Mammals of the Pacific Northwest
This remarkable book offers an intimate look at the life histories and habitats of mammals in the Pacific Northwest, from the coast to the high Cascades. In introducing the region's mammals, Chris Maser combines current scientific knowledge with personal accounts and anecdotes drawn from over a quarter century of fieldwork in Oregon. The book covers the natural history of 89 mammals in Oregon, 70 in Washington, 67 in British Columbia, and 83 in Northern California.
For each species of mammal, the book provides a physical description and detailed information on distribution, habitat, and behavior. A keen observer of animal life, Maser relates his own encounters in the wild-from a rare, firsthand description of how shrews hunt and kill their prey to a tour of a mountain beaver's burrow-to help readers better understand the animals he has come to know. Maser delves into the secrets of how mammals live and explores the dynamic relationships between the mammals of the Pacific Northwest and their habitats.
Intended for general readers and students, Mammals of the Pacific Northwest provides a fascinating natural history of the region's wildlife. The book is illustrated with over 100 photographs of mammals and their tracks, dens, nests, and young.
About the author
Chris Maser spent over 20 years as a research scientist in natural history and ecology. He currently lives in Corvallis, Oregon, where he writes about and consults on sustainability issues. He is the author of numerous books, including Forest Primeval: The Natural History of an Ancient Forest (Oregon State University Press, 2001), and co-author of Fleas of the Pacific Northwest (Oregon State University Press, 1988).
Read more about this author
Map of Zones in Western Oregon
Pouched Mammals, Didelphimorpha
- Opossums, Didelphis
- Opossum, Dedelphis virginianus
Insect-eating Mammals, Insectivora
- Long-tailed shrew, Sorex
- Wandering shrew, Sorex vagrans
- Dusky and Yaquina shrews, Sorex obscurus and Sorex yaquinae
- Pacific shrew, Sorex pacificus
- Marsh shrew, Sorex bendirei
- Northern water shrew, Sorex palustris
- Trowbridge shrew, Sorex trowbridgei
- Moles, Talpidae
- American Shrew-mole, Neürotrichus
- American Shrew-mole, Neürotrichus gibbsi
- Western American Moles, Scapanus
- Townsend mole, Scapanus townsendi
- Coast mole, Scapanus orarius
- Broad-handed mole, Scapanus latimanus
Winged Mammals, Chiroptera
Evening Bats, Vespertilionidae
- Mouse-eared Bats, Myotis
- Little brown bat, Myotis lucifugus
- Yuma bat, Myotis yyumanensis
- Long-eared bat, Myotis evotis
- Fringed bat, Myotis thysanodes
- Long-legged bat, Myotis volans
- California bat, Myotis calcus
- Silver-haired Bats, Lasionycteris
- Silver-haired bat, Lasionycteris noctivagans
- Big Brown Bats, Eptesicus
- Big brown bat, Eptesicus fuscus
- Hairy-tailed Bats, Lasiurus
- Hoary bat, Lasiurus cinereus
- Big-eared Bats, Plecotus
- Western big-eared bat, Plecotus townsendi
- Pallid Bats, Antrozous
- Pallid bat, Antrozous pallidus
Free-tailed Bats, Mastiff Bats, Molossidae
- Free-tailed Bats, Tadarida
- Brazilian free-tailed bat, Tadarida brasiliensis
Hopping Mammals, Lagomorpha
Pikas or rock Rabbits, Ochotonidae
- Pikas, Ochotona
- Pika, Ochotona princeps
Hares and Rabbits, Leporidae
- Hares, Lepus
- Snowshoe hare, Lepus americanus
- Black-tailed hare, Lepus californicus
- Rabbits, Sylvilagus
- Brush rabbit, Sylvilagus bachmani
- Eastern cottontail, Sylvilagus floridanus
Gnawing Mammals, Redentia
Mountain Beaver, Aplodontidae
- Mountain Beaver, Aplodontia
- Mountain beaver, Aplodontia rufa
Chipmunks and Squirrels, Sciuridae
- Chipmunks, Tamias
- Townsend chipmunk, Tamias townsendi
- Yellow-pine chipmunk, Tamias amoenus
- Ground Squirrels, Spermophilus
- Beechey ground squirrel, Spermophilus beldingi
- Mantled ground squirrel, Spermophilus lateralis
- Marmots, Marmota
- Yellow-bellied marmot, Marmota flaviventris
- Gray Squirrels and Fox Squirrels Sciurus
- Western gray squirrel, Sciurus griseus
- Eastern gray squirrel, Sciurus carolinensis
- Eastern fox squirrel, Sciurus niger
