A Description of the Small Mammal Community (Orders Rodentia and Insectivora) in the Hells Canyon Study Area

Anthonie M. A. Holthuijzen Wildlife Ecologist

Technical Report Appendix E.3.2-23 January 2001 Revised July 2003 Hells Canyon Complex FERC No. 1971 Copyright © 2003 by Idaho Power Company

Idaho Power Company Description of Small Mammal Communities

TABLE OF CONTENTS

Table of Contents ...... i

List of Tables...... iii

List of Figures ...... iii

List of Appendices ...... iv

Abstract ...... 1

1. Introduction ...... 2

2. Study Area...... 3

2.1. Location...... 3

2.2. Physiography...... 4

2.3. Land Features and Geology...... 4

2.4. Soils...... 5

2.5. Climate ...... 5

2.6. Vegetation ...... 6

2.7. Land Use ...... 8

3. Plant Operations ...... 8

4. Methods...... 9

4.1. Small Mammal Trapping ...... 9

4.1.1. Sampling Design: Trap Site Selection ...... 9

4.1.2. Sampling Design: Trap Placement...... 10

4.2. Shrew Trapping...... 10

4.2.1. Sampling Design: Trap Site Selection ...... 10

4.2.2. Sampling Design: Trap Design ...... 11

4.2.3. Data Collection...... 11

Hells Canyon Complex Page i Description of Small Mammal Communities Idaho Power Company

4.3. Vegetation Cover Typing...... 11

4.4. Data Analysis ...... 11

5. Results ...... 12

5.1. Trapping Effort and Success ...... 12

5.2. Species Composition and Abundance...... 12

5.3. Species Diversity and Evenness...... 13

5.4. Small Mammal Community–Habitat Relationships ...... 13

6. Discussion ...... 14

6.1. Species Richness ...... 14

6.2. Species Composition...... 15

6.2.1. Upland Habitat ...... 15

6.2.2. Riparian Habitat ...... 16

6.3. Relative Abundance ...... 16

6.4. Species of Special Concern...... 17

6.5. Habitat Associations...... 18

7. Acknowledgments...... 18

8. Literature Cited ...... 18

Page ii Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities

LIST OF TABLES

Table 1. Small mammals of the Order Rodentia present or potentially present in the Hells Canyon Study Area or vicinity...... 25

Table 2. Cover types (acreage and percentages) present in the Hells Canyon Study Area...... 26

Table 3. Trapping locations, trapping year, first trapping night, and trapping effort, Hells Canyon Study Area, 1997 and 1998...... 27

Table 4. Location, operating dates, trap days, and species of small mammals caught in shrew trapping arrays in the Hells Canyon Study Area, spring 1997...... 28

Table 5. Species and numbers of small mammals caught per 100 trap nights, Hells Canyon Study Area, 1997 and 1998...... 29

Table 6. Small mammal relative abundance (average number of mammals per 100 trap nights ± 1STD) for each cover type and reach sampled in the Hells Canyon Study Area, 1997 and 1998...... 30

Table 7. Shannon diversity (H΄) and evenness (E) indices for small mammal communities trapped at each of the three study reaches and vegetation cover types, Hells Canyon Study Area, 1997 and 1998...... 31

Table 8. Small mammal community composition (% of total captures) in shrub- steppe vegetation communities, Intermountain West...... 32

Table 9. Small mammal community composition (% of total captures) in riparian vegetation communities, Intermountain West...... 33

LIST OF FIGURES

Figure 1. Location of the Hells Canyon Study Area, small mammal trap sites, and shrew arrays, Idaho–Oregon border...... 35

Figure 2. Köppen climate diagrams for the Weiser, Richland, Brownlee, and Lewiston weather stations, Hells Canyon Study Area, Idaho–Oregon border...... 37

Hells Canyon Complex Page iii Description of Small Mammal Communities Idaho Power Company

Figure 3. Principal Component Ordination of small mammal trap sites for each of the vegetation cover types, based on small mammal composition and abundance, Hells Canyon Study Area, 1997 and 1998...... 38

LIST OF APPENDICES

Appendix 1. Criteria and definitions used to identify cover types in the Hells Canyon Study Area, eastern Idaho...... 39

Appendix 2. Two-Way INdicator SPecies ANalysis (TWINSPAN) of the Hells Canyon small mammal trap sites, based on relative abundance (small mammal species/100 trap nights), 1997 and 1998...... 41

Page iv Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities

ABSTRACT

In 1997 and 1998, small mammals were sampled at nine sites along 30 trap lines in the Hells Canyon Study Area (1997: one site at Brownlee Reservoir [Dukes Creek] and one at Hells Canyon Reservoir [Bob Creek]; 1998: two sites along Hells Canyon Reservoir [Eckles and Limepoint creeks], two sites at Brownlee Reservoir [Quicksand and Grouse creeks], and three sites below Hells Canyon Dam in the Pittsburgh Creek area [Klopton Creek, Kurry Creek, and Pittsburg Landing]). The objectives were to determine: 1) relative abundance and distribution of small mammals, 2) community composition of the small mammal community, and 3) habitat relationships between dominant cover types and the small mammal community. In both years, trapping was conducted in April. Trap lines were placed in all available cover types at each site. Nine cover types were sampled (Shore & Bottomland Wetland, Scrub-Shrub Wetland, Forested Wetland, Desertic Shrubland, Grassland, Shrub Savanna, Shrubland, Mountain Shrubland, and Forested Upland). Trap lines consisted of 25 stations set 10 m apart, with two traps at each station. Sherman live traps and snap traps (either Museum Specials at every fifth station or Victor mouse traps) were placed at each station. Before the traps were opened, they were baited for one day. Trapping continued for three consecutive nights following the prebaiting period, for a total of 4,205 trap nights. Shrews were selectively trapped at three creeks (Dukes Creek, Cottonwood Creek, and the mouth of the Powder River) using pit-falls. Each site was operated for 18 trap days between April 1 and May 8, 1997. Eight species of small mammals were captured along trap lines. Four species were relatively common: the deer mouse (Peromyscus maniculatus), montane vole (Microtus montanus, western harvest mouse (Reithrodontomys megalotis), and vagrant shrew (Sorex vagrans). The four remaining species, Great Basin pocket mouse (Perognathus parvus), western jumping mouse (Zapus princeps), long-tailed vole (Microtus longicaudus), and bushy-tailed woodrat (Neotoma cinerea) were caught in small numbers. One additional species, the northern pocket gopher (Thomomys talpoides), was caught at one of the pit-fall sites. Other species that were observed or collected incidentally were the coast mole (Scapanus orarius), least chipmunk (Tamias minimus), yellow-pine chipmunk (Tamias amoenus), white-tailed antelope ground squirrel (Ammospermophilus leucurus), Townsend’s ground squirrel (Spermophilus townsendii), Belding’s ground squirrel (S. beldingi), golden-mantled ground squirrel (S. lateralis), Columbian ground squirrel (Spermophilus columbianus), and possibly the southern Idaho ground squirrel (S. brunei endemicus). Small mammal abundances in cover types ranged between 14.2 and 41.6 small mammals captured/100 trap nights and averaged 21.8 ± 10.5 small mammals/100 trap nights for all cover types combined. Differences in small mammal abundance were not significant among study reaches or cover types. Relative abundance of small mammals in the study area is similar to those reported in southern Idaho. Overall, small mammal abundance tended to increase from Brownlee Reservoir (18.8 ± 9.8 mammals/100 trap nights) to the reach below Hells Canyon Dam (31.3 ± 7.2 mammals/100 trap nights). Species diversity differed considerably among cover types. The highest species diversity was found for the Mountain Shrubland cover type (H′ = 1.03) and the lowest for Shore & Bottomland Wetland (H′ ≤ 0.01). Small mammal species were not associated with specific cover types. Small mammal communities in upland and riparian habitats of the Hells Canyon Study Area were similar in both relative abundance and composition.

