Forest Service

Pacific Northwest

Research Station

in Douglas-Fir Forests

General Technical Report

PNW-GTR-276

November 1991 Andrew B. Carey

5z; 3. _ _~. -zzz~

United States

Department. of

Agriculture i

+ 1l.d.

The Biology of Arboreal Rodents
Biology and Management

of Old-Growth Forests

Mark H. Huff, Richard S. Holthausen, and

Keith B. Aubry, Technical Coordinators

The Biology of Arboreal Rodents

in Douglas-Fir Forests

Andrew B. Carey

Principal Research Biologist

USDA Forest Service

Pacific Northwest Research Station

3625 93d Avenue SW

Olympia, Washington 98502

U.S. Department of Agriculture, Forest Service

Pacific Northwest Research Station

Portland, Oregon

General Technical Report PNW-GTR-276

November 1991
Abstract Carey, Andrew B. 1991. The biology of arboreal rodents in Douglas-fir forests.

Gen.Tech. Rep. PNW-GTR-276. Portland, OR: U.S. Department of Agriculture,

Forest Service, Pacific Northwest Research Station. 46 p. (Huff, Mark H.;

Holthausen, Richard S.; Aubry, Keith B., tech. coords.; Biology and management of old-growth forests).

Arboreal rodents in Douglas-fir forests west of the Cascade crest in Oregon and

Washington include (listed in decreasing order of dependence on trees) red tree

vole (Phenacomys longicaucfus), northern flying squirrel (Glaucomys sabrinus),

Douglas’ squirrel (Tamiasciurus douglasii), dusky-footed woodrat (Neotoma

fuscipes), bushy-tailed woodrat (Neotoma cinerea), and Townsend’s chipmunk

(Tamias townsendi). The arboreal rodents constitute an ecological communitya group of species that interact and influence one another’s pattern of abundance

and use of resources. All but the Douglas’ squirrel and Townsend’s chipmunk are

important prey of the spotted owl (Strix occidentalis). The arboreal squirrels are

mycophagists and have important functions in ecosystem processes. Individual

species exist in many habitats, but the arboreal rodent community reaches its

highest diversity and abundance in old-growth forests. The rodents are not evenly

distributed, however, across the Pacific Northwest; maximum diversity and

abundance in the community occurs in mixed-conifer, old-growth forests that

contain streams. Although the species differ in life histories and ecologies, all seem

sensitive to timber harvesting because of both elimination of habitat and creation of

barriers to dispersal.

Keywords: Bushy-tailed woodrat, Douglas’ squirrel, dusky-footed woodrat,

northern flying squirrel, old growth, red tree vole, Townsend’s chipmunk, Oregon,

Washington.
Preface Information about old-growth Douglas-fir forests and the wildlife species associated

with them is critical to forest managers in the Pacific Northwest. Management of

these forests has become a major public policy issue. Extremely high levels of

concern have been expressed for a broad variety of values associated with

old-growth forests. These include ecological, social, and religious values as well as

commodity values derived from timber production. Forest managers are faced with

a need to devise balanced strategies that retain all these values at levels acceptable to the public and consistent with the National Forest Management Act.

Forest acreage in the “old-growth” stage of development has declined rapidly in

the Pacific Northwest during the past three decades. This has caused increasing

concern about species’ associations with old forests and maintenance of viable

populations for those species most closely associated. Decisionmakers need to

know which species show strong associations with old-growth forests, and understand the ecological requirements of those species. They need methods and tools

to effectively manage and monitor these species and their habitat.

The purpose of this series of publications on the “Biology and Management of OldGrowth Forests” is to summarize the life history characteristics and habitat relations

of species showing strong associations with old-growth forests in Washington,

Oregon, and northern California, and to suggest options for their management.

University and Federal scientists who collaborated in the USDA Forest Service,

Pacific Northwest Research Station old-growth research program have produced a

comprehensive list of associated species. Their technical research results were

presented at a symposium in March 1989 in Portland, Oregon, and published in a

book entitled “Wildlife and Vegetation of Unmanaged Douglas-fir Forests.” We offer

this series of management publications as a sequel to their research and to address

other issues surrounding the management of late-seral ecosystems. The series is

funded by the Wildlife Habitat Relationships Program, Pacific Northwest Region,

USDA Forest Service. Our goal is to provide timely information to managers so they

can make well-informed decisions about the management of old-growth forests.

Mark H. Huff

Richard S. Holthausen

Keith B. Aubry
1 introduction

6 Species Descriptions and Habits

6 Red Tree Vole

9 Northern Flying Squirrel

13 Douglas’ Squirrel

18 Dusky-Footed Woodrat

24 Bushy-Tailed Woodrat

29 Townsend’s Chipmunk

32 Maintenance of the Arboreal Rodent Community

36 Scientific Names

38 Literature Cited

46 Appendix
Intmductisn The word “arboreal” means inhabiting or frequenting trees. Few mammals confine 

their activities to trees, and many mammals occasionally climb trees. We consider 

rodents to be arboreal when their nests are usually in trees, when they routinely 

forage in trees, or when they use trees as avenues for travel. Pacific Northwest 

rodents show a wide range of dependence on trees; the extent of dependence on 

trees of six species is listed in table 1. The geographic ranges of these species are 

shown in figure 1. West of the Cascade crest, there are three highly arboreal rodents: 

Douglas’ squirrel, northern flying squirrel, and red tree vole. The Douglas’ squirrel 

nests, forages, and travels among trees and travels and forages on the ground. The 

Douglas’ squirrel changes its foraging emphasis with season, thereby reflecting the 

abundance of cones and fungi. The flying squirrel nests in trees, glides from tree to 

tree, runs and climbs among boles and branches, travels on the ground, and forages 

primarily on the ground for fungi and secondarily in trees for lichens. The red tree vole 

rarely ventures onto the ground, unless harassed in a tree. When harassed, the vole 

often will escape to the ground by running down the tree or by deliberate free falling 

(Maser and others 1981 b). The red squirrel replaces the Douglas’ squirrel in forested 

environments east of the Cascade crest and north of Washington and is similar to the 

Douglas’ squirrel in habits. The western gray squirrel usually is not found in coniferous 

forests and prefers deciduous and evergreen hardwood forests. 

Table l-Degree of dependence on trees of selected species of 

rodents in the Douglas-fir forests of the Pacific Northwesta 

Speciesb 

Activity RTVO FLSQ DOSQ DFWR BTWR TOCH 

Travel: 

Ground l tt t l * l *+ 

Trees,shwbs **** tt* tt *** l * * 

Nest: 

Ground l l * l * l ** 

Trees,&.,,,,bs ttt* tttt l ** l t l t l 

Forage: 

Ground l ** *it l * l * l * 

,-rees,s,,rubs l *et l tt ** hh *C 

Arborealityc 12 8 7 7 6 4 

a Ratings are subjective. 

b’ Occasional, l * common, *** dominant, **** almost exclusive; RTVO, red tree vole; 

FLSQ, northern flying squirrel; DOSQ, Douglas’ squirrel; DFWR, dusky-footed 

woodrat; BTWR, bushy-tailed woodrat; TOCH, Townsend’s chipmunk. 

CSum of arboreal asterisks. 
1 11Y

Dusky-footed woodrat (Neotoma

fuscipes)

115 1 00

N.c. fusca,

N.c. @/al

Bushy-tailed woodrat (Neotoma cinerea)

Townsend’s 

townsendii)

Figure l-The geographic ranges of the arboreal rodents commonly found in Douglas-fir forests of the Pacific Northwest.
Douglas’ squirrel (Tamiasciufus douglasii)

Northern flying squirrel (Glaucomys sabrinus)

5

4

0

4

134

Red tree vole (Phenacomys longicaudas)

Figure l-Continued

w
The dusky-footed woodrat, the bushy-tailed woodrat, and Townsend’s chipmunk are

less arboreal than the tree vole, flying squirrel, and Douglas’ squirrel. The dusky-footed

woodrat builds nests of sticks in trees (up to 50 feet or more aboveground) and lodges

of sticks and debris on the ground around the bases of trees, fallen trees, or stumps.

The bushy-tailed woodrat usually travels and forages on the ground and nests in rock

outcrops, fallen trees, stick nests in trees, or in cavities in trees. The chipmunk climbs

well, forages (for cones), and sometimes nests in trees. It generally forages on the

ground and in shrubs (for fungi, cones cut by Douglas’ squirrels, and fruits of vascular

plants), and nests in burrows. The semiarboreal rodents use some of the same foods,

structures, and space as the arboreal rodents. The dusky-footed woodrat and the

bushy-tailed woodrat have similar diets and may compete with each other for food and

for space. Bushy-tailed woodrats and northern flying squirrels both use cavities in trees

as well as stick nests, which also may be used by Douglas’ squirrels, dusky-footed

woodrats, and red tree voles.

The relation of arboreal rodents with trees makes them sensitive to timber harvest.

Sensitivity reflects the degree of dependence on trees for food and shelter and the

ability of the species to travel on the ground and across nonforested environments.

This latter ability is crucial for colonizing young forests as they develop into suitable

environments for arboreal rodents.

The red tree vole is associated with old growth for reasons not readily apparent and

may be limited in ability to traverse nonforested areas. Ruggiero and others

(1991) conclude that the red tree vole is closely associated with mature and old-growth

forests and that significant reduction in these old forests will lead to a marked reduction

in tree vole populations. The cavity-using flying squirrels are closely associated with

old forests perhaps because of the greater abundance of cavities in old as opposed to

young forests; “closely associated” means that loss of old-growth forest will precipitate

a significant decline in flying squirrel numbers (Carey 1989, Carey and others 1991a).

The conifer seed-eating Douglas’ squirrels apparently benefit from the abundance of

conifer seed in old growth; Buchanan and others (1990) conclude that loss of oldgrowth forests in western Washington will adversely affect populations of Douglas’

squirrels. The relation between forest age and the abundance of Douglas’ squirrels is

not entirely clear, however, because of regional differences in forest composition,

conifer seed variety and abundance, and perhaps abundance of hypogeous fungi and

Townsend’s chipmunks.

Arboreal rodents constitute an ecological community: a group of species interacting

and potentially influencing one another’s pattern of abundance and use of resources.

Of particular significance is that four of the arboreal rodents (flying squirrel, red tree

vole, and the two woodrats) constitute a major portion of the prey of the spotted owl.

Thus, they influence and are influenced by spotted owl populations. The flying squirrel,

Douglas’ squirrel, and Townsend’s chipmunk are of additional ecological significance

because they eat the sporocarps of ectomychorrizal hypogeous fungi and disseminate

the spores of the fungi and nitrogen-fixing bacteria (Li and others 1986; Maser and

others 1978a, 1978b, 1985, 1986). The ectomychorrizal fungi are essential to nutrient

uptake in trees; inoculation of the soil with the fungi and bacteria through rodent feces

is an important part of the nutrient cycling process in the forest.
The Douglas’ squirrel, red squirrel, and the woodrats will under certain circumstances cause damage to trees (Fisch and Dimock 1978, Franklin 1964, Maser and

others 1981b). The Douglas’ squirrel, red squirrel: and Townsend’s chipmunk

consume large quantities of conifer seed and once were considered a problem by

foresters. They no longer seem to be of concern, perhaps because planting seedlings has become more routine than reliance on natural seeding for regeneration.

This paper summarizes the information on the life histories of the arboreal rodents,

describes how the community might function in relation to the sere of forest development, and identifies those species and processes that seem to be affected by

forest management. I emphasize especially the conversion of naturally regenerated,

unmanaged stand-oId growth and stands with old-growth componentsto managed stands. The terminology used is from Brown (1985) for plant communities and stand conditions and Franklin and Dyrness (1973) for physiographic

provinces and vegetation zones; the correspondence between the terminology used

by the Old Growth Forest Wildife Habitats Research and Development Program

(USDA Forest Service, Pacific Northwest Research Station) and Brown (1985) is

provided in appendix 1. In addition, I examine both stand-level and landscape-level

effects. I attempt to identify the critical elements of the habitat of each species to

allow managers to determine where management can be used to ameliorate the

effects of harvesting natural stands.

There is limited information in the-published literature on arboreal rodents in the

Pacific Northwest; much of the life history information I present comes from a few,

faunistic references: Bailey 1936, Brown 1985, Dalquest 1948, Hall 1981, lngles

1965, and-Maser and others 1981b. Because these references draw on much of the

same primary literature and therefore are redundant, I usually do not specifically

reference them in the text. I do reference pertinent primary literature, and I summarize the findings of my own studies that are in different stages of analysis and

publication and those of the Old Growth Forests Wildlife Habitats Research and

Development Program (Ruggiero and others, in press). Where information is

lacking, I intentionally speculate about factors that might be limiting to a species to

provide managers with at least a subjective basis on which to make recommendations. This paper emphasizes west-side Douglas-fir forests of Washington, Oregon,

and northern California. Where I can, I incorporate information on the species

pertinent to the east-side forests and Alaska. Monitoring and inventory techniques

are presented by Carey and others (in press a).
Species Descriptions The nocturnal red tree vole is the smallest and least studied of the arboreal rodents

and Habits of Douglas-fir forests in the Pacific Northwest. Maser and others (1981b) provide

the best single description of the species. There is some doubt about the red tree

Red Tree Vole vole being only one species; future taxonomic work could result in recognition of two

species (Hall 1981). The red tree vole is about 7.5 inches long, including a 3-inch

tail. It averages just under 1 ounce in weight. The pelage is thick, long, and soft,

brown red to bright brown to orange brown on the back, and light gray below. The

long, hairy tail is black to brown. The ears are almost hairless.

Life history-Red tree voles breed throughout the year but generally produce a

litter of one to four (usually two or three) young from February to September.

Gestation is 28 days but may be extended to 48 days in lactating females. Females

can breed immediately after parturition. Reproduction in red tree voles is characterized by a long reproductive period, small litter size, slow development of young, and

extended nursing of young all of which may be interpreted as physiological adaptations to the difficulties of converting conifer needles into energy for metabolism.

I know of no information on the longevity, population structure, population density,

or social behavior of red tree voles. In captivity, voles will not drink free water but do

drink from water-saturated moss or sponge. They eat only conifer needles. Brown

(1985) lists the home range as one or more trees. Red tree voles may spend their

entire lives in tree tops (they move easily from tree to tree through the canopy).

Terrestrial activity is reported by Corn and Bury (1986) and Raphael (1988); the

nature of this activity is unknown.

