douglas-fir (Ruggiero 

and Pearson unpublished data). 

Douglas-fir likely historically persisted in these pockets in low numbers due to their escape from lowintensity fires. Retaining some Douglas-fir in these 

microsites will favor small mammal diversity and 

diversity of other taxa within seral ponderosa pine 

stands. If this is true, low intensity under burning is 

not a threat to Douglas-fir on these wet areas since 

the natural process of escape from fire will be mimicked. However, cutting could be a threat. Removal of 

Douglas-fir from these sites would open the canopy, 

thereby accelerating evaporation and greatly reducing 

the functionality of these oases for small mammals, 

plants, insects, and other species that associate with 

them. 

37 
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USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
PART II -ANNOTATED BIBLIOGRAPHY 

Introduction ----------------------------

The following annotated bibliography presents selected work on small mammal ecology and habitat use 

deemed most pertinent to land management on the 

Bitterroot National Forest. The primary focus is 

western Montana and the northern Rocky Mountains, 

but the Pacific Northwest is included for more general 

information and for information not currently available in the Northern Rocky Mountains. 

Since I have synthesized the abstracted materials 

above as they pertain to the various categories reviewed, I restrict annotation here to author abstracts 

where possible to preserve the author's insights into 

the work. I provide summaries for research not abstracted. Additionally, I list study location, habitat, 

and key words. Habitats listed are the primary habitats presented by dominant species and successional 

stages reported in the study. I list key words that will 

best guide the reader in searching for information 

about the species and habitats available in a paper as 

it pertains to the topic of this review. These are not 

necessarily the "key words" presented in published 

works. 

Annotated Bibliography ___ _ 

Adelman, E. B. 1979. A survey of the nongame 

mammals in the upper Rattlesnake Creek drainage 

of western Montana. Master's Thesis, University of 

Montana, Missoula, Montana. 129 pp. 

Location: Rattlesnake Creek drainage, near Missoula, 

Montana. 

Habitat: Cottonwood bottom, ponderosa pine, 

Douglas-fir, grand fir, subalpine fir, clearcut, disturbed meadow. 

Keywords: Diversity, elevational gradient, habitat 

associations, niche breadth, niche overlap. 

Abstract: During two field seasons, snap trap lines 

were used to determine small mammal diversity within 

each habitat, niche width for each mammal species, 

and niche overlap between species in the Upper Rattlesnake Creek Drainage, Montana. The 14 trapping locations represented 18 habitat types with varying diversities. Diversity was strongly related to elevation but 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

was not correlated with either shrub development or 

tree canopy closure. Cinereus shrews, northern bog 

lemmings, long-tailed and meadow voles, and northern flying squirrels had the narrowest niches; redbacked voles, yellow-pine chipmunks, vagrant shrews, 

red-tailed chipmunks, jumpi-ng mice, and deer mice 

had progressively larger niches. Most species pairs did 

not show much, if any, niche overlap, especially when 

habitat abundance was considered. Mammal species 

diversity varied greatly from one habitat to another 

along a scent station line, ran twice during summer 

1977, but was influenced more by the presence of the 

road than by habitat features. Additional mammals 

that visited the scent stations included golden-man tied 

ground and columbian ground squirrels, red squirrels, porcupines, bushy-tailed woodrats, black bears, 

weasels, badgers, bobcats, red foxes and coyotes. Niche 

overlap was moderate for most species pairs; predators did not overlap much although use tended to 

concentrate in a few areas. Diversity, niche breadth, 

and niche overlap varied between months as a result 

of food availability, population sizes, and hibernation. 

Other species present throughout the drainage as 

determined from sign or mammal sightings include: 

pocket gophers, hoary and yellow-bellied marmots, 

muskrats, beavers, snowshoe hares, pikas, short- and 

long-tailed weasels, mink, striped skunks, wolverine, 

lynx, cougar, wolf, and grizzly bear. 

The implications of logging, burning, recreation, 

and wilderness as management options are examined. The effects, both favorable and unfavorable, of 

these options on the different species of wildlife are 

summarized. 

Amaranthus, M., J. M. Trappe, L. Bednar, and 

D. Arthur. 1994. Hypogeal fungal production in 

mature Douglas-fir forest fragments and surrounding plantations and its relation to coarse woody 

debris and animal mycophagy. Canadian Journal of 

Forest Research 24:2157-2165. 

Location: Siskiyou National Forest, Klamath Mountains, Oregon. 

Habitat: 180-year-old mature Douglas-fir, and 4, 10, 

12, 14, 27-year-old plantations in clearcuts. 

Keywords: Coarse woody debris, habitat associations, mycophagy, mycorrhizal fungi, truffle. 

45 
Abstract: Production ofhypogeous fungi (truffles) in 

high-elevation, 180-year-old mature forest fragments 

of Pseudotsuga menziesii (Mirb.) Franco was compared with surrounding regenerated clearcut ranging 

from four to 27 years since harvest at two study areas. 

Thirty pairs of plots, one of each pair in soil, the other 

in brown-cubical-rotted coarse woody debris (CWD), 

were searched for truffles in each stand during four 

perio4s: August and November, 1990, and February 

and May, 1991. Overall analysis of presence/absence 

of truffles from using log-linear models revealed that 

CWD and mature forest status of stands each significantly influenced truffle occurrence. Mature forest 

fragments had greater percent frequency of occurrence and truffle number and dry weight than did 

plantations. The plantations did not differ significantly among each other for any parameter. CWD 

yielded higher numbers and biomass of truffles than 

soil in mature forest, but production in plantations 

did not differ between substrates. The total dry 

weight of truffles in CWD exceed that in soil by more 

than 10 times in mature forests. Forest practices that 

emphasize the retention of mature trees and coarse 

woody debris promote the abundance and diversity of 

truffles, which are integral and functionally important members of forest ecosystems. 

Anthony, R. G., E. D. Forsman, G. A. Green, G. 

Witmer, and S. K. Nelson. 1987. Small mammal 

populations in riparian zones of different-aged coniferous forests. The Murrelet 68:94-102. 

Location: Willamette National Forest, Oregon. 

Habitat: Riparian zones of young, mature, and oldgrowth stands of western hemlock/Dougls-fir forests. 

Keywords: Habitat associations, old growth, riparian zones, clearcutting. 

Abstract: Small mammals were trapped in riparian 

zones in young, mature, and old-growth coniferous 

forests during spring and summer of1983. Peromyscus 

maniculatus was the most abundant species and comprised 76 percent and 83 percent of the total captures 

during spring and summer, respectively. More species, but fewer individuals, were captured on the 

streamside transects in comparison to the riparian 

fringe transects, which were 15-20 m from the stream. 

Six species of Insectivora, including five species of 

Sorex, were captured in these riparian zones. No 

species was solely dependent on riparian zones in oldgrowth forests; however, additional studies are needed 

to define the specific habitat requirements of Sorex 

bendirii, Sorex palustris, Neurotrichus gibbsii, 

Phenacomys albipes, and Microtus richardsoni. 

46 

Beg, M.A.1969. Habitats, food habits, and population 

dynamics of the red-tailed chipmunk, Eutamias 

ruficaudus, in western Montana. Phd, University of 

Montana, Missoula, Montana. 153 pp. 

Location: Pattee Canyon, near Missoula, Montana; 

Boulder Creek, on the Flathead Indian Reservation, 

MT; and University of Montana Biological Station, 

Yellow Bay, western Montana. 

Habitat: Primarily ponderosa pine and Douglas-fir 

forests; also western larch, Engelmann spruce and 

grand fir. 

Keywords: Breeding, food habits, habitat associations, morphometries, population demographics, 

reproduction. 

Summary: M. A. Begs studied habitat use, food 

habits and population dynamics of the red-tailed chipmunk (Tamias ruficaudus) at the University of Montana Biological Station, Flathead Lake; at Boulder 

Creek, also near Flathead Lake; and at Pattee Canyon, near Missoula, Montana. Tamias amoenus inhabited two of the sites and was studied where both 

species occurred. Tamias amoenus was found in dry 

savanna-type habitat predominantly in ponderosa pine 

but also occurred in Douglas-fir (Pseudotsuga menziesii) where it was associated with dry exposures 

supporting some ponderosa pine. Tamias ruficaudus 

inhabited shady coniferous forest dominating the 

subalpine (Abies lasiocarpa) zone. In the Douglas-fir 

zone, where habitats intermixed to produce a mosaic, 

the two species maintained strict habitat segregation. 

Considerable overlap was observed in diets between 

the two species. Examination of 158 cheek-pouches of 

T. ruficaudus and visual observations of both species 

in the field indicated that seeds ofbull thistle ( Circium 

vulgare), shrubs, and conifers and fruits were the 

primary foods. In the spring, when seeds were unavailable, leaves sprouts and flowers were consumed. 

Populations were low in May after spring emergence 

and peaked in August. After August a rapid decline in 

populations was observed. Between-year differences 

were slight. Survivorship curves were calculated. Some 

individuals were believed to reach 7 or 8 years of age. 

Males moved farther than females and females moved 

farther than juveniles as determined by average distances moved between capture points. 

Bonnell, M. L. 1967. Emergence and foraging behavior in small populations of Idaho bats. Master's 

Thesis, University of Idaho, Moscow, Idaho. 

Location: Near Moscow, Idaho. 

Habitat: Caves and mine shafts. 

Keywords: Barometric pressure, food habits, foraging behavior, temperature, territoriality, threshold of 

illumination, relative humidity, roost habitat. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
Abstract: In the summer and fall of 1966, bats 

belonging to the genera Myotis and Eptesicus were 

investigated at five roosts near Moscow, Idaho. The 

threshold of illumination at which bats of the genus 

Myotis began their foraging was shown to be 0.8 foot 

candles or less. Eptesicus fuscus emerged at 1.6 foot 

candles. The illumination at which bats of the genus 

Myotis emerged appeared to decrease slightly from 

August through September of 1966. Temperature and 

relative humidity were found to play little or no role in 

determining the time of evening emergence. On the 

nights of highest temperature, the greatest number of 

bats were seen. All roosts were associated with high 

relative humidity and running or standing water. 

Foraging was intermittent on the part of individual 

bats. Bats foraged primarily in flyways immediately 

adjacent to the roosts. The flight of Myotis was very 

erratic. These bats flew from 10 to 25 feet high. 

Eptesicus flew more directly and at an altitude of 100 

to 200 feet. Territoriality and investigative behavior 

appeared to be present. 

Collection of discarded insect wings beneath the 

roost revealed the use of Lepidoptera and Hymenoptera as food. Light sampling behavior was observed on 

two occasions in Myotis evotis. Similar behavior was 

induced well after foraging had begun by directing 

bright light sources on a mine entrance. Bats of different species were never seen to roost less then 10 feet 

apart. 

Brown, L. N. 1967. Ecological distribution of six 

species of shrews and comparisons of sampling 

methods in the central Rocky Mountains. Journal of 

Mammalogy 48(4):617 -623. 