Hells Canyon Complex Page 1 Description of Small Mammal Communities Idaho Power Company

1. INTRODUCTION

In the general vicinity of the Hells Canyon reach of the Snake River, 31 small mammal species are likely to be present (Davis 1939, Groves and Marks 1985, Marshall 1986, Csuti et al. 1997, Verts and Carraway 1998) (Table 1). Seventeen species have been reported within the river corridor, or approximately 0.5 mi on either side of the Snake River (Asherin and Claar 1976, Groves and Marks 1985) (Table 1). An additional six species are likely to occur within the river corridor (Hall 1981) (Table 1). Other species occurring in the vicinity of Hells Canyon (Table 1) are unlikely to be present along the Snake River corridor because these species, such as the American pika (Ochotona princeps), only are found at higher elevations.

Few studies have been conducted along the Hells Canyon reach of the Snake River. Davis (1939) used museum records to investigate the small mammal community in Adams and Idaho counties. Davis (1939) identified 11 species: vagrant shrew (Sorex vagrans ), water shrew (Sorex palustris), Columbian ground squirrel (Spermophilus columbianus), yellow-pine chipmunk (Tamias amoenus), northern pocket gopher (Thomomys talpoides), deer mouse (Peromyscus maniculatus), bushy-tailed woodrat (Neotoma cinerea), montane vole (Microtus montanus), long-tailed vole (Microtus longicaudus), big-footed meadow vole (Microtus richardsoni), and American pika. Asherin and Claar (1976) used primarily snap, pit, and live traps to survey small and medium-sized mammals in Hells Canyon. Ten species of small mammals were trapped: the vagrant shrew, montane vole, house mouse (Mus musculus), deer mouse, Great Basin pocket mouse (Perognathus parvus), western harvest mouse (Reithrodontomys megalotis), Ord’s kangaroo rat (Dipodomys ordii), golden-mantled ground squirrel (Spermophilus lateralis), Townsend’s ground squirrel (Spermophilus townsendii), and northern pocket gopher. Brownlee Reservoir had the most diversity with nine species, followed by Oxbow and Hells Canyon reservoirs with five species each. Six species were recorded below Hells Canyon Dam. The Ord’s kangaroo rat, golden-mantled ground squirrel, and Townsend’s ground squirrel were found only at Brownlee Reservoir. Deer mice comprised most of the small mammals caught (86%), followed by house mice (4%), and montane voles (3%). Other species, namely the western harvest mouse, Great Basin pocket mouse, Ord’s kangaroo rat, vagrant shrew, golden mantled ground squirrel, and bushy-tailed woodrat, each comprised less than 1% of the total number. Species diversity was much higher in riparian areas than in upland plant communities.

The general objective of this study was to provide baseline data on a cross-section of the small mammal community in the Hells Canyon Study Area. The specific objectives were to determine: 1) relative abundance and distribution of small mammals, 2) community composition of the small mammal community, and 3) habitat relationships between dominant vegetation cover types and the small mammal community.

The purpose of collecting wildlife data in Hells Canyon is to provide Idaho Power Company (IPC) with the information necessary to relicense the Brownlee, Oxbow, and Hells Canyon dams with the Federal Energy Regulatory Commission (FERC). FERC requires relicensing documents to include a general description of the environment.

Page 2 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities

2. STUDY AREA

2.1. Location

Hells Canyon is situated in west-central Idaho and northeastern Oregon (Figure 1). The Snake River, a major tributary to the Columbia River, is the focal point of Hells Canyon. Its generally northward flow forms part of the boundary between Idaho and Oregon. The Hells Canyon Hydroelectric Complex is located on the Snake River in the southern portion of Hells Canyon and includes three reservoirs: Brownlee, Oxbow, and Hells Canyon. The reach below Hells Canyon Dam is unimpounded, although flows are controlled by the three-dam complex. The study area itself is located between the city of Weiser and the confluence of the Salmon and the Snake Rivers (approximately RM 351 to 188).

Federal agencies, including the U.S. Department of Interior (USDI), Bureau of Land Management (BLM), U.S. Department of Agriculture (USDA), and U.S. Forest Service (USFS), are responsible for managing the majority of public land in Hells Canyon. Land in this area falls within the jurisdictional boundaries of the Wallowa–Whitman National Forest, Oregon; Payette National Forest, Idaho; Nez Perce National Forest, Idaho; Cascade Resource Area (RA) of the Boise District, BLM-Idaho; Cottonwood RA of the Coeur d’Alene District, BLM-Idaho; Baker RA of the Vale District, BLM-Oregon; and Northern Malheur RA of the Vale District, BLM-Oregon. Other agencies with natural resource jurisdiction in the greater project area include the USDI National Marine Fisheries Service (NMFS), USDI Bureau of Indian Affairs (BIA), USDI Fish and Wildlife Service (USFWS), and Idaho and Oregon state agencies.

The area upstream and downstream of Hells Canyon Dam can be broadly divided into five reaches, based on distinct geomorphic features, river characteristics, and legal project boundaries. Generally, the study area extends to land within 0.5 mi of each shoreline in the reaches above Hells Canyon Dam and all land within 0.25 mi of each shoreline in the reach below Hells Canyon Dam. However, the lateral extent of the study area may vary depending on the resources under study. The study area below Hells Canyon Dam is extremely difficult to access. The following are the five reaches:

• Upstream of Brownlee Reservoir to the Weiser Bridge (approximately 12 miles; RM 351.2 to 339.2) • Brownlee Reservoir (approximately 55 miles; RM 339.2 to 284.6) • Oxbow Reservoir (approximately 12 miles; RM 284.6 to 272.2) • Hells Canyon Reservoir Reach (approximately 25 miles; RM 272.2 to 247.0) • Downstream of Hells Canyon Dam to the confluence of the Snake and Salmon Rivers (approximately 59 miles, RM 247.0 to 188.2)

In the upstream reach, the Snake River is a low-gradient (0.2 to 0.4 m/km) river with several island complexes. Agricultural impacts are apparent with high amounts of irrigation returns causing higher turbidities and increased nutrient loading. This reach is surrounded by farmland

Hells Canyon Complex Page 3 Description of Small Mammal Communities Idaho Power Company and rural development on flat to gentle topography. Brownlee Reservoir is a steep-sided reservoir with a maximum depth approaching 300 feet near the dam. Large rock outcrops occur throughout the entire length. Oxbow Reservoir is a small re-regulating reservoir surrounded by moderate to steep topography (20% to 75% slopes). Shorelines are primarily basalt outcrops and talus, except where small tributaries created alluvial fans. Hells Canyon Reservoir is also a re-regulating reservoir with maximum depths approaching 200 feet. Shorelines in the reservoir are generally very steep, with substrates primarily composed of basalt outcrops and talus slopes. The Snake River in the downstream reach is a high-gradient river (1.8 m/km) with a wide diversity of aquatic habitat, including numerous large rapids, shallow riffles, and deep pools. Substrates are highly diverse, ranging from large basalt outcrops and boulders to cobble and sand bars. This unimpounded reach of the Hells Canyon is considered the deepest gorge in North America. The Hells Canyon reach is surrounded at the upstream end by nearly vertical cliff faces.