- Red Squirrels and Chickarees Tamiasciurus
- Chicarees, Tamiasciurus douglasi
- Flying Squirrels Galaucomys
- Northern flying squirrel, Galaucomys sabrinus
Pocket Mice and Kangaroo Rats, Heteromyidae
- Kangaroo Rats, Dipodomys
- Heermann kangaroo rat, Dipodomys heermanni
Pocket Gophers, Geomyidae
- Western Pocket Gophers, Thomomys
- Camas pocket gophers, Thomomys bulbivorus
- Mazama pocket gophers, Thomomys mazama
- Botta pocket gophers, Thomomys bottae
True Beavers, Castoridae
- True Beaver, Castor
- North American beaver, Castor canadensis
Rats and Mice, Muridae
Indigenous Rats and Mice, Sigmodontinae
- Harvest Mice, Reithrodontomys
- Western harvest mouse, Reithrodontomys megalotis
- Deer Mice and White-footed Mice, Peromyscus
- Deer Mouse, Peromyscus maniculatus
- Piñon Mouse, Peromyscus truei
- Woodrats, Neotoma
- Dusky-footed woodrat, Neotoma fuscipes
- Bushy-tailed woodrat, Neotoma cinerea
- Red-backed Voles, Clethrionomys
- California red-backed Vole, Clethrionomys californicus
- Heather Voles, Phenacomys
- Heather vole, Phenacomys intermedius
- White-footed Vole and Tree Voles, Arborimus
- White-footed vole, Arborimus albipes
- Oregon red tree vole, Arborimus longicaudus
- Meadow Voles, Microtus
- Townsend vole, Microtus townsendi
- Long-tailed vole, Microtus longicaudus
- Creeping or Oregon vole, Microtus oregoni
- Gray-tailed vole, Microtus canicaudus
- Montane vole, Microtus montanus
- California vole, Microtus californicus
- Water vole, Microtus richardsoni
- Muskrats, Ondatra
- Muskrat, Ondatra zibethicus
Old World Rats and Mice, Murinae
- Old World Rats, Rattus
- Black Rats, Rattus rattus
- Norway Rats, Rattus norvegicus
- House Mice, Mus
- House Mouse, Mus musculus
Birch Mice and Jumping Mice, Zapodidae
- North American Jumping Mice, Zapus
- Pacific jumping mouse, Zapus trinotatus
New World Porcupines, Erethizontidae
- North American Porcupines, Erethizon
- North American porcupine, Erethizon doratum
- Coypus, Myocastor
- Coypu or Nutria Myocastor coypus
Flesh-eating mammals, Carnivora
Dogs and Foxes, Canidae
- Dogs, Coyotes, Wolves, Canis
- Coyote, Canis latrans
- Red foxes, Vulpes
- Red fox, Vulpes vulpes
- Gray foxes, Urocyon
- Gray fox, Urocyon cinereoargenteus
- North American Black Bear, Ursus
- North American black bear, Ursus americanus
Ringtails, Raccoons, and Allies, Procyonidae
- Ringtail, Bassariscus
- Ringtail, Bassariscus astutus
- Raccoons, Procyon
- Raccoon, Procyon lotor
Martens, Weasels, Skumks, Otters, and Allies, Mustelidae
- Martens and Fishers, Martes
- North American marten, Martes americana
- Fisher or Pekan, Martes pennanti
- Wolverine, Gulo
- Wolverine, Gulo gulo
- Weasels, Minks, and Allies, Mustela
- Short-tailed weasel, Mustela erminea
- Long-tailed weasel, Mustela frenata
- Mink, Mustela vison
- Spotted Skunks, Spilogale
- Spotted skunk, Spilogale putorius
- Striped and Hooded Skunks, Mephitis
- Striped skunk, Mephitis mephitis
- River Otters, Lutra
- River Otter, Lutra canadensis
Cats, Lynxes, and Allies, Felidae
- True Cats, Felis
- Puma, cougar, or mountain lion, Felis concolor
- Lynxes, Bobcats, and Caracals, Lynx
- Bobcat, Lynx rufus
Even-toed hoofed Mammals, Artiocactyla
North American Elk, Deer, and Allies, Cervidae
- North American Elk, and Allies, Cervus
- North American Elk, Cervus elephus
- Mule Deer and White-tailed Deer, Odocoileus cervus
- Mule deer, Odocoileus hemionus
- White-tailed deer, Odocoileus virginianus
Appendix 1: Common and Scientific Names
Appendix 2: Table of Mammals' Location in the Northwest
When I was asked to write this book for the Oregon State University Press, I was thrilled. My first conscious memory, at age two, is of a sand crab along the ocean's edge. My next searing memory is of a garter snake that would not come out of the bush into which it had crawled to escape the clutch of my four-year-old hands. Ever since, I have wanted to study animals as a scientist. I have now spent over thirty years in a consummate love affair with science--mostly studying mammals in the wild to understand their habitats and habits and how they intersect.