Location: Medicine Bow Mountains, southern 

Wyoming. 

Habitat: Cottonwood-willow, short-grass prairie, sagebrush, mountain mahogany, aspen, lodgepole pine, 

spruce-fir, alpine tundra. 

Keywords: Habitat associations, sampling methods, 

trap bias. 

Abstract: The ecological distribution of six species 

of shrews was studied using sunken cans in 14 montane and intermountain habitats in southern Wyoming. 

The vagrant shrew and cinereus shrew were cosmopolitan in distribution. Cinereus shrew was slightly 

more abundant in moist plant communities, whereas 

vagrant shrew predominated in slightly drier communities. Merriam's shrew (Sorex merriami) occurred 

only in arid portions of the plains and foothills, and in 

short-grass prairie was the only shrew taken. The 

water shrew occurred only along or near cold mountain streams and ponds. The dwarf shrew (Sorex 

nanus) and the pygmy shrew (Microsorex hoyi) occupied restricted mountain habitats. The dwarf shrew 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

was abundant in rocky locations in both alpine and 

subalpine plant communities; the pygmy shrew was 

taken only in peat-moss bogs in the spruce-fir zone. 

A comparison of snap traps and sunken cans as methods of collecting shrews revealed that snap traps 

failed to demonstrate the presence of So rex nan us and 

Microsorex hoyi in areas where they were abundant. 

Also densities of Sorex nanus and cinereus shrew 

indicated by snap traps were considerably below those 

demonstrated by sunken cans. 

Campbell, T. M., and T. W. Clark. 1980. Short-term 

effects oflogging on red-backed voles and deer mice. 

Great Basin Naturalist 40(2):183-189. 

Location: Bridger-Teton National Forest, Wyoming. 

Habitat: Climax spruce-fir, lodgepole pine, Douglas-fir. 

Keywords: Clearcut, habitat associations, logging, 

selective cut, small mammals. 

Abstract: Clearcutting and selective logging effects 

on red-backed voles (Clethrionomys gapperi) and 

deer mice (Peromyscus maniculatus) were studied 

(September-November, 1975; June-October, 1976) in 

Bridger-Teton National Forest, Wyoming. Five selective cuts (total137 ha) removed 57 percent (range 34 

to 7 4 percent) of the trees. One clearcut (9.6 ha) 

eliminated 84 percent of the trees. Soils remained 

mesic in selective cuts but became xeric in the clearcut. Snap-trapping indicated that voles were most 

abundant on the unlogged and selectively cut mesic 

sites (76 percent of 408 captures), whereas deer mice 

were more common on the xeric clearcuts (80 percent 

of 60 captures). Species composition remained unchanged on selective cuts following logging (77 percent 

voles of 266 captures) but changed from predominantly voles to mostly deer mice (80 percent of 60 

captures) in the clearcut. Intraspecific age and sex 

ratios, litter sizes, and morphological measurements 

were compared between logged and unlogged areas. 

Carey, A. B., and M. L. Johnson. 1995. Small 

mammals in managed, naturally young, and old 

growth forests. Ecological Applications 5(2):336-

352. 

Location: Olympic peninsula, Washington. 

Habitat: Old growth and managed stands ( 40-60 

years old) ofDouglas-fir/western hemlock at 85-610 m. 

Keywords: Biomass, old growth, CWD, CWD 

management 

Abstract: Forest managers in the Pacific Northwest 

are faced with new challenges of providing for all 

wildlife in managed forests. The objective was to 

elucidate the factors governing the composition and 

biomass of forest floor mammal communities that are 

47 
amenable to management. Small mammal communities were sampled in forests of various management 

histories on the Olympic Peninsula and contrasted 

our results with those of other large studies in the 

Pacific Northwest. Forest floor mammal communities 

in forests >35 yr old in the Western Hemlock Zone of 

Washington and Oregon are composed of five to 

eight characteristic species. These include Sorex 

trowbridgii (numerically the most dominant); one species each of Clethrionomys, the So rex uagrans complex, 

and Peromyscus; and Neurotrichus gibbsii. Species 

composition changes from south to north, and the 

communities on the Olympic Peninsula contain two or 

three additional species compared to communities to 

the south. Communities in naturally regenerated and 

clearcutting regenerated (managed) young forests are 

similar in composition to those in old growth; old 

growth, however, supports 1.5 times more individuals 

and biomass than managed forest. Community diversity seems related to the south-north moisturetemperature gradient that is reflected in increased 

diversity of canopy conifers, development of forest 

floor litter layers, accumulation of coarse woody debris, and abundance of herbs, deciduous shrubs, and 

shade-tolerant seedlings (as opposed to understories 

dominated by evergreen shrubs). Previous work found 

few habitat variables that were good predictors of 

species abundance in natural young and old-growth 

stands. Naturally regenerated young stands had 

higher levels of coarse woody debris than old growth. 

Managed stands had much lower abundance of 

coarse woody debris and tall shrubs than old growth. 

Understory vegetation (herbs and shrubs) and coarse 

woody debris accounted for a major part of the variation in abundance of six of eight species in managed 

stands, but only two species in old growth. Management ofWestern Hemlock Zone forest for conservation 

of biodiversity and restoration of old-growth conditions should concentrate on providing multispecies 

canopies, coarse woody debris, and well-developed 

understories. 

Clarkson, D. A., and L. S. Mills. 1994. Hypogeous sporocarps in forest remnants and clearcuts in southwest 

Oregon. Northwest Science 68(4):259-265. 

Location: Klamath Mountains, Southwestern 

Oregon. 

Habitat: Clearcut and old-growth Pseudotsuga 

menziesii I Abies concolor forest. 

Keywords: Clearcut, forest remnants, habitat associations, hypogeous sporocarp, mycophagy, mycorrhizal fungi, old growth, truffles. 

Abstract: During June-August, 1991, we sampled 

hypogeous sporocarps on four late seral remnants 

ranging in size from 1.3 to 3.6 ha and on clearcuts 

48 

surrounding two of the remnants. In particular our 

sampling of these southwestern Oregon sites 

(dominated by Pseudotsuga menziesii I Abies co nco lor) 

targeted three questions: 1) Are hypogeous sporocarps 

more abundant in remnants oflate seral forest than in 

the surrounding clearcuts? 2) Are hypogeous sporocarps more abundant under coarse woody debris? 3) Is 

the California red-backed vole (Clethrionomys californicus) positively associated with areas having 

hypogeous sporocarps? Two forest remnants had 20-

40 times more hypogeous sporocarps than the young 

clearcuts which surrounded them. Hypogeous sporocarps were four times more abundant in plots having 

logs. Voles were more likely to be caught at traps 

having hypogeous sporocarps nearby. Remnant stands 

of late seral forest appear to provide a refuge for 

hypogeous sporocarps used by the California redbacked vole and other small mammals, and coarse 

woody debris may contribute to an abundance of 

hypogeous fungal sporocarps. 

Clothier, R. R. 1955. Contributions to the life history 

of Sorex uagrans in Montana. Journal ofMammalogy 36:214-221. 

Location: Missoula Co.; Yellow Bay, Flathead Lake; 

Glacier National Park. 

Habitat: Damp areas near water. 

Keywords: Age, activity patterns, dermal glands, 

elevation, food habits, life history, molts, 

morphometries, reproduction, associated species. 

Summary: Clothier trapped 188 vagrant shrews in 

western Montana. These shrews and an additional 

118 taken from the same areas by other collectors were 

examined for information on life histories. Clothier 

determined the age of specimens based on dental wear 

and assessed the variability of size with age. Based on 

a number of measurements taken, he concluded that 

only cranial height differed with age. The upper 

elevationallimit was determined to be 6,000 feet for 

vagrant shrews based on unsuccessful trapping above 

this elevation and review of captures above 5,000 feet 

by other authors trapping in the area (but see earlier 

discussion for this species). Habitat preferences could 

not be determined, because the author focused only on 

what was believed to be prime habitat. However, his 

success indicates that the moist habitats trapped near 

streams are important for this species. Food habit 

results indicated that the vagrant shrew consumed 

primarily insects. Determination of sexual activity 

indicated the earliest date of pregnancy was 1 April 

and the latest date was 8 August. The mean number of 

embryos from 32 gravid females was 6.4. All but two 

pregnant females were born the previous year. One 

female showed signs ofmatingmore than once. Mean 

weights of males and females was 4. 7 g and did not 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
differ between males and females in the non-reproductive season. The author found extensive habitat overlap between the vagrant and cinereus shrews, although the vagrant shrew was always more abundant. 

Shrews were active at all times of day and night 

including periods of inclement weather. 

Conaway, C. H. 1952. Life history of the water shrew 

(Sorex palustris navigator). American Midland 

Naturalist 48(1):219-248. 

Location: Missoula Co., western Montana. 

Habitat: Wet sites next to streams, primarily near 

overhanging banks. 

Keywords: Age structure, dermal glands, elevation, 

food habits, habitat association, life history, longevity, 

parasites, reproduction. 

Summary: This study was based upon 119 water 

shrews taken in Montana, west of the Continental 

Divide. The majority of specimens were snap trapped 

along streams in the Canadian zone at elevations of 

2900 to 6950 feet. All specimens were taken very close 

to the edges of streams and most frequently in traps 

placed beneath overhanging banks and within a few 

inches of the water. Age determination was based 

upontooth-wear.Nospecimenslivedbeyond18months. 

Male water shrews were not sexually active during 

the breeding season in which they were born. Spermatogenesis began the following December and 

January, at which time an increase in body weight 

was apparent. All males born the previous year between January and August were in active spermatogenesis. Pregnant or lactating females were taken 

between February and August. Ovulation is presumably induced by copulation. A post-partum estrus 

occurs, and pregnancy follows in some animals. Some 

animals that had experienced a post-partum estrus 

and ovulation were not pregnant. In these individuals 

it is thought that reabsorption of the embryos had 

occurred at some stage in development. One young 

female was pregnant, and two others showed some 

ovarian activity. The majority of breeding females, 

however, were old animals born the preceding year. 

Several litters are produced during the breeding season. The modal number of embryos was six. Forty-nine 

percent of the stomachs examined contained immature forms of aquatic insects. Thirteen species of 

parasites of the water shrew were found. Dermal 

glands were found only in sexually active males. Two 

annual molts occur, one during the spring between 

February and May, and one in the autumn during 

July and August. A specimen was maintained in 

captivity for seven weeks. This animal was capable of 

capturing small minnows in the water. The average 

food consumption of the captive was 10.3 grams of 

food during a twenty-four hour period. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

Fogel, R., and J. M. Trappe. 1978. Fungus consumption (mycophagy) by small animals. Northwest 

Science 52(1):1-31. 

Location: United States. 

Habitat: Various. 

Keywords: Fungi, hypogeous, literature review, 

mycophagy, mycorrhizae, small mammals, truffles. 

