The Status of Ecological Research on the Mammal Fauna of California's Central Valley Riparian Communities^[1]

Gene R. Trapp, Gail L. Linck, and Edward D. Whisler^[2]

Abstract.—An extensive literature search was conducted, and various local authorities questioned, regarding: 1) the species of mammals present in the riparian communities of California's Central Valley; and 2) the status of information on these species in relation to the communities. The result was a realization that the mammal fauna of these riparian communities has been studied very little. A checklist of 55 mammalian species was developed. It appears that about half the species listed have had no ecologically oriented research, and most others have had little.

Introduction

Each fall semester from 1970 to 1980, the senior author examined the results of comprehensive bibliographic searches on the biology of most species of California mammals. These searches were conducted under his supervision by mammalogy students at California State University, Sacramento (Trapp 1971–80). Much less ecological research has been published on the approximately 173 non-cetacean California species perse than might be expected, considering the relative abundance of research institutions in the state. Less ecologically oriented research had been published on mammals of Central Valley riparian communities than on those of the rest of the state. Riparian communities are rapidly being lost (Gaines 1976; Sands 1977; Warner 1979); those interested in their preservation would be helped by a clarification of the status of our knowledge of the mammal fauna of these communities. Our objectives in this study were: 1) to revise the checklist of mammalian species begun by Roberts etal . (1977) to include all riparian communities of the entire Central Valley; and 2) to determine the status of ecologically oriented research on these species.

Procedure

The expression "riparian communities" is used here according to Warner (1979). We considered these communities to fall within the boundaries of the Central Valley "California Prairie" according to Küchler (1977).

We used the following sources to construct the checklist: Roberts etal . (1977); Grinnell etal . (1937); Ingles (1965); Williams (1979, 1981); Hall (1981); Elems and Medeiros (1981); and various other reports, e.g., Stone (1976), Brumley (1976), Schempf and White (1977). In addition to drawing upon the senior author's personal experience, we questioned the following authorities about their knowledge of mammals present in the Central Valley or their local areas: Robert Rudd;^[3] Robert Schwab, Rex Marsh, Ron Cole;^[4] Stan Elems;^[5] Howard Leach and William Grenfell;^[6] Terry Mansfield;^[7] Gary Shook;^[8] and Daniel Williams.^[9]

[1] Paper presented at the California Riparian Systems Conference. [University of California, Davis, September 17–19, 1981].

[2] Gene R. Trapp is Associate Professor, Gail L. Linck is a Graduate Student, and Edward D. Whisler is a Senior in the Department of Biological Sciences, California State University, Sacramento.

[3] Robert Rudd. 1981. Personal conversation. Department of Zoology, University of California, Davis.

[4] Robert Schwab, Rex Marsh, and Ron Cole. 1981. Personal conversations. Division of Wildlife and Fisheries Biology, University of California, Davis.

[5] Stan Elems. 1981. Personal conversation. Department of Biology, Modesto Junior College, and Great Valley Museum, Modesto, Calif.

[6] Howard Leach (retired) and William Grenfell. 1981. Personal conversations. Wildlife Investigations Laboratory, California Department of Fish and Game, Sacramento.

[7] Terry Mansfield. 1981. Personal conversation. Big Game Investigations, California Department of Fish and Game, Sacramento.

[8] Gary Shook. 1981. Personal conversation. Woodson Bridge State Recreation Area, Corning, Calif.

[9] Daniel Williams. 1981. Personal communication. Department of Zoology, California State University, Stanislaus, Turlock.

We searched the literature for species on the checklist using two approaches. The first and less productive was a "habitat approach", using key words to search the following sources for the dates indicated:

Zoological Record: 1940–1975 (latest issue) for river, fresh water habitat, riparian habitat, terrestrial habitat, and (in older issues) ecology and habitats;

Wildlife Abstracts: 1935-June 1981 for natural areas and refuges, faunas, communities, and wetlands and wildlife. Prior to 1970—mammals in general, biotas, faunas, and populations;

Wildlife Reviews: as per Wildlife Abstracts;

Biological Abstracts: 1974-early 1981 for riparian, riverine.

The second and more productive approach was a search for articles about the mammal species on the checklist. We went through the California State University Bibliographies of Selected Mammalian Species (Trapp 1971–80), which generally reach back into the 1930–40 period, and updated each to the dates indicated below with the following sources:

Zoological Record: through 1975;
Wildlife Abstracts: 1935–June 1981;
Wildlife Review: 1935–June 1981;
Mammalian Species: Numbers 1–156 (May 1981);
Journal of Mammalogy indices: through 1980.

Some specialized searches made by others were examined also: Newberry (1973), Trapp and Hallberg (1975), McGrade (1978), and Antonius (1981).