I shall not present you with a scientific treatise in the strict sense; instead I shall do rny best to acquaint you with the mammals through the love, respect, and fascination with which I have over many years learned to know them. I do this in the hope of giving you a greater appreciation of the mammals with whom we share the Earth.
Because I am presenting a general natural history covering a wide range of information, I have dispensed with referencing the literature in the text, including my own studies, to keep this book as simple and readable as possible, but I have included a section of selected references. Having said this, however, I want it clearly understood that I have liberally used my own previous work and also that of many others. Therefore, this book should in no way be construed as solely my work. Where I have used published works of which I was the major contributor, I have occasionally written in the first person because the experiences about which I am writing are my own. Where I have had a major hand in a comparative study that has been published in a journal, I have, when it seems in the reader's interest, used it freely.
For anyone interested in a current scientific review of the mammals of Oregon, as well as their known geographical distributions within the state, I recommend The Land Mammals of Oregon by Verts and Carraway. This book also includes the contemporary scientific thinking about the taxonomic relationships of mammals in Oregon.
Natural history inquires into the secrets of an animal's life, not only how it lives as an individual but also how it relates to other individuals of its own kind, to other kinds of animals, and to its environment as a whole.
One of the early natural historians was Vernon Bailey, who in 1936 published The Mammals and Life Zones of Oregon, the first comprehensive work on mammals in the state. From 1962, when I entered graduate school at Oregon State University, until I left active research in 1987, I spent many years following Bailey's footsteps around the state as I too studied the mammals of Oregon. Although I had more sophisticated tools at my disposal than did Bailey and therefore learned things beyond his knowledge, I did not in any way improve on the quality of his work. To this day, I hold in awe the dedication, accuracy, integrity, and insight of Vernon Bailey's field work. Sadly, I never had the opportunity to meet him; I should very much have liked to.
Natural history, in my experience, seems to have been carried out primarily by two kinds of people those who were gentlemen in the true sense of the word (such as Kenneth L. Gordon, Murray L. Johnson, Tracy I. Storer, and Walter P. Taylor) and those who were lovable characters (such as Bill Hamilton Jr. or "Wild Bill," as he was affectionately known, and Robert M. Storm--the only one of my role models still living.
It is with a real sense of loss that I watch the era of natural history drawing swiftly to a close, an era that allowed a softer personal touch into our relationship with Nature. I say this because the natural history that I knew was truly a science of forest, meadow, and fen, of mountain, desert, and sea, where I and others lived for weeks at a time out in the elements with the creatures we studied. It was a science of mutual relationships in a slower, gentler, quieter period in human history when there was ample time to reflect on a sunrise, a drifting cloud, a passing thought. It is thus in the spirit of natural history as I knew it that I pen this book as a tribute not only to the era of science that I loved so much but also to the men who helped to shape that era and who, as gentleman and character alike, shared it with me.
I have, to the best of my ability, written this book for a general audience. For this reason, I have included information acquired from places beyond the geographical scope of this book to help you, the reader, round out your understanding of the species as a whole. If I were to limit my discussion to data derived solely within the boundaries of western Oregon, where I have done most of my work, I would have far less to share with you, because one person can only do so much in a lifetime, and the mammals of Oregon have seldom been studied in the field over long periods of time by resident mammalogists who lived with them and got to know them intimately in their own habitats.