Abstract: A review of the natural history literature of 

small mammal feeding habits, based on many fortuitous field observations, some analysis of stomach 

contents, and a few feeding experiments, shows that 

diverse animals feed on similarly diverse fungi. The 

interdependence of animals and fungi has evolved to a 

high degree in some cases. An example is the loss of 

alternative spore dispersal mechanisms by some fungi 

and the strong reliance of some mammals on fungi as 

a primary food. Consequently adaptation for 

mycophagy and the effects on mycophagy of habitat, 

fungal toxicity, and the food value of fungi have implications in the interpretation of ecosystem structure 

and function. 

Foresman, K., and C. B. Henderson. 1992. Summary report: small mammal populations in harvested and mature Douglas-fir stands: Rivulet site 

1991. Rocky Mountain Research Station, Forestry 

Sciences Lab, Missoula, MT 59812. 

Location: Lolo National Forest, Montana. 

Habitat: Mature and clearcut Douglas-fir stands. 

Keywords: Abundance, clearcutting, management, 

habitat associations, community assemblages 

Summary: This report presents the results of a oneyear trapping study comparing the small mammal 

communities of mature and harvested Douglas-fir 

stands. Harvested plots had more individuals and a 

substantial increase in deer mice and red-tailed chipmunks. Long tailed voles were present on the harvested plots but not mature stands. Red-backed voles 

were caught on harvested plots at about the same 

levels as the mature stands. Their persistence may be 

due to the woody debris left over from logging and 

high shrub cover. This study supports others that 

find red-backed voles will use cut areas ifthey have not 

been burned. 

Gashwiler, J. S. 1959. Small mammal study in 

West-central Oregon. Journal of Mammalogy 

40(1):128-139. 

Location: Central Oregon, H. J. Andrews Experimental Forest, west slope Cascade Mountains. 

Habitat: Old-growth Douglas-fir, western hemlock, 

western red-cedar, and clearcuts in the same habitats. 

Keywords: Clearcut, preliminary results, small mammal abundance, vegetation changes. 

49 
Summary: This paper presents results for the first 

three years of a 12-year study on the effects of 

clearcutting and burning on small mammal abundance and changes in vegetation in the Pacific Northwest. This paper functions as a companion paper for 

the following research (Gashwiler, 1970). It contains 

some information not present in the comprehensive 

review ofthe full12-year study. 

Gashwiler, J. S. 1970. Plant and mammal changes 

on a clearcut in west-central Oregon. Ecology 

51(6):1018-1026. 

Location: Central Oregon, H. J. Andrews Experimental Forest, west slope of the Cascade Mountains. 

Habitat: Old-growth Douglas-fir, western hemlock, 

western red-cedar, and clearcuts in the same habitats. 

Keywords: Clearcut, small mammal abundance, vegetation changes. 

Abstract: Plant composition and coverage and small 

mammal populations were compared in virgin forest 

(control) and clearcut (experimental) areas from April 

1954 to October 1965. Changes in ground cover vegetation were modest on the control area but marked 

on the experimental area. A late fall burn on the 

experimental area may have retarded herbaceous 

plant establishment. Nearly half of the herbaceous 

species were invaders not found in the virgin Douglasfir (Pseudotsuga menziesii) forest. Ground plant coverage was less than 23 percent in the virgin forest; a 

year after the clearcut area was burned, the cover 

was 2 percent; and by 10 years it was above 53 percent. 

Woody plant coverage (mostly sprouts) was slightly 

more abundant the first two years after burning. 

Herbaceous species then became dominant for a 3-year 

period, after which woody plants gradually gained 

dominance. Deer mice (Peromyscus maniculatus) increased on the experimental area soon after the burn. 

The populations varied from an estimated 0.9 to 12.8 

animals per acre and fluctuated widely and irregularly. Townsend's chipmunk (Eutamias townsendii), 

Oregon vole (Microtus oregoni) and snowshoe hare 

(Lepus americanus) also increased on the area at 

different periods after the burn. Trowbridge's shrew 

(So rex trowbridgii), vagrant shrew, and ermine 

(Mus tela erminea) were present on both areas in 

relatively low numbers. Red back voles ( Clethrionomys 

occidentalis ), Douglas squirrels (Tamiasciurus 

douglasii), and northern flying squirrels (Glaucomys 

sabrinus) were not found on the clearcut. California 

ground squirrels (Spermophilus beecheyi) migrated to 

the clearcut and established a modest population. 

Richardson's vole (Microtus richardsoni),jumpingmice 

(Zap us trinotatus ), bushy-tailed woodrats (Neotoma 

cinerea), and a pika ( Ochotona princeps) were visitors. 

50 

Gunther, P.M., B.S. Horn, and G. D. Babb. 1983. 

Small mammal populations and food selection in 

relation to timber harvest practices in the western 

Cascade Mountains. Northwest Science 57( 1): 

32-44. 

Location: Central Washington, western Cascade 

Mountains. 

Habitat: Mature western hemlock, burned and unburned clearcuts. 

Keywords: Food habits, habitat associations, small 

mammal abundance, timber management. 

Abstract: Small mammals were snap-trapped in a 

mature conifer forest, unburned clearcuts, and burned 

clearcuts in the western Cascade Mountains in central Washington. The largest populations were in 

unburned clearcuts, and the smallest overall population was in the forest. Sorex trowbridgii was the most 

abundant insectivore caught. Clethrionomys gapperi 

was the most abundant rodent caught in most clearcuts and its population was the largest of any species 

in the study area. Other species caught include montane shrew ,Neurotrichus gibbsii,Eutamias townsendii, 

Glaucomys sabrinus, Peromyscus maniculatus, Microtus townsendii, and Zapus trinotatus. Vegetation 

and percent cover were analyzed in the study area, 

and small mammal stomach contents of all nine animal species were examined. In unburned clearcuts, 

fungi and epiphytic lichens, especially Alectoria 

sarmentosa, and conifer seeds were the major foods 

eaten by rodents. 

Halvorson, C. H. 1982. Rodent occurrence, habitat 

disturbance, and seed fall in a larch-fir forest. 

Ecology 63(2):423-433. 

Location: Newman Ridge, western Montana. 

Habitat: Clear cut and mature western larch and 

Douglas-fir forest. 

Keywords: Clearcut, broadcast burn, habitat associations, old growth. 

Abstract: Small mammal population changes were 

measured for five years (1970-1974) by live trapping 

on broadcast burned western larch (larix occidentalis)/Douglas-fir (Pseudotsuga menziesii) clearcuts 

and in uncut timber on a north and south slope in 

western Montana. Four species comprised 96 percent 

of the 1324 animals caught: deer mice (Peromyscus 

maniculatus) 42 percent, red-backed voles 

(Clethrionomys gapperi) 27 percent, red-tailed chipmunks (Eutamias ruficaudus) 22 percent, and longtailed voles (Microtus longicaudus) 5 percent. Deer 

mice and chipmunks were common on clearcut and 

timber plots. The red-backed vole and long-tailed voles 

were associated with moist sites but showed local 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
allopatry. The red-backed voles were present only 

under tree canopy and the long-tailed vole was found 

only in absence of tree canopy. A hard burn effect was 

to eliminate most of the organic mantle and small 

mammals except deer mice, who existed as the single 

species for two years, and as 80-90 percent of numbers 

for five postburn years. A light burn that left duff 

intact was associated with retention of species diversity and a low initial postburn (two years) mammal 

population, followed by the largest increases. Numbers of deer mice varied inversely with numbers of 

red-backed voles in the timber. Deer mice increased 

sharply on all plots the first fall after a heavy seed 

crop, an occurrence reported by other workers. From 

these pattern observations it is theorized that redbacked voles may dominate deer mice, but a heavy 

seed crop can temporarily enhance competitive standing of deer mice. An open xeric pioneering situation 

(hard burn) was conducive to consistently high deer 

mouse populations. The most obvious habitat feature 

associated with an inverse spatial relationship between the two voles was tree canopy. The long-tailed 

vole may be further discriminated against by drier 

habitats. Clearcutting appeared to be the principal 

determinant of total population size, but burn intensity seemed to influence species composition. 

Harvey, A. E., M. J. Larsen, and M. F. Jurgensen. 

1976. Distribution of ectomycorrhizae in a mature 

Douglas fir/larch forest soil in western Montana. 

Forest Science 22(4):393-398. 

Location: Corum Experimental Forest, northwest 

Montana. 

Habitat: Douglas-fir/western larch. 

Keywords: Coarse woody debris, ectomycorrhizae, 

habitat associations, mycorrhizal fungi, prescribed 

burning, timber harvest. 

Abstract: The top 38 em (15 inches) of a western 

Montana forest soil was 60 percent mineral, 23 percent humus, 15 percent decayed wood, and 2 percent 

charcoal. Most (to 95 percent) of the active 

ectomycorrhizae were associated with the organic 

fractions. Five percent of all active ectomycorrhizae 

occurred in the mineral soil fraction, 66 percent in the 

humus, 21 percent in the decayed wood, and 8 percent 

in the charcoal. Thus, the organic reserves in this 

forest soil were the most important substrates for 

ectomycorrhizae formation. Therefore, the parent 

materials (leaves, litter, and woody residues) for soil 

organic reserves may require management during 

timber harvesting and prescribed burning to prevent 

a subsequent loss in the capacities of soils of this 

type (limestone base) to support ectomycorrhizal 

associations in mature Douglas-fir/larch forests. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

Harvey, A. E., M. F. Jurgensen, M. J. Larsen, 

and R. T. Graham. 1987. Decaying organic materials and soil quality in the inland northwest: a 

management opportunity. USDA Forest Service, 

Intermountain Research Station General Technical Report GTR-INT-225. 

Location: Inland Northwest. 

Habitat: Broad range of forest cover types. 

Keywords: Coarse woody debris, mycorrhizae, fungi, 

soil microbes, soil, litter 

Abstract: Organic debris, including wood residues, 

provide parent materials for development and function of organic mantles on forest soils. Along with 

providing a storehouse of nutrients and moisture, 

organic materials provide either the environment or 

the energy source for microorganisms critical to both 

the nutritional quality of forest soils and the ability of 

conifers to extract nutrients and moisture from the 

soil. The role and relative importance of specific organic components can vary substantially with site 

and conifer species. Age of the trees appears to have 

less of an effect on importance of organic matter than 

site or species. Of the many organic materials incorporated in a forest soil, the woody component is in 

many ways the most important. To protect productive potential of forest soils, a continuous supply of 

organic materials must be provided, particularly in 

harsh environments. In case of excess losses of the 

organic mantle, complete recovery of the site may 

require several hundred years, even with proper 

management. 

Hayward, G. D., and P. H. Hayward. 1995. Relative 

abundance and habitat associations of small mammals in Chamberlain Basin, Central Idaho. Northwest Science 69(2):114-125. 

Location: Central Idaho. 