6
Distribution and habitat-Red tree voles are confined to western Oregon and

northwestern California (Hall 1981). Populations are widely scattered and are

disappearing in many localities because of logging (Benson and Borell 1931, Howell

1926, Maser and others 1981b, Zentner 1977). Early mammalogists reported that

red tree voles occupied only areas of extensive forest or areas of recently isolated

forest (Bailey 1936). Brown (1985) states that the primary habitat of the red tree

vole is closed sapling-pole-sawtimber, large sawtimber, and old-growth temperate

coniferous forest stands. Secondary habitat includes large sawtimber and oldgrowth high temperate coniferous forest, closed sapling-pole, large sawtimber, and

old-growth coniferous wetlands, and closed sapling-pole, large sawtimber, and oldgrowth mixed-conifer forest. But Corn and Bury (1988, 1988) report that red tree

voles are three times more abundant in old growth than in younger stands along the

west side of the Cascade Range. Red tree voles are rare in closed sapling-polesawtimber and large sawtimber stands but relatively abundant in old growth in the

Cascade and Coast Ranges of Oregon (Carey 1989; see also Corn and Bury,

1991). In California, Zenter (1977) and Meiselman and Doyle (in press) found red

tree voles are more abundant in old growth than in younger forests.

Nests and shelters-Red tree voles build nests wherever there is a suitable

foundation and a readily accessible food supply; nests range from 6 to 160 feet

aboveground (Benson and Borell l931, Maser and others 1981b). Nests may be

placed at any height in trees of any size (Howell 1926). Recent studies suggest,

however, that the voles prefer old-growth trees (Meiselman and Doyle, in press;

Zenter 1977). Whorls of branches provide support in young trees; single, large

branches in old-growth trees can support large nests. Nests are constructed of resin

ducts, lichen, feces, conifer needles, and fine twigs. In old-growth trees, nests may

be covered with a heavy layer of moss and are firmly attached to the tree. The vole

also will use nests constructed by other species and sometimes will make nests

within hollow trees. In California, males sometimes nest, in burrows under fallen

trees or coarse woody debris. Arboreal nests used by red tree voles may have been

used or constructed by western gray squirrels, Douglas’ squirrels, northern flying

squirrels, dusky-footed woodrats, bushy-tailed woodrats, deer mice, and various

birds (Maser and others 1981b).

In southwestern Oregon, red tree voles select the largest available trees for nesting,

even in old growth. Nest tree d.b.h. (diameter at breast height) and number of nests

per tree are correlated; the sample with the highest mean d.b.h. (46 inches) had 4.1

nests per tree, and the sample with the smallest mean d.b.h. (28 inches) had 1.8

nests per tree. Nests were distributed throughout the live canopy but were most

abundant in the lower third of the canopy (Gillesberg and Carey 1991). Meiselman

and Doyle (in press), Vrieze (1980),and Zenter (1977) reported the same for red

tree voles in California. Food and cover are abundant in the lower canopy where the

crown interweaves with adjacent trees, thereby effectively increasing forage abundance and escape routes (Vrieze 1980). Half the nests were on branches and half

were against boles, similar to what Zentner (1977) reports. Single, large limbs of

old-growth trees provide not only support for nests but also escape routes from
predators, access to mates, and proximity to green foliage (Maser and others

1981 b). Large trees can accommodate more than one vole, which thereby may

promote colony formation and increased access to mates.

Food-The principal food of the red tree vole is Douglas-fir needles. The voles

occasionally eat the needles of grand fir, white fir, Sitka spruce, and western

hemlock. Water is obtained by licking dew, rain, or condensation from fog off

needles.

Predators-The chief predator of the red tree vole is the spotted owl (Maser and

others 1981 b); the northern saw-whet owl (Forsman and Maser 1970) and the longeared owl (Reynolds 1970) also prey on the vole. Far more important than predation

in limiting vole abundance are forest fires and logging. Clearcutting “decimates

entire populations and is responsible for the disappearance” of the vole in many

areas (Maser and others 1981b).

Limiting factors-The red tree vole is the most highly specialized vole in the world

(Maser and others 1981b). Its dependence on Douglas-fir for shelter and food and

its restricted diet have resulted in life history characteristics that permit only slow

growth of the population and that are adaptive only in a relatively stable environment. Old growth provides such stability; trees in young forests are continuously

growing and presumably require continual nest relocation. Primary production is

high in old growth, and leaves are concentrated on fewer individuals, thereby

providing maximum food availability. The tall, multilayered canopies have high

water-holding capacity, humidity, and fog interception, thus providing free (chemically unbound) water for the voles. Large branches and boles provide stable nest

sites within green foliage that allow construction of large nests that may be used by

generations of tree voles, thereby promoting formation of colonies and maximizing

access to mates. Thus, limiting factors of importance within its preferred environment (old growth) would seem to be the size of the old-growth stand, the length of

time it has been colonized by red tree voles, and the noncatastrophic influences of

fire, windstorms, and predation by owls. Limiting factors within the landscape that

determine the pattern of abundance and persistence of red tree vole colonies are

the major catastrophes (fire, windstorm, clearcutting) that destroy stable old growth

and result in rapidly developing (changing, unstable) younger forests.

8
Northern Flying Squirrel The single best reference on northern flying squirrels is Wells-Gosling and Heaney

(1984). Most published information on the northern flying squirrel in the Pacific

Northwest, however, is anecdotal (see Maser and others 1981 b). Only the diet of

the squirrel has been reported in detail (Maser and others 1985, 1986; Mclntire and

Carey 1989).

The northern flying squirrel is nocturnal and rarely seen by people. But it is readily

recognizable from its large dark eyes, fine, soft hair that is dark reddish brown on

the back and tan to white on the belly, its wide and horizontally flat tail, and the flaps

of skin (patagia) that extend from the wrists to the ankles. Dorsal pelage changes

color with age (Davis 1963) but the changes are subtle and not readily evaluated in

the field. Flying squirrels do not fly by flapping the patagia, rather they glide. They

maneuver well while gliding and can make sharp, right-angle turns. Glides can be

long, in excess of l00-150 feet. The squirrels are graceful flyers and can land gently

on a tree trunk; sometimes, however, they deliberately crash onto the leafy surface

of a shrub or small tree.

The squirrels average just under 12 inches long, including 5 inches of tail. The ears

are prominent, about 0.8 inch high. Adult northern flying squirrels average 4.3

ounces in Washington and Oregon. Flying squirrels are not highly vocal and do not

sound alarm or territorial calls, but they do sometimes make a high-pitched chitter

while flying and guttural sounds when threatened or angry.

9
Life history-Flying squirrels breed during late April through early July; the peak of

breeding is from late May to early June; young are born from mid-June through

mid-August and are not weaned until mid-October or mid-November. One litter of

two or three young is produced per year. Most yearling females do not breed. About

25 percent of the adult females do not breed in any one year. Young squirrels may

disperse in the fall or they may spend the winter with their mother. Sex ratio is

approximately 1 to 1. Little is known about the social behavior, mating system

(promiscuous vs. monogamous), or dispersal behavior of northern flying squirrels.

Often several adult flying squirrels occupy the same nest. Aggregations are usually

segregated by sex (Maser and others 1981a, Osgood 1935). Life expectancy is

probably less than 4 years; Davis (1963) reports a mean of 1.8 years.

Distribution and habitat-Northern flying squirrels occur across northern North

America in areas of coniferous forest. Their range is continuous through Canada

and extends to the edge of the continuous forest, to Alaska, southward in the lower

United States through the Appalachian Mountains, the Black Hills, the southern

Rocky Mountains, and the Sierra Nevada. The squirrel is associated primarily with

coniferous forest and mixed coniferous-deciduous forest and occasionally broadleafdeciduous forest (Wells-Gosling and Heaney 1984). In the Pacific Northwest, flying

squirrels are associated primarily with large sawtimber and old-growth temperate,

high temperate, subalpine, and mixed conifer-coniferous forest types. Hardwood,

pine, and riparian/wetland types are considered to be secondary habitats (Brown

1985).

Within the Pacific Northwest, densities of flying squirrels differ greatly. On the Olympic Peninsula, I found densities to average 0.2/acre in old-growth Douglas-fir/western

hemlock and climax western hemlock/Sitka spruce forests and only O.O8/acre in

managed, small Douglas-fir or western hemlock sawtimber. Some small sawtimber

stands had no flying squirrels. In southwestern Oregon, densities averaged 0.8/acre

in old-growth Douglas-fir and mixed-conifer stands (with densities averaging O.4/acre

where predation by spotted owls was high and reaching 1.5/acre where owl predation was low) and O.4/acre in managed, small Douglas-fir and mixed-conifer sawtimber stands. In the Oregon Cascade Range, densities averaged 0.8/acre in both oldgrowth and managed Douglas-fir/western hemlock sawtimber in a preliminary

analysis (with owl predation not considered). The average movements by squirrels

differed with each stand; overall, the mean maximum distance moved between

subsequent recaptures was about 325 feet (Carey and others 1991a). Thus, an

estimate of home range size (for a 10-day period) is 1.9 acres. In Alaska, density

was 0.3/acre, and home ranges were over 70 acres in 150-year-old white sprucepaper birch forests (Mowrey and Zasada 1984). The squirrels moved in 1.2-mile

circuits around their home ranges. In North Carolina and Tennessee, northern flying

squirrels used many distantly spaced nests and moved more than 1,600 feet in a

night in spruce-fir/northern hardwoods ecotones (Knowles and others 1990).

Nests and shelters-Flying squirrels use two types of nests: nests in cavities in

trees and nests on limbs. The cavities may be natural cavities formed by mechanical

damage to the tree or rot or cavities excavated by woodpeckers or other birds. The

cavities may be in live or dead trees. External nests are generally built of moss

10
and lichen by the squirrels or may be abandoned nests of birds or other arboreal

mammals. External nests usually are used only in summer. Each individual flying

squirrel will use several dens, cavities, or external nests (Cowan 1936). The number

of cavities or nests required by northern flying squirrels is not known. Mowrey and

Zasada (1984) report individuals used between 1 and 13 dens. In Oregon, I found

individual northern flying squirrels using up to seven nest sites. Snags containing

nest cavities averaged 35 inches in d.b.h.; live conifers with nests averaged 49

inches d.b.h. Cavity trees used in small sawtimber stands were obviously trees

carried over from the preceding old-growth stand. Large (>20 inches d.b.h.) snags

are 10 times more abundant in old growth than in small sawtimber (Carey and others

1991 b). Use of multiple dens by northern and southern flying squirrels is common

(Cowan 1936, Jordan 1948). Carey and Gill (1983) found that southern flying squirrels in captivity used up to four nest boxes, Doby (1984) reports use of multiple nest

boxes and natural dens, and Bendel and Gates (1987) report southern flying squirrels use an average of four dens in a l00-day period.

Food-In the Pacific Northwest (including Alaska), the diet of flying squirrels is

primarily fungi and lichens (Maser and others 1986, Mclntire and Carey 1989,

McKeever 1960, Mowrey and others 1981); lichens are important east of the Cascade crest and in Alaska. Flying squirrels consume a large variety of fungi including

Basidiomycetes, Ascomycetes, and Zygomycetes; Maser and others (1986) report

20 taxa annually, and Mclntire and Carey (1989) report 12 taxa from two stands in

one season in 1 year. In contrast, the principal diurnal consumer and disperser of

fungal spores, Townsend’s chipmunk, consumed only 7 of the 12 taxa of fungi

(Mclntire and Carey 1989). Year-round consumption was documented in southwestern Oregon (Maser and others 1986) despite marked seasonal (fall and spring)

production of sporocarps; there are substantial differences among years in sporocarp

production also (Fogel 1976, Hunt and Trappe 1987, Luoma 1991). Similar studies

have not been completed for the Olympic Peninsula where densities of flying squirrels are low. But the diversity of hypogeous fungi apparently increases markedly from

the peninsula (8 species) to the Oregon Cascades (47 species) to southwestern

Oregon (97 species).

Predators-The major predator of the northern flying squirrel in the Pacific Northwest is the spotted owl. Spotted owls can reduce the flying squirrel population around

nest groves by 50-67 percent-from 0.8-1.2/acre to O.4/acre. Great horned owls also

could be an important predator in the Pacific Northwest: In some areas, the barred

owl is becoming abundant and could be an important predator. Where marten are

abundant, they prey on flying squirrels and other arboreal rodents. Other species

may prey on flying squirrels too, but I found no documentation that their predation is

significant.

.$, ‘,‘.

Limiting factors-Limiting factors for flying squirrels seem to be food, shelter

(cavities), and the spotted owl. It is not clear how limiting food and shelter are.

I found no apparent relation between the abundance of Townsend’s chipmunks and

Douglas squirrels and the abundance of flying squirrels. The three species use the

same food resource (hypogeous fungi). Townsend’s chipmunks often outnumber

.

‘: .’ flying squirrels; Douglas: squirrels can be equally abundant. This would suggest that :. ,. .’

11
food is not limiting continually; it does not suggest that food might not be limiting at

certain times of the year (for all three species) or in certain years. Marked variability

in the production of fungi affects all the mycophagists by periodically reducing their

densities; such variation in resource abundance allows species of similar habits to

coexist. The chipmunk and Douglas’ squirrel have conifer seed as a major part of

their diet. Like fungi, conifer seed abundance differs markedly among seasons and

years. I found no information on differences in abundance of hypogeous fungi

between old growth and managed, small saw-log stands.

I found no negative correlation between the abundance of flying squirrels and bushytailed woodrats, even though both use tree cavities. The bushy-tailed woodrat seems

to be limited in abundance more by its social behavior and, perhaps, the presence of

rock outcrops (perhaps predation, too) than by the abundance of tree cavities

(Escherich 1981). Although the red tree vole, Townsend’s chipmunk, and Douglas’

squirrel use cavities in trees too, they more often use external nests (I doubt they

provide competition to the flying squirrel for tree cavities). Flying squirrels will use the

abandoned external nests of other mammals as well as bird nests and, thus, may

benefit from the presence of these other species. Most of the cavities used by flying

squirrels seem to be abandoned woodpecker holes; the presence of woodpeckers

may be essential for high populations of northern flying squirrels. Woodpeckers are

three times more abundant in old growth than in young forests in southwestern

Oregon (Carey 1989, Carey and others 1991b, Lundquist 1988, Nelson 1989);

throughout the Pacific Northwest, woodpeckers are more abundant in old growth

than in younger forests (Carey 1989, Huff and Raley 1991). Placing nest boxes in

young stands in southwestern Oregon led to increases in flying squirrel populations

but this research is not complete. In many other areas, nest boxes have led to

increases in squirrel populations (Carey and Gill 1983, Carey and Sanderson 1981).

It seems that flying squirrel populations are constrained by at least three different

factors: food, shelter, and predation. These factors differ in importance with year,

season, habitat type, and individual stand. Of these factors, the one most easily

ameliorated by management is shelter. Provision of snags for woodpeckers, retention of live trees with top rot, artificial creation of cavities in trees, and provision of

nest boxes are ways to provide shelter for cavity-using wildlife. The greatest potential

for increasing flying squirrel populations with these techniques lies in young stands.