In addition, the coverage of individual species in this book varies. Some species have been more widely studied and/or have been studied over longer periods of time. Consequently, the data available on any given species are uneven and there are always some data of which I am unaware.
To make the text as readable as possible, I provided an appendix of common and scientific names of plants and animals mentioned in the book, as well as a glossary of terms. I have endeavored to avoid as much jargon as possible and to make the format as simple as possible by moving from the general to the specific as follows:
In so doing, it is necessary at times to be consciously repetitious in that similar information may appear in more than one place in the text so that each species account will stand on its own. From those of you with some familiarity with the mammals, I ask your forgiveness and your patience. For the sake of those readers who are in fact unfamiliar with mammals, I have assumed that all readers possess little or no knowledge of our global traveling companions.
In order to be able to talk to one another about mammals--or any other organisms--we must agree on what to call them. In everyday conversation, we use a common name, like mouse or bat. Scientists need names that are more precise, and they use a system that was first proposed in a book published in 1758 by the Swedish naturalist Carl von Linné, better known by his Latinized name Carl Linnaeus. His system divided living beings into five kingdoms, and then into smaller and smaller groups as follows: phyla, classes, orders, families, genera, and finally species, of which about 1.5 million have been named, though scientists estimate that there are perhaps as many as 30 million on Earth.
The mammals are in the Kingdom Animalia, Phylum Cordata (sub-phylum Vertebrata), and comprise the Class Mammalia, which Linnaeus created from the Latin word mamma, meaning the breast, for those animals that produce milk and nurse their young. The Class Mammalia is divided into 21 orders, only seven of which are represented by terrestrial mammals living in western Oregon.
The system of nomenclature that Linnaeus invented combines two names--that of the genus and of the species--to describe a given organism. As an example, the small treedwelling red tree vole of western Oregon, is called Arborimus longicaudus. The generic name Arborimus is derived from the Latin words arboris (tree) and mus (mouse); the specific name longicaudus is derived from the Latin words longus (long) and cauda (tail). This accurately describes the "longtailed tree mouse," which also happens to have reddish fur and is thus commonly know as the red tree mouse or vole.
The white-footed vole also lives in western Oregon. Although it is related to the red tree vole, it is primarily a ground-dweller, though it can and does climb. The relationship between the two is indicated by including both animals in the same genus Arborimus, but the latter is identified as a separate species by the specific name albipes, derived from the Latin words albus (white) and pes (foot). While the specific name identifies the individual kind of mammal, the generic name identifies the close relationship among two or more kinds of individuals. So, the scientific binomial, say Arborimus albipes, describes both the individual and collective properties of the animal.
Just because a mammal has been given a scientific name does not mean that the evolutionary relationship implied by the name is accepted by everyone, though many are. In part, this is because each person who studies mammals weighs the reported evidence independently against his or her own measure of experience in the field as a whole and/or with that particular mammal. Coupled with this is the fact that each person sees the data and its interpretation through his or her own particular lens.
I am no exception. I, too, am subjective without recourse because I am human with all the frailties that encompasses. But, while I may respect the quality of another persons' work and the integrity of her or his perceptions and interpretations, I reserve the right to disagree. It is possible, after all, that the ideas of one who disagrees with conventional wisdom may prevail in the end. Having said this, however, I hasten to add that I do not know what is right, of course, but neither does anyone else. Science is predominantly a process of hypothesizing, testing, and testing again. We are never completely certain of the accuracy of a hypothesis; we just know it has not been disproved--yet.
The word "species" has one significance to a student of taxonomy and another to the student of evolution. To the student of taxonomy, the concept of a species is a practical device designed to reduce the almost endless variety of living things to a comprehensible system of classification. To the student of evolution, a species is a passing stage in the stream of everchanging habitats to which the species must adapt or become extinct.
Before 1935, scientists based most definitions of species on the degree to which they were distinct in form and structure. They paid little attention to evolutionary relationships. In 1937, scientists revisited the definition and began to emphasize the dynamic aspects of species--their potential for change. Today, species are thought of as groups of natural populations that can and do interbreed with one another but are reproductively isolated from other such groups, which means that, even if members of the two species were put together, they could not produce fertile offspring of both sexes.