2.2. Physiography

Hells Canyon is the deepest and one of the most rugged river gorges in the continental U.S. It ranges between 2000 feet and 3000 feet deep from Weiser to Oxbow Dam. Below Oxbow Dam, the river enters a narrow, steep-sided chasm up to 5500 feet deep. From the confluence with the Grande Ronde River, the Snake River then flows into a lava-filled basin and through a much shallower canyon to Lewiston, Idaho (DOE 1985). The elevation of the Snake River near Weiser, Idaho, is about 2090 feet msl, descending to about 910 feet msl at the confluence of the Salmon River, about 59 miles below Hells Canyon Dam.

Throughout the canyon, topography is generally steep and broken with slopes often dominated by rock outcrops and talus slopes. At the deepest points of the canyon, the walls rise almost vertically. Canyon walls are deeply dissected by numerous side canyons that contain tributaries to the Snake River. The upper reaches of the canyon walls are formed by the Seven Devils Mountains to the east and the Wallowa Mountains to the west. These mountains form a series of jagged peaks reaching almost 10,000 feet with subalpine and alpine conditions (USDA 1990) to the west.

2.3. Land Features and Geology

Hells Canyon is formed from a series of folded and faulted metamorphosed sediments and volcanic materials overlain uncomformably by nearly horizontal flows of Columbia River basalt. This basalt group covered much of eastern Washington, northern Oregon, and adjacent parts of Idaho (Bush and Seward 1992). The older rocks in the series are Permian to Jurassic in age and represent at least two episodes of island arc volcanism and adjacent marine sedimentation similar to those found today in the Aleutian Islands west of Alaska. These rock units represent old island arc chains that were sequentially “welded” to the west coast of North America during the late Paleozoic and early to mid-Mesozoic eras by subduction of a tectonic plate beneath the North American continental tectonic plate (Asherin and Claar 1976, USDA 1994).

Page 4 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities

In more recent geologic time, Hells Canyon was formed as the Snake River eroded the Blue Mountains in Oregon and Seven Devils Mountains in Idaho (DOE 1985). The Snake River has existed from the Pliocene and probably cut to its present level during the Pleistocene. During the Pleistocene, glacial meltwater provided abundant runoff for down-cutting, while regional uplifting created weak points in the 2000- to 3000-foot-thick basalt plateau that overlaid the Blue and Seven Devils Mountains. Resulting erosion formed the currently observed drainage pattern that established the Snake River (DOE 1985). Northeast-trending, high-angle fault patterns characterize the extensive Snake River fault system running throughout the study area (Fitzgerald 1982).

Besides basalt, other rock types are also present within the study area. Extensive limestone outcrops are found in some tributary drainage areas, and local granitic outcrops also occur.

2.4. Soils

The soils throughout Hells Canyon are derived primarily from Columbian River basalt, covered in most areas with a thin mantle of residual soils from weathered native rock. Isolated areas contain deposits of windblown silt. Unconsolidated materials include ash-loess from the Mount Mazama eruption of 6900 years ago, river sands and gravel deposited during the Bonneville floods of 15,000 years ago, and more recent colluvium and talus. The amount of soil cover declines northward through Hells Canyon near Hells Canyon Dam (RM 247). Most rock faces are nearly vertical with little soil cover (USDA 1994).

Most soil complexes are well drained and vary from very shallow to moderately deep. Loams, the dominant textural class, vary from very stony to silty, often with a clay subsoil component (NRCS 1995).

2.5. Climate

From late fall to early spring, the climate of west-central Idaho and eastern Oregon is typically influenced by cool and moist Pacific maritime air. Periodically this westerly flow is interrupted by outbreaks of cold, dry continental air from the north, which is normally blocked by mountain ranges to the east. During the summer, a Pacific high-pressure system dominates weather patterns, resulting in minimal precipitation and more continental climatic conditions overall (Ross and Savage 1967). Hells Canyon, located in the High Desert region, is significantly influenced by the rain shadow of the Cascade Mountain range to the west.

Climatological information is summarized for Weiser, Richland, Brownlee and Lewiston (Figure 2). The average annual precipitation ranges from about 380 to 500 mm (15 to 20 inches), depending on elevation. It is lowest at the southern end of the study area (Weiser, 286 mm), increases northward (Richland, 298 mm), peaks around Brownlee (445 mm) and declines towards Lewiston (326 mm). Nearly 45% of the average annual precipitation at the Brownlee weather station (445 mm [17.8 inches]) falls between November and January, which contrasts strongly with the 9% that falls between July and September. Thus, most precipitation occurs in the spring and winter (Tisdale et al. 1969, Tisdale 1986, Johnson and Simon 1987), and little or

Hells Canyon Complex Page 5 Description of Small Mammal Communities Idaho Power Company no precipitation falls during the hottest months. Average annual evapotranspiration is estimated to be about 1300 mm (52 inches).

Mean annual temperatures are similar among the four weather stations. Generally, the climate tends to become drier and warmer downstream of Brownlee. Climatological information from Brownlee Dam (RM 284.6) is probably characteristic of the central section of the study area and is discussed in more detail here. The canyon bottom area is dry with seasonal temperatures ranging from about –5 °C in January to about 35 °C in July (Figure 2). Temperatures may fall below freezing between mid-November through mid-April. Mean temperatures above 2000 m (6562 feet msl) elevation range from –9 °C in January to 13 °C in July. By contrast, mean temperatures below 1000 m (3281 feet msl) elevation range from 0 °C in January to between 28 °C and 33 °C in July (Johnson and Simon 1987). As a general rule, winters in the canyons are mild, while summers on the canyon floor may be hot.

2.6. Vegetation

The types of vegetation growing along the canyon slopes of the Middle Snake River are the result influenced primarily by three ecological factors: topography, soils, and climate. Climate exerts the strongest influence on the development of plant life. The relatively mild winters below the canyon rim have allowed the development of disjunct species such as hackberry (Celtis reticulata), which is most often found in the southwestern states, though it commonly occurs in the Middle Snake River area (Tisdale 1979, DeBolt 1992).

Within the context of regional climate, topography is a major influence on the development and distribution of vegetation (Tisdale et al. 1969, Tisdale 1979, Tisdale 1986). The topographical complexity of Hells Canyon has produced a mosaic of vegetation types (Tisdale 1979, BPA 1984, USDI 1987). Grassland, shrubland, riparian, and coniferous forest communities exist in close proximity. Grassland and forest, for example, interweave at a number of sites throughout the canyon due to variations in aspect (Tisdale 1979).

Twenty-six cover types were identified along the Snake River in the Hells Canyon Study Area (Table 2). The area that was classified covered approximately up to one mile on both sides of the Snake River or associated reservoirs. The dominant cover types were Grassland (35.5%), Shrub Savanna (21.0%), Lotic (16.1%), Shrubland (6.6%), and Cliff/Talus (5.6%) All remaining cover types covered less than 5% of the area classified (Table 2).

Wetland and Riparian CommunitiesInformation is limited on wetland and riparian communities in Hells Canyon (Huschle 1975, Asherin and Claar 1976, Miller 1976, Miller and Johnson 1976, DeBolt 1992). Emergent wetland communities are composed mostly of common cattail (Typha latifolia), narrowleaf cattail (Typha angustifolia), American bulrush (Scirpus americanus), and common spikerush (Eleocharis palustris). Willows are sparsely represented, and various forbs grow on the shoreline side of the stands (Asherin and Claar 1976). A narrow band of diverse riparian communities follows the course of the Snake River and its many tributaries. Although it is limited in geographic area, this riparian zone is vital because of the biological diversity it provides (USDI 1987). Predominant tree species in riparian areas include white alder (Alnus rhombifolia), water birch (Betula occidentalis), and black cottonwood

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(Populus trichocarpa). Predominant shrub species include syringa (Philadelphus lewisii), netleaf hackberry, chokecherry (Prunus virginiana), black hawthorn (Crataegus douglasii), and poison ivy (Toxicodendron radicans).

