Lloyd Tevis

Stomach Contents of Chipmunks and Mantled Squirrels in Northeastern California

A study of feeding habits is important to an understanding of the rodent factor in forest ecology. But a mere list of foods does not indicate the complexity of interrelations between animals and food supplies, which differ markedly in kind and amount from place to place and vary enormously between seasons and from one year to another. Interpretation of the data is necessary. This paper attempts an interpretation of stomach analyses of 509 chipmunks of four species (Eutamias amoenus, speciosus, townsendi, and quadrimaculatus) and 273 mantled squirrels (Citellus lateralis), which are important kinds of diurnal rodents of the commercial timber belt of northeastern California. The area studied lies within a thirty mile radius of Quincy, Plumas County, California, where the granitic Sierra Nevada meets the Great Volcanic Plateau to the north and the arid Great Basin to the east. The merging of these vast geographic regions creates a complicated and congested biota, for many species come together which are widely separated elsewhere. Some habitats are occupied by all four kinds of chipmunks as well as the mantled squirrel. The forest is composed of ponderosa, Jeffrey, and sugar pines, Douglas fir, ,white fir, and incense cedar. It has been subjected to every degree of logging, and is broken by brushfields that are the heritage of disastrous fires. The chief shrubs of Volcanic and Sierran brushfields are manzanita (Arctostaphylos patula) and whitethorn (Ceanothus cordulatus). The technique of stomach analysis was described in an earlier paper (Tevis, 1952). The main point to be noted here is that the food was classified into types. An attempt was made to learn which foods maintained high numbers of rodents, to determine seasonal trends in feeding habits, and to compare the diets of different species. The work was done as part of an investigation of the influence of rodents on reforestation conducted by the Department of Zoology, University of California at Davis in cooperation with the California Forest and Range Experiment Station of the United States Forest Service. I am grateful to Dr. Tracy I. Storer for advice and assistance. Specimens were collected in 1951 from mid-March, when hiberators appeared, until the third week of the following September. This paper, then, is an account of feeding habits during one year. No two years are alike, and a sulmmary of the main features of 1951 follows. In spring-when occasional rain hastened the melting of patches of snowsurface fungi (Gyromitra, Peziza, and Morchella) were locally abundant; forbs and grasses greened the forest floor; one of the earliest of the herbs, a figwort, set quantities of seeds; manzanita yielded the heaviest flower crop in years; winged termites emerged from rotten logs on sultry afternoons; and ants and spiders were numerous.

Responses of Small Mammal Populations to Logging of Douglas-Fir

Virgin forest in the Douglas-fir ( Pseudotsuga taxifolia ) region of northwestern California is a sterile habitat for wildlife. Dense shade and competition from large old trees prevent the growth of nearly all bushy and herbaceous vegetation except a weak understory of tan oak ( Lithocarpus densiflora ). Food for animals is scarce. The immediate effect of logging is to flood the ground with light. Then tan oak begins a rapid, aggressive growth, and many kinds of herbs, of which fireweed ( Erechtites ) is one of the most abundant, become established. In terms of plant succession, the cutover changes from bare ground to weeds to brush and finally to a climax of Douglas-fir or more often, tan oak. During the middle stages, food for animals is plentiful. Small seed-eating mammals are one of the factors that result in the economically undesirable climax of oaks instead of conifers. Mice in particular, because of their fondness for coniferous seeds, are responsible in part at least for the failure of natural seeding to restock many cutovers with firs; and they make artificial seeding difficult and often impossible. In the Douglas-fir region of California, large tracts of old timber are slated to be logged within the next few years. The usual method is to clear-cut blocks that are fifteen to twenty acres in size and burn the resulting slash. Before silvicul-turists can prepare a successful plan for reforesting these cutovers, information is needed about the various factors that hinder coniferous reproduction. As a contribution toward that end, this paper gives the results of a trapping survey of small mammals at elevations between 2,000 and 4,000 feet in Humboldt and Trinity counties near Salyer. The purpose of the survey, which was undertaken in cooperation with the California Forest and Range Experiment Station of the United States Forest Service, was to …

Effect of a Slash Burn on Forest Mice

A discouraging aftermath of the clear-cutting of virgin forest in the Douglas-fir region of northwestern California is the enormous accumulation of waste slash. When loggers finish their work, they leave the ground cluttered and strewn with interlocking tangles of branches and tops of conifers, splintered trunks, shattered sections of bark, great piles of culled logs, and entire trees of madrone (Arbutus menziesii Pursh) and tanoak ( Lithocarpus densiflorus [Hock & Am.] Rehd.), uprooted or smashed.