For example, Oregon and California red tree voles live primarily in Douglas fir trees in western Oregon and northwestern California. The two species meet occasionally in the vicinity of the Smith River just south of the Oregon-California border and may interbreed now and then. But hybrid males, those produced by such a union, are sterile. Hybrid females, on the other hand, though fertile, can breed only with a male of one species or the other. Because the habitat is not well suited for either species, there are not enough voles to populate the area and the hybrid females are therefore unlikely to find a mate; thus is the integrity of the two species maintained.
Darwin himself was of the opinion that evolution was both continual and gradual. His theory says that evolution proceeds by mutation and natural selection. Mutations, which are simply random "mistakes" in the repetition of the genetic code passed from parent to offspring, are produced by all species at a more or less constant rate. Most individuals with mutations are eliminated through time, because they are "faulty" in some respect and unable to reproduce or adapt as well as "normal" individuals.
But occasionally a mutation arises that renders the individual more, rather than less, fit to survive and reproduce. When this happens, the individual is given a chance to pass its mutant genes on to its own offspring, which in turn passes them to its own offspring, and so on until the mutant trait becomes both dominant and "normal" in the population.
So through the combination of random mutations and natural selection, species continue to evolve, weeding out the less fit in favor of the more fit, until they occupy all available habitat niches in the biosphere, which keeps changing, so that the species must continue adapting.
Darwin probably adopted these two basic but unnecessary assumptions--that evolution is both gradual and continual--more out of innate conservatism than weighty scientific evidence. He thought that Nature made no "great leaps," which for him resembled the uncomfortable, sudden changes, such as revolutions, that transform human society. The dominant personalities of Darwin's time abhorred the revolutionary process of wholesale transformations, clinging instead to the idea of tiny, continual changes. Then, a hundred and twenty years after Darwin's On the Origin of Species was first published, Stephen Jay Gould and Niles Eldredge, two American paleobiologists, wrote a seminal paper introducing the theory of evolutionary leaps. In their theory, these leaps, although dramatic, occur relatively infrequently.
Evolutionary stability, it appears, is the normal course of events in the persistence of species over long periods of time. Paleontologists have long dismissed the lack of evidence of evolutionary change, assuming that it simply reflected gaps in the fossil record. But the fossil record, although perhaps imperfect, does not prove that evolution is a continual process.
In fact, evolution, as it now appears, proceeds through leaps of "speciation" (the sudden dominance of new species) rather than through a slow, gradual, continual perfecting of existing species to fit changing conditions. In this new theory of periodic leaps of speciation, evolutionary change, rather than affecting individuals as survivors and reproducers, affects the entire system, which is composed of living organisms as they interact within their environments. Evolution occurs when a dominant species fails to adapt successfully to changes in its habitat, so that it can be challenged by a new species, which may have emerged "haphazardly" at the edge of the cycle of dominance. Thus the dynamic equilibrium is broken as the old species is suddenly replaced by the emerging new species in a leap of evolution. So, according to this most recent theory, new species are selected in sudden bursts of evolution during periods of critical instability for dominant species.
Some ancient species, such as opossums, are unlikely to become extinct because they live in environments that vary so much from day to day, month to month, and year to year, that they are unlikely to meet anything in the future they have not already survived in the past. Some other organisms are in much more severe danger of extinction. Perhaps they are the only surviving species of a taxonomic group that was once considerably richer. Perhaps they have not changed in millions of years. Most likely they are adapted only to specific habitats threatened with drastic modification.
Extinction carries two meanings, one local and one global. A local extinction refers to a particular population, such as the red squirrel on Mt. Graham, a "mountaintop island" in the desert of Arizona. A global extinction, on the other hand, refers to an entire species (all the red squirrels in the world). Local populations may and often do disappear, either temporarily or permanently, without implying the extinction or even the near extinction of the species. A species, on the other hand, is composed of the sum of its populations, so the loss of populations will affect the species as a whole and may imply danger to its survival. Global extinction happens at the exact moment when either one of the last breeding pair dies. The minimum size of a population is thus critical to its continued survival in the face of change; the smaller a population is, the more susceptible it is to extinction from a variety of causes. Why do we need such a variety of species anyway? Is the loss of one or two species very important?