Little or no riparian vegetation exists along many shoreline sections; rather, upland vegetation on steep canyon slopes simply meet the rocky shoreline. Grassland communities are also common along the Snake River and its tributaries. Where these grassland communities occur along the Snake River and its tributaries, as on the canyon slopes, the dominant species are bluebunch wheatgrass (Pseudoroegneria spicata), cheatgrass (Bromus tectorum), and Idaho fescue (Festuca idahoensis) (Asherin and Claar 1976).

Herbaceous-Dominated Vegetation TypesThe dry climate and typically stony, shallow soils of the canyon have favored the development of grassland steppe communities at the lower and middle elevations (Tisdale 1979, Tisdale 1986). Commonly occurring grass species in the study area include bunchgrasses such as bluebunch wheatgrass, Sandberg bluegrass (P. secunda), and Idaho fescue (Franklin and Dyrness 1973, Garrison et al. 1977, BPA 1984, Tisdale 1986). Sand dropseed (Sporobolus cryptandrus) and red threeawn (Aristida longiseta) are also common and, at times, dominant (BPA 1984, Tisdale 1986).

Habitat types in which bluebunch wheatgrass is dominant occur throughout the study area and occupy over half of its grassland area (Tisdale 1986). Bluebunch wheatgrass flourishes on deep, loamy soils but adapts to coarser and shallower soils as well. Generally, it is associated with Idaho fescue on deeper soils and with Sandberg bluegrass on shallower soils.

Shrub-Dominated Vegetation TypesShrub species comprise a large segment of the canyon’s overall vegetation composition. Shrub-steppe vegetation types occur at mid-elevations in the Hells Canyon study area, especially in the upstream part of the study area. For example, big sagebrush (Artemisia tridentata) is a dominant species in the southern sector of the study area, particularly in the area around Brownlee Reservoir (BPA 1984). Commonly occurring shrubs include big antelope sagebrush, bitterbrush (Purshia tridentata), hackberry, serviceberry (Amelanchier alnifolia) and bitter cherry (Prunus emarginata) (BPA 1984, Tisdale 1986). Other species of sagebrush, such as low sagebrush (Artemisia arbuscula), stiff sagebrush (Artemisia rigida), and silver sagebrush (Artemisia cana), are also present (Franklin and Dyrness 1973, Tisdale and Hironaka 1981). For the most part, sagebrush stands are limited to the area around Brownlee Reservoir. In these stands, the herbaceous layer is dominated by Sandberg bluegrass, with a variety of forbs also occurring.

Stands of hackberry may be found throughout the study area, either on lower slopes with rocky residual/colluvial soil, or on alluvial terraces with sandy soil (Tisdale 1986). In these stands, hackberry is often mixed with a number of other shrub and tree species, including antelope bitterbrush, blue elderberry (Sambucus cerulea), and ponderosa pine (BPA 1984). The herbaceous layer is most often dominated by bluebunch wheatgrass, with cheatgrass and sand dropseed dominant in those areas that have been heavily disturbed by the grazing and trampling of cattle.

Tree-Dominated Vegetation Types—Although coniferous forest communities are generally restricted to the higher elevations of steep canyon slopes, they do reach down to the Snake River

Hells Canyon Complex Page 7 Description of Small Mammal Communities Idaho Power Company in certain locations of the study area. The predominant forest community is a ponderosa pine (Pinus ponderosa)/bluebunch wheatgrass plant association, which extends to the river on north- facing slopes at sites along Oxbow and Hells Canyon reservoirs (Asherin and Claar 1976, Bonneville Power Administration 1984). This association typically occurs as a savanna of ponderosa pine trees distributed over a grassland steppe dominated by bluebunch wheatgrass. Shrubs are almost completely absent, except for sparsely distributed, drought-resistant species such as antelope bitterbrush and serviceberry (Garrison et al. 1977, Johnson and Simon 1987). A ponderosa pine/hackberry type may also extend down to the river in this area. Hackberry dominates the shrub layer in moderate density, and poison ivy is also abundant (Asherin and Claar 1976).

2.7. Land Use

The study area and vicinity is still dominated by the land-use patterns established at the turn of the century: irrigated and non-irrigated agriculture, livestock grazing, mining, large areas of open space, scattered rural development, and rapidly growing recreational activities. The bottomlands adjacent to the reservoirs are generally used for grazing, some farming, and recreation.

3. PLANT OPERATIONS

Hells Canyon, on the Oregon–Idaho border, is the deepest canyon in North America and home to IPC’s largest hydroelectric generating complex, the HCC. The HCC includes the Brownlee, Oxbow, and Hells Canyon dams, reservoirs, and power plants. Operations of the three projects of the complex are closely coordinated to generate electricity and to serve many other public purposes.

IPC operates the complex to comply with the FERC license, as well as to accommodate other concerns, such as recreational use, environmental conditions and voluntary arrangements. Among these arrangements are the 1980 Hells Canyon Settlement Agreement, the Fall Chinook Recovery Plan adopted in 1991, and, between 1995 and 2001, the cooperative arrangement that IPC had with federal interests in implementing portions of the Federal Columbia River Power System (FCRPS) biological opinion flow augmentation, which is intended to avoid jeopardy of the FCRPS operations below the HCC.

Brownlee Reservoir is the only one of the three HCC facilities—and IPC’s only project—with significant storage. It has 101 vertical feet of active storage capacity, which equals approximately 1 million acre-feet of water. On the other hand, Oxbow and Hells Canyon reservoirs have significantly smaller active storage capacities—approximately 0.5 and 1.0% of Brownlee Reservoir’s volume, respectively.

Brownlee Dam’s hydraulic capacity is also the largest of the three projects. Its powerhouse capacity is approximately 35,000 cubic feet per second (cfs), while the Oxbow and Hells Canyon powerhouses have hydraulic capacities of 28,000 and 30,500 cfs, respectively.

Page 8 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities

Target elevations for Brownlee Reservoir define the flow through the HCC. However, when flows exceed powerhouse capacity for any of the projects, water is released over the spillways at those projects. When flows through the HCC are below hydraulic capacity, all three projects operate closely together to re-regulate flows through the Oxbow and Hells Canyon projects so that they remain within the 1-foot per hour ramp rate requirement (measured at Johnson Bar below Hells Canyon Dam) and meet daily peak load demands.

In addition to maintaining the ramp rate, IPC maintains minimum flow rates in the Snake River downstream of Hells Canyon Dam. These minimum flow rates are for navigation purposes and IPC’s compliance with article 43 of the existing license. Neither the Brownlee Project nor the Oxbow Project has a minimum flow requirement below its powerhouse. However, because of the Oxbow Project’s unique configuration, a flow of 100 cfs is maintained through the bypassed reach of the Snake River below the dam (a segment called the Oxbow Bypass).

4. METHODS

Small mammal population densities can be expressed either per unit of area or in relative densities (i.e., catch per effort). The capture–recapture procedures, which estimate density, require strict adherence to assumptions (e.g., closed population) (Caughley 1977, Davis and Winstead 1980). These assumptions are difficult to meet; therefore, capture–recapture methods were not considered. Instead, relative densities of small mammal populations were estimated using trap lines.