Management for diversity and abundance of fungi in closed canopy forests has not

been attempted. It seems to me that retention of coarse woody debris, enhancement of tree species diversity, the diversity of herbs and shrubs (perhaps through

thinnings that open the canopy), and mycophagous rodent populations should lead

to increased fungal diversity and abundance. Thinnings, however, will retard

natural snag production. Thus, management prescriptions for flying squirrels must

be thoughtfully formulated to achieve the right combination of management

practices.
Douglas’ Squirrel The Douglas’ squirrel has been a subject of intensive investigation (Koford 1982;

Sanders 1983; Smith 1965, 1968a, 1970, 1978,1981; Smith and Balda 1979; Smith

and Reichman 1984; and others). The Douglas’ squirrel is a diurnal, conspicuous

resident of coniferous forests in the Pacific Northwest. It calls attention to itself with

its loud, repeated territorial calls: the long, trilling “burr” or “rattle,” a “screech,” a

“growl,” and a “buzz;” it also gives an alarm call (chirp) in response to predators and

people (Smith 1978). The Douglas’ squirrel is about 13 inches long, including 5

inches of bushy tail. Its ears are 0.9 inch tall; the squirrel averages 9 ounces.

Pelage color can differ among individuals, geographic locations, and seasons but

tends to be dusky olive on the back, white to orange on the belly, with a dark stripe

on each side.

Llfe hlstory-The breeding season is March-August, sometimes with two peaks

and a lull in May (Koford 1982; Smith 1965, 1968a). Reproduction differs markedly

with food (cone) abundance; breeding may be delayed or deferred, and litter size

differs. Up to two litters of 4-8 young may be produced in one year with births

peaking in June and with young leaving the nest before September. The young are

weaned 2-3 weeks later in mid-September. Young squirrels begin giving their first

territorial calls in mid-September and establish territories by late September or

October. Families have been observed together as late as December, however,

perhaps a reflection of second litters. Woods (1980) reports that mortality is high for

juvenile Douglas’ squirrels and that life expectancy for adults is less than 3 years.

13
Both male and female Douglas’ squirrels defend individual territories with calls and

chases. Territories are relaxed during the 1 or 2 days per year that the female is in

estrus. Mating is promiscuous. Territories may also be relaxed in the spring when

male cones are abundant and may be abandoned in years of food shortage.

Territories are small (0.53 acres) and average 425 feet in diameter. Size may differ

with food abundance; territories usually contain 0.7-2.9 times the annual energy

requirements of the squirrel. Territories are exclusive and contiguous. Douglas’

squirrel densities average 0.6-0.9 per acre. Territories are defended not only

against other Douglas’ squirrels but also against Townsend’s chipmunks.

Distribution and habitat-Douglas’ squirrels are found from southwestern British

Columbia through the western half of Washington, the western two-thirds of

Oregon, northern California, and the Sierra Nevada. The Douglas’ squirrel may

intergrade with the red squirrel along the eastern edge of its range. If this occurs,

the four subspecies of the Douglas’ squirrel will be reclassified as additional subspecies of the red squirrel (Hall 1981). Within the Pacific Northwest, Douglas’ squirrels

are found in the open sapling-pole, closed sapling-pole, large sawtimber, and oldgrowth stands in the temperate and high temperate coniferous forests, mixedconifer forests, and subalpine forest parks. Secondary habitats include hardwood

and shrubby wetlands, coniferous wetlands, and lodgepole pine, shorepine, and

conifer-hardwood forests (Brown 1985). In northern California, Raphael (1984)

found a positive correlation of Douglas’ squirrel abundance and stand age (55-315

years), as did Ralph and others (1991). But in riparian areas in the Oregon Cascades, Anthony and others (1987) found no differences in the abundance of Douglas’ squirrels among young (closed sapling-pole), mature (large sawtimber), and

old-growth forests in the spring. There were no differences in Douglas’ squirrel

abundance in the spring among closed sapling-pole-small sawtimber, large sawtimber, and old-growth Douglas-fir forests in southwestern Oregon, the Oregon

Cascades, and the Washington Cascades (Carey 1989). In a small sample of

stands in the Washington Cascades in the winter, however, Buchanan and others

(1990) found Douglas’ squirrels to be more abundant in old-growth stands than in

closed sapling-pole-small sawtimber and large saw-log stands. It is not clear why

these results differ; the results Carey (1989) reported included spring samples from

the stands sampled by Buchanan and others (1990). The Douglas’ squirrel is not

known to routinely switch territories with seasons; however, immigration to areas of

high food abundance has been reported (Sullivan and Sullivan 1982). The spring

population is that surviving the period of lowest food abundance and is generally the

lowest population of the year (Sullivan and Sullivan 1982). If old growth provides

more diverse and abundant food than younger forests, then the spring population

should demonstrate differences more markedly than winter populations; but winter

populations are composed of adults and juveniles. Perhaps the differences

observed were due to old growth providing better overwintering habitat for juveniles

than young forests can. If most of the juveniles died by spring, or dispersed in

spring into young stands, then the different results would be accounted for. Sullivan

and Moses (1986) report that young stands serve as a dispersal sink for juvenile

and yearling red squirrels.

14
Nests and shelters-Douglas’ squirrels use various shelters: tree cavities, hollow

trees, hollow logs, nests of grass, lichens, and sticks in trees, and burrows in the

ground (Maser and others 1981 b, Smith 1968a). Most commonly used are loosely

constructed stick nests in summer, hollow trees or tree cavities in winter, weathertight

nests in dense foliage as alternate winter nests, and an underground nest in the main

midden (cone cache) pile during prolonged, severe weather. Den sites do not seem

limiting to Douglas’ squirrels. Douglas’ squirrel external nests may be used by red

tree voles and northern flying squirrels, but there is no evidence suggesting that other

arboreal rodents expropriate the nests of Douglas’ squirrels.

Food-Douglas’ squirrels are behaviorally and anatomically adapted toward exploiting their primary foods: conifer seed and fungi (Smith 1970, 1981). The genus

Tamiasciurus is known for storing cones in caches. The caches of the red squirrel

may be very large: one red squirrel in Ontario picked and cached at least 1,000

cones in 1 day (Clarke 1939); caches in Alaska contained up to 8,500 cones each

with individual squirrels cutting and caching 12,000-16,000 cones (Smith 1968b);

caches in Michigan averaged 4 bushels or 1,300 cones (Yeager 1937); caches in the

Rocky Mountains were 20-30 feet across and 1-1.5 feet deep (Finley 1969); and in

Arizona, caches contained 8-24 bushels of cones and were 15 by 30 feet in area

(Patton and Vahle 1986). Red squirrels may cache enough cones to support themselves through one or more years of poor cone crops. Douglas’ squirrels also are

capable of harvesting cones at a high rate and storing them in a centrally located

cache; for example, 277 cones in 23 minutes (Smith 1981). But caches of Douglas’

squirrels seem to be smaller than those of red squirrels. Caches of 1,800-2,500

cones were cached in springs and seeps in the Sierra Nevada, but more commonly,

cones were cached in groups of 1-20, averaging 6, under fallen trees (Shaw 1936);

in Oregon, caches were 0.5 bushels (200 cones) along streams, in moist depressions, in or under fallen trees, and under moss on the ground (Lavender and

Engstrom 1956). Caches are in moist, cool locations to keep the cones from drying,

opening, and spilling their seeds. I could not find any large caches in southwestern

Oregon, but I did find a few small caches (<30 cones); squirrels in the areas I studied

seemed to be scatterhoarding (hiding small groups of cones). In California, Koford

(1982) found that Douglas’ squirrels cached only enough cones to last 6-9 months;

enough to carry them through the winter and spring only. Fungi also may be cached

(by both species). The Douglas’ squirrel is adept at finding hypogeous fungi; Fogel

and Trappe (1978) report that Douglas’ squirrels ate more species (89 species) of

fungi than any other mycophagist; however, they do not report data on the northern

flying squirrel (and Maser and others [1981a] thought Townsend’s chipmunk was the

foremost diurnal consumer of hypogeous fungi).

Both species of Tamiasciurus depend on caches of cones (and sometimes fungi)

for winter food (Lindsay 1986). Why then the absence of large caches? The

nocturnal flying squirrel will raid caches of fungi, and Townsend’s chipmunks are

abundant and raid caches of cones. It may be too difficult for the Douglas’ squirrel

to defend single, large caches in the face of other Douglas’ squirrels, flying squirrels,

and Townsend’s chipmunks. I found small caches and observed squirrels

scatterhoarding among fallen trees. Koford (1982) describes similar behavior in

15
California, and Sanders (1983) notes that cache locations were near fallen trees.

It also may be that hemlock and Douglas-fir cones do not retain their seed as long

as lodgepole pine cones do aboveground or above-water.

Both fungi and cones differ markedly in abundance among seasons and among

years. Fruiting of hypogeous fungi peaks in spring and fall (Fogel 1976), but seasonality differs by species with up to sixfold changes in annual production (Luoma

1991). The abundance of hypogeous fungi also seems related to the amount of

decaying wood in forest stands (Maser and others 1986). Young, managed stands

do not have the coarse woody debris accumulations that old forests have; thus,

young forests may provide a greater seasonality and a lower overall abundance of

hypogeous fungi than do old forests, with the summer drought having a greater

influence on soil moisture in the absence of large amounts of decaying wood.

Cone production differs among species of tree, years, seasons, age classes of

stands of trees, sites, and individual trees (see Eis and others 1965, Fowells 1965,

Garman 1951, Hoffman 1924, Lowry 1966, Ruth 1955, Schopmeyer 1974, Smith

and Balda 1979). The great fluctuations in seed production by conifers west of the

Cascades result in parallel fluctuations in Douglas’ squirrel populations (Smith 1970,

Buchanan and others 1990). Variability is accentuated by synchrony among species

of trees: Douglas-fir, grand fir, western hemlock, and western redcedar are generally synchronous in cone production. Production is not truly cyclic but peaks occur

with an interval of 1-5 years. There is at least one failure and two light to medium

crops every 5-7 years (Fowells 1965); failures occur every 4 years on the average

in western Oregon and Washington (Lowry 1966). In all species, heavy cone crops

are typically followed by one or two off years. Cone and seed production are

physiologically expensive and result in reduced height and diameter growth.

Variability and synchrony in cone production not only reflect tree physiology and

weather but also are adaptations to seed predation. Crop failures among years of

heavy seed production lead to dramatic reduction in populations of seed predators

(five orders of insects, six families of birds, and two orders of mammals) and allow a

large percentage of the seeds in productive years to go uneaten (Smith and Balda

1979).

Ability of a tree to bear cones increases with age up to 300 years. An old-growth

tree may produce 14 times more seed than a 40-year-old tree. Young old growth

(275 years) produces 24 times more seed than a 40-year-old stand, but still produces much less seed than old growth that is 300-350 years old. Seed production

may decline at 600 years. Old stands also produce cone crops in years that young

stands do not. There seems to be a much greater variation in cone production

among individuals in old stands than in young stands. Thus, there is a more consistent minimum seed production in old stands than in young stands.

Conifer species differ in amount of seed produced and seasonality of seed fall.

Douglas-fir may produce averages of 0, 300, 1,500, or 2,000 cones per tree per

year, depending on the year; good producers may produce 5,000-12,000 cones

16
(with a maximum of 20,120) in good years. Years of poor cone production also

have low numbers of seeds per cone. Western hemlock produces more seed than

Douglas-fir or grand fir; western redcedar is second only to western hemlock.

Western hemlock also produces some seed, every year and will have seed-bearing

cones throughout the winter, with greatest seed fall occuring in March. Grand fir,

western redcedar, and Douglas-fir seed fall peaks in September-October; western

redcedar may retain some seed throughout the winter; and Douglas-fir will have a

secondary seed fall in March in some areas.

Old-growth forests, especially old-growth Douglas-fir/western hemlock/western

redcedar forests, provide a more abundant,. more consistent, less seasonal (due to

the great variety of species in old growth), and more diverse seed resource for

Douglas’ squirrels (and Townsend’s chipmunks and the seed-eating birds) to exploit

than does a young Douglas-fir forest. In addition, the multilayered canopies of old

growth also include other seed- and mast-producing species, especially deciduous

species such as maples and huckleberries, that can be of great importance in years

of conifer cone crop failure. Old growth, then, provides the best environment

available to Douglas’ squirrels. But the key question remains unanswered: Is old

growth necessary for the continued existence of Douglas’ squirrels? This question

and its corollary (Are young forests just dispersal sinks for Douglas’ squirrels?) can

be answered only after research during a major cone crop failure, and perhaps a

failure followed by another failure or poor cone crops.

Predation-The principal predators of the Douglas’ squirrel in the Pacific Northwest

are the northern goshawk and the great homed owl; the marten may be an important predator in some areas (Smith 1965, Woods 1980). I could find no quantitative

measures of predation on the Douglas’ squirrel; all references to predation seem to

be anecdotal or speculative.

Limiting factors-Food seems to be the single-most limiting factor for Douglas’

squirrels. Of particular importance seems to be the large difference in seasonal and

-annual cone production. Sullivan and Sullivan (1982) show that supplemental food

can increase Douglas’ squirrel populations in forests of 45-110 years by 5 to 10

times through immigration, increased reproduction, and increased survival of

juveniles. In a related study, Sullivan and Moses (1986) show that decreasing a

stand’s production of cones through silvicultural thinning reduces red squirrel

densities (they observed a twofold reduction). Certain thinnings, however, may

increase seed production in Douglas-fir over time. Other factors do not seem nearly

as important as food in regulating numbers of Douglas’ squirrels.

17
Dusky-Footed Woodrat The dusky-footed woodrat is primarily nocturnal but sometimes forages during the

day; it may be considered crepuscular, with peaks of activity at dawn and dusk. It is

actually more arboreal than the bushy-tailed woodrat (Escherich 1981, Walters

1949). Walters (1949) felt that the dusky-footed woodrat is more proficient at

traveling through trees and shrubs than on the ground; he found parts of plants

remaining from feeding activity scattered below the arboreal pathways used by the

woodrats. Linsdale and Tevis (1951) thought the woodrat is equally proficient on the

ground and in branches. They report that woodrats follow well-established

travelways both on the ground and in the foliage of trees and shrubs.

The dusky-footed woodrat is about the same size (12.5-inch body, 3.5-inch tail) and

weight (10 ounces for males, 8 ounces for females) as the bushy-tailed woodrat.

The pelage is soft and long, red to yellow brown on the back and tan to white on the

undersides. The feet are grayish brown with white toes and claws. The tail is

covered with short, black hair. The feet and tail are the best field characteristics

distinguishing the dusky-footed woodrat from the bushy-tailed woodrat.