One marvelous effect of a wide variety of species is that they increase the stability of ecosystems by means of feedback loops--the means by which processes reinforce themselves. Strong, self-reinforcing feedback loops characterize and strengthen many interactions in Nature and have long been thought to account for the stability of complex systems. Ecosystems with such strong interactions among components can be complex, productive, stable, and resilient under the conditions to which they are adapted. But when these critical loops are disrupted, such as by the extinction of species, these same systems become fragile and easily affected by slight changes.
Although an ecosystem may be stable and able to respond effectively to disturbances to which it is adapted, it may be exceedingly vulnerable to the introduction of foreign disturbances to which it is not adapted. Nevertheless, ecosystems have a certain amount of redundancy built into them, which means that more than one species is able to perform similar functions. This is a type of ecological insurance policy that strengthens the ability of the system to retain the integrity of its basic relationships. Redundancy means that the loss of a species or two is not likely to result in such severe functional disruptions of the ecosystem as to cause its collapse because other species can make up for the functional loss. But there comes a point, a threshold, when the loss of one or two more species may tip the balance and cause the system to begin a noticeable and irreversible change.
Each species of living organism performs a specific function that in one way or another benefits the whole ecosystem. Diversity of plants and animals therefore plays a seminal role in buffering an ecosystem against disturbances from which it cannot recover.
As forests become poorer in species of plants through the conversion of forests into biologically simplified tree farms, the number of species of birds, mammals, and other creatures will also decline. The complex, interconnected, interdependent feedback loops among plants and animals will gradually simplify. Some of the species of which the feedback loops are composed will be lost forever--and the feedback loops with them. This is how the evolutionary process works. Ecologically, it is neither good nor bad, right nor wrong, but these changes may make the forest less attractive, less usable by species, including humans, that use to rely on it for their livelihoods and for products.
Most people are probably aware of predator-prey relationships and especially those of the charismatic grazing megafauna of the African plains, thanks in large part to television. But few of us have any concept of the intricate relationships between the small, secretive mammals of the forest and the health of those forests, which stand as a symbol of western Oregon and the Pacific Northwest. With this in mind, let's take a peek into the incredible web of life in our western Oregon coniferous forests.
All things in Nature's forest are neutral; Nature assigns no extrinsic values to this mammal or that, to this plant or that. Each piece of the forest, whether a bacterium, mushroom, mouse, or 800-year-old Douglas fir tree, carries out its prescribed function, interacting with other components of its habitat through their prescribed interrelated processes. None is more valuable than another; each is only different from the other. The northern flying squirrel is a primary example of the dynamic interactions of small mammals, fungi, water, nutrients in the soil, and trees in the coniferous forests of western Oregon.
The northern flying squirrel is common in conifer and mixed conifer-hardwood forests from the Arctic tree line throughout the northern conifer forests of Alaska and Canada, South through the Cascade Mountains of Washington and Oregon and the Sierra Nevada mountains of California almost to Mexico, the Rocky Mountains to Utah, and the Appalachian Mountains to Tennessee.
It is seldom seen because it is nocturnal. It is primarily a mycophagist, a fungus eater. in northern Oregon, it eats mostly truffles, which are the reproductive bodies of below ground fruiting fungi, and epiphytic lichens (that grow on trees). In northeastern Oregon, truffles are the principal food from July to December; from December through June, the lichen Bryoria fremonti is the squirrel's predominant food, as well as its sole nest material. In southwestern Oregon, truffles are the major food throughout the year, and lichens are not important in the overall diet.
The term mycorrhiza which literally means "fungus root," denotes the symbiotic relationship between certain fungi and the plant roots on which they live. Fungi that produce truffles are probably all mycorrhizal. Woody plants in the families Pinaceae (pine, fir, spruce, larch, Douglas-fir, hemlock), Fagaceae (oak), and Betulaceae (birch, alder) in particular depend on mycorrhiza forming fungi for the uptake of nutrients. This phenomenon can be traced back some 400 million years to the earliest known fossils of plant rooting structures.