Trapping procedures described by Call (1986) and Johnson and Keller (1983) were followed. Each site was trapped for three consecutive days. The traps were set in late afternoon to early evening and checked the next morning. Weight and breeding condition of trapped animals were determined (Groves and Keller 1983, Groves and Steenhof 1988). Individuals caught in live traps and pit traps were color marked and released. Specimens that could not be identified to species were collected and deposited at the Idaho Museum of Natural History, Idaho State University, Pocatello.

4.1. Small Mammal Trapping

4.1.1. Sampling Design: Trap Site Selection

A cluster sampling approach was taken at each sample site. A cluster sample is a simple random sample in which each sampling unit is a collection or cluster of elements (in this study cover types). Clusters were defined as those sample areas that were accessible and contained the maximum number of habitat types. Generally, sites were selected near a tributary to maximize the potential for sampling different habitat types that exist near each other. Thus, tributaries were considered to be clusters. Trapping (cluster) sites were spaced as evenly as possible throughout the study area on both the Oregon and Idaho sides. The sites, covering at least 10 hectares (25 acres), were accessible by vehicle, boat, or foot. Two sites were sampled in 1997 (Dukes

Hells Canyon Complex Page 9 Description of Small Mammal Communities Idaho Power Company

Creek on Brownlee Reservoir and Bob Creek on Hells Canyon Reservoir) and seven sites in 1998 (Grouse and Quicksand creeks [Brownlee Reservoir], Eckles and Limepoint creeks [Hells Canyon Reservoir], and Klopton Creek, Kurry Creek, and Pittsburg Landing [below Hells Canyon Dam]) (Figure 1). Within each site, all available cover types were sampled.

All cover types of potential importance as small mammal habitat were sampled (Tables 2 and 3), though not proportional to their coverage of the study area. Agriculture, Cliff/Talus, Desertic Herbland, Grazing Land, Tree Savanna, and Lotic cover types comprise about 29.9% of the landscape (Table 2); however, Agriculture, Cliff/Talus, and Lotic cover types (26.7%) provide little or no habitat to small mammals and were therefore not sampled.

Nine vegetation cover types were sampled (Table 3) though no trapping site included all nine cover types. Definitions of each of these cover types are found in Appendix 1. Trapped sites in the riparian cover types (Scrub-Shrub Wetland and Forested Wetland) were in polygons at least 250 m long and 10 m wide. Upland sites were at least 50 × 250 m.

4.1.2. Sampling Design: Trap Placement

Cover types in each cluster were sampled with trap lines. Though these trap lines were placed within the same general vicinity, they were not closer than 75 m to each other. Each trap line was placed subjectively in the center of a homogeneous cover type, away from the cover type boundary or edge.

Trap lines consisted of 25 stations set 10 m apart, with two traps at each station. Sherman live traps were used at each trapping station. In addition, Museum Specials were systematically placed at 6 trapping stations (i.e., every fifth station) and Victor snap traps at the remaining 19 sites. Trap lines were prebaited for one day, including one night, before they were opened. Bait consisted of a mixture of peanut butter and oats placed on the treadle or inside the trap. Trapping continued for three consecutive nights following the prebaiting period. Traps were closed during the day and opened in late afternoon or early evening.

The location of each trap line was recorded using a Global Positioning System (Trimble Systems®). Three photographs were taken at each trap line: 1) a close-up of the station, 2) a photograph showing the vegetation cover at each trap line, and 3) a landscape photo to capture the general setting of the trap site in the surrounding landscape.

4.2. Shrew Trapping

4.2.1. Sampling Design: Trap Site Selection

Generally, quality shrew habitat is adjacent to a perennial stream and provides adequate vegetation cover (e.g., Call 1986). Therefore, drainages were selected based on accessibility, geographic location in the study area, and the described (e.g., Hall 1981, Csuti et al. 1997, Groves et al. 1997) and perceived habitat requirements of shrews. To maximize capture potential

Page 10 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities and meet logistical constraints, the pit-fall arrays were subjectively placed in Dukes Creek, Cottonwood Creek (Oxbow), and at the mouth of the Powder River (Figure 1).

4.2.2. Sampling Design: Trap Design

Pit-fall traps provide the most effective means of capturing the smallest (<10 g) terrestrial mammals such as shrews (Jones et al. 1996). Capture rates of most species of small mammals are considerably enhanced if a drift fence crosses the open pits (Jones et al. 1996). Therefore, designs described by Call (1986) and Handley and Varn (1994) were used for pit-fall traps with drift fences. The pit-falls were arranged in a trihedron (120º angles), with one-gallon cans placed at the center and other one-gallon cans placed at the distal end of each arm. The fences were made of three pieces of aluminum flashing (60 cm high and 5 m long) buried 15 cm in the ground. The pit traps were baited with sardines or peanut butter. The tops of the pit traps were placed flush with the soil. The drift fences ran up to or over the rim of the pit traps.

Each trap site was operated for 18 trap days over a 4-week period beginning on April 1 and ending on May 8, 1997 (Table 4). When traps were closed, their lids were put in place or shrews were provided means for escape, such as sticks.

4.2.3. Data Collection

Each specimen captured was identified to species, checked for reproductive condition (scrotal or non-scrotal male; or lactating, pregnant, or immature female), and weighed with a Pesola scale. Specimens that could not be positively identified to species were collected, frozen, and sent to Washington State University, Department of Zoology, Conner Museum for identification.

4.3. Vegetation Cover Typing

The vegetation cover at each of the trapping sites was classified according to the standard cover types (Table 3).

4.4. Data Analysis

All captures were tabulated by year, habitat type, trap site, type of trap, species, sex, age group (subadult and adult), and reproductive condition. Because similar trapping procedures were followed at each trap site, small mammal communities among different vegetation cover types could be compared.

Small mammal communities at trap sites were classified based on the composition of dominant species using TWo-way INdicator SPecies ANalysis (Program TWINSPAN) (Hill 1979). TWINSPAN constructs ordered two-way tables that show the differential species and differential species groups sorted into blocks and separated from the other species. Shannon’s diversity index (H′) was calculated for each trap site and trapping year. Evenness (E) was calculated as H′/ln(S), whereby S is the total number of species reported. Relationships between small mammal

Hells Canyon Complex Page 11 Description of Small Mammal Communities Idaho Power Company populations and habitat variables were investigated using standard univariate and multivariate statistical procedures.

5. RESULTS

5.1. Trapping Effort and Success

Trapping Efforts—Trapping lines were placed at nine sites in the Hells Canyon Study Area for a total of 4205 trapping nights (Table 3). Though nine cover types were sampled (Shore and Bottomland Wetland, Scrub-Shrub Wetland, Forested Wetland, Desertic Shrubland, Grassland, Shrub Savanna, Shrubland, Mountain Shrubland, and Forested Upland), no site included all nine cover types. The number of cover types at each site ranged from one to five (Table 3).

The three shrew-trapping arrays were operated for 18 days between April 1, 1997 and May 8, 1997. During this time, the arrays were open for three periods: April 1–11, April 22–25, and May 6–8 (Table 4).

Trapping Success—Three trap types were used at the trapping stations along trapping lines: Museum Specials, Victor mouse traps, and Sherman live traps. Significant differences were found among these traps in trap success, or percent catches of total trap nights (χ2 = 58.2, df = 2, P = 0.001). The highest trap success was found for the Museum Specials (40.6%), followed by the Sherman live traps (31.1%) and the Victor mouse traps (10.2%). Trapping success of the three trap types followed a similar pattern for the deer mouse, the most frequently trapped small mammal. However, no significant differences in trap success among the three trap types were found for the meadow vole (χ2 = 2.50, df = 2, P = 0.28).