The dusky-footed woodrat seems to have a vocal repertoire limited to an alarm

chatter, squeal of rage, and squeal of distress. When agitated, it vibrates its tail

against vegetation or parts of its house, producing a rattle. It is quite noisy in its

movements; its footfalls on its trails often can be heard, and it can be heard moving

through vegetation. The dusky-footed woodrat is often reluctant to move through

plant litter because of the noise that would result, and it prefers to use branches and

limbs rather than the ground when traveling (Linsdale and Tevis 1951).

18
Life history--The social biology of the dusky-footed woodrat is markedly different

from that of the bushy-tailed woodrat. The dusky-footed woodrat lives in coloniesgroups of houses. Each house that is a residence is occupied by one adult and is

vigorously defended against other adults, but there is extensive overlap among home

ranges (foraging areas) and amicable interactions outside the houses. Not all houses

are used equally. About 80 percent are occupied by single animals; some are infrequently used and in disrepair; some are “common” houses, used by many individuals.

Adults generally have more than one house. Individuals will visit one another, with

most of the visits being meetings of a male and female. About one-fourth as frequent

are meetings of two females; with meetings of males being rare. Most visits take place

at common houses. Males initiate more visits than do females. Individuals know and

recognize each other. Females investigate other individuals (familiars or strangers).

Males avoid familiars (other than visits to females) and are antagonistic to strangers

(Wallen 1982).

Pair-bonding for mating is temporary; fighting increases during the breeding season

(Caldwell and others 1984, Cranford 1977). In Oregon, breeding begins in January and

February; partuition takes place during February-May. There is generally one litter per

year, sometimes two. There are one to four young per litter, generally two or three

(Maser and others 1981b, Walters 1949). Juveniles disperse to establish home ranges

in or adjacent to the maternal range before establishing home ranges in unoccupied

but suitable areas. Juvenile home ranges may overlap those of adults by 62 percent.

Juvenile dispersal distances are generally less than 50 feet (Linsdale and Tevis 1951).

In a stable environment (for example, streamside alder and willows in California

chapparal), colonies and houses may be occupied for more than 25 years (Wallen

1982). The social group (colony) is fairly stable; the number of adults remains fairly

constant. Females usually stay near their houses: males travel farther than females,

but distances traveled still are short. The restriction to small home ranges allows only a

slow spread of the colony into new areas. In addition, new houses are rarely constructed outside an occupied colony. individual houses will be used by a succession of

woodrats-sometimes by a dozen individuals, sometimes by hundreds (Linsdale and

Tevis 1951). Disruption of a colony (for example by flooding) can lead to dispersal from

the colony (Cranford 1977). Population density can be as high as 8-18/acre (Cranford

1977, Wallen 1982). In Oregon, densities ranged from 0.2/acre to O.6/acre in my study

areas and 0.6-2.1/acre in Hooven’s (1959) study areas. In California, annual home

(ranges average 0.6 acre for males and 0.5 acre for females; males may expand their

ranges to 1.O acre on average in November and December; females reduce their

ranges during lactation. Home range overlap between males averages 15 percent;

between females, 25 percent; and between males and females, 28 percent. During the

breeding season, overlap may increase to 57 percent between males and females. But

in the preferred foraging areas, there is no overlap. Individuals average four such

centers of activity within their ranges; these areas are high in value for both food and

cover. Individuals average 1.8 houses per home range; mean residence time per

house is 34 days (Cranford 1977). In Oregon, recaptures suggest seasonal home

ranges of 0.7 acre (Walters 1949), 1.1 acres (Hooven 1959), and in my studies, 1.0

acre.

19
Distribution and habitat-The dusky-footed woodrat is found south of the Columbia River in the dry interior valleys of the Willamette, Umpgua, and Rogue Rivers in

western Oregon, throughout the Siskiyou Mountains of southwestern Oregon,

through California, to Mexico. Whereas the bushy-tailed woodrat is associated with

northern coniferous forests, the dusky-footed woodrat is a more southern species,

generally associated with chapparal types.

Although the dusky-footed woodrat generally is considered to be an animal of the

chapparal, even in chapparal types it is most abundant along brushy creek bottoms

(for example, in wooded canyons) and in chapparal characterized by a dense

mixture of trees and shrubs (Linsdale and Tevis 1951). It also thrives in the mixedevergreen and mixed-conifer forests of southwestern Oregon and northern California. Brown (1985) lists their primary habitats in Oregon as shrub-old-growth stages

of deciduous hardwood, conifer-hardwood, mixed-conifer, and temperate coniferous

forests; hardwood and shrubby wetlands and coniferous wetlands; and shrubclosed sapling-pole stages of alder and shorepine forests. In southwestern Oregon,

I found dusky-footed woodrats to be relatively abundant in mixed-conifer, streamside saw-log stands (0.6/acre), managed pole stands (O.2/acre), old growth (0.2/

acre), and managed saw-log stands (0.2/acre). They generally were absent from

Douglas-fir types in the Western Hemlock Zone (Franklin and Dyrness 1978).

Raphael (1984) reports a bimodal pattern of abundance in northern California:

woodrats were more abundant in young-growth (<150 years) and old-growth (>250

years) forests than in the intervening age class.

Walters (1949) surveyed several habitat types ranging from grasslands and pastures to old growth in the Willamette Valley. He found the distribution of the duskyfooted woodrat to be sporadic and discontinuous. The woodrats were absent from

isolated pockets of seemingly good habitat. Woodrats were abundant where there

was heavy cover: fir-oak-brush, fir-brush, oak-fir-brush-willow, fence row thickets,

and willow strips. In areas with little understory or brushy ground cover, woodrats

were absent. Hooven (1959) also reports an association with dense underbrush.

The components of the underbrush may differ, but include hawthorns, blackberries,

snowberry, poison oak, and tree saplings-overstory can be absent or composed of

Douglas-fir, oaks, madrone, ash, or other trees. Habitat may be markedly different

in east-side Oregon forests; Hammer and Maser (1973) link dusky-footed woodrats

with junipers.

In summary, in west-side Oregon the dusky-footed woodrat is found in the interior

valleys (which have Upper Sonoran Life Zone characteristics) and in the Klamath

Mountains Province (which includes the Siskiyou Mountains). Within these areas

the woodrat favors environments characterized by dense understories or underbrush. These conditions exist most often in streamside areas, sapling-pole stands,

brushy patches within old-growth and sawtimber stands of coniferous forest, in

mixtures of brush and forest, and in thickets in the dry valley types.

20
Nests and sheIter--Dusky-footed woodrats build houses in trees and shrubs and

on the ground. Terrestrial houses are large, conical, and composed of sticks and

debris. The construction is shinglelike, which aids in shedding water. In the

Willamette Valley, houses ranged from 1 to 11 feet high and averaged 5 to 6 feet

high and 4 to 5 feet wide (at the base). Terrestrial houses are generally built over a

stump, around a clump of sprouts, or over a log. The house may have seven to

eight chambers, including up to five sleeping nests when young are present. The

nests are made of grass and shredded bark. Terrestrial houses often have a ground

retreat or burrow system beneath them. The woodrats can move into the burrow

system when the house is disturbed; they even can survive complete destruction of

the house by fire when in the ground retreat. Houses may be built in clumps of

sprouts and multistemmed shrubs; tree houses may be up to 50 feet high in a tree.

The aboveground houses are smaller, on average, than the terrestrial houses but

still are well constructed. Tree houses are necessarily absent from nonforested

areas. Terrestrial houses may be absent in areas subject to seasonal flooding.

Along the Oregon Coast, the dusky-footed woodrat often does not build conspicuous houses. The dusky-footed woodrat prefers to build its large houses in thickets;

for example, in Douglas-fir saplings 20 feet tall. At one time, it was thought that the

arboreal houses were used primarily by males, but that has been proven untrue

(Cranford 1977, Hammer and Maser 1973, Hooven 1959, Linsdale and Tevis 1951,

Maser and others 1981b, Walters 1949).

21
The houses of dusky-footed woodrats may be used concomitantly by other species

such as deer mice and western spotted skunks; in California, the presence of woodrat

houses significantly increased the deer mouse population (Cranford 1983). Other

inhabitants of woodrat houses include arthropods-74 species in Oregon and 90

species in California (Ashley and Bohnsack 1974). As with the bushy-tailed woodrat,

the house is critical to the survival and lifetime reproductive success of the duskyfooted woodrat, even to the extent of influencing the social biology of the species

(Caldwell and others 1984, Wallen 1982).

Food-The diet of the dusky-footed woodrat is general. Maser and others (1981a)

summarize the diet for Oregon: leaves and cambium of Douglas-fir, western

redcedar, Port-Orford-cedar, rhododendron, wax myrtle, salal, blackberries and

thimbleberries; leaves and fruit of California laurel; tanoak acorns; and fronds of

bracken and deer fern. Walters (1949) examined food stored in houses and found

green clippings of red alder, oceanspray, willow, hazelnut, white oak, ash, cascara,

serviceberry, snowberry, blackberry, vine maple, and poison oak; maple samaras;

and ash seed. White oak clippings were the most common item found; clippings of

Douglas-fir were common as were green cones of Douglas-fir. Hooven (1959) conducted studies of food acceptance by captive dusky-footed woodrats; they accepted

the foliage of oak, snowberry, maple, and poison oak and acorns, berries, and fruit.

Hooven (1959) also examined food in houses and found leaves of madrone and

blackberry. Linsdale and Tevis (1951) found that fungi (hypogeous and epigeous) can

be a significant part of the diet of the woodrat. This evidence of general food habits

may be misleading, however.

Atsatt and Ingram (1983) state that despite apparently generalized food habits,

woodrat diets often reflect local feeding specialization. The dusky-footed woodrat is

particularly specialized. The dusky-footed woodrat in captivity can maintain its weight

on a pure diet of evergreen oak leaves. Evergreen oak leaves are high in fiber,

phenolics, and tannins; other woodrats (for example, the desert woodrat) cannot exist

on such a diet. Atsatt and Ingram (1983) also observed that in the natural environment the dusky-footed woodrat selectively feeds on evergreen sclerophyll (hardleaved) vegetation high in fiber, tannins, and related polypeptides. There are a series

of adaptations that allow dusky-footed woodrats to survive on a diet of toxic plants.

These adaptations increase the feeding efficiency and energy efficiency of the

woodrats allowing them to minimize the amount of toxin that must be ingested. The

adaptations include:

l Dietary uniformity that increases microflora efficiency permits increased ingestion

rates necessary to maintain a nitrogen balance.

. Reingestion of feces reinoculates the gut flora.

l Large houses insulate against temperature extremes and decrease energetic

requirements.

l Houses established in or near preferred food plants decrease foraging time (and

energy).

. Hoarding of food is a detoxification mechanism that permits relatively continuous,

high-volume feeding.

1

22
Ability to digest sclerophylls in conjunction with other, less toxic, plants might

account for the ability to maintain such high population densities and small home

ranges compared to the bushy-tailed woodrat. It might also be part of the reason for

their occupation of northern California mixed-conifer and mixed-evergreen forests

almost to the exclusion of the bushy-tailed woodrat.

Predators-Linsdale and Tevis (1951) list 11 significant predators of the duskyfooted woodrat in southern California. In Oregon, the primary predators seem to be

the spotted owl and the bobcat; hawks, other owls, coyotes, long-tailed weasels, and

western spotted skunks also may prey on dusky-footed woodrats. Bubonic plague

has been found in dusky-footed woodrats in northern California (Clover and others

1989) and in southeastern Oregon and northeastern California (Maser and others

1981 b). The significance of plague to woodrat populations is unknown, however.

Limiting factors--The dusky-footed woodrat seems to be limited by the extent of

dense, brushy environments that are stable in nature and by its limited ability to

disperse and establish new colonies in recently developed brushy plant communities. Stable environments seem to be brushy streamsides in plant communities

ranging from chapparal to mixed-conifer forests. Old-growth mixed-conifer forests

with brushy understories also are stable environments. Late, brushy clearcuts

through closed sapling-pole stands provide suitable environments but generally are

not stable (they develop to small saw-log stands that usually are not suitable). The

mechanisms and frequency with which dusky-footed woodrats find and colonize

such stands has not been determined. Streamsides could be the source for colonization of these areas. Similarly, brushy roadsides through areas of intense timber

activity may function as dispersal routes to old clearcuts and other brushy types for

dusky-footed woodrats. Linsdale and Tevis (1951) state that the dusky-footed

woodrat lives where low-growing woody vegetation provides protection from carnivores, shelter from the elements, and shade. Such a mass of plants ensures

sufficient food, suitable limbs for runways between houses, materials for houses and

nests, and the vertical, anchoring woody support necessary for the stability of a

large house.

23
Bushy-Tailed Woodrat The nocturnal bushy-tailed woodrat is large: body length is 11-18 inches, tail length

is 5-9 inches, and ears are 1.0-1.5 inches in height. Weights from southwestern

Oregon averaged 9.7 ounces for 27 males and 9.0 ounces for 47 females. Males

may grow to weigh 21 ounces, almost twice the maximum weight for females

(Escherich 1981). Their pelage is soft, dark-gray brown to reddish on the back and

gray to white on the underside; the tail is bushy with hairs longer than 0.8 inch; the

large ears have little hair. Pelage color differs with subspecies but still tends toward

gray brown. Bushy-tailed woodrats do not use territorial or alarm calls like the

Douglas’ squirrel or Townsend’s chipmunks, but they do communicate by stamping

their feet.

Life history-The bushy-tailed woodrat is the only polygynous woodrat-males

keep harems of one to three females. Males are territorial and aggressive and

defend both dens and foraging areas. Scent marking is used to define territories.

Males may engage in serious fights; members of pairs may begin fighting after the

breeding season ends in July or August (Escherich 1981). Dixon (1919) aptly

describes them as “quick in movement” and “fierce”; they fight vigorously when

captured. Their territoriality may be interspecific; a male bushy-tailed woodrat in

captivity killed both a dusky-footed woodrat and a northern flying squirrel (even with

surplus nest boxes and food present). The distribution of woodrat families is patchy,

and the families are generally well separated. These well-separated concentrations

of woodrat biomass attract predators; the loss of a few individual woodrats from

24
these small family groups may lead to the extinction of the colony (Escherich 1981).

Thus, dispersal of offspring is an important component of population viability;

frequent recolonization of vacated habitats is necessary. Dispersal may occur

shortly after weaning or after several years. Dispersal distances of 1.4-2.0 miles

have been recorded. My studies in southwestern Oregon confirmed Escherich’s

(1981) observations of woodrats in California. I found 2.3 females per male where

bushy-tailed woodrats were present; in areas of old-growth Douglas-fir forest that I

studied for 5 years, woodrats were present only 50 percent of the time. In mixedconifer old growth, however, populations seemed more stable and larger than in the

Douglas-fir areas. Spotted owls preyed heavily on bushy-tailed woodrats in both

areas.