Mycorrhizal fungi absorb nutrients and water from soil and translocate them to the host plant. in turn, the host plant provides sugars from its own photosynthesis to the mycorrhizal fungi. Threadlike fungal hyphae (the "mold" part of the fungus) extend into the soil and serve as extensions of the host's root system and are both physiologically and geometrically more effective for nutrient absorption than the roots themselves.
The most obvious relationship between the squirrel and the forest occurs on the surface of the ground, when the squirrels forage for food. The nesting and reproductive behavior of these squirrels remains relatively obscure because of their nocturnal habits, as will discussed in a later chapter on rodents. In probing the secrets of the flying squirrel, however, some functionally dynamic, interconnecting cycles emerge, beginning with mycorrhizal fungi.
The host plant provides simple sugars and other metabolites to the mycorrhizal fungi, which lack chlorophyll and are not good at deriving their nutrients from dead or decaying organic material. Fungal hyphae penetrate the tiny, nonwoody rootlets of the host plant to form a balanced, harmless mycorrhizal symbiotic relationship with the roots. The fungus absorbs minerals, other nutrients, and water from the soil and translocates them into the host. Also, nitrogen fixing bacteria inside the mycorrhiza use a fungal "extract" as food and in turn fix atmospheric nitrogen (To "fix" nitrogen is to take gaseous, atmospheric nitrogen and alter it in such a way that it becomes available and usable both by the fungus and the host tree.)
In effect, mycorrhiza-forming fungi serve as a highly efficient extension of the host root system. Many of the fungi also produce growth regulators that induce production of new root tips and increase their useful life span. At the same time, host plants prevent mycorrhizal fungi from damaging their roots. Mycorrhizal colonization enhances resistance to attack by pathogens. Some mycorrhizal fungi produce compounds that prevent pathogens from contacting the root system.
Flying squirrels nest and reproduce in the tree canopy and come to the ground at night, where they dig and eat truffles. As a truffle matures, it produces a strong odor that attracts the foraging squirrel. Evidence of a squirrel's foraging remains as shallow pits in the forest soil and occasional partially eaten truffles.
Truffles contain nutrients necessary for the small animals that eat them. When flying squirrels eat truffles, fungal tissue that contains nutrients, water, viable fungal spores, nitrogen fixing bacteria, and yeast, which are all important in the forest network. Pieces of truffle move to the stomach, where fungal tissue is digested, then through the small intestine, where absorption takes place, and then to the cecum. The cecum is like an eddy along a swift stream; it concentrates, mixes, and retains fungal spores, nitrogen fixing bacteria, and yeast. Captive deer mice, for example, retained funga spores in the cecum for more than a month after ingestion. Undigested material, including cecal contents, is formed into fecal pellets in the lower colon; these pellets contain all the viable elements necessary to inoculate the root tips of trees with prolonged life.
A fecal pellet is thus more than a package of waste products; it contains four components of potential importance to the forest: (1) viable spores of mycorrhizal fungi; (2) yeast, which is a part of the nutrient base, has the ability to stimulate both growth and nitrogen fixation in the bacteria, and may also stimulate spore germination; (3) nitrogen-fixing bacteria; and (4) the entire nutrient requirement for nitrogen fixing bacteria, and an "antifreeze" that protects them during the cold of winter, without which the bacterial cells would rupture and die when feces deposited during winter thawed in spring.
The California redbacked vole and the deer mouse serve similar ecological functions in the same forest as the flying squirrel. When squirrels, mice, and voles dig at the bases of trees, the organisms in their feces can inoculate the trees' rootlets with nitrogen-fixing bacteria, yeast, and spores of mycorrhizal fungi. The deer mouse, however, not only lives within the forest but also is one of the first small mammals to occupy clearings after logging or fire, so it can inoculate the soil with viable nitrogen fixing bacteria, yeast, and spores of mycorrhizal fungi--even the soil that has been severely altered by a hot fire.
The fate of fecal pellets varies, depending on where they fall. In the forest canopy, the pellets might remain and disintegrate in the tree tops, or drop to a fallen, rotting tree and inoculate the wood. On the ground, a squirrel might defecate on a disturbed area of the forest floor, where a pellet could land near a conifer feeder rootlet that may become inoculated with the mycorrhizal fungus when spores germinate. If environmental conditions are suitable and root tips are available for colonization, a new fungal colony may be established. Otherwise, hyphae of germinated spores may fuse with an existing fungal thallus (the nonreproductive part of the fungus) and thereby contribute and share new genetic material.