Effect of Vertebrate Animals on Seed Crop of Sugar Pine

prohibiting passage of wild predatory mammals, twenty-one individuals comprising seven predatory species were tested to find the size of the smallest holes they could pass. Most of the mammals were considerably larger than weanlings so the results are only strictly applicable to the animals tested. No correlation existed between body dimensions and hole dimensions or area. The findings indicated that all species tested were adequately barred by 14gauge 1 x 2 inch mesh electrically welded wire fabric except small mink and weasel; the latter species would be stopped by 20-gauge 1/2-inch wire cloth. Accepted for publication April 8, 1952.

A Five-Year Change in an Assemblage of Wood Rat Houses

The house of the dusky-footed wood rat ( Neotoma fuscipes ) in California is an impressive structure compared with the small size of the animal that makes it. The owner of a house assembles sticks, bark, plant cuttings, and miscellaneous objects that it deposits in a conical heap, which may tower six feet or higher above the ground and have a basal diameter of eight feet. Passageways penetrate the interior and one or more chambers contain a soft nest for the repose of the occupant. Old and dominant individuals generally maintain and control several houses from which they exclude all other members of the colony. A mother and her young may occupy a house, but otherwise a single rat lives in a house. Long residence in the same house is rare. More often a rat shifts its headquarters frequently to a different dwelling within its sphere of influence. Occasionally, too, abandoning its own property, it may make a major move to a new area where it takes over a group of houses that belonged to an animal that died or moved elsewhere. As a rule only established rats build new houses. When young rats leave the maternal abode, they must find unoccupied dwellings in which to live, for construction of new homes is time consuming, and homeless rats cannot survive long enough to make a new shelter. Increase of a population of rats, therefore, is dependent in part upon the frequency with which established animals build houses and the vigor with which they maintain old houses. Most houses are occupied by a succession of tenants that persist in the upkeep of the structure, which then represents the work of many generations of rats. If a house is vacant for a considerable time, it loses its rat sign, such as deposits of feces …

Behavior of a Population of Forest-Mice When Subjected to Poison

A belt of Douglas-fir fronting the inland border of the north coast redwoods comprises the last great stand of virgin timber in California. Not previously-exploited because of ruggedness of the mountains on which it grows, it is yielding now to the logging truck and caterpillar tractor. A timber rush is on. Within two or three decades little of the old forest will remain (Pine, 1953; Vaux, 1955). As a rule, natural reproduction of conifers in the region is not sufficiently vigorous to replace timber removed by logging or destroyed by fire. Compared with the Douglas-fir belt of Oregon and Washington, environmental conditions in northern California are severe. The dry season is long and intense, and tan oak, which sprouts aggressively when felled or burned, often captures denuded land. The answer to the problem of reforestation might be direct (artificial) seeding except for the presence of small mammals which are adept at finding and devouring coniferous seed. White-footed mice ( Peromyscus maniculatus and P. truei ), abroad only by night and inconspicuous out of proportion to their numbers, are the chief offenders. The diurnal and more obvious chipmunks ( Eutamias townsendii ) are of secondary importance, and shrews ( Sorex trowbridgii ) and red-backed mice ( Clethrionomys occidentalis ) are relatively scarce. The recommended method of dealing with seed-eating rodents of the forest is to poison them (Eadie, 1954). In theory, foresters can wipe out a population of wild mice with lethal baits, then sow seed in the autumn and have a dense stand of seedlings after germination occurs in the following spring. But every attempt to protect seed by killing rodents with cereal baits in the California Douglas-fir region has failed. Assuredly a rodenticide such as sodium fluoroacetate, commonly known as Compound 1080 (Kalmbach, 1945), is exceedingly effective when first applied. It can decimate a population …

Invasion of a Logged Area by Golden-Mantled Squirrels

At the southern terminus of their range in northwestern California, golden-mantled squirrels ( Citellus lateralis ) of the subspecies trinitatis (Merriam) occupy a narrow, rugged crest dividing the drainages of the New and Trinity rivers. They occur in small numbers at elevations from 5,500 to 6,200 feet on outcroppings of granite. Being sun-lovers and wanting a variety of vegetation for food, they avoid the dark forest of virgin Douglasfir ( Pseudotsuga taxifolia ) and white fir ( Abies concolor ) which clothe the slopes of the mountain. In 1949 when logging operations were first started in the virgin timber, these squirrels were not expected to be present to hinder reforestation, as they do in the Sierra Nevada by eating coniferous seeds. Two and a half miles of continuous forest separated their natural habitat from …