Along the Oregon coast, bushy-tailed woodrats begin breeding in January or

February, and young are born in March. There is generally one litter per year, but

sometimes there are two; litter size ranges from one to six, and averages two to four

(Maser and others 1981b). In California, parturition occurred from March through

July or August (Escherich 1981): In my studies in southwestern Oregon, 55 percent

of the females were lactating or just postlactating throughout the summer and fall,

which suggested more extended breeding than Maser and others (1981b) report. In

California, Dixon (1919) reported one litter per year with a mean size of four.

Dlstribution and habitat-The bushy-tailed woodrat occurs throughout the greater

Pacific Northwest, from Yukon to North Dakota, northern New Mexico, and the

Sierra Nevada. Brown (1985) lists its primary habitats as shrub through closed

sapling-pole red alder forests, shrub through old-growth mixed-conifer forest, and

closed sapling-pole through old-growth temperate, high temperate, and coniferous

wetland forests. Almost all other stand conditions and plant communities are

considered to be secondary habitats. He lists coarse woody debris as a special

habitat feature of primary importance. Cliffs and talus are listed as having secondary importance.

There are four subspecies of bushy-tailed woodrats in the Pacific Northwest (Hall

1981). I will discuss each of the three west-side subspecies briefly because I

believe their ecologies differ significantly. Neofoma cinerea occidentalis occurs from

Yukon Territory through British Columbia, Washington, northern Idaho, and the

Oregon Cascade Range. In Washington, it is common in all mountainous areas

wherever high altitude or steep slopes result in accumulation of talus or outcrops of

broken rock (sea level to 10,000 feet), but it is most abundant in the Columbia River

canyon (Dalquest 1948). These woodrats also will inhabit buildings, caves, tunnels,

mines, and railroad beds (Dalquest 1948, Maser and others 1981). During extensive

trapping in managed and old-growth forests around the Olympic Peninsula, I did not

‘catch woodrats in areas without rock outcrops or talus. Bushy-tailed woodrats occur

in rocky areas and rocky streamsides on the Olympic Peninsula. It seems that rock

or talus is of primary importance to this species and that, in some places at high

elevations, log piles also can be important.

25
The bushy-tailed woodrat in the Oregon Coast Ranges is N. c. fusca. This subspecies seems to be able to substitute hollow trees, tree cavities, and fallen trees for

rock outcrops. There are few areas of extensive rock outcropping or heavy talus in

the Coast Ranges. In my studies in southwestern Oregon, the woodrats were most

abundant in mixed-conifer, streamside, saw-log forest (O.4/acre), the one rocky site

I could find (0.2/acre), Douglas-fir, streamside saw-log forest (0.2/acre), managed

mixed-conifer pole stands (0.2/acre), and mixed-conifer old growth (0.8/acre). They

were irregularly (in space and time) abundant in Douglas-fir old growth (averaging

0.2/acre) and rare in large saw-log stands on ridgetops and upland managed sawlog stands. Densities in other types were less than O.O3/acre. These densities seem

low because of the wide distance from one family group to another. Dixon (1919)

reports average densities of O.O5/acre in California. In southwestern Oregon, rock

outcrops and talus did not seem to be a requirement. Bailey (1936) states that the

woodrat in Oregon generally occurs in heavily timbered forests among rocks

overgrown with vegetation; where there is a scarcity of rocks, buildings, old logs,

and log piles suffice.

In southwesternmost Oregon and northern California, is N. c. pulla. Many studies

have been conducted in northern California and most associate N. c. pulla with

rocky environments. Dixon (1919) describes the bushy-tailed woodrat as a member

of the rockslide community. Escherich (1981) states that bushy-tailed woodrats are

associated with rock outcrops, rockslides, caves, and buildings. Raphael (1984,

1988), in extensive studies of forest wildlife in northern California, did not find

bushy-tailed woodrats away from rock outcrops. Ward (1990) did not find bushytailed woodrats in the wide array of mixed-conifer stands he studied in northern

California. Tevis (1956) found that although bushy-tailed woodrats were rare in the

mixed-conifer forests, they did occur in redwood forests. And Maguire (1983) caught

bushy-tailed woodrats along a stream in mixed-conifer old growth in northern

California.

In summary, throughout most of the Pacific Northwest, bushy-tailed woodrats are

associated primarily with rocky environments. But in the transition zone between the

Douglas-fir/western hemlock forests and the mixed-conifer forests in southwestern

Oregon, the bushy-tailed woodrat persists without rock outcrops or talus. There,

streamside forests provide the best environment followed by mixed-conifer closed

sapling-pole stands and old growth. Woodrat populations fluctuate markedly in

Douglas-fir old growth. Upland managed saw-log stands contain few woodrats. It is

not clear whether persistence in nonrocky environments is limited to the transition

zone; there have been few studies in the Cascade Range. Throughout their range,

bushy-tailed woodrats seem to occur in small family groups, the groups often widely

separated. I could find little information on their home ranges. Dixon (1919) states

the bushy-tailed woodrat will forage up to 450 feet from its den (a 15-acre home

range). But I recorded movements of up to 1,250 feet (within trapping grids that

were only 1,300 feet wide) which suggests a maximum home range of about 110

acres. Average mean maximum distance moved was 280 feet-possibly an underestimate because of grid size (Carey and others 1991a). Brown (1985) lists the

minimum habitat per family group as 80 acres.

26
Nests and shelters-Woodrat shelters consist of two parts, the house (external

structure-rock outcrop; hollow tree and woody debris plug; loose collection of

sticks, woody debris, and other material) and the nest (internal nest cup). Bushytailed woodrats build small, open (cuplike) nests; like most packrats, the nest may

be surrounded by a remarkable array of items the woodrat has collected. The

nests often are in rock crevices or burrows under overhanging rock. In these

cases, the woodrat often will accumulate sticks and woody debris in front of the

entrance to the nest. Nests in rocky areas are often easily found by distinctive

urine stains on the rocks. Nests also may be placed in hollow trees; I have seen

the ground-level entrances to such trees jammed with woody debris-in the case

of one old-growth tree having a fire-scar opening 3 feet high and 2 feet wide at the

base, the entire opening was packed with woody debris. Cavities in trees, hollow

logs, log piles, and burrows under logs also may be used. Bushy-tailed woodrats

along the Oregon coast and in the Coast Ranges also will build arboreal nests up

to 50 feet aboveground that are loosely constructed of sticks and twigs (Maser

1965, 1966). Apparently, these nests are not especially common and should not

t be confused with the tightly constructed nests of dusky-footed woodrats.

Food-The bushy-tailed woodrat has a broad, flexible diet (Escherich 1981). Food

includes the leaves and cambium of Douglas-fir, Sitka spruce, and western

hemlock, the leaves of western redcedar, the green parts of Pacific bleeding heart,

angled bittercress, red elderberry, waterleaf, trailing blackberry, Himalaya blackberry (Maser and others 1981 b), and many other plants.

Predators-Bushy-tailed woodrats are prey for many predators: spotted owls,

great horned owls, marten, and bobcats are thought to be important. Other,

perhaps more incidental, predators include long-tailed weasels, coyotes, western

spotted skunks, and large hawks.

Limiting factors-Escherich (1981) states that adequate rock shelter is the most

important resource for the bushy-tailed woodrat, especially in areas that have cold

weather and heavy snowfall. Stick houses are inadequate shelters in such areas.

In areas of mild climate without rock housing available, hollow trees, tree cavities,

and fallen trees might be the limiting resource. In such areas, stream cuts might

also provide rock crevices that would be suitable shelters. The house is a defensible resource. Possession of a house is so important to woodrat survival that a

high level of aggression and solitary house occupancy are basic to the genus.

Bushy-tailed woodrats will defend food resources near their houses from exploitation by other bushy-tailed woodrats. The strong territoriality of the bushy-tailed

woodrat over food and shelter leads to separation of family groups. Isolation leads

to greater threat of local extinction through predation, immigration, and stochastic

(random) demographic processes (lack of births, deaths of individuals).

Persistence, then, depends on routes of connectivity among the family groups.

27
Streamside zones might play a key role in providing dispersal corridors for

recolonization of discrete habitats vacated by local extinction. Heavily timbered

streamsides are characterized by a diversity of plant species and vertical diversity of

vegetation that includes forbs, shrubs, and deciduous trees. These provide food,

and together with the noise of the stream, some protection from predation. One of

the major preferred habitats, closed pole-sapling stands, is relatively ephemeralit is replaced by small saw-log stands in a relatively short time and appears (as a

result of timber harvesting) at a frequency and in a pattern unpredictable by

woodrats. Managed, upland saw-log stands seem poorly suited to bushy-tailed

woodrats. Saw-log stands might lend to the ecological isolation of family groups.

Mixed-conifer old growth provides, however, a stable environment and might act as

a source of dispersing colonizers. Densities in Douglas-fir old growth may be lower

than in the preferred habitats, and local extinctions may be common within parts of

a greater stand. But extensive areas of Douglas-fir old growth may be capable of

maintaining a viable population of bushy-tailed woodrats. Populations in large tracts

of old growth are not as subject to local extinction as populations in small, managed

stands or short stretches of suitable streamsides because barriers to dispersal and

recolonization are minimal. Within spotted owl home ranges, especially near nest

groves, the rate of predation may be very high. Thus, it would seem that rock

housing, old growth, and heavily timbered streamsides are the limiting factors on

the “metapopulation’-the group of woodrat populations present in the landscape.

In southwestern Oregon, I found the abundances of bushy-tailed woodrats and

dusky-footed woodrats to be inversely related among jointly occupied sites. The

inverse relation suggests a degree of competitive exclusion. All jointly occupied

sites were in mixed-conifer zones. As one proceeds southward into mixed-conifer

forest dominated landscapes, it seems the bushy-tailed woodrat disappears from

the forest in the absence of rock outcrops. It is not clear to me whether the rocks

are important in conferring a competitive advantage or whether they only occur in

plant communities or at elevations not suited to the dusky-footed woodrats. The

bushy-tailed woodrat seems restricted to the higher mountains of eastern and

northern California.

28
Townsend’s Chipmunk There are 11 species of chipmunks in the .Pacific States; they are difficult to

distinguish by external characteristics, and the present taxonomy is not clear,

especially in southwestern Oregon, where there may be three or more species.

But, presently, Townsend’s chipmunk may be confused with the least chipmunk

and the yellow-pine chipmunk in the Washington and Oregon Cascade Range and

the Sonoma chipmunk in southwestern Oregon and northern California (Ingles

1965, Jones and others 1986). Townsend’s chipmunk is the largest, darkest, and

most arboreal chipmunk in Washington and Oregon. Its sides are tawny with black

to dark-brown stripes and pale, whitish to cinnamon stripes that are not sharply

defined. The underside of the tail is tawny; other underparts are dull white. There is

a prominent white patch on the back of each ear. The ears are prominent and

0.8 inch tall. Townsend’s chipmunk is 10 inches long-with a 5.5-inch body and

4.5-inch tail. The average weight of 625 Townsend’s chipmunks from southwestern

Oregon that we measured was 3 ounces. Weights in the north and central Cascades were slightly less than 3 ounces (Gashwiler 1976). Townsend’s chipmunk

gives a quiet, birdlike call (“PO-PO-PO”). The chipmunk is an expert climber and may

forage, hide, or sun itself in bushes or trees.

Life history-In the coldest parts of their geographic range, Townsend’s chipmunks hibernate. Along the west side of the Cascades, males are active from

March through October and females are active from April through October;

juveniles may stay active a month or two longer than adults (Gashwiler 1976).

29
Along the Oregon coast, chipmunks may stay active all year (Maser and others

1981b). Breeding activity begins in March in the Cascades and peaks in May, with

lactation from June through August. One litter of two to six young (averaging four)

is produced per year (Gashwiler 1976). In southwestern Oregon, I found that

females were in estrus from April through June, pregnant from late April through

June, and lactating from early May through June (I did not collect late summer

data). Litter size was three to seven, averaging 4.4. Sex ratios tend to be even.

Townsend’s chipmunks may live up to 7 years in the- wild (Brand 1974).

Distribution and habitat-Townsend’s chipmunk occurs on the southeastern tip

of Vancouver Island, along the southwestern border of British Columbia, and

throughout western Washington and Oregon. Hall (1981) considers the Townsend’s

chipmunk in the Siskiyou Mountains to be a separate species: the Siskiyou chipmunk. Similarly, he considers the chipmunk along the east side of the Cascades in

Oregon (and northern California and the Sierra Nevada) to be a separate species:

the California chipmunk. For the purposes of this paper, I will follow the checklist by

Jones and others (1986), which does not recognize the Siskiyou chipmunk. If this

subspecies becomes recognized as a distinct species, it may become of greater

concern than it is now because of its restricted geographic distribution.

Brown (1985) lists the primary habitat of the Townsend’s chipmunk to be the open

sapling-pole through old-growth seral stages of temperate coniferous, high temperate coniferous, conifer-hardwood, and mixed-conifer forests and subalpine forest

parks and the open and closed sapling-pole shorepine and the large sawtimber and

old-growth, deciduous-hardwood forests. Almost all other forest categories are

listed as secondary habitat. Raphael (1984) found, however, that Townsend’s

chipmunks increase in abundance with stand age (55-315 years) in northern

California. I found Townsend’s chipmunks to be 1.7 times more abundant in old

growth than in young, managed stands in southwestern Oregon. Studies in the

Oregon Cascades also found chipmunks to be more abundant in old growth than in

managed, young forests. In riparian zones, Townsend’s chipmunks are more

abundant in young (small sawtimber) forests than in old growth and more abundant

in old growth than in large sawtimber (Anthony and others 1987). Doyle (1990)

found that the densities of chipmunks do not differ between upland areas and

riparian areas. She reports exceptionally high mean densities: 4.9-5.3/acre. Densities in upland sites in a subsequent study were 1.5-50/acre. Densities may get as

high as 2/acre, with home ranges of less than 2.5 acres in Canada (Woods 1980);

the average densities I found in old growth in southwestern Oregon were 0.6/acre in

spring and 0.8/acre in fall. The differences in density among these studies may

reflect technique: Doyle used small grid sizes (which often lead to inflated densities). The chipmunks’ ranges (as measured by mean maximum distances moved

between subsequent recaptures, 338 feet) averaged 2 acres. Like flying squirrels,

Townsend’s chipmunks were very low in abundance in the western hemlock and

Douglas-fir forests on the Olympic Peninsula.