Trapping success differed among habitat types for both the deer mouse (χ2 = 19.7, df = 2, P = 0.001) and the montane vole (χ2 = 24.5, df = 2, P = 0.001). Trapping success was highest in riparian habitat (28.6%), followed by upland habitat and Mountain Shrubland (20.6 and 15.1%, respectively). The montane vole, however, showed higher capture rates in Mountain Shrubland (5.9%), followed by upland and riparian habitat (2.0 and 1.6%, respectively). Since the deer mouse was by far the most commonly trapped mammal, overall trap success in the three habitat types studied tended to parallel those described above for this species (riparian 33.8%, upland 24.4%, and Mountain Shrubland 24.3%).

5.2. Species Composition and Abundance

Species Composition—Eight species of small mammals were trapped along trap lines: the deer mouse, montane vole, Great Basin pocket mouse, western harvest mouse, vagrant shrew, western jumping mouse (Zapus princeps), long-tailed vole, and bushy-tailed woodrat (Table 5). The most abundant species caught was the deer mouse (81.1%), followed by the montane vole (9.3%), western harvest mouse (4.8%), and vagrant shrew (3.4%). All other species were caught in very

Page 12 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities small numbers (< 1%): Great Basin pocket mouse, western jumping mouse, bushy-tailed woodrat, and long-tailed vole.

Four species were reported from the three pit-fall sites (Table 4). In order of trapping frequency, these were the vagrant shrew (N = 14), montane vole (N = 7), deer mouse (N = 2), and the northern pocket gopher (N = 1).

Species Abundance—Small mammal abundance ranged between 14.2 and 41.6 small mammals captured/100 trap nights and averaged 21.8 ± 10.5 small mammals/100 trap nights (Table 6). Significant differences in small mammal abundance were found among neither study reaches nor cover types (ANOVA, F = 3.87, df = 2, P = 0.45 and F = 1.71, df = 8, P = 0.18, respectively), although small mammal abundance tended to increase from Brownlee Reservoir (18.8 ± 9.8 mammals/100 trap nights) to the reach below Hells Canyon Dam (31.3 ± 7.2 mammals/100 trap nights) (Table 5). Cover types were combined into three broad habitat types (riparian, upland, and Mountain Shrubland) for comparisons of small mammal abundances. No differences were found, however, in small mammal abundance among habitat types (ANOVA, F = 0.65, df = 26, P = 0.53).

5.3. Species Diversity and Evenness

Species diversity differed considerably among cover types (Tables 5 and 7). The highest species diversity was found for the Mountain Shrubland cover type (H′ = 1.03) and the lowest for Shore & Bottomland Wetland (H′ ≤ 0.01). Intermediate values (H′ ≥ 0.50) were calculated for Forested Wetland (H′ = 0.83), Shrub Savanna (H′ = 0.75), and Grassland (H′ = 0.69). Scrub-Shrub Wetland, Desertic Shrubland, Shrubland and Forested Upland showed relatively low diversities (H′ = 0.33, 0.45, 0.50, and 0.47, respectively) (Table 7). Species diversity was highest in the reach below Hells Canyon Dam (H′ = 0.76) compared with species diversity for the other two reaches (t-tests, Ps ≤ 0.001), but diversity did not differ between the Brownlee and Hells Canyon Reservoir reaches (H′ = 0.62 and 0.65, respectively; t-tests, P = 0.10). Evenness tended to follow the same trends as those described for diversity (Table 7).

5.4. Small Mammal Community–Habitat Relationships

The TWINSPAN analysis showed groupings of neither species nor sites (Appendix 2). Small mammal species were not associated with specific cover types. Principal Component Analysis (PCA) of sample sites, based on the small mammal composition and relative abundance, showed almost complete overlap of upland and riparian cover types (Figure 3).

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6. DISCUSSION

6.1. Species Richness

Upland Habitat—Species richness reported in sagebrush or shrub-steppe dominated plant communities in the Intermountain West differed considerably among studies (Table 8). The highest number of species reported was ten (Holthuijzen 1998) in sagebrush communities in southwestern Idaho and the lowest was one in a similar environment in southeastern Washington (Lewke and Buss 1977). The species richness averaged for 20 studies in the Intermountain West was six. Five species were reported in upland habitat in the Hells Canyon Study Area, slightly below the average species richness for similar habitats. This finding is somewhat surprising considering the variety of upland cover types sampled (Table 5).

Riparian Habitat—In both desert and montane regions, riparian vegetation supports more species of rodents, and greater densities of some species than surrounding uplands do (Stamp and Ohmart 1979, Doyle 1990). Kauffman (1988) suggested that riparian habitats may be used by large numbers of wildlife species, including small mammals, and play significant roles in maintaining wildlife communities in adjacent upland habitats. Species richness reported in riparian habitats in the Intermountain West ranged from two species in southwestern Idaho (USDI 1979) to nine species in the Hells Canyon reach of the Snake River (Asherin and Claar 1976). On average, investigators reported six small mammal species in riparian studies in the Intermountain West (Table 9). In the Hells Canyon Study Area, seven species were detected, which was slightly higher than the average number of species detected in similar habitats in the Intermountain West but lower than the nine species reported by Asherin and Claar (1976) in the same general study reach (Table 9).

Study Area and Vicinity—Thirty-one small mammal species have been reported to occur in the vicinity of the study area (Marshall 1986, Csuti et al. 1997, Verts and Carraway 1998; Table 1). Seventeen of these species are known to occur in the study reach (Asherin and Claar 1976, Groves and Marks 1985) (Table 1). In this study, nine species were detected (Tables 4 and 5), all of which were reported by either Asherin and Claar (1976), Groves and Marks (1985), or both. Other species that were observed incidentally were the coast mole (Scapanus orarius), least chipmunk (Tamias minimus), yellow-pine chipmunk (Tamias amoenus), white-tailed antelope ground squirrel (Ammospermophilus leucurus), Townsend’s ground squirrel (Spermophilus townsendii), Belding’s ground squirrel (S. beldingi), golden-mantled ground squirrel (S. lateralis), Columbia ground squirrel (Spermophilus columbianus), and possibly the southern Idaho ground squirrel (S. brunei endemicus).

Few records of coast moles are available for Idaho. Yensen et al. (1986) found a road-killed specimen at the rim of Hells Canyon near Cuprum. Caswell collected other specimens outside the canyon near Cambridge (1953, in Yensen et al. 1986). Coast moles inhabit a variety of vegetation and soil types ranging from coastal-dune, pastureland and soil types ranging from coastal-dune, pastureland, and meadow habitats and to sagebrush-grass associations (Hartman and Yates 1995). Coast moles tend to occupy streamside and forested habitats with light, well- drained soils (Verts and Carraway 1998). This description appears to fit the location where the

Page 14 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities coast mole was found in the study area. It was found along a hiking trail at Limestone Creek, a tributary to the Snake River at Oxbow Reservoir (A. Utz, IPC, pers. comm.). The trail parallels and occasionally crosses the small perennial stream. However, the soils can hardly be described as light or well drained. The specimen was collected and sent to Washington State University for identification.

The yellow-pine chipmunk was occasionally sighted in forested vegetation associated with gullies and creeks in the Hells Canyon Study Area. The species typically occurs in brush-covered areas where snowberry (Symphoricarpus), mountain mahogany (Cercocarpus), serviceberry, antelope bitterbrush, currant (Ribes aureum), and buckbrush (Ceanothus) are interspersed with a variety of grasses and herbs (Sutton 1992).