Habitat: Lodgepole pine, Douglas-fir, spruce-fir, mixed 

conifer. 

Keywords: Habitat selection, species richness, 

wilderness. 

Abstract: We sampled small mammal populations 

and measured habitat structure in forested and nonforested habitats in the wilderness of central Idaho 

over a 5-year period using pit and snap traps. Although results from pit and snap trapping differed for 

northern pocket gophers (Thomomys talpoides), capture rates for the two methods were similar across 

habitats for the other common species. Southern redbacked voles (Clethrionomys gapperi) and shrews 

(So rex vagrans and S. cinereus) were the most common 

species captured. Spruce-fir forests exceeded other 

habitats in the abundance of small mammals while 

51 
all sites had low species richness (s = 4. 7). Habitat 

association of the common small mammals (southern 

red-backed voles, shrews, deer mice (Peromyscus 

maniculatus) and yellow-pine chipmunks (Tamias 

amoenus )) differed, based on both broad patterns and 

microhabitat gradients. Our data corroborate theresults of other investigations by demonstrating the 

relatively low abundance of small mammals in subalpine habitats of the Rocky Mountains. Furthermore, 

the differences in small mammal communities among 

forest types suggests a mosaic pattern of small mammal communities in the Rockies that results from the 

patchy nature of forests in this region. 

Hoffman, G. R. 1960. The small mammal components of six climax plant associations in eastern 

Washington and northern Idaho. Ecology 41(3): 

571-572. 

Location: Eastern Washington and northern Idaho 

Habitat: Pinus ponderosa, Pseudotsuga menziesii, 

Thuja plicata, and Tsuga heterophylla forests 

Keywords: Habitat associations, small mammals 

Summary: Small mammals were trapped in six plant 

associations (Pinus ponderosa-Agropyron spicatum, 

Pseudotsuga menziesii-Calamagrostis rubescens, 

Thuja plicata I Tsuga heterophylla-Pachistima 

myrsinites, Thuja plicata I Tsuga heterophyllaOplopanax horridum, Alnus sinuata, and Carex 

lasiocarpa) in eastern Washington and northern Idaho. 

The deer mouse and vagrant shrew were most widespread, being found in four and five of the six plant 

associations, respectively. The deer mouse was 

abundant in Pinus ponderosa-Agropyron spicatum 

savanna and the only small mammal of 11 species 

trapped to be found in this habitat. Vagrant shrew was 

similarly the only species taken in the Pseudotsuga 

menziesii-Calamagrostis rubescens habitat, but only 

one individual was taken. Cinereus shrew was taken 

only in Thuja plicata I Tsuga heterophylla-Pachistima 

myrsinites habitat. Phenacomys intermedius and 

Tamias amoenus were taken only in Thuja plicataTsuga heterophylla associations. Only one Tamias 

ruficaudus was taken. This individual was captured 

in the Alnus sinuata community. Two Clethrionomys 

gap peri were taken in the Thuja I Tsuga-Oplopanax 

habitat and nine were taken in the Alnus sinuata 

association. Zapus princeps and Microtus montanus 

were taken only in the Alnus sinuata association. 

Microtus pennsylvanicus was the most abundant 

species trapped, but all individuals were found in the 

Carex lasiocarpa habitat. The Thuja plicata I Tsuga 

heterophylla-Pachistima myrsinites, Thuja plicatal 

Tsuga heterophylla-Oplopanax horridum and Alnus 

sinuata were the most diverse habitats having six, 

five, and six species each, which were fairly evenly 

52 

represented. This was true even though the Thuja 

plicata I Tsuga heterophylla-Oplopanax horridum 

association was under-trapped relative to the others. 

The Carex lasiocarpa habitat contained only two species but had the greatest number of captures due to 

the abundance ofvagrant shrew andM. pennsylvani- \ 

cus found in this habitat. The Pinus ponderosaAgropyron spicatum and Pseudotsuga menziesii-Calamagrostis rubescens associations were relatively 

depauperate. 

Hoffmann, R. S., P. L. Wright, and F. E. Newby. 

1969. The distribution of some mammals in 

Montana. I. Mammals other than bats. Journal of 

Mammalogy 50(3):579-604. 

Location: Montana. 

Habitat: Various. 

Keywords: Distribution, habitat associations. 

Abstract: Information on current distribution of 40 

species of mammals in Montana is given. Four species, 

Preble's shrew, Sciurus niger, Perognathus parvus, 

and Procyon lotor are reported for the first time in 

Montana. 

Key, C. H.1979. Mammalian utilization offloodplain 

habitats along the North Fork of the Flathead River 

in Glacier National Park, Montana. Master's Thesis, University of Montana, Missoula, Montana. 

151 pp. 

Location: Northwest Montana, North Fork Flathead 

River, Glacier National Park. 

Habitat: Riparian including spruce and cottonwood 

dominated forest. 

Keywords: Floodplain, habitat utilization, small mammal abundance, succession. 

Abstract: Mammalian communities on the North 

Fork of the Flathead River Floodplain in Glacier 

National Park were investigated during 1976 and 

1977 to provide baseline data on the small mammal 

fauna, to evaluate the importance of floodplains to 

medium-sized carnivores, and to establish monitoring procedures so that park resource managers might 

better assess the future impact ofhuman disturbance. 

Six permanent plots were established from which 

estimates of small mammal distribution and a bundance can be made in future years. Floodplains were 

productive areas for small mammals. Twelve species 

were captured. Both density and biomass were greater 

in frequently flooded habitats than in most other 

types, including adjacent communities not subject to 

periodic flooding. Young seres were characterized by 

low species diversity and high relative abundance of 

deer mice. Older coniferous seres supported more 

species, but total abundance, though similar to early 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
seres in some cases, was more equally distributed 

between the species present. Statistically significant 

differences existed in small mammal densities between study plots but decreased significantly the second field season when total small mammal density 

was low. 

A plea is made to exercise great care when interpreting data from floodplain plots due to the high 

degree of natural variation in small mammal abundance. The mere density of a small mammal species 

would represent a good indicator of human disturbance. Given slight inter-plot variation, species diversity may be the best indicator of community change, 

provided the analysis controlled for expected variation 

due to changes in total small mammal density. Several 

small predators frequented floodplains, which provided access to prey, shelter, and travel routes. Otter 

and mink, linked directly to the aquatic system, would 

be good indicators of water quality changes and easily 

censused if utilized in environmental monitoring. 

Additional baseline data are needed on those species 

as a prerequisite to monitoring, however. 

Landres, P, D. Spildie, and R. Lee. 1995. Progress 

Report: Bitterroot Ecosystem Management- small 

mammal report. Submitted to Rocky Mountain 

Research Station, Missoula, MT. 

Location: Headwaters of Smith Creek, Selway-Bitterroot Wilderness, Bitterroot National Forest. 

Habitat: Habitat is not given. Clearcut; burn; uncut 

stand adjacent to clearcut and burn treatments; and 

control within contiguous stand in wilderness. 

Keywords: Disturbance, fire, populations estimates, preliminary report, species composition, timber harvest. 

Abstract: This is a preliminary report presented by 

the authors to briefly summarize initial results. The 

goals of the project were to 1) determine whether 

"timber harvesting or fire disturbances influence the 

species composition and population densities of small 

mammal communities on adjacent but undisturbed 

sites" and 2) determine "what are the effects of timber 

harvest and fire disturbances on species composition 

and population densities of small mammal communities that were similar before these disturbances?" The 

preliminary conclusion was drawn that no effect from 

burn or clearcut was observed in small mammal populations in the stand adjacent to the two types of 

disturbance. 

Lee, S.D. 1995. Comparison of population characteristics of three species of shrews and the shrew-mole 

in habitats with different amounts of coarse woody 

debris. Acta Theriologica 40(4):415-424. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

Location: Fort Lewis Military Reservation, Pierce 

county, Washington. 

Habitat: 50-60 year old Douglas-fir/western hemlock 

forests. 

Keywords: Coarse woody debris, habitat associations, population dynamics, reproductive rates 

Abstract: Seasonal fluctuation and its causes for 

three species of Sorex shrews and the shrew-mole 

Neutrichus gibbsii Baird, 1857 were investigated in 

three sites with high amounts of coarse woody debris 

(CWD) and three sites with low amounts of CWD in 

managed forests of western Washington, USA. So rex 

trowbridgii Baird, 1857 was more abundant on sites 

with high amounts ofCWD (captures per 100 trapping 

nights) and had higher reproductive rates than in 

sites with low amounts of CWD. Sorex monticolus 

Merriam, 1890 showed higher reproductive rates on 

sites with high amount of CWD. Population of Sorex 

vagrans Baird, 1857 fluctuated greater and abundance was higher in sites with low amounts of CWD. 

Most reproduction occurred from January to April and 

declined rapidly in May. Previous studies also have 

shown an early onset ofbreedingin Coastal California 

and Oregon. It seems that local species ofsoricids and 

N eutrichus gibbsii gain reproductive benefits by breeding primarily in January through May. 

Luoma, S. N. 1970. A study of hibernation in the 

western jumping mouse, Zap us princeps. Master's 

Thesis, Montana State University, Bozeman, 

Montana. 

Location: Western Montana. 

Habitat: High elevation grassy meadows; laboratory. 

Keywords: Brown fat, hibernation, torpor, weight 

gain, weight loss. 

Abstract: A field and laboratory study of hibernation 

inZapus princeps was conducted. Males gained weight 

more gradually and reached a higher peak than female Z. princeps. Hibernation was preceded in all 

animals by a period oflethargy and weight loss during 

which body temperatures were very labile. Torpor was 

easily induced during the summer by removing either 

food or water at any temperature below 22C. Arousal 

from induced torpor during the summer did not occur 

at temperatures below 10C, probably due to lack of a 

sufficient amount of brown fat. Animals kept at constant temperature (3±1C) in 24 hours of light per day 

hibernated two to three weeks earlier than animals 

caged outside. The characteristics of hibernation in Z. 

princeps appear to place it between the large obligatory hibernators and the smaller mammals that 

hibernate. 

53 
Malloy, J. C. 1981. The effects of 1080 baiting on 

columbian ground squirrels and nontarget mammal and bird populations. Master's Thesis, University of Montana, Missoula, Montana. 65 pp. 

Location: Blackfoot Valley, western Montana. 

Habitat: Grasslands. 

Keywords: Nontarget mortality, pesticide, populations estimates, rodent control, 1080 baiting. 

A-bstract: Target and nontarget mortality from 1080 

baiting of columbian ground squirrels (Spermophilus 

columbian us) was investigated in the Blackfoot Valley 

of western Montana. Ground squirrel population 

estimates declined to 0 on the treatment area immediately after poisoning but returned to approximately 

20 percent of their former levels within 1 year after 

treatment. Immigrants apparently came from the 

nearest untreated site, less than 246 feet (75 m) away. 