30
Nests and shelter-Maser and others (1981 b) state that Townsend’s chipmunk nest

primarily in burrows. Brand (1974) found Townsend’s chipmunks nesting 40 to 90 feet

aboveground in trees; all but one of the nests he found were occupied by a female

and her young. In the laboratory, he found that Townsend’s chipmunks selected the

highest nest boxes available, thereby indicating an innate preference for elevated

nests. Broadbooks (1974) discussed the arboreality of chipmunks in general. He

noted that the home ranges of chipmunks have an important vertical dimension and

that chipmunks seem to occupy niches intermediate between the strictly arboreal tree

squirrels and the terrestrial ground squirrels. Whereas many authors have noted that

chipmunks forage on the ground, in shrubs, and in trees (Brand [1974] reports that

Townsend’s chipmunks will even cache food in trees and shrubs), most have assumed that chipmunks nest in burrows. Broadbrooks (1974) concludes that chipmunks are the only squirrels, and perhaps the only rodents, that have substantial

nests both underground and in trees in a given year. Burrows generally are used in

winter. The tree nests of chipmunks can be mistaken for bird nests or may be in

cavities. All species of chipmunks use fallen trees and rock crevices for nest sites

(Callahan and Estep 1982). Western chipmunks dig their own burrows. Entrances to

burrows are inconspicuous (without dirt around the entrance). Chipmunks are quiet

while entering or leaving the nest;, even when nursing is required, the family will visit

the nest only once per day for a silent, brief period (Broadbooks 1974).

Food-Townsend’s chipmunks consume many foods: fruits (evergreen huckleberry,

red huckleberry, salal, blackberry, and others), seeds (acorns, maple seeds, laurel

thistles, grasses, Douglas-fir, western hemlock, Sitka spruce), fungi, and insects

(Maser and others 1981b). Townsend’s chipmunk is the only chipmunk with a

tendency to open western hemlock cones to get the seeds (Smith 1968a, Woods

1980).

Predation-Species most commonly listed as preying on Townsend’s chipmunk are

long-tailed weasels and mink. Western spotted skunks, bobcats, and great horned

owls are potential predators. I know of no quantitative data on predation on

Townsend’s chipmunks. During my live-trapping studies, predation on chipmunks in

traps by long-tailed weasels and spotted skunks often was heavy.

Limiting factors-l assume that food is the most limiting factor on Townsend’s

chipmunk populations. The marked annual difference in conifer seed production and

fungi production can lead to marked changes in population density. Hooven and

Black (1976) report fourfold changes in abundance in 3 years in a 125-year-old

Douglas-fir stand. Population changes in a recent clearcut were even more variable;

marked reduction was seen in the same year in a recent clearcut, an advanced

clearcut, and a large saw-log stand, which suggested to me a cone crop failure was

responsible. Sullivan and others (1983) were able to increase Townsend’s chipmunk

population by 40 to 50 percent in second-growth forests by providing supplemental

food; withdrawal of the supplemental food precipitated a decline in the population,

which led them to conclude that food limits the size of Townsend’s chipmunk

populations.

31
Maintenance of the My species accounts provide the basis for some generalizations about arboreal 

Arboreal Rodent rodents. Zoogeography limits arboreal rodent communities in Washington; the red 

Community tree vole and the dusky-footed woodrat do not occur north of the Columbia River 

(fig. 1, table 2). The west-side forests of the Pacific Northwest differ markedly with 

geographic location (physiographic province). Northern forests tend more toward 

dominance by western hemlock; for example, on the western Olympic Peninsula. 

Southern forests are composed of a mixture of conifers and, in the southernmost 

areas, a mixture of conifers and evergreen hardwoods, which reflect climatic 

influences. Concomitant with the changes in the tree flora seems to be parallel 

changes in the abundance and diversity of hypogeous fungal communities. These 

changes seem to influence the overall abundance of the mycophagous northern flying 

squirrel and Townsend’s chipmunk. Dusky-footed woodrats seem confined to the 

mixed-conifer and mixed-conifer-mixed-evergreen types. Bushy-tailed woodrats seem 

especially dependent upon rock outcrops or talus in the colder areas, but are able to 

persist in the absence of rock outcrops in the transition from the Western Hemlock 

Zone to the Mixed Conifer Zone. Deep into the Mixed Conifer Zone, however, the 

bushy-tailed woodrat once again seems dependent on rock outcrops or talus. These 

zoogeographic, physiographic, and climatic effects are beyond the control of the 

manager. 

Table 2-Zoogeography of arboreal rodents in Douglas-fir forests of the 

Pacific Northwest 

Species abundancesb 

Physiographic province a DFWR RTVO TOCH BTWR FLSQ DOSQ 

Northern Cascades + t + t* 

Olympic Peninsula t l l l * 

Puget Trough + + + 

Southern Washington Cascades - - + + + ’ 

Washington Coast Ranges - - + + + + 

Oregon Coast Ranges tt l * l * l * tt 

Interior valleysc l * t* l * l * .* t. 

Western Cascades l * l * l l * l * 

Klamath Mountains l * l * 

+d * ** l * 

a From Franklin and Dyrness (1973). 

b Codes: -absent; + present, but no information on relative abundance; l present, low abundance; 

** present, relatively high abundance; RTVO, red tree vole; DFWR, dusky-footed woodrat; TOCH, 

Townsend’s chipmunk; BTWR, bushy-tailed woodrat; FLSQ, northern flying squirrel; DOSQ, Douglas’ 

squirrel. 

C Rogue, Umpqua, Willamette and perhaps other river valleys. 

d Replaced by other species. 

Within a physiographic province, stand condition plays an influential role in structuring 

the arboreal rodent community. The influence of stand condition reflects both the 

degree of dependence on trees of the members of the community (table 1) and the 

habitat elements used by the rodents (table 3). Maximal diversity, abundance, and 

stability of the arboreal rodent community are achieved in old growth, especially old 

growth with streamside zones. The ameliorative physical, botanical, and climatic 

effects of old growth may be offset to a major degree by predation when the stand is 

a primary foraging area of a breeding pair of spotted owls. 

32 
Table 3-Habltat elements of recognized importance to arboreal rodents In 

Douglas-fir forests in the Pacific Northwesta 

Habiiat element RTVO FLSQ DOSQ DFWR BTWR TOCH 

Large, live tree9 x-nest 

cavity 

food 

Cavity 

nest 

Cavity 

nest 

Cavity Cavity 

x-nest 

Fallen trees Fungus Fungus House Den Fungus 

(food) cache site den 

... ... . . . . . ,:::: ... . ..... . . ..........: ::::.:: .... .................................... ::.: ...................... . ..... ............ .... ................... 

........................... :.>: :,:.. ......................................................................... 

.............................. ~~~~~d~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

.:.:.:...:...:........................ ............. ................ ,:::.:.:.:.:.:.:.:.: .... .,>: .,.>:.,.>:: ................. ... .. ,., ..:.:. ... . . . . 

......... ,.:: ................................................... . ..................................... ............ 

....... .................... ,,., ., .................................................. ............ 

,I:: I:..:....::::& ~:ili;~niateriaiiiiiiilii:iiii;ii:i 

... 

,, :...:.:.:.......:,..:.: . :,:.:.:.:.:.:.:.: .............................. :.:.:.:.:.:.:.:.:.::.:.:.::.:.:.:.:.:.:>:x ........................................... ................................. .:.::.:.:.:.:.:.:.:.:.:.:.:.: ....... 

............................. 

.... .......................... 

....................................................... 

Multilayered canopy Cover Nests 

travel 

cover 

Nests 

cover 

Cover 

.,.,.,:.::. . . . . . ,.:~.,:.:.:.:.:.:.:......,...,... ,. ,. ,. ., ,... . . . : . ,. ., .,. ., . ,. . ..:,. .,j../.,.,...,.,.,...... . . . . . . . 