These rodents exert a dynamic, functionally diverse influence within their habitat--the forest. The complex of effects ranges from the crown of the tree, down through the surface of the soil into its mantle where, through mycorrhizal fungi, nutrients are conducted through roots, into the trunk, and up to the crown of the tree, perhaps into the squirrel's own nest tree.
Such relationships are by no means confined to the northern flying squirrel or even to the North American continent. Many mammals, such as deer mice, white-footed mice, red-backed voles, chipmunks, mantled ground squirrels, chickarees or Douglas squirrels, western gray squirrels, and even pikas, heather voles, deer, elk, and black bear depend more or less on truffles for food.
Unfortunately, small mammals, especially rodents, can be destructive to young trees and millions of small rodents and other animals have died as a result of poisons and purposeful habitat manipulation. But the more forests are altered by human actions, the greater becomes the need to understand the interaction of all the organisms in the ecosystem. How each component functions is often far more complex than might be anticipated, and the role it plays may be essential in maintaining ecosystem health. The mammals of western Oregon and their habitats must therefore be understood in relation to one another in order to understand either the mammals or their functions within their respective habitats. This understanding is the purpose of studying natural history.
As the statement on the back cover of the book indicates, my field work was carried out in western Oregon, the boundaries of which I define as follows:
- The northern boundary is the Columbia River because it acts as a natural barrier to the dispersal of some mammals.
- The eastern boundary is the interface between the lower edge of the moist subalpine fir forest and the upper edge of the dry ponderosa pine forest, which occurs along the upper to middle elevation of the eastern flank of the High Cascade Mountains. The High Cascade Mountains are the geologically younger eastern portion of the range that is characterized by such peaks as Mt. Hood, Mt. Jefferson, and the Three Sisters, as opposed to the geologically older western portion, which lacks high snow-clad peaks in summer.
I have chosen this line of demarcation for the following reasons: (1) It makes sense ecologically because the height and nature of these mountains, which run north and south, form a "rain shadow" by trapping most of the precipitation west of the mountain's crest; (2) this rain-shadow effect creates wetter habitats west of the crest and drier habitats east of the crest; the boundary between these two extremes is remarkably abrupt at the interface between the lower edge of the moist subalpine fir forest and the upper edge of the dry ponderosa pine forest, which is easily defined in most places in the field within a few hundred yards; (3) this interface of forest types acts as a natural barrier to a number of mammalian species from both sides of the mountains; and (4) you know on the ground when you have crossed from one type of forest into the other.
- The southern boundary of this book is of necessity the California border for two reasons. First, there is a dramatic change in vegetation--habitats--along the southern coastal area that straddles the Oregon-California border. This juxtaposition of habitats also extends eastward from the coast to some extent, but not with the clarity of the forest types on the eastern flank of the High Cascade Mountains. Second, and less satisfactory, I have to draw the line somewhere, and on a map at least people have an idea of where they are.
- The western boundary of a book on land mammals seems intuitively obvious as one stands on the shore of the Pacific Ocean and gazes out over a seemingly endless expanse of water.
I have also devised a simple map, shown on page 16, which divides western Oregon into five physiographical zones, each of which enjoys some ecological integrity. The distribution of each species of mammal is thus designated on the map by the number of the zone or zones in which it is known to occur. Although the map pertains to western Oregon, the physiographical zones, such as the Coast Ranges, the interior valleys, and the Cascade Mountains, have their counterparts into western Washington and northwestern California, and to some extent in British Columbia. Of the 89 species of mammals in western Oregon, 70 occur in western Washington, 67 going all the way into Canada; and 83 occur in northwestern California, some extending to San Francisco and beyond (see Appendix 2).
I am deeply grateful to an anonymous reader for his or her candor in reviewing the manuscript of this book. I have over the years found that the more critical a review is, the more helpful it is, and this review was most helpful.
I extend special thanks, however, to Jo Alexander for a truly excellent job of editing. I say this with sincerity and respect. Hers was, in my estimation, a difficult task given the complexity of the job.