Juvenile squirrels were disproportionately less abundant on the treatment area in 1980 than in 1979, the 

treatment year. Capture rates and population estimates for small mammals declined immediately after 

baiting on the treatment area and increased on the 

control area. Population estimates declined further 

over the following winter on both treatment and control areas and reached a low point in the spring of 

1980. The over-winter decline was greater than the 

decline following baiting and was presumably a natural fluctuation. Passerine bird population indices varied after baiting but not in a manner attributable to 

the poisoning campaign. Granivorous birds were apparently unaffected by 1080 baiting. Three common 

raven (Corvus corax) carcasses were recovered. 

Carnivore populations were not reliably surveyed. 

Scent station indices and carcass recoveries indicated 

that coyote (Canus latrans) mortality occurred, but 

the magnitude of population reduction was not quantifiable. Post-treatment observations indicated that 

coyotes and other carnivores were not extirpated, 

even on treated areas. Carcass recovery indicated 

that mortality may be locally high where coyotes are 

traditional users of a treated area. Toxicity testing 

suggested that coyotes could easily acquire a lethal 

dose of squirrel carcasses, but because of their high 

tolerance levels, badgers (Taxidea taxus) and Golden 

Eagles (Aquila chrysatos) would seldom eat lethal 

amounts before carcass decomposition or removal by 

other species. Monitoring of rodent carcasses available aboveground showed that such carcasses were 

available to scavengers for less than two weeks after 

baiting. 

Maser, C., J. M. Trappe, and R. A. Nussbaum. 

1978. Fungal small mammal interrelationships with 

emphasis on Oregon coniferous forests. Ecology 

59(4):799-809. 

54 

Location: Oregon. 

Habitat: Various. 

Keywords: Food habits, hypogeous mycorrhizal fungi, 

mycorrhizal symbiosis, spore dispersal, rodent 

mycophagy. 

Abstract: Most higher plants have evolved with an 

obligatory symbiotic relationship with mycorrhizal 

fungi. Epigeous mycorrhizae formers have their 

spores dispersed by air currents, but hypogeous 

mycorrhizal fungi are dependent upon small mammals as primary vectors of spore dissemination. 

Mammalian mycophagists defecate within the coniferous forest ecosystem, spreading the viable spores 

necessary for survival and health 9f the conifers. As 

one unravels and begins to understand the interrelationships between small mammals mycophagists 

and mycorrhizal fungi, it becomes apparent that the 

various roles of small mammals in the coniferous 

forest ecosystem need to be reevaluated. One can no 

longer accept such simplistic solutions to timber management as poisoning forest rodents to "enhance" tree 

survival. One must consider the direct as well as the 

indirect costs and benefits of timber management 

decisions if one is to maintain balanced, healthy coniferous forests. 

Maser, Z., C. Maser, and J. M. Trappe. 1985. Food 

habits of the northern flying squirrel ( Glaucomys 

sabrinus) in Oregon. Canadian Journal of Zoology 

63:1084-1088. 

Location: Northern Oregon 

Habitat: Old-growth Douglas-fir, old-growth lodgepole pine, mixed conifer forests including grand fir, 

Engelmann spruce, and western larch; and some ponderosa pine forests. 

Keywords: Food habits, hypogeous fungi, mycophagy, 

mycorrhizal symbiosis, spore dispersal, stomach content analysis. 

Abstract: Digestive tracts of 91 northern flying 

squirrels (Glaucomys sabrinus) were analyzed for 

food items; 28 were from northwestern Oregon and 63 

from northeastern Oregon. Ninety percent or more of 

the ingested materials were fungi and lichens, including 20 genera ofhypogeous fungi. The northern flying 

squirrel, in using hypogeous fungi as a major food 

source, is an important nocturnal disperser of the 

spores. In Oregon coniferous forests, these fungi are 

obligatory ectomycorrhizal symbionts with the trees 

in which the squirrels live. 

Maser, C., Z. Maser, J.W. Witt, and G. Hunt. 1986. 

The northern flying squirrel: a mycophagist in southwestern Oregon. Canadian Journal of Zoology 

64:2086-2089. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
Location: Southwestern Oregon. 

Habitat: Douglas-fir/western hemlock/western red 

cedar. 

Keywords: Dietary specialist, fecal analysis, food 

habits, fungi, hypogeous sporocarps, mycophagy. 

Abstract: Fecal samples were collected over 27 months 

from the northern flying squirrel (Glaucomys 

sabrinus(Shaw)), a mycophagist in the Pacific Northwest portion of its range. Nine genera of hypogeous 

Basidiomycetes, 10 of hypogeous Ascomycetes, and 

one of hypogeous Zygomycetes were identified from 

fecal samples (hypogeous fungi fruit underground). 

The squirrel food habits generally paralleled the 

seasonal availability of the hypogeous fungi, but with 

notable exceptions. Our data demonstrate the functional diversity an individual species lends to its 

habitat when viewed in a functional context. 

McCracken, K. E. 1990. Microhabitat and dietary 

partitioning in three species of shrews at Yellow 

Bay, Montana. Master's Thesis, University of Montana, Missoula, Montana. 38 pp. 

Location: University of Montana, Biological Station, 

Yellow Bay, Flathead Lake, western Montana. 

Habitat: Mature grand fir forest. 

Keywords: Competition, food habits, logs, habitat 

use, mature forest, mesic, xeric. 

Abstract: Habitat use patterns and food habits of 

three species of shrews (vagrant shrew, cinereus shrew, 

and montane shrew) were analyzed in a grand fir 

(Abies grand is )/queencup beedlily ( Clintonia uniflora) 

habitat in northwestern Montana. Distribution of the 

three species differed significantly across mesic and 

xeric sites, with vagrant shrew captures being most 

numerous on the mesic site and cinereus shrew captures more numerous on the xeric site. The montane 

shrew, at its lower elevational range, was infrequently 

captured on both plots. Thirty-five live-trapped vagrant shrew and cinereus shrew were marked with 

phosphorescent dust and released at their site of 

capture. Mapping of individual's movements revealed 

no discernable differences between species, but the 

most conspicuous habitat component used by both 

was the space between fallen trees (decomposition 

classes 1-3) as runways. Microhabitat used by the 

three species was investigated using multivariate 

analysis of 15 trapsite characteristics. There were 

significant differences between vagrant shrew and 

cinereus shrew on five variables, and between vagrant 

shrew and montane shrew on one variable. These 

results suggest that vagrant shrew and cinereus shrew 

partition the space within the habitat at both large 

and small scales. Habitat segregation may be due to 

asymmetric competition between the two species, 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

involving interference competition, exploitative competition, or both. 

Summer foods of the three species (20 vagrant 

shrew, 10 cinereus shrew, and four montane shrew) 

were examined using stomach contents. Major foods 

in order by percent frequency were vagrant shrew: 

ants, true flies, beetles, and adult lepidopterans; 

cinereus shrew: ants, adult lepidopterans, beetles, 

and spiders; montane shrew: ants, spiders, true flies, 

and millipedes. No significant difference in prey 

items consumed was observed among the three species. These data indicate that, at the taxonomic level 

of Order, there is a high degree of overlap in foods 

among the three species. However, they could be 

separating food on the basis of prey size, foraging 

method, or at a lower taxonomic level. 

Medin, D. E. 1986. Small mammal responses to 

diameter-cut logging in an Idaho Douglas-fir forest. 

USDA Forest Service, Intermountain Research Station, Research Note, INT -362. 

Location: West-central Idaho. 

Habitat: Douglas-fir and ponderosa pine dominate 

with some grand fir lodgepole pine and Engelmann 

spruce. 

Keywords: Composition changes, diameter-cut logging, population changes. 

Abstract: Relative small mammal populations were 

estimated on logged and unlogged plots from 197 5 

(first year prelogging) through 1979 (third year postlogging) by using live-trapping and mark-recapture 

methods. Three species made up 93 percent of 698 

individual animals caught: deer mice (Peromyscus 

maniculatus), yellow-pine chipmunks (Tamias 

amoenus), and Gapper's red-backed voles (Clethrionomys gap peri). Deer mice populations were similar on 

both logged and unlogged plots. Numbers of yellowpine chipmunks increased on logged sites. Red-backed 

voles disappeared from the small mammal community 

after logging. Other species including the goldenmantled ground squirrel (Spermophilus lateralis) and 

shrews (Sorex spp.) were trapped irregularly and in 

smaller numbers. 

Medin, D. E., and G. D. Booth. 1989. Responses of 

birds and small mammals to single-tree selection 

logging in Idaho. USDA Forest Service, Intermountain Research Station, Research Paper, INT-408. 

Location: West-central Idaho. 

Habitat: Douglas-fir and ponderosa pine dominate 

with some grand fir lodgepole pine and Engelmann 

spruce. 

Keywords: Composition changes, population changes, 

single-tree selection logging. 

55 
Summary: Responses of birds and small mammals to 

logging depends on the cutting methods used and the 

degree to which forest stands are altered. This study 

examined short-term changes in the composition and 

abundance of small mammals and breeding birds 

following single-tree selection logging in an Idaho 

Douglas-fir forest. Populations of birds and mammals 

were estimated on a logged plot and on a nearby 

unlogged plot from 1975 (two years prelogging) to 

1979 (three years post-logging). Total numbers of 

breeding birds were relatively stable between years 

and between logged and unlogged plots. More pronounced patterns of response occurred in the populations making up the breeding bird communities. Species with positive numerical responses to the selection 

cut were olive-sided flycatcher, Swainson's thrush, 

yellow-rumped warbler, and chipping sparrow. Species with negative numerical responses to logging 

were red-breasted nuthatch and brown creeper. Fourteen other species showed little numerical response to 

the timber harvest. Birds that forage by gleaning 

the surface of the bark (timber gleaners) declined in 

number after logging. Foliage feeders, aerial-sally 

feeders, and timber drillers were about equally abundant before and after logging. The ground gleaning 

guild showed a slightly positive pattern of response. 

Of six nesting guilds represented only the secondary 

cavity nesters were adversely affected by logging. 

Bush and small tree nesters tended to increase after 

timber harvest. Deer mice, yellow-pine chipmunks, 

and boreal redback voles accounted for 93 percent of 

815 individual animals trapped during the study. 

Postlogging estimates of deer mice density were generally similar on both the logged and the unlogged 

plots. But when results were expressed as the mean 

number of individual animals trapped each year, significantly fewer deer mice were trapped on the logged 

plot. Numbers of yellow-pine chipmunks increased 

on logged sites; it was the most commonly trapped 

small mammal in postlogging environments. No significant difference was found in the number of redbacked voles trapped in the cut and uncut forest. 

Other species were trapped irregularly and in smaller 

numbers. 

Metzgar, L. H., Pearson, D. E., and P. Todd. 1990. 

Teller Wildlife Refuge wildlife assessment and recommendations. Wildlife Biology Program, University of Montana, Missoula Montana. 111 pp. 