..,.. .,.,.,.,., ;.....:: :::::: *:.:.:.:.:p:::...:. ,.,.,::,:,..:. ,, ,,.., Ij:.::::::::::::::::::':~:':'::~:~:~::::~:.j.j:::.:::::::::::::::.:.:::::.:..::.:.:.::::~:.:..~ :.',::::.:.::.:::::..::. ,.:.:.:.:.:.:.:.:.:.. ..::..:.::.::.:.:.::.:.:.:.:.j:.,.:.: :: ~~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~: 

~~~~~alirers~~~i:~:i:I;I:I~‘;,~-I,-::':11~~1.:I:i~Ru~~~~li il;,li.i~eed~ .i:-':l:l.,::'i:ii;l:::.'I;:-.::iii..iiil 

: : ,:::.,. ,:.. .:: ::: .::. I ,,. . . . . :..":".::::::.:.:.:.:: i:::li'gungus;'i:;'i:~~,."~~~:~:~~~~:~~~~~:~~ j 

". ,:.:.. j::: 1'. 

:,I, iii,:i::::iii:~fungus~:j 

:,:,.;:., :' .;: ,.., . . . . . . . :.: .,: ..:., :::::.:.:.:':::':',':'.'. . 

Understory diversity Fungus Seeds 

fungus 

Cover 

food 

Cover 

food 

Seeds 

Fog interception Water 

Connectednesse Very Important Important Very Important 

important important 

a From table, x-nest means an external big leaf, twig, or lichen nest. 

bRTV0, red tree vole, FLSO, northern flying squirrel; DOSQ, Douglas’ squirrel; DFWR, dusky-footed 

woodrat; BTWR, bushy-tailed woodrat; TOCH, Townsend’s chipmunk. 

C Includes live trees with broad limbs, broken tops, and cavities; >30 inches; x-nest is an external nest. 

d Long-lasting stand condition; late seral stage. 

eLarge, contiguous areas of suitable habitat or corridors connecting areas of suitable habitat. 

Members of the arboreal rodent community differ in their ecological flexibility (also 

referred to as niche breadth and width) and in their ability as colonizers. Landscapes 

can be viewed as being composed of elements that can be classified as ecological 

sources of dispersers, dispersal sinks, unsuitable for occupancy, and barriers to 

33 
dispersal (table 4). To interpret the table, it is important to understand that there is

considerable variability in the structure of plant communities in each of the stand

conditions. Not only does the structure differ with forest type (for example, western

hemlock vs. mixed conifers) but also with site (aspect, elevation, soils), presence of

seeps, streams, and rock outcrops, stocking of canopy trees (both density of stems

and canopy closure), and history (fire, windstorm, and insect damage). Thus, I list

old forest as a source and sink for bushy-tailed woodrats. Mixed-conifer old growth

with a stream seems to provide a good, stable environment (a source) for bushytailed woodrats. Other types of old forest with rocks or talus might do the same. But,

Douglas-fir old growth within a spotted owl home range often fails to support a

stable population of bushy-tailed woodrats and thus functions as a sink. Perhaps an

extensive area of Douglas-fir old growth, one capable of supporting multiple local

populations (in other words, a metapopulation), might be a source with the

metapopulation composed of local populations that become established, send out

colonizers, go extinct, and get recolonized.

Table 4-Habitat ratings for stand conditions in Douglas-fir forests In the Pacific

Northwest relative to 6 arboreal rodents

Stand conditiona

Speciesb

Years RTVO FLSQ DOSQ DFWR BTWR TOCH

Grass-forb 2-5 U,B U,B U,B UB + U,B

Shrub 3-10 B U U Sink- t

source

Source

-sink

Open sapling-pole 8-20 B U U Sink- +

source

Source

-sink

Closed sapling-pole 20 Sink- U Sink Sink- Source Source

B source -sink -sink

Small sawtimber 60 Sink- Sink Source Sink- Sink Source

B -sink source -sink

Large sawtimber 100 Sink- Source Source Sink- Sink

source -sink -sink B

Source

-sink

Old forest 700 Source Source Source Source Source Source

-sink

a From Brown (1985); old forest includes old growth and old growth mixed with younger stand types.

* RTVO, red tree vole; FLSQ, northern flying squirrel, DOSQ, Douglas’ squirrel; DFWR, dusky-footed

woodrat, BTWR, bushy-tailed woodrat, TOCH, Townsend’s chipmunk; U, unsuitable for occupancy;

B, barrier to dispersal and population growth; sink is defined as an environment capable of maintaining a

population for a while but either permitting only low reproduction or subject to periods in which the sink

becomes unsuitable for occupancy; source is defined as an environment capable of sustaining a viable

population that produces a surplus of offspring that are potential colonizers of unoccupied suitable environments or sinks; + indicates that the species has been found in the stand conditions, but the rating

is unknown.

34
1

An innate feature of stand condition is stability, or the duration over which the stand

remains in that condition (table 4). Early stages of forest development change more

rapidly than late stages. Thus, I list shrub stages as sinks and sources for the duskyfooted woodrat. Only shrub stages of mixed-conifer or mixedconifer-mixed-evergreen

forest function in this way. And only shrub stages with a dense cover of shrubs are

suitable environments for dusky-footed woodrats. Shrub stand conditions can support

dense colonies of dusky-footed woodrats. But eventually the stage will pass to an

environment unsuited for the woodrat. In the interim, presuming successful colonization, the stand may function as a source of dispersing and potentially colonizing

woodrats.

I list closed-canopy, early stand conditions as sinks and barriers for red tree voles.

I have found colonies (both active and inactive) in such stages: it does not seem that

colonization of these types is common. Creation of early seral stages within or

adjacent to old forests probably would serve to inhibit the continued growth (or even

persistence) of a colony of red tree voles.

Of major significance is my conclusion that old forest can serve as sources for five of

the six rodents (and a source and sink for the sixth species) with no other stand

condition being as consistently amenable to the rodents; Small or large sawtimber, or 1

both, can serve as a source and a sink for three of the species-the flying squirrel,

the Douglas squirrel and Townsend’s chipmunk. Two other species-the duskyfooted woodrat and the bushy-tailed woodrat-find suitable habitat in younger stages.

The value of these habitats as population sources is reduced by their ephemeral

status in the successional. process. Possibly the most significant finding is that nonold-forest types do not seem to be sources of red tree voles-only old growth seems

to do that. And other types might routinely function as barriers to red tree voles. Given

the patchy, relatively uncommon abundance of red tree voles and the susceptibility of

the voles to timber harvest, immediate action should be taken to identify and protect

existing colonies of red tree voles. The status (numbers, sizes, and locations) of red

tree vole metapopulations (and local populations) along the west side of the Cascades, in interior valleys, in the Coast ‘Ranges, and in the Klamath Mountains is not

known. Continued timber harvesting could threaten the persistence of red tree voles,

either locally or on a larger scale, unless steps are taken for inventory and conservation of the species.

3

35
Scientific Names Common name* Scientific name

Mammals:

Bobcat

Bushy-tailed woodrat

California chipmunk

Coyote

Deer mouse

Desert woodrat

Douglas’ squirrel

Dusky-footed woodrat

Least chipmunk

Long-tailed weasel

Marten

Mink

Northern flying squirrel

Red squirrel

Red tree vole’

Siskiyou chipmunk

Sonoma chipmunk

Southern flying squirrel

Townsend’s chipmunk

Western gray squirrel

Western spotted skunk

Birdsb

Barred owl

Great horned owl

Long-eared owl

Northern goshawk

Northern saw-whet owl

Spotted owl

Microorganisms:

Bubonic plague

Plantsc

Angled bittercress

Ash

Blackberry

Bracken fern

California laurel

Cascara

Deerfem

Douglas-fir

Evergreen huckleberry

Felis rufus

Neotoma cinerea

Tamias obscurus

Canis latrans

Peromyscus spp.

Neotoma lepida

Tamiasciurus douglasii

Neotoma fuscipes

Tamias minimus

Mustela frenata

Martes americana

Mustefa vison

Glaucomys sabrinus

Tamiasciurus hudsonicus

Phenacomys longicaudas

Tamias townsendii siskiyou

Tamias sonomae

Glaucomys volans

Tamias townsendii

Sciurus griseus

Spilogale gracilis

Strix varia

Bubo virginianus

Asio otus

Accipiter gentilis

Aegolius acadicus

Strix occidentalis

Yersinia pestis

Cardamine L.

Fraxinus latifolia Benth.

Rubus L.

Pteridium aquilinum (L.) Kuhn

Umbellulatia californica (Hoot. & Am.)

Rhamnus purshiana DC

Blechnum spicant (L.) With.

Pseudotsuga menziesii (Mirb.) Franco.

Vaccinicim ovatum Pursh.

36
Commonname ” ’ Scientific name

Grand fir

Hawthorn

Hazelnut

Himalaya blackberry

Juniper

Laurel

Lodgepole pine

Madrone

Maple

Oak

Oceanspray

Oregon ash

Pacific bleeding heart

Pacific madrone

Paper birch

Poison oak ‘.

Port-Orford-cedar

Red alder

Red elderberty

Red huckleberry

Redwood

Rhododendron

Sal al

Serviceberry

Shorepine

Sitka Spruce

Snowberry

Tanoak

Thimbleberry

Trailing blackberry

Vine maple

Waterleaf

Waxmyrtle

Western redcedar

Western hemlock’

White fir

White oak

White spruce

Willow

Vaccinium parvifolium Smith

Sequoia sempervirens (D. Don) Endl.

Rhododendron L.

Gaultheria shallon Pursh.

Amelanchier alnifolia Nutt.

Pinus contorta Dougl. ex Loud.

Picea sitchensis (Bong.) Carr.

Symphoricarpos L.

Lithocarpus densiflorus (Hook. & Am.)

Rubus parvilorus Nutt.

Rubus ursinus Cham. & Schlect.

Acer circinatum Pursh.

Hydrophyllum (Tourn.) L.

Myrica californica Cham.

Thuja plicata Donn.

Tsuga heterophylla ( Raf .) Sarg.

Abies concolor (Gard. & Glend.) Lindl.

Quercus garryana Dougl.

Picea glauca (Moench) Voss

Salix L.

a Jones and others 1666: S

bAmerkan.Omitholo@tS’ Union 1962.

CCommon names are those used by the authors cited; scientific names are from Franklin and Dyrness

1973.

Abies grandis (Dougl.) Lindl.

Crataegus L.

corylus L.

Rubus procerus Muell.

Juniperus L.

Umbellularia californica (Hook & Am.)

Pinus contorta Dougl. ex Loud.

Arbutus menziesii Pursh.

Acer L.

Quercus L.

Holodiscus disco/or Pursh.

Fraxinus latifolia Benth.

Dicentra Bernh.

“Arbutus menziesii Pursh.

Betula papyrifera Marsh.

Rhus diversiloba T. & G.

Chamaecyparis lawsoniana (A.Murr.) Parl.

Alnus rubra Bong.

Sambucus racemosa L. var. arborescens

(T. & G.) Gray

37
Literature Cited Anthony, R.G.; Forsman, ED.; Green, G.A. [and others]. 1987. Small mammal

populations in riparian zones of different-aged coniferous forests. Mutrrelet.

68: 94-102.

American Ornithologists’ Union. 1982. Thirty-fourth supplement to the American

Ornithologists’ Union checklist of North American birds. Supplement to The Auk.

99(3): 1cc-16cc.

Ashley, Tom R; Bohnsack, Kurt K. 1974. Seasonal abundance of acarine populations in the sleeping nests of the dusky-footed woodrat, Neotoma fuscipes Baird,

in southern California, U.S.A. Proceedings of the 4th International Conference on

Acarology: 615-621.

Atsatt, Peter R.; Ingram, Trudy. 1983. Adaptation to oak and other fibrous,

phenolic-rich foliage by a small mammal, Neotoma fuscipes. Oecologia.

60: 135-143.

Bailey, Vernon. 1936. The mammals and life zones of Oregon. North American

Fauna No. 55. Washington, DC: U.S. Department of Agriculture, Bureau of

Biological Survey. 416 p.

Bendel, Peter R.; Gates, J. Edward. 1987. Home range and microhabitat partitioning of the southern flying squirrel (Glaucomys volans). Journal of Mammalogy.

66: 243-255.

Benson, Seth B.; Borell, Adrey E. 1931. Notes on the life history of the red tree

mouse, Phenacomys longicaudus. Journal of Mammalogy. 12: 226-233.

Brand, Leonard R. 1974. Tree nests of California chipmunks (Eutamias). American

Midland Naturalist. 91: 469-491.

Broadbooks, Harold E. 1974. Tree nests of chipmunks with comments on

associated behavior and ecology. Journal of Mammalogy. 55: 630-639.

Brown, E. Reade. 1985. Management of wildlife and fish habitats in forests of

western Oregon and Washington. Part 2: Appendices. RG-F&WL-192-1985.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Region. 302 p.

Buchanan, J.B.; Lundquist, R.W.; Aubry, K.B. 1990. Winter populations of

Douglas’ squirrels in different-aged Douglas-fir forests. Journal of Wildlife

Management. 54: 577-581.

Caldwell, Gloria S.; Glickman, Stephen E.; Smith, Erla R. 1984. Seasonal

aggression independent of seasonal testosterone in woodrats. Proceedings of the

National Academy of Sciences of the United States of America. 61: 5255-5257.

Callahan, J.R.; Estep, D.Q. 1982. Tree and ground nests of southern Eutamias.

Southwestern Naturalist. 27: 234-238.

Carey, Andrew B. 1989. Wildlife associated with old-growth forests. Natural Areas

Journal. 9: 151-162.

Carey, Andrew B.; Biswell, Brian L.; Witt, Joseph W. 1991a. Methods for

measuring populations of arboreal rodents. Gen. Tech. Rep. PNW-GTR-273.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Research Station. 24 p.

38
Carey, Andrew B.; Gill, John D. 1983. Direct habitat improvement-some recent

advances. In: Davis, J.W.; Goodwin, G,A.; Ockenfels, R.A., tech. coords. Snag

habitat management: Proceedings of the symposium; 1983 June 7-9; Flagstaff, AZ.

Gen. Tech. Rep. RM-99. Fort Collins, CO: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Forest and Range Experiment Station: 80-87.

Carey, Andrew B.; Hardt, Mary Mae; Horton, Scott P.; Biswell, Brian L.

1991 b. Spring bird communities in the Oregon Coast Ranges. In: Ruggiero, L.F.;

Aubry, K.B.; Carey, A.B.; Huff, M.H., tech. coords. Wildife and vegetation of

unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR-285. Portland, OR:

U.S. Department of Agriculture, Forest Service, Pacific Northwest Research

Station: 123-144.

Carey, Andrew B.; Sanderson, H. Reade. 1981. Routing to accelerate tree-cavity

formation. Wildlife Society Bulletin. 9: 14-21.

Clarke, C.H.D. 1939. Some notes on hoarding and territorial behavior of the red

squirrel Sciurus hudsonicus (Erxleben). Canadian Field Naturalist. 53: 42-43.

Clover, J.R.; Hofstra, T.D.; Kuluris, B.G. [and others]. 1989. Serologic evidence of

Yersinia pestis infection in small mammals and bears from a temperate rainforest

of north central California. Journal of Wildlife Diseases. 25: 52-60.

Corn, Paul Stephen; Bury, R. Bruce. 1986. Habitat use and terrestrial activity by red

tree voles (Arborimus longicaudus) in Oregon. Journal of Mammalogy. 67: 404-406.

Corn, Paul Stephen; Bury, R. Bruce; Spies, Thomas A. 1988. Douglas-fir forests in

the Cascade mountains of Oregon and Washington: is the abundance of small

mammals related to stand age and moisture? In: Szaro, R.C.; Severson, K.E.;

Patton, D.R., tech. coords. Management of amphibians, reptiles, and small mammals in North America: Proceedings of the symposium; 1988 July 19-21; Flagstaff,

AZ. Gen. Tech. Rep. RM-166. Fort Collins, CO: U.S. Department of Agriculture,

Forest Service, Rocky Mountain Forest and Range Experiment Station: 340-352.

Corn, Paul Stephen; Bury, R. Bruce. 1991. Small mammal communities in the

Oregon Coast Ranges. In: Ruggiero, L.F.; Aubry, K.B.; Carey, A.B.; Huff, M.H.,

tech. coords. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech.

Rep. PNW-GTR-265. Portland, OR: U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station: 241-256.

Cowan, Ian McTaggart. 1936. Nesting habits of the flying squirrel Glaucomys volans.

Journal of Mammalogy. 17: 58-60.

Cranford, Jack A. 1977. Home range and habitat utilization by Neotoma fuscipes as

determined by radiotelemetry. Journal of Mammalogy. 58: 165-172.

Cranford, Jack A. 1983. The effect of woodrat houses on population density of

Peromyscus. Journal of Mammalogy. 63: 663-666.

Dalquest, Walter W. 1948. Mammals of Washington. University of Kansas

Publications, Museum of Natural History. 2: 1-444.

Davis, Wayne. 1963. Reproductive ecology of the northern flying squirrel in

Saskatchewan. Saskatoon, Saskatchewan: University of Saskatchewan. 87 p.

M.S. thesis.

39
Dixon, Joseph. 1919. Notes on the natural history of the bushy-tailed woodrats of

California. University of California Publications in Zoology. 21: 49-74.

Doby, Wiley J. 1984. Resource base as a determinant of abundance in the southern

flying squirrel (Glaucomys volans). Winston-Salem, NC: Wake Forest University.

108 p. Ph.D. dissertation.

Doyle, A.T. 1990. Use of riparian and upland habitats by small mammals. Journal of

Mammalogy. 71: 14-23.

Eis, S.; Garman, E.H.; Ebell, L.F. 1965. Relation between cone production and

diameter increment of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco, grand fir

(Abies grandis [Dougl.] Lindl.), and western white pine (Pinus monticola Dougl.).

Canadian Journal of Botany. 43: 1553-1559.

Escherich, Peter C. 1981. Social biology of the bushy-tailed woodrat, Neotoma

cinerea. University of California Publications in Zoology. 110: 1-121.

Finley, R.B., Jr. 1969. Cone caches and middens of Tamiasciurus in the Rocky

Mountain region. University of Kansas Museum of Natural History Miscellaneous

Publications. 51: 233-273.

Fisch, Gordon G.; Dimock, Edward J., II. 1978. Shoot clipping by Douglas’ squirrels

in regenerating Douglas-fir. Journal of Wildife Management. 42: 415-418.