Results and Discussion

The checklist (table 1) contains 55 species compared to 39 in the initial list begun by Roberts etal . (1977). The amount of evidence for the following species' presence in the natural riparian communities of the Central Valley varies. However, Ingles (1965) shows the following species absent or less widely distributed than reported by the authority indicated in parentheses:

broad-handed mole (Elems 1981⁵ );
western (greater) mastiff bat (Hall 1981; Elems 1981⁵ );
western gray squirrel (Stienecker 1977);
porcupine (Rudd 1981,³ Shook 1981⁸ );
ringtail (Naylor and Wilson 1956; Michny etal . 1975; Stone 1976; Brumley 1976; Belluomini and Trapp, in press);
mountain lion (Brumley 1976; Elems 1981⁵ );
black-tailed and California mule deer (Dasmann 1968; Brumley 1976; Mansfield 1981⁷ ); and
feral hog (Dasmann 1968; Mansfield 1981⁷ ).

The presence of these species needs to be better documented for the riparian communities of the Central Valley. This is also true for the following species:

brush rabbit
eastern gray squirrel
fox squirrel
San Joaquin pocket mouse
Heermann's kangaroo rat
deer mouse
dusky-footed woodrat
spotted skunk.

The fox squirrel seems to be spreading out into the suburbs from what in the past has been an urban habitat, e.g., in Sacramento suburbs. On 2 July 1981 Michael Lacy and Trapp saw one on the west side of the Sacramento River on the outskirts of Knights Landing (Yolo County).

The nutria (Myocastorcoypus ), though released in the past at various points in California (Ingles 1965), is thought to have been exterminated by the California Department of Agriculture (Leach 1981;^[6] Marsh 1981^[4] ). However, Williams (1981,^[9] ) has had reports from ranchers and biologists that nutria are still present in the San Joaquin Valley.

The spread of the black rat, Norway rat, house mouse, and feral hog into natural riparian communities is not well documented. The feral hog occurs along the upper Sacramento River south of Red Bluff in Tehama County; on the Colusa National Wildlife Refuge in Colusa County; and on Grizzly Island in Suisun Marsh, Solano County (Dasmann 1968; Mansfield 1981^[7] ); it is apparently extending its range.

The tule elk presently exists free-living only on Grizzly Island at the northeast end of Suisun Bay, Solano County. The only other potentially riparian herd of tule elk is in a 308-ha. (761-ac.) enclosure of annual grassland, wooded sloughs, and marsh on the San Luis National Wildlife Refuge along the San Joaquin River in Merced County (Dasmann 1968; USDI Bureau of Land Management 1979; Leach and Grenfell 1981^[6] ).

The black-tailed deer is found along the Sacramento River and its tributaries, extending south to the Cosumnes River/Stockton region. There its range overlaps and the deer hybridizes with the California mule deer, which occurs along drainages in the San Joaquin system (Mansfield 1981^[7] ). Dasmann (1968) fails to show these deer in the San Joaquin Valley or in the lower Sacramento Valley.

The following species are not included on the checklist, although they may occur in Central Valley riparian communities. Hall (1981) extrapolates their ranges into the Central Valley, but Ingles (1965) does not. These species are:

small-footed myotis (Myotissubulatus )
little brown myotis (M . lucifugus )
long-legged myotis (M . volans )
fringed myotis (M . thysanodes )
long-eared myotis (M . evotis )

The Status of Research

Authoritative contributions to the knowledge of mammalian ecology in the riparian communities of the Central Valley are relatively few, considering the number of species and the number of research institutions in the state. "Furbearing Mammals of California" (Grinnell etal . 1937) still stands as the most important contribution regarding furbearers of the state, though it needs to be updated. The information is largely of a natural history nature with many contributions made by interviewed trappers.

"Mammals of the Pacific States" (Ingles 1965) is another major contribution to mammalogy in California. It contains general information on mammals, a key to the species, distribution maps, and information from the literature and the author's experience summarizing the biology and natural history of the species. This work, however, makes a limited contribution to the riparian mammal ecology in the Central Valley and is in need of revision. Two other helpful works of synthesis, including information collected by game department biologists, are California Department of Fish and Game (DFG) booklets "Big Game of California" (Dasmann 1968), in need of revision, and "Furbearers of California" (Seymour 1977).

Limited information on the distribution of mammals in riparian communities has been included in unpublished reports by the DFG (e.g., Leach 1963, Michny etal . 1975, Stone 1976, and Brumley 1976). Brumley's report is especially useful because it includes a list of 41 mammal species observed in the Upper Butte Basin northeast of Colusa. Schempf and White's (1977) survey of six furbearers in the mountains of northern California makes some brief but useful comments pertaining to the Central Valley on the distribution of ringtail, river otter, and red fox.

Turning to the scientific journals for research papers on Central Valley riparian mammals, we found no information for about half the species on the checklist and very limited amounts for the rest. We found research reports ecologically oriented to riparian communities only for the species mentioned below.

Opossum (Introduced)

Campbell (1981a) reported capturing some albinotic individuals in north San Joaquin County near the Mokelumne River. He also studied activity patterns of captive young Central Valley opossums (kept in outdoor cages in north Sacramento) correlated with elements of weather and photoperiod (Campbell 1981b). Reynolds (1952) reported on reproduction in Central Valley opossums.

Black-tailed Hare

Hardy etal . (1977) reported on natural and experimental arboviral infections in this species along the Sacramento River in Butte County.