Location: Western Montana, Teller Wildlife Refuge, 

Bitterroot Valley. 

Habitat: Riparian cottonwood (Populus tricocarpa) 

and ponderosa pine (Pinus ponderosa) and some upland grasslands. 

56 

Keywords: Habitat assessment, species inventory, 

management recommendations. 

Summary: This document presents the results of a 

wildlife inventory on the Teller Wildlife Refuge, near 

Corvallis, Montana. Management recommendations 

were made for wildlife habitat improvement in seven 

areas: habitat; fish and aquatics; waterfowl; nongame 

and upland game birds; small mammals; carnivores 

and fur bearers; deer. Includes species lists and maps. 

Morris, D. W.1984. Patterns of scale and habitat use 

in two temperate zone small mammal faunas. 

Canadian Journal of Zoology 62:1540-1547. 

Location: Rocky Mountains, south~rn Alberta, Point 

Pelee National Park, southern Ontario. 

Habitat: Clearcut to climax mature forest in white 

spruce, Douglas-fir, subalpine fir. 

Keywords: Clearcut, habitat use, macrohabitat, microhabitat, scale, succession. 

Abstract: Small mammals were livetrapped and 

habitat quantified in replicates of six macrohabitats 

in Alberta and in temporal replicates in four macrohabitats in Ontario, Canada. Similar patterns 

emerged in both locations. The relative abundances of 

small mammals depended upon macrohabitat; within 

macrohabitats, species differed significantly in microhabitat use. The patterns were dynamic and probably 

the result of habitat preferences instead of species 

interactions. Macrohabitat differences may in part be 

outcomes of microhabitat selection but are unlikely to 

be completely understood without superimposing 

colonization and extinction probabilities on habitat 

selection models. Field biologists must recognize both 

scales of habitat to interpret patterns of species 

distribution. 

Nordyke, K. A., and S. W. Buskirk. 1991. Southern 

red backed vole, Clethrionomys gapperi, populations in relation to stand succession and old growth 

character in the central Rocky Mountains. Canadian 

Field-Naturalist 105(3):330-334. 

Location: Southeastern Wyoming, Medicine Bow 

Mountains. 

Habitat: Lodgepole pine stands and Engelmann 

spruce/subalpine fir stands representing early-seral, 

mid-seral and old-growth conditions. 

Keywords: Log decay, old-growth indicator species, 

old-growth rating, successional stage. 

Abstract: The effects of old -growth character, microhabitat characteristics, and successional stage on the 

Southern Red-backed vole (Clethrionomys gapperi) 

were investigated in conifer forests of southeastern 

Wyoming in 1986 and 1987. Small mammals were 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
snap-trapped in Lodgepole Pine, mature spruce-fir, 

and old-growth spruce-fir habitat types. Vole abundance was greatest and body condition best in oldgrowth spruce-fir. Vole captures best fit a seconddegree polynomial model when regressed on old-growth 

rating in 1987; understory cover followed a similar 

pattern with rating. Abundance was positively correlated with understory cover both years, and because 

of this relationship and the binomial response ofboth 

of these to old-growth rating, understory cover may 

influence distribution of C. gap peri more than do other 

habitat features. Vole abundance was positively correlated with stage of decay of logs. 

Pattie, D. L. 1967. Dynamics of alpine small mammal 

populations. Ph.D. Dissertation, UniversityofMontana, Missoula, Montana. 103 pp. 

Location: Beartooth Pass, Montana-Wyoming 

boarder. 

Habitat: Krummholz whitebark pine and subalpine 

fir; alpine. 

Keywords: Activity patterns, demographics, habitat 

associations, home range, population density. 

Abstract: A study to determine characteristic of alpine populations of Peromyscus maniculatus, Microtus montanus and Arvicola richardsoni was centered 

near Beartooth Pass on the Montana-Wyoming border 

at an elevation of 10,500 ft. A 3-day visit in late 

December 1963 and another during late August 1965 

supplemented information collected during 350 days 

spent in the field during the summers of 1961-1964. 

Data were collected by both snap and live trapping. 

Numbers and species of all mammals trapped are 

listed; a general description of the communities, geology, and topology of the plateau is given. Characteristics described for the three species include estimated 

of density and movement, home range, activity patterns, and sex ratios. Habitat distribution of the species, reproductive patterns, and mortality factors are 

also considered. Similar information is given for other 

alpine mammals if sufficient data were available. The 

absence of cyclic -population fluctuations was considered in the light of both extrinsic and intrinsic 

factors. It is postulated that the absence of cycles in the 

alpine is related to extrinsic factors that prevent 

buildup of populations to levels where intrinsic factors such as stress may operate to limit reproduction 

and thus produce a decline in numbers. 

Pearson, D. E. 1994. Habitat use by the southern red 

backed vole ( Clethrionomys gap peri): response of an 

old-growth associated species to succession. Master's 

Thesis, University ofMontana, Missoula, Montana. 

P. 105. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

Location: Lake McDonald Valley, western Montana, 

Glacier National Park. 

Habitat: Western red-ceder/western hemlock forests 

dominated by lodgepole pine in the youngest stands. 

Includes four age classes: 65, 138, 256 and 457 years. 

Keywords: Competition, habitat generalist, habitat 

specialist, macrohabitat selection, microhabitat selection, old-growth associate, successional stages. 

Abstract: Populations of the southern red-backed 

vole (Clethrionomys gapperi) and deer mouse 

(Peromyscus maniculatus) were examined in four successional stages (65, 138, 256, 457 years) in cedarhemlock (Thuja plicata-Tsuga heterophylla) forests of 

Glacier National Park to d.etermine macrohabitat 

selection among stands and microhabitat selection 

within stands. Abundance of Clethrionomys gapperi 

and Peromyscus maniculatus increased with increasing stand age. Microhabitat use differed from available habitat for both species within most age classes 

but was not consistent for either species among age 

classes. The inconsistency in microhabitat use among 

successional stages and lack of correspondence between 

micro- and macrohabitat variables selected leads to 

the conclusion that macrohabitat associations determine microhabitat selection. In order to properly assess habitat use at either scale, the difference between 

scales must be addressed in the design and analysis of 

habitat studies. Peromyscus maniculatus behaved as 

a generalist at the macrohabitat scale but exhibited 

stronger microhabitat selection than did C. gapperi. 

P. maniculatus may exhibit "habitat switching" and 

respond to local site conditions by developing search 

images that manifest themselves as distinctive foraging patterns at the microhabitat scale. Such behavior 

would render P. maniculatus a potentially formidable 

competitor for resources and explain its tenacity for a 

wide variety ofhabitats. Clethrionomys gap peri exhibits a strong positive linear relationship with stand 

age and old-growth conditions near the forest floor. 

If monitored in conjunction with other species such 

as the pine marten (M artes americana), pile a ted woodpeeker (Dryocopus pileatus) and barred owl (Strix 

asia), C. gap peri could contribute significantly to an 

"indicator guild" for identifying and monitoring the 

old-growth condition. Fluorescent pigment tracking 

and live trapping were compared to determine microhabitat use by Clethrionomys gap peri. The two methods generally agreed, but fluorescent pigment tracking 

may allow more sensitive analyses of microhabitat 

use. 

Pearson, D. E. 1991. The northern bog lemming in 

Montana and the contiguous United States: distribution, ecology, and relict species theory. Senior 

Thesis, University ofMontana, Missoula, Montana. 

33 pp. 

57 
Location: Western Montana. 

Habitat: Bogs, fens and wet meadows. 

Keywords: Bog lemming survey, habitat associations, literature review, sensitive species, sphagnum 

bogs. 

Abstract: The northern bog lemming is a rare mammal in the contiguous United States. This paper presents results from a distributional study of the species 

in Montana. Results from a literature review of trapping data from the contiguous United States are also 

presented. Additionally, the northern bog lemming's 

status with regard to relict species theory is examined. 

Ramirez, P. Jr., and M. Hornocker. 1981. Small 

mammal populations in different-aged clearcuts 

in northwest Montana. Journal of Mammalogy 

62(2):400-403. 

Location: Northwest Montana, Sullivan and 

Quintonkon Creek drainages of the South Fork Flathead River. 

Habitat: Subalpine fir-clintonia and subalpine firwoodrush habitat types. 

Keywords: Clearcut, habitat associations, uncut forest, small mammal abundance. 

Summary: Small mammals were sampled in clearcut 

and uncut stands of Abies lasiocarpa-Clintonia uniflora and Abies lasiocarpa-Luzula hitchcockii habitat types using snaptraps for all but Spermophilus 

columbian us, for which wiremesh traps were used. 

Peromyscus maniculatus densities were higher in 

5-year-old clearcuts than in older clearcuts or uncut 

forest. Clethrionomys gapperi densities were highest 

in Abies-Clintonia and Abies-Luzula uncut forests 

than in clearcuts. Spermophilus columbianus were 

most abundant in clearcuts of all ages (5-15 years old). 

Raphael, M. G. 1988. Habitat associations of small 

mammals in a subalpine forest, southeastern 

Wyoming. Pp. 359 - 367. In Management of amphibians, reptiles and small mammals in North 

America. Symposium, Flagstaff, AZ. 

Location: Southcentral Wyoming. 

Habitat: Lodgepole pine and Engelmann spruce-subalpine fir. 

Keywords: Ecological indicator, habitat associations, 

old-growth forest. 

Abstract: Mammal capture rates were greatest at 

sites with mature timber and other old-growth attributes. Shrews (both dusky (Sorex monticolus) and 

masked (S. cinereus)) and southern red-backed voles 

( Clethrionomys gap peri) were much more abundant at 

sites dominated by spruce or fir compared to dryer 

sites dominated by lodgepole pine. Deer mice 

(Peromyscus maniculatus), in contrast, were most 

58 

abundant on dryer pine-dominated sites. The southern red-backed vole, because of its high abundance 

and strong association with mature forest, is a good 

ecological indicator of late seral conditions for forest 

planning purposes. 

Reichel, J.D., and S. G. Beckstrom. 1994. Northern bog lemming survey. A report to the USDA 

Forest Service, Kootenai National Forest, Flathead 

National Forest, and Lewis and Clark National 

Forest. Montana Natural Heritage Program, 

Helena, Montana. P. 87. 

Location: Western Montana. 

Habitat: Bogs, fens and wet meadpws. 

Keywords: Annotated bibliography, bog lemming survey, bogs, moss mats, sensitive species. 

Abstract: During the 1993 field season we surveyed 

for small mammals at 30 sites, catching northern bog 

lemmings at five new sites. One site, Wood Creek on 

the Rocky Mountain Ranger District, Lewis and Clark 

National Forest, is the eastern-most site known in 

Montana and 90 km from the nearest previously 

known site. Three sites on the Kootenai National 

Forest were in the Sunday Creek drainage, 1-6 km 

from the site discovered there in 1992. The last new 

site, also in the Kootenai National Forest, was found 

at Cody Lake, 32 km from the nearest known site. 