Fogel, Robert. 1976. Ecological studies of hypogeous fungi. II: Sporocarp phenology

in a western Oregon Douglas-fir stand. Canadian Journal of Botany. 54: 1152-

1162.

Fogel, Robert; Trappe, James M. 1978. Fungus composition (mycophagy) by small

mammals. Northwest Science. 52: 1-31.

Forsman, Eric; Maser, Chris. 1970. Saw-whet owl preys on red tree mice. Murrelet.

51:10.

Fowells, H.A. 1965. Silvics of forest trees of the United States. Agric. Handb. 271.

Washington, DC: U.S. Department of Agriculture, Forest Service. 762 p.

Franklin, Jerry F. 1964. Douglas’ squirrels cut Pacific silver fir cones in Washington

Cascades. Res. Note PNW-15. Portland, OR: U.S. Department of Agriculture,

Forest Service, Pacific Northwest Forest and Range Experiment Station.

Franklin, Jerry F.; Dyrness, C.T. 1973. Natural vegetation of the Pacific Northwest.

Gen. Tech. Rep. PNW-8. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range Experiment Station. 417 p.

Garman, E.H. 1951. Seed production by conifers in the coastal region of British

Columbia related to dissemination and regeneration. Tech. Publ. T-35. Victoria,

BC: British Columbia Forest Service, Department of Lands and Forests. 67 p.

Gashwiler, Jay S. 1976. Biology of Townsend’s chipmunk in western Oregon.

Murrelet. 57: 26-31.

Gillesberg, Anne-Marie; Carey, Andrew B. 1991. Arboreal nests of Phenacomys

/ongicaudus in Oregon. Journal of Mammalogy. 72: 784-787.

40
Hail, E. Raymond. 1981. The mammals of North America, 2d ed. New York: John

Wiley & Sons. 1175 p., Vol. 2.

Hammer, E. Wayne; Maser, Chris. 1973. Distribution of the dusky-footed woodrat,

Neotoma fuscipes Baird, in Klamath and Lake Counties, Oregon. Northwest

Science. 47: 123-l 27. ‘.

Hofmann, J.V. 1924. Natural regeneration of Douglas-fir in the Pacific Northwest.

Agric. Bull. 1200. Washington, DC: U.S. Department of Agriculture. 62 p.

Hooven, Edward F. 1959. Dusky-footed woodrat in young Douglas-fir. Res. Note 41.

Corvallis, OR: Oregon Forest Lands Research Center. 24 p.

Hooven, Edward F.; Black, Hugh C. 1976. Effects of some clearcutting practices on

small mammal populations in western Oregon. Northwest Science. 50: 89-209.

Howell, A. Brazier. 1926. Voles of the genus phenacomys.II: Life history of the red

tree mouse Phenacomys longicaudus. North American Fauna. 48: 39-64.

Huff, M.H.; Raley, C.M. 1991. Regional patterns of diurnal breeding bird communities

in Oregon and Washington. In: Ruggiero, L.F.; Aubry, K.B.; Carey, A.B.; Huff,

M.H., tech. coords. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen.

Tech. Rep. PNW-GTR-285. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Station: 207-220.

Hunt, Gary; Trappe, J.M. 1987. Seasonal hypogeous sporocarp production in a

western Oregon Douglas-fir stand. Canadian Journal of Botany. 65: 438-445.

Ingles, Lloyd G. 1965. Mammals of the Pacific states. Stanford, CA: Stanford

University Press. 506 p.

Jones, J. Knox; Carter, Dilford C.; Genoways, Hugh H. [and others]. 1986.

Revised checklist of North American mammals north of Mexico, 1986. Occasional

Papers. The Museum Texas Tech University. 107: 1-22.

Jordan, James S. 1948. A mid-summer study of the southern flying squirrel. Journal

of Mammalogy. 37: 294-295.

Knowles, T.W.; Weigl, P.D.; Smith, A.B.; Boynton, A.C. 1990. Radiotracking

northern flying squirrels (Glaucomys sabrinus) in the southern Appalachians: a

chronicle of the unexpected. [Abstract]. in: American Society of Mammalogists

abstracts: 70th Annual Meeting of the American Society of Mammalogists; 1990

June 9-13; Frostburg, MD. Frostburg, MD: American Society of Mammalogists:

167.

Koford, Rolf R. 1982. Mating system of a territorial tree squirrel (Tamiasciurus

douglasii) in California. Journal of Mammalogy. 63: 274-283.

Lavender, D.P.; Engstrom, W.H. 1956. Viability of seeds from squirrel-cut Douglasfir cones. Res. Note 27, Cotvallis, OR: Oregon State University, Forestry Laboratory. 19 p. jQ I 1

Li, C.Y.; Maser, Chris; Maser, Zane; Caldwell, Bruce A. 1986. Role of three

rodents in forest nitrogen fixation in western Oregon: another aspect of mammal

mycorrhizal fungus-tree mutualism. Great Basin Naturalist. 46: 411-414.

41
Lindsay, Stephen L. 1986. Geographic size variation in Tamiasciurus douglasii:

significance in relation to conifer cone morphology. Journal of Mammalogy.

67: 317-325.

Linsdale, J.M.; Tevis, L.P., Jr. 1951. The dusky-footed woodrat. Berkeley, CA:

University of California Press. 664 p.

Lowry, William P. 1966. Apparent meteroiogical requirements for abundant conce

crops in Douglas-fir. Forest Science. 12: 185-192.

Lundquist, Richard William. 1988. Habitat use by cavity-nesting birds in the southern Washington Cascades. Seattle, WA: University of Washington. 168 p.

M.S. thesis.

Luoma, D.L. 1991. Annual changes in seasonal production of hypogeous sporocarps

in Oregon Douglas-fir forests. In: Ruggiero, L.F.; Aubry, K.B.; Carey, A.B.; Huff,

M.H., tech. coords. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen.

Tech. Rep. PNW-GTR-285. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Research Station: 83-90.

Maguire, Christine Chitko. 1983. First year responses of small mammal populations

to clearcutting in the Klamath Mountains of northern California. Rutgers, NJ:

Rutgers University. 239 p. Ph.D. dissertation.

Maser, Chris. 1965. Nest of busy-tailed woodrat fifty feet above the ground. Murrelet.

46: 346.

Maser, Chris. 1966. A second Neotoma cinerea nest fifty feet above the ground.

Murrelet. 47: 72.

Maser, C.; Anderson, R.; Bull, E.L. 1981a. Aggregation and sex segregation in

northern flying squirrels in northeastern Oregon, an observation. Murrelet.

62: 54-55.

Maser, Chris; Maser, Zane; Witt, Joseph W.; Hunt, Gary. 1986a. The northern

flying squirrel: a mycophagist in southwestern Oregon. Canadian Journal of

Zoology. 64: 2086-2089.

Maser, Chris; Trappe, James M.; Nussbaum, Ronald A. 1978a. Fungai-small

mammal interrelationships with emphasis on Oregon coniferous forests. Ecology.

59: 799-809.

Maser, Chris; Trappe, James M.; Ure, Douglas C. 1978b. Implications of small

mammal mycophagy to the management of western coniferous forests.

Transactions of the North American Wildlife and Natural Resources Conference.

43: 78-88.

Maser, Chris; Mate, Bruce R.; Franklin, Jerry F.; Dyrness, C.T. 1981b. Natural

history of Oregon coast mammals. Gen. Tech. Rep. PNW-133. Portland, OR: U.S.

Department of Agriculture, Forest Service, Pacific Northwest Forest and Range

Experiment Station. 496 p.

Maser, Zane; Maser, Chris; Trappe, James M. 1985. Food habits of the northern

flying squirrel (Glaucomys sabrinus) in Oregon. Canadian Journal of Zoology.

63: 1084-1088.

42
Mcintire, Patrick W.; Carey, Andrew B. 1989. A microhistological technique for

analysis of food habits of mycophagous rodents. Res. Pap. PNW-RP-404.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Research Station. 16 p.

McKeever, Sturgis 1960. Food of the northern flying squirrel in northeastern

California. Journal of Mammalogy. 41: 270-271.

Meiselman, N.; Doyle, A.T. [in press]. Habitat and microhabitat selection by the red

tree vole, Arborimus iongicaudus. American Midland Naturalist.

Mowrey, Robert A.; Laursen, Gary A.; Moore, Terry A. 1981. Hypogeous fungi and

small mammal mycophagy in Alaska taiga. Proceedings of the Alaska Science

Conference. 32: 120-121.

Mowrey, Robert A.; Zasada, John C. 1984. Den tree use and movements of

northern flying squirrels in interior Alaska and implications for forest management.

in: Meehan, W.R.; Merrell, T.R., Jr.; Hanley, T., eds. Fish and wildlife relationships

in old-growth forests: Proceedings of symposium; 1982 April 2-5; Juneau.

Morehead City, NC: American Institute of Fishery Research Biologists: 351-356.

Nelson, S. Kim. 1989. Habitat use and densities of cavity-nesting birds in the Oregon

Coast Ranges. Corvallis, OR: Oregon State University. 157 p. M.S. thesis.

Osgood, F.L. 1935. Apparent segregation of sexes in flying squirrels. Journal of

Mammalogy. 16: 231.

Patton, David R.; Vahle, J. Robert. 1986. Cache and nest characteristics of the red

squirrel in an Arizona mixed-conifer forest. Western Journal of Applied Forestry.

1:48-51.

Ralph, C.J.; Paton, P.W.C.; Taylor, CA. 1991. Habitat associations of breeding

birds and small mammals in Douglas-fir stands in northwestern California and

southwestern Oregon. In: Ruggiero, L.F.; Aubry, K.B.; Carey, A.B.; Huff, M.H.,

tech. coords. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech.

Rep. PNW-GTR-285. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Research Station: 379-394.

Raphael, Martin G. 1984. Wildlife populations in relation to stand age and area in

Douglas-fir forests of northwestern California. in: Meehan, W.R.; Merreli, T.R., Jr.;

Hanley, T., eds. Fish and wildlife relationships in old-growth forests: Proceedings

of a symposium; 1982 April 2-5; Juneau. Morehead City, NC: American institute of

Fishery Research Biologists:, 259-274.

Raphael, Martin G. 1988. Long-term trends in abundance of amphibians, reptiles,

and mammals in Douglas-fir forests of northwestern California. In: Szaro, R.C.;

Severson, K.E.; Patton, D.R., tech. coords. Management of amphibians, reptiles,

and small mammals in North America: Proceedings of the symposium; 1988 July

19-21; Flagstaff. Fort Collins, CO: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Forest and Range Experiment Station: 23-31.

Reynolds, Richard T. 1970. Nest observations of the long-eared owl (Ado otus) in

Benson County, Oregon, with notes on their food: habits. Murrelet. 51: 8-9.

43
Ruggiero, L.F.; Aubty, K.B.; Carey, A.B., Huff, M.H., tech. coords. 1991. Wildlife

and vegetation of unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-GTR285. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 533 p.

Ruth, Robert H.; Bernsten, Carl M. 1955. A 4-year record of Sitka spruce and

western hemlock seed fail on the Cascade Head Experimental Forest. Res.

Pap. 12. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Forest and Range Experiment Station. 13 p.

Sanders, Susan D. 1983. Foraging by Douglas tree squirrels (Tamiasciurus

douglasii: Rodentia) for conifer seed and fungi. Davis, CA: University of California.

95 p. Ph.D. dissertation.

Schopmeyer, C.S. 1974. Seeds of woody plants in the United States. Agric.

Handb. 450. Washington, DC: U.S. Department of Agricutture: 674-683.

Shaw, W.T. 1936. Moisture and its relation to the cone-storing habit of the western

pine squirrel. Journal of Mammalogy. 17: 337-349.

Smith, Christopher C. 1970. The coevolution of pine squirrels (Tamiasciunrs) and

conifers. Ecological Monographs. 40: 349-374.

Smith, Christopher C. 1978. Structure and function of the vocalizations of tree

squirrels (Tamiasciums). Journal of Mammalogy. 59: 793-808.

Smith, Christopher C. 1981. The indivisible niche of Tamiasciums: an example of

nonpartitioning of resources. Ecological Monographs. 51: 343-363.

Smith, Christopher Carlisle. 1965. interspecific competition in the genus to tree

squirrels Tamiasciurus. Seattle: University of Washington, 269 p. Ph.D. thesis.

Smith, Christopher Carlisle. 1968a. The adaptive nature of social organization in

the genus of three [sic] squirrels Tamiasciurus. Ecological Monographs. 38: 31-63.

Smith, Christopher C.; Balda, Russell P. 1979. Competition among insects, birds,

and mammals for conifer seeds. American Zoologist. 19: 1065-1083.

Smith, Christopher C.; Reichman, O.J. 1984. The evolution of food caching by

birds and mammals. Annual Reviews of Ecology and Systematics. 15: 329-351.

Smith, M.C. 1968b. Red squirrel responses to spruce cone failure in interior Alaska.

Journal of Wildlife Management. 32: 306-316.

Sullivan, Thomas P.; Moses, Richard A. 1986. Red squirrel populations in natural

and managed stands of lodgepole pine. Journal of Wildlife Management.

50: 595-601.

Sullivan, Thomas P.; Sullivan, Druscilla S. 1982. Population dynamics and regulation of the Douglas squirrel (Tamiasciums douglasii) with supplemental food.

Oecologia. 53: 264-270.

Sullivan Thomas P. ; Sullivan, Druscllia S.; Krebs, Charles J. 1983. Demographic

response of a chipmunk (Eutamias townsendii) population with supplemental food.

Journal of Animal Ecology. 52: 743-755.

44
Tevis, Lloyd, Jr. 1956. Responses of small mammal populations to logging of

Douglas-fir. Journal of Mammalogy. 37: 189-196.

Vrieze, John M. 1980. Spatial patterning of red tree mouse nests. Arcata, CA:

Humboldt State University. 37 p. M.S. thesis.

Wallen, Kurt. 1982. Social organization in the dusky-footed woodrat (Neotoma

fuscipes): a field and laboratory study. Animal Behavior. 30: 1171-1182.

Waiters, Roland Dick. 1949. Habitat occurrence and notes on the life history of the

dusky-footed woodrat, Neotoma fuscipes Baird. Corvallis, OR: Oregon State

College. 122 p. M.S. thesis.

Ward, James Patrick, Jr. 1990. Spotted owl reproduction, diet and prey abundance

,in northwest California. Arcata, CA: Humboldt State University. 70 p. M.S. thesis.

Wells-Gosling, Nancy; Heaney, Lawrence R. 1984. Glaucomys sabrinus. Mammalian Species. 229: 1-8:

Woods, S.E. 1980. The squirrels of Canada. Ottawa: National Museums of Canada.

199 p.

Yeager, L.E. 1937. Cone piling by Michigan red squirrels. Journal of Mammalogy.

18: 191-194.

Zentner, Phillip Lee. 1977. The nest of Phenacomys longicaudus in northwestern

California. Sacramento; CA: California State University. 59 p. M.S. thesis.
Appendix Stand condition categories and their Old Growth Forest Wildlife Habitats Research 

and Development Program (OGWHP) equivalents. 

Stand condition Descriotion a 

Grass-forb Shrubs ~40 percent cover and ~5 feet tall; 

ranges from no vegetation to dominance by 

herbs; tree seedlings c5 feet tall and <40 

percent cover. OGWHP: clearcut, late 

clearcut 

Shrub 

Open sapling-pole 

Shrubs >40 percent cover; trees c40 percent 

cover and ~1 inch d.b.h. OGWHP: late 

clearcut, shrub stage of forest development 

Average d.b.h. >l inch and tree cover 

~60 percent; saplings l-4 inches d.b.h.; poles, 

4-9 inches d.b.h. OGWHP: late clearcutsapling stage of forest development 

Closed sapling-pole-sawtimber Average d.b.h. 1-21 inches, crown cover 

>60 percent. OGWHP: sapling-pole; young 

forest (sawtimber) 

Large sawtimber Average d.b.h. >21 inches; crown cover 

<lOO percent; decay and decadence lacking. 

OGWHP: mature forest. 

Old growth Stand >200 years old, at least 2 tree layers, 

decay in living trees, snags, fallen trees. 

0GWH.P: old growth. 

a Most stands studied by the OGWHP were naturally regenerated; however, most of the young stands 

studied in the arboreal rodent studies were regenerated through timber harvesting. Naturally regenerated 

young forest and mature forest often had substantial carryovers of old-growth components from the 

previous stand, including coarse woody debris, snags, and large trees. When such components were 

major parts of stands studied in the arboreal rodent studies, I designated the stand “old forest” when the 

components were major parts of the stand and “mixed-age” forests when they were minor but significant 

parts of the stand. 

Source: Brown 1985. 

46 *U.S. GOVERNMENTPRINTINGOFFICE: 199%891~9W/6Wll 
Carey, Andrew B. 1991. The biology of arboreal rodents in Douglas-fir forests. Gen.Tech.

Rep. PNW-GTR-276. Portland,OR: U.S. Departmentof Agriculture, Forest Service, Pacific

Northwest Research Station. 46 p. (Huff, Mark H.; Holthausen, Richard S.; Aubry, Keith B.,

tech. coords.; Biology and management of old-growth forests).

Arboreal rodents in Douglas-fir forests west of the Cascade crest in Oregon and Washington

include (listed in decreasing order of dependence on trees) red tree vole (Phenacomys

longicaudus), northern flying squirrel (Glaucomys sabrinus), Douglas squirrel (Tamiasciurus

douglasii), dusky-footed woodrat (Neotoma fuscipes), bushy-tailedwoodrat (Neotoma cinerea),

and Townsend’s chipmunk (Tamias townsendii). The arboreal rodents constitute an ecological

community-a group of species that interact and influence one another’s pattern of abundance

and use of resources. All but the Douglas’ squirrel and Townsend’s chipmunk are important

prey of the spotted owl (Strix occidentalis). The arboreal squirrels are mycophagists and have

important functions in ecosystem processes. Individual species exist in many habitats, but the

arboreal rodent community reaches its highest diversity and abundance in old-growth forests.

The rodents are not evenly distributed, however, across the Pacific Northwest; maximum

diversity and abundance in the community occurs in mixed-conifer, old-growth forests that

contain streams. Although the species differ in life histories and ecologies, all seem sensitive

to timber harvesting because of both elimination of habitat and creation of barriers to dispersal.

Keywords: Bushy-tailed woodrat, Douglas’ squirrel, dusky-footed woodrat, northern flying

squirrel, old growth, red tree vole, Townsend’s chipmunk, Oregon, Washington.

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