The least chipmunk was reported on both sides of Brownlee Reservoir. The Townsend’s ground squirrel was observed in the upper reaches of Brownlee Reservoir near Cobb Rapids. The white-tailed antelope ground squirrel and the golden-mantled ground squirrel were only observed along Brownlee Reservoir, and though the golden-mantled ground squirrel was reported on both sides of Brownlee Reservoir (Bartels and Thompson 1993), it was never observed north of that reservoir. Columbian ground squirrels were reported at Barber Flats and at the upper Imnaha River.

The southern Idaho ground squirrel was not observed, but the burrowing systems found near Cobb Rapids on the Idaho side of the Snake River closely resembled those constructed by this species (K. Wilde, IPC, pers. comm.) All species that were incidentally observed, except for the southern Idaho ground squirrel, appear to be widespread in the Brownlee Reservoir reach of the study area.

6.2. Species Composition

6.2.1. Upland Habitat

Generally, small mammal species diversity is low in sagebrush-dominated communities. Four common species usually dominate such communities, which indicates low small mammal diversity. These are an herbivore (ground squirrel), a granivore (pocket mouse), an insectivore (grasshopper mouse), and an omnivore (deer mouse) (Rogers et al. 1988). The species composition of the small mammal community in upland habitats of the study area was similar to results of 20 other studies of small mammal communities in shrub-steppe environments in the Intermountain West (Table 8). As in these other studies, the deer mouse was the dominant species (84.0% of all catches) in the study area. The proportion of deer mice in small mammal communities reported in other studies ranged between 11% and 100% (0 = 64.7%) (Table 8). Asherin and Claar (1976) reported that the deer mouse was the most common species trapped in the Hells Canyon Reach (86%), followed by the house mouse (4%), and montane vole (3%). In this study, the deer mouse comprised 81% of the total sample (upland and riparian cover types combined), followed by the montane vole (9.3%), western harvest mouse (4.8%), and the vagrant shrew (3.4%). Interestingly, the house mouse was never caught at any of the sites trapped.

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Asherin and Claar (1976) also showed a higher species diversity in riparian than upland plant communities. Such differences were not found in this study.

Other important species reported in studies conducted in the Intermountain West were the least chipmunk; Ord’s kangaroo rat; chisel-toothed kangaroo rat; Great Basin pocket mouse; western harvest mouse; and, to a lesser extent, montane vole; canyon mouse; northern grasshopper mouse; and house mouse (Table 8). The Great Basin pocket mouse, western harvest mouse, and montane vole were reported in small, but varying, percentages by other authors for the Intermountain West (Table 8). One species, the vagrant shrew, was trapped in small numbers in both upland and riparian habitats in the Hells Canyon Study Area, but it was rarely reported in other studies where shrub-steppe habitats were sampled (Table 8). Upland locations trapped in the study area were near riparian habitat, which may explain the presence of the vagrant shrew at these sites.

6.2.2. Riparian Habitat

The small mammal species composition for riparian habitat in the study area was comparable to that for other such communities reported in the Intermountain West (Table 9). In this study, the deer mouse was, once again, the predominant species (76.5% of all catches). Other studies also reported the deer mouse as the most abundantly present species (Table 9). The proportion of deer mice in the small mammal communities ranged between 48.1% (Knopf and Olson 1984) and 99.0% (USDI 1979). Two other species trapped in this study, the western harvest mouse and montane vole, were also detected in other studies in riparian habitat (Table 9). The bushy-tailed woodrat and western jumping mouse were caught in small numbers in the Hells Canyon Study Area. Most surprising was the relatively high proportion of vagrant shrews captured in this study (7.1% of all catches) (Table 8). The species were caught in a variety of cover types classified as upland (Grassland) and riparian (Forested Wetland and Mountain Shrubland) habitats.

6.3. Relative Abundance

Comparisons were made in small mammal abundances among the Hells Canyon, Hagerman, and C.J. Strike study areas (Holthuijzen 1995, 1998). The latter two areas were particularly useful as comparison areas because similar trapping techniques had been used and results were reported as numbers of small mammals/100 trap nights. Differences were not found among study areas when all cover types were combined (ANOVA, F = 0.66, df = 2, P = 0.52) or when comparisons were made with upland and riparian cover types collapsed into one upland and one riparian habitat type, respectively (ANOVAs, F = 0.24, df = 2, P = 0.78 and F = 0.52, df = 2, P = 0.60, respectively). In the Hells Canyon Study Area, one new cover type, Mountain Shrubland, was sampled, though it was not encountered along the Middle Snake River. Inclusion of these data as riparian habitat did not change the results of the analyses reported above.

The deer mouse dominated the small mammal communities in all three study areas (Hells Canyon –x = 81.0%, Hagerman –x = 71.8%, and C.J. Strike –x = 62.2%). Separate analyses were conducted to determine whether relative abundance of deer mice differed among study areas when upland and riparian cover types were combined. Not surprisingly, given the results

Page 16 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities using total small mammal relative abundances in previous analyses, differences were not detected (ANOVA, F = 0.35, df = 2, P = 0.70). Likewise, differences were not found among the study areas when upland and riparian cover types were collapsed into one upland and one riparian habitat type, respectively (ANOVAs, F = 0.24, df = 2, P = 0.78 and F = 0.35, df = 2, P = 0.70, respectively). Inclusion or exclusion of the Mountain Shrubland cover type within the riparian cover type did not change the above results.

Differences were not found in small mammal relative abundance between upland and riparian habitats or among cover types (Section 5.2.). Relative abundance of small mammals averaged 21.8 ± 10.5 mammals/100 trap nights in the study area compared with 23.2 mammals/100 trap nights in shrubland-grass habitats in southeastern Idaho (Koehler and Anderson 1991). Boone and Keller (1993) reported relative abundances varying from between 25 and 45 mammals/100 trap nights in edge habitat to between 10 and 25 mammals/100 trap nights in interior shrub habitat in southeastern Idaho. Thus, the relative abundance of small mammals in the study area is similar to relative abundances reported in both southeastern and southwestern Idaho (Holthuijzen 1995, 1998).

6.4. Species of Special Concern

The pit-fall trapping effort was conducted to determine the presence of shrews, in particular the Preble’s shrew (Sorex preblei) or other species of shrews associated with riparian habitat. The vagrant shrew was the only species of shrew trapped. This species tends to be a habitat generalist (Verts and Carraway 1998). It is usually captured in greatest numbers in moist grassy areas and more open areas with patches of shrubs and deciduous trees. Gomez and Anthony (1998) captured vagrant shrews in higher numbers in upland than riparian habitat in the Coast Range of western Oregon. In this study, vagrant shrews were trapped in four of five Forested Wetland, three of four Mountain Shrubland, and two of seven Grassland cover type locations (Table 5). The latter two cover types fit the description of vagrant shrew habitat fairly well. All specimens were caught in snap traps. The vagrant shrew has been reported to consume a wide variety of food items of plant and animal origin, including rolled oats that were used to bait traps (Verts and Carraway 1998). Therefore, the presence of the species in snap traps is probably not unusual. The species is also readily caught in pit-fall traps (Verts and Carraway 1998), as was further demonstrated in this study (Table 4).