Despite surveys at 5 sites with apparently goodexcellent habitat on the Flathead National Forest, no 

new lemming sites were found there. The total number 

of known bog lemming sites in Montana is 17, the 

most sites in any of the lower 48 states. All sites found 

during 1993 had moss mats at or near the trap location. Known sites in Montana range in size from one to 

approximately 340 acres. The habitat predictor for 

potential northern bog lemmings sites in Montana is 

the presence of large, thick moss mats, particularly 

sphagnum moss. More sites with apparently good 

quality habitat were trapped unsuccessfully in 1993 

than in 1992; whether lemmings are actually present 

at some or all of those sites is unknown. 

Reichel, J.D., and S. G. Beckstrom. 1993. Northern bog lemming survey 1992. A report to the USDA 

Forest Service, Kootenai National Forest. Montana 

Nat ural Heritage Program, Helena, Montana. 

Location: Western Montana. 

Habitat: Bogs, fens and wet meadows. 

Keywords: Bog lemming survey, bogs, management 

recommendations, moss mats, sensitive species. 

Abstract: This document provides a preliminary report on results from a survey for bog lemmings 

conducted in western Montana by the MontanaN atural Heritage Program. Reichel and Beckstrom report 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
on five new sites for the northern bog lemming in 

Montana. These sites were Hawkins Pond, Sunday 

Creek, and Bowen Creek in northwest Montana, and 

Meadow Creek and Maybee Meadows in southwestern 

Montana. The Meadow Creek site is on the BNF. The 

Maybee Meadows site is the southern-most extent of 

the northern bog lemming's range in the western US. 

The authors discuss the potential importance of 

sphagnum mats in bog-like habitats and provide management recommendations for protecting this rare 

microtine. 

Roemer, D. M. 1994. Results of field surveys for 

bats on the Kootenai National Forest and the Lolo 

National Forest of western Montana, 1993. MontanaN atural Heritage Program, Helena, Montana. 

19 pp. 

Location: Western Montana, Kootenai and Lolo National Forests. 

Habitat: Primarily moist forests. 

Keywords: Bats, bat detectors, echolocation, mist 

netting, survey. 

Summary: This report documents the findings of 

field investigations into the relative abundance and 

distribution of bats on the Kootenai National Forest 

and parts of the Lolo National Forest of western 

Montana from May 15 to September 28, 1993. Two 

primary methods of investigation of species composition and abundance were used. Bat echolocation calls 

were monitored along selected transect routes beginning at sunset to record the relative abundance and 

activity patterns of bats. Mist nests were deployed 

across creeks, roads, trails, and adits to capture bats, 

providing the most reliable means for documenting 

species presence, and providing information of age, 

sex, and reproductive status. A total of 123 bats representing eight species were captured in the study area. 

Bats of the genus Myotis accounted for 91 percent of 

all captures. M. lucifugus was captured most frequently (48 percent), followed by M. californicus (15 

percent), M. evotis (13 percent), M. volans (8 percent), 

Lasionycteris noctivagans (7 percent), and M. ciliolabrum (7 percent). One specimen each of Plecotus townsendii and Lasiurus cinereus were captured, comprising less than one percent of the total capture. Relative 

bat abundance varied greatly between 24 sites monitored during the study. High levels of bat activity 

were found at Camp 32 (74 passeslhr), Upper Fortine 

Creek (72 passeslhr), and Trout Creek (60 passeslhr). 

Sites demonstrating the most foraging activity as 

measured by feeding buzzes per hour were Camp 32 

(n=29), Big Creek (n=14), and Bull Lake (n=13). The 

mean index of bat activity at the 24 transect locations was 33.5 = 8.9 passes per hour, and 6.3 = 2. 7 

feeding buzzes per hour (.X= 0.025). Bats were regularly 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

encountered foraging over roads, creeks, and ponds in 

the study area. Of 1,031 bat passes detected at 24 

transect locations, 19 percent (n=196) were attempting to capture prey. Foraging activity was highest at 

Camp 32 where 43 percent of bats passes contained a 

feeding buzz. Foraging bats were absent at three sites 

in the study area but comprised at least 8 percent of 

all bat passes at every other site. Two adits investigated during this study were utilized by bats as night 

roosts. Myotis evotis were captured at the entrances 

of two adits on the Superior Ranger District. The Trout 

creek adits, located on the west side of Trout Creek at 

approximately 3800' and 4100' elevation, were visited 

by male and female M. evotis on 13 July. The lower 

adit contained bat guano and culled moth wings. Only 

three juvenile bats (2 percent) were captured during 

the study-two male M. lucifugus at Lower Fortine 

Creek on 29 August, and one female M. volans at Rock 

Creekon27 September. Females comprised 62 of120 

adults captured in mist nets (52 percent). Lactating 

M. Lucifugus, M. californicus, M. ciliolabrum, and 

M. evotis were captured during the study between 15 

July and 1 September. Lactating females represented 

7 percent of the total bats captured, and 13 percent of 

adult female bats captured. During the study, 24 

percent of ~.dult female bats captured were classified 

as either lactating (n:::8), gravid (n=6), or postpartum 

(n=l). The observed low fecundity is likely due to the 

cold and wet weather experienced during the study. 

Information needs for the effective management ofbat 

populations include knowledge of distribution, population status, and habitat requirements. Echolocation 

monitoring and mist-netting can provide much-needed 

information that is the first step toward protecting bat 

habitat. 

Rosenberg, D. K., and R. G. Anthony. 1992. Characteristics of northern flying squirrel populations 

in young second- and old-growth forests in western 

Oregon. Canadian Journal of Zoology 70:161-166. 

Location: Western Oregon. 

Habitat: Second-growth and old-growth Douglas-fir 

forest in the Willamette National Forest on the west 

slope of the Cascade Mountains. 

Keywords: Demographics, density, forest management, succession. 

Abstract: We compared density, sex-ratio, body 

mass, and annual recapture rate of northern flying 

squirrels (Glaucomys sabrinus) populations in secondgrowth and old-growth Douglas-fir (Pseudotsuga menziesii) stands in the Oregon Cascade Range. Densities 

averaged 2.0 and 2.3 squirrels/ha in second- and oldgrowth stands, respectively. Although densities varied between years within stands, average densities 

were similar between years. Body mass and annual 

59 
recapture rate were similar between stand-age classes, 

although a higher proportion of females was recaptured in subsequent years in second-growth than in 

old-growth stands. Similarly there was a higher proportion of females than males in second-growth but 

not in old-growth stands. Squirrel densities were not 

correlated with habitat characteristics; we concluded 

that flying squirrels may be habitat generalists, and 

not a species associated with old-growth stands, as 

was previously hypothesized. We suggest that studies 

be carried out with radiotelemetry to more accurately 

assess the habitat associations of this species. 

Rosenberg, D. K., K.A. Swindle, andR. G. Anthony. 

Habitat associations of California red-backed 

voles in young and old-growth forests in western 

Washington. Northwest Science 68(4): 266-271. 

Location: Western Oregon. 

Habitat: Douglas-fir, western hemlock stands 30-

60 yr and >400 yr. 

Keywords: Early seral, habitat associations, old 

growth, succession. 

Abstract: Because of the reduction of old-growth 

forests in the Pacific Northwest, and the controversy 

over timber management practices, patterns of animal abundance in young and old-growth forests have 

gained attention. Results from previous studies on 

California red-backed voles (Clethrionomys californicus), however, have been inconsistent; unmanaged 

young stands were reported to have similar abundance of California red-backed voles as old-growth 

stands, while other studies suggested that numbers 

are higher in older stands. We compared California 

red-backed vole abundance in five young (30-60 years 

old) and five old-growth (>400 years old) Douglas-fir 

(Pseudotsuga menziesii) stands in the central Oregon 

Cascade Range during spring 1988-1991. The average 

number of red-backed voles captured was consistently 

higher in old-growth stands ( x ± SE, 8.4 ± 1.9) than in 

young stands (2.0 ± 0.8) during the five years of the 

study; 80 percent of the voles captured in the five 

young stands were from one, unmanaged fireregenerated stand. Our results support hypotheses 

of lower abundance of California red-backed voles in 

managed young forests than in unmanaged older 

forests. Providing components of old-growth forests 

such as deep organic soil depths, residual large trees 

and snags, and coarse woody debris in managed 

young stands will likely increase their potential as 

suitable habitat for California red-backed voles. 

Scrivner, J. H., and H. D. Smith. 1984. Relative 

abundance of small mammals in four successional 

stages of spruce fir in Idaho. Northwest Science 

58(3):171-176. 

60 

Location: Idaho, Pierce Ranger District, Clearwater 

National Forest. 

Habitat: Grand fir; four stand ages (1-10, 11-39, 40-

79, 80+ years post-disturbance). 

Keywords: Habitat associations, small mammal abundance, successional stages. 

Abstract: This paper discusses the relative abundance of four small mammal species in successional 

stages (1-10, 11-39, 40-79, and 80+ years following 

disturbance) of spruce-fir forest in Idaho. Species 

evaluatedincludePeromyscus maniculatus,Eutamias 

ruficaudus, Zap us princeps, and Clethrionomys 

gapperi. For the specific study sites we investigated, 

intraspecific comparisons indicated P. maniculatus 

increased with succession; E. ruficaudus abundance 

varied but was generally most common in midsuccessional stages; Z. princeps preferred willow -alder 

thickets within mid-successional stages; and C. gap peri 

was most abundant in the mature forest. 

Shepherd, J. F.1994. Initial response of small mammals to new forestry and overstory removal timber 

harvests. Master's Thesis, University of Montana, 

Missoula, Montana. 84 pp. 

Location: Western Montana, Swan Valley. 

Habitat: Mature Douglas-fir. 

Keywords: Habitat selection, new forestry, overstory removal, small mammal abundance, timber 

management. 

Abstract: This study examined the initial response 

of small mammals to new forestry and overstory removal timber harvest methods as part of a larger 

biodiversity project. Four sets of experimental plots 

were located within 13 km of each other in the Swan 

Valley of western Montana. Each set of plots contained an uncut control and two treatment types: new 

forestry and overstory removal. Small mammals were 

trapped on all12 experimental plots during June and 

August of the pre- and post-harvest field seasons. 

Vegetation was sampled on each trapping grid in 

August of each field season. Analysis of pre-treatment 

vegetation showed no significant difference among 

understory or overstory variables. No significant 

change in vegetative cover or density of small trees 

was found in the post-treatment season. Density of 

large trees was significantly different between the 

controls and treatments in the post-treatment season. 