California Ground Squirrel

Owings and his associates at the University of California, Davis, have made several contributions to the literature on this species. Owings and Borchert (1975) studied correlates of burrow location; Owings etal . (1977) described general behavior; Coss and Owings (1978) reported on snake-directed behavior by snake-naive and experienced ground squirrels; and Owings etal . (1979) described time budgets of this species during reproduction.

Eastern Gray Squirrel and Fox Squirrel (Introduced)

Byrne (1979) studied distribution and ecology of eastern gray squirrel and fox squirrel in northern California.

Western Gray Squirrel

Ingles (1947) studied several aspects of the life history of western gray squirrel, including food habits, in a Sacramento Valley riparian forest on Big Chico Creek at Bidwell Park in Chico, Butte County. Stienecker (1977) provided an improved range map (cf. Ingles 1965) in his paper on food habits, but had no study sites in the Central Valley. Swift (1977) studied the reproductive cycle of this species in Butte County.

Beaver

For this species, there are only status reports by Tappe (1942); Cram (1951); and Lee (1977).

Deer Mouse

Fuller (1978) mentioned Peromyscusmaniculatus as part of the diet of a gray fox at Davis, Yolo County. Biggerstaff (1977) studied swimming behavior of this species and three other mice (Reithrodontomysmegalotis , Microtus californicus , and Musmusculus ) found in the Sacramento/San Joaquin River delta.

California Vole

Haynie (1974) studied high population density stress and resistance to pasteurellasis in the California vole in outdoor enclosures near Sacramento. Smith (1975) studied the association between small mammal populations and certain plant communities in the Graylodge Wildlife Area of Butte County.

Muskrat (Introduced)

Distribution and status of muskrat were reported on by Twinning and Hensley (1943), Seymour (1954), and Lee (1977). Messa (1981) studied population dynamics and home range of this species along irrigation canals in east Yolo County, northeast of Davis.

Norway Rat and Black Rat (Introduced)

Brooks and Barnes (1972) reported on an outbreak and decline of Norway rat populations in California rice fields. Stroud (1982) studied population dynamics of Norway and black rats in a riparian habitat on Putah Creek in Yolo County. The role of rodents in plague ecology was examined by Nelson (1980).

Coyote

Dow (1975) analyzed four coyote populations in several counties of the Sacramento Valley region. Crellin (1977) related helminths in coyotes to ecological factors in the San Joaquin Valley.

Red Fox (Introduced)

Gray (1977) and Gould (1980) reported on distribution and status of red fox; Roest (1977) examined taxonomic status compared to the native Sierran red fox.

Gray Fox

Lee (1977) reported on status, and Fuller (1978) described variable home-range sizes in four females of this species in relation to habitat on Putah Creek at Davis, Yolo County. Hallberg and Trapp (1981) described temporal behavior and home-range characteristics in two males and two females east of Davis on Putah Creek.

Ringtail

Belluomini and Trapp (1981) summarized earlier ringtail sightings, plus their own work, and reported on distribution and density of this species in the Central Valley, which Grinnell etal . (1937), Ingles (1965), and Hall (1981) indicated was not present to the extent that it is.

Raccoon, Mink, and Badger

Lee (1977) reported on these species' status as furbearers.

Spotted Skunk

Mead (1962) studied several aspects of this species' life history. Orloff (1980) reported on present distribution.

Striped Skunk

Mead (1962) also studied several aspects of striped skunk natural history. Gray (1975) studied home range, movements, activity, and den characteristics; while Peck (1980) studied the family unit's activity patterns, home range, and denning habits, both along Putah Creek, Yolo County. Belluomini (1980) reported on the status of this species.

River Otter

Gould (1977) reported on river otter status; and Grenfell (1978) studied their food habits in Suisun Marsh.

Feral House Cat (Introduced)

Hubbs (1951) reported on food habits of the feral house cat in the Sacramento Valley.

Feral Hog (Introduced)

Dasmann (1968) commented on status and distribution of feral hog; and Barrett (1978) studied several aspects of ecology, including movements and food habits, on the Dye Creek Ranch southeast of Red Bluff in Tehama County.

Tule Elk

Dasmann (1968) commented on this species' status and distribution. A more recent report was made by the USDI Bureau of Land Management (1979).

Summary

Roberts etal . (1977) offered their mammal species checklist for the Sacramento Valley riparian forests as a starting point. The checklist presented here has been refined and broadened to include the San Joaquin Valley. It also is offered to interested biologists for further refinement. We have found that the composition of the mammal fauna of the Central Valley's riparian communities is poorly documented.

More research is also needed to improve our knowledge of life histories of riparian mammals, and the ecological relationships between them and the communities they inhabit in the Central Valley. Opportunities for conducting this research have been diminishing with the destruction of natural riparian communities, so we recommend that field biologists turn their attention without delay to the remaining opportunities for research in this poorly understood area.

Acknowledgments

We would like to thank Daniel F. Williams, Stan W. Elems, Carolyn Stallard, and Jo Ellen Diem for reading the manuscript and offering helpful suggestions. We also thank Richard Warner for suggesting this project and guiding in its preparation, and Gordon Gould for providing information.

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