Although no significant treatment effect on the abundance of any small mammal species was found, trends 

in abundance were apparent. The red-tailed chipmunk (Tamias ruficaudus) appeared to decline in 

response to harvest while the yellow-pine chipmunk 

(Tamiasamoenus)andred-backedvole(Clethrionomys 

gapperi) increased. Further analysis was conducted 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
to determine habitat associations for the most numerous small mammal species in the pre- and post-harvest seasons. Small mammal trapping in riparian 

buffers examined the initial response of small mammals to overstory removal timber harvest adjacent to 

riparian areas. Differences in small mammal abundances for riparian traps rows (A and B) versus upland 

trap rows (C through E) and harvested versus unharvested plots were statistically tested. Numbers of 

individuals caught for all species combined and for the 

red-backed vole (Clethrionomys gapperi) were significantly higher than expected in riparian rows of the 

overstory removal grids and upland rows of the control grids. Distribution of the meadow vole (Microtus 

pennsylvanicus) was not significantly different from 

random. 

Spencer, A. W., and D. Pettus. 1966. Habitat preferences of five sympatric species of long-tailed 

shrews. Ecology 47(4):677-683. 

Location: Larimer county, Colorado. 

Habitat: Sedge marsh, subalpine forest (lodgepole 

pine, spruce, and fir), and clearcut forest at 9,700 feet. 

Keywords: Habitat association, population estimates, 

shrews, clearcutting 

Abstract: Long-tailed shrews of five species were 

captured throughout four years at a single 60-acre site 

at 9,700 ft elevation in western Larimer County, 

Colorado. Interspecific differences were significant in 

the proportions of captures in three main habitats: 

sedge marsh, subalpine forest, and clearcut forest. All 

species except one, So rex palustris, were captured in 

all three types, however. S. palustris was taken only 

adjacent to bodies of water. Sorex cinereus and Sorex 

vagrans were captured with the greatest relative frequency in marsh situations. The frequency of captures 

of the former species in the clearcut habitat was 

proportionally lower than for the latter species. Sorex 

nanus and Microsorex hoyi were taken with high 

frequency in the forest. S. nanus was taken with the 

greatest frequency of any species in the clearcut area 

and also at the greatest mean distance from permanent surface water. M. hoyi was captured more frequently than any other species at sites intermediate 

in character between marsh and forest. It was captured much less frequently in the clearcut area and 

more frequently in the marsh than S. nanus but less 

frequently in the marsh than either S. cinereus or S. 

vagrans. Indices of relative abundance of S. cinereus 

and S. vagrans synchronously declined sharply in 

1963 from high points in 1962 but increased again in 

1964. Indices for S. nanus and M. hoyi remained 

approximately uniform throughout the four years. 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

Stoecker, R. E. 1967. A population study of five 

species of small rodents in the Bridger Mountains of 

Montana. Master's Thesis, Montana State University, Bozeman, Montana. 32 pp. 

Location: Bridger Mountains, southwestern Montana. 

Habitat: Grass-forb, sedge and clove communities 

within a Douglas-fir clearcut at 6100 feet. 

Keywords: Habitat association, home r~nge, population estimates. 

Abstract: Beginning in June 1966, a one year study 

of five species of rodents was conducted in the Bridger 

Mountains of southwestern Montana. Live trapping 

was performed each month except during winter 

(December through April). The main objectives were 

to study the home ranges, population sizes, and habitat preferences of the following species: Microtus 

montanus, M. pennsylvanicus, Peromyscus maniculatus, Zapus princeps and Clethrionomys gapperi. 

The vegetation on the 9.6 acre study plot was quantitatively sampled using 1.5 x 3 foot quadrats. Grassforb, sedge, and clover communities were described. 

M. montanus and M. pennsylvanicus were lumped 

in the analysis because they could not be distinguished 

in the field. Mean home range sizes for 29 males and 

37 females were 0.32 and 0.18 acre respectively. A 

marked population fluctuation was noted, and a peak 

density of 10.3 Microtus per acre was estimated for 

early August. The breeding season was from July 

through September. Winter survival was estimated to 

be 20.6 percent. The overall sex ratio was 1:1, but 

significantly more females were present in August 

and significantly more males were present in October 

and November. The grass-forb community was the 

preferred habitat. 

Mean home range sizes for five male and seven 

female Peromyscus were 0.82 and 0.52 acres, but 

differences between sexes were not significant. The 

population remained small with generally from five to 

eight individuals present. The more xeric areas were 

the preferred habitats. 

The mean home range of eight Zap us was 0.40 acres. 

Estimates of numbers were not made because few 

recaptures occurred. A total of 55 individuals was 

captured. The last capture of 1966 occurred on August 

18; the earliest capture occurred on May 23, 1967. 

The possibility of animals moving away from the 

study plot and returning at a later date was discussed. 

The more mesic areas were the preferred habitats. 

The mean home range of four Clethrionomys was 

0.19 acre. The largest number ofindividuals known to 

be present on the study plot was five during September. Old log piles were the preferred habitats. 

61 
Tallmon, D. and L. S. Mills. 1994. Use oflogs within 

home ranges of California red-backed voles on a 

remnant of forest. Journal of Mammalogy 75(1): 

97-101. 

Location: Klamath Mountains, Siskiyou National 

Forest, southwestern Oregon. 

Habitat: Old-growth Douglas-fir. 

Keywords: Coarse woody debris, home range, logs, 

microhabitat use, radiotelemetry. 

Abstract: We used radiotelemetry to investigate patterns of space use of the California red-backed vole 

(Clethrionomys californicus) on a remnant forest in 

southwestern Oregon. We radiotracked four voles and 

mapped the locations of logs of varying decay classes 

within the home range of each vole. Of the collective 

locations of voles, 98 percent coincided with downed 

logs even though logs covered only 7 percent of the 

areas of estimated home ranges. Furthermore, voles 

used logs in later stages of decay significantly more 

often than logs in earlier stages of decay. This high 

use of decayed logs suggests that decayed logs are a 

critical component of suitable habitat for voles. 

Ure, D. C., and C. Maser. 1982. Mycophagy of redbacked voles in Oregon and Washington. Canadian 

Journal of Zoology 60:3307-3315. 

Location: Oregon and Washington. 

Habitat: Various coniferous forests. 

Keywords: Elevation, hypogeous, food habits, fungi, 

mycophagy, mycorrhizal. 

Abstract: We analyzed stomach contents from two 

subspecies of Clethrionomys californicus and three 

subspecies of southern red-backed vole from coniferous forests of Oregon and western Washington. Seasonal diets were determined for each subspecies of 

C. californicus. Major foods eaten were the fruiting 

bodies of hypogeous ectomycorrhizal fungi, predominantly Gastromycetes, and fruiticose lichens, regardless of season. Fungus consumption partially depended 

on availability. When fungi became scarce, lichens 

were substituted. Other foods were important only in 

winter in Cascade Range. Clethrionomys gap peri from 

Washington consumed large quantities of conifer seed 

and green plant parts in midautumn. These materials 

were a small part of the diets of Oregon red-backed 

voles in midautumn, but this may relate to localized 

small seed crops. Dependence on ectomycorrhizal 

fungi by western red-backed voles probably accounts 

for the latter's disappearance from deforested sites. 

Walters, B. B. 1991. Small mammals in subalpine 

old-growth forest and clearcuts. Northwest Science 

65(1):27 -31. 

Location: British Columbia. 

62 

Habitat: Old-growth hemlock/fir, clearcut burned, 

clearcut unburned. 

Keywords: Burn, clearcut, old growth, population 

estimates. 

Abstract: This study examined the differences between small mammal populations in a subalpine 

old-growth forest and adjacent burned and unburned 

clearcuts. Small mammals were lived trapped, 

marked, and recaptured weekly during July and 

August of 1987. Deer mice (Peromyscus maniculatus) 

and chipmunks (Tamias amoenus) were most abundantin the two clearcuts; shrews (Sorex cinereus)were 

common in all three habitats; and red-backed voles 

(Clethrionomys gapperi) were com:r;,non in all but the 

burned clearcut and the forest edge adjacent to the 

unburned clearcut. This latter finding may reflect an 

"edge effect." There were more adult female deer mice 

and a smaller ratio of juvenile to adult female deer 

mice in the forest than in the clearcuts. This study 

suggests that the general effects of clearcutting. on 

small mammals are similar in lowland and subalpine 

forests, and that edge effects are an important consideration for future research, particularly in old-growth 

forests. 

Worthington, David J. 1991. Abundance, distribution and sexual segregation of bats in the Pryor 

Mountains ' of South Central Montana. Masters ' 

Thesis, University ofMontana, Missoula, Montana. 

40 pp. 

Location: Prior Mountains, southcentral Montana. 

Habitat: Arid desert, caves, Douglas-fir. 

Keywords: Bats, caves, demographics, habitat use, 

mist netting, roosts, sex ratios. 

Abstract: Bat occurrence in the Pryor Mountains of 

south-central Montana was examined between June 

and September in 1989 and 1990. A total of 1,319 

individuals representing 10 species were captured. 

Bats were captured at ponds, springs, and at the 

entrance offive caves. Numbers ofbats captured were 

generally greater at the caves. Capture success was 

considerably lower at water sources, but a greater 

diversity of species was noted at these sites. While 

several of the species captured occurred throughout 

the area, the spotted bat, Euderma maculatum, the 

pallid bat, Antrozous pallidus, and the silver-haired 

bat, Lasionycteris noctivagans, were more restricted 

in distribution. Two specimens of the spotted bat, 

Euderma maculatum, were captured, representing 

the first spotted bats captured in Montana since 

1949. Spotted bats were observed throughout the 

eastern portion of the study area. Townsend's Bigeared bat, Plecotus Townsendii, was previously 

known only from winter records in the Pryor Mountains· nine individuals of Antrozous pallidus were ' 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 
captured, the first specimens observed since the species was first documented in Montana in 1979. Several of the species ofbats found in the Pryor Mountains 

were captured in numbers significantly different 

from an expected 1:1 sex ratio. This was especially 

true at the caves, where males of most species greatly 

out numbered females, suggesting that males and 

females may be differentially utilizing habitat. The 

generally low temperatures of the caves investigated 

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-25. 1999 

in this study may preclude their summer use by many 

female bats, especially pregnant or lactating individuals, which require higher roost temperatures to 

maintain the higher metabolic rate necessary for 

raising young. Bat activity at the caves, especially 

Mystery Cave, indicated that these caves provide 

important summer roosting habitat. Additionally, 

these caves possess characteristics which may make 

them important as hibernacula. 

63 
The Rocky Mountain Research Station develops scientific information and technology to improve management, protection, and use of

the forests and rangelands. Research is designed to meet the needs

of National Forest managers, Federal and State agencies, public and

private organizations, academic institutions, industry, and individuals.

Studies accelerate solutions to problems involving ecosystems,

range, forests, water, recreation, fire, resource inventory, land reclamation, community sustainability, forest engineering technology,

multiple use economics, wildlife and fish habitat, and forest insects

and diseases. Studies are conducted cooperatively, and applications

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Research Locations

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*Station Headquarters, 240 West Prospect Road, Fort Collins, CO 80526

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