The target species for the shrew trapping effort was the Preble’s shrew. The little information available on the ecology of the Preble’s shrew provides only scant clues about habitat affinities. Throughout its range the species has been captured in a wide variety of habitats, including marshes, streambanks, dry bunchgrass, and wet alkaline habitat (Verts and Carraway 1998). Grasses and sagebrush were common to most habitats. The Preble’s shrew has been most extensively captured at and near Steens Mountain, Oregon. Most capture locations described by Verts and Carraway (1998) appear to be much higher in elevation than the trapping sites in the study area. Therefore, it may not be surprising that the Preble’s shrew was not detected during this study. When the species is present, its capture appears to take relatively little effort (Verts and Carraway 1998).

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6.5. Habitat Associations

In the study area, small mammal communities from upland and riparian habitats were similar in composition of dominant species (e.g., deer mouse, and montane vole), but densities of individual species differed though not significantly. Associations between small mammal communities and habitat were weak, as shown by the ordination results. Special mammal communities were not identified.

The lack of clear habitat associations is directly related to the overwhelming abundance of the deer mouse. This species was trapped at all sites (Table 5) and comprised between 19.3% and 100% of all small mammals trapped at a site.

7. ACKNOWLEDGMENTS

I wish to thank all field assistants for their exertions in the field, often under adverse weather conditions. Kelly Wilde, Von Pope, and Aaron Utz expertly organized the field work, logistical support, data entry and data organization. Kelly Wilde, Von Pope, Aaron Utz, and Natalie Sunderman provided valuable comments on the report. Natalie Chavez, Chavez Writing and Editing, Inc., edited the manuscript. Corporate Publishing, IPC, formatted the document. GIS support was provided by Mike Butler, IPC.

8. LITERATURE CITED

Asherin, D. A., and J. J. Claar. 1976. Inventory of riparian habitats and associated wildlife along the Columbia and Snake Rivers. Volume IIIA. University of Idaho, College of Forestry, Wildlife and Range Sciences, Moscow, ID. 556 pp.

Alldred, D. M. 1973. Small mammals of the National Reactor Testing Station, Idaho. Great Basin Nat. 33:251-250.

Bartels, M. A., and D. P. Thompson. 1993. Spermophilus lateralis. Mammalian Species 440:1-8.

Bonneville Power Administration (BPA). 1984. Hells Canyon environmental investigation. Prepared by CH2M-Hill, Boise, ID. 300 pp.

Boone, J. D., and B. L. Keller. 1993. Temporal and spatial patterns of small mammal density and species composition on a radioactive waste disposal area: the role of edge habitat. Great Basin Nat. 53:341-349.

Bush, J. H., and W. P. Seward. 1992. Geologic field guide to the Columbia River Basalt, northern Idaho and southeastern Washington. Information Circular 49. University of Idaho, Idaho Geographical Survey, Moscow, ID. 35 pp.

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Call, M. W. 1986. Rodents and insectivores. Pages 429-452 in A. Y. Cooperrider, R. J. Boyd, and H. R. Stuart, eds. Inventory and monitoring of wildlife habitat. U.S. Dep. Inter., Bur. Land Manage., Serv. Cen., Denver, CO.

Caughley, G. 1977. Analysis of vertebrate populations. J. Wiley and Sons, New York, N.Y. 234 pp.

Cowardin, L. M., V. Carter, F. C. Colet, and E. T. LaRoe. 1979. Classification of wetlands and deepwater habitats of the United States. U.S. Dept. Inter., Fish and Wildl. Serv., Washington, D.C. 131 pp.

Csuti, B., A. J. Kimerling, T. A. O’Neil, M. M. Shaughnessy, E. P. Gaines, and M. M. P. Huso. 1997. Atlas of Oregon wildlife: Distribution, habitat, and natural history. Oregon State University Press, Corvallis, OR. 492 pp.

Davis, W. B. 1939. The recent mammals of Idaho. Caxton Printers Ltd., Caldwell, ID. 400 pp.

Davis, D. E., and R. L. Winstead. 1980. Estimating the numbers of wildlife populations. Pages 221-245 in S. D. Schemnitz, ed. Wildlife management techniques. 4th ed. The Wildl. Soc., Washington, D.C. 686 pp.

DeBolt, A. 1992. The ecology of Celtis reticulata Torr. (Netleaf Hackberry) in Idaho. M.Sc. Thesis, Oregon State University, Corvallis, OR. 166 pp.

Doyle, A. T. 1990. Use of riparian and upland habitat by small mammals. J. Mamm. 71:14-23.

Fitzgerald, J.F. 1982. Geology and basalt stratigraphy of the Weiser Embayment, west-central Idaho. Pages 137-141 in B. Bonnichsen, and R. M. Breckenridge, eds. Cenezoic geology of Idaho. University of Idaho, Idaho Bureau of Mines and Geology, Moscow, ID.

Franklin, J. F., and C. T. Dyrness. 1973. Natural vegetation of Oregon and Washington. Oregon State Univ. Press, Corvallis, OR. 452 pp.

Fautin, R. 1946. Biotic communities of the northern desert shrub biome in western Utah. Ecol. Monogr. 16:251-310.

Garrison, G. A., A. J. Bjugstad, D. A. Duncan, M. E. Lewis, and D. R. Smith. 1977. Vegetation and environmental features of forest and range ecosystems. U.S. Dep. Agric., For. Serv., Agric. Handb. No. 475. 68 pp.

Germano, D. J., and D. N. Lawhead. 1986. Species diversity and habitat complexity: does vegetation organize vertebrate communities in the Great Basin? Great Basin Nat. 46:711-720.

Gomez, D. M., and R. G. Anthony. 1998. Small mammal abundance in riparian and upland areas of five seral stages in western Oregon. Northw. Sci. 72:293-302.

Hells Canyon Complex Page 19 Description of Small Mammal Communities Idaho Power Company

Groves, C. R., and B. L. Keller. 1983. Ecological characteristics of small mammals on a radioactive waste disposal area in southeastern Idaho. Am. Midl. Nat. 109:253-265.

Groves, C. R., and J. S. Marks. 1985. Annotated checklist of Idaho vertebrates. Tebiwa 22:10-27.

Groves, C. R., and K. Steenhof. 1988. Responses of small mammals and vegetation to wildfire in shadscale communities of southwestern Idaho. Northw. Sci. 62:205-210.

Groves, C. R., B. Butterfield, A. Lippincott, B. Csuti, and J. M. Scott. 1997. Atlas of Idaho’s wildlife: integrating gap analysis and natural heritage information. Idaho Dept. Fish and Game, Nongame and Endangered Wildlife Program, Boise, ID. 372 pp.

Hall, E. R. 1981. The mammals of North America. Vol. 1. John Wiley and Sons, New York, N.Y. 600 pp.

Handley, C. O., and M. Varn. 1994. The trapline concept applied to pitfall arrays. Spec. Publ. Carnegie Mus. Nat. Hist. No. 18.

Hartman, G. D., and T. L. Yates. 1995. Scapanus orarius. Mammalian Species 253:1-5.

Hill, M. O. 1979. TWINSPAN: a FORTRAN program for arranging multivariate data in an ordered two-way table by classification of the individuals and attributes. Cornell University, Ecology and Systematics, Ithaca, N.Y. 90 pp.

Holthuijzen, A. M. A. 1995. An investigation of small mammals in the Hagerman Study Area. New license application for the Upper Salmon Falls, Lower Salmon Falls, and Bliss hydroelectric projects. Technical Appendices. Volume 3. Idaho Power, Boise, ID. Technical Report E.3.2-H. 46 pp.

Holthuijzen, A. M. A. 1997. An investigation of small mammals in the Shoshone Falls Study Area. New license application for the Shoshone Falls hydroelectric project. Technical Appendices. Volume 2. Idaho Power, Boise, ID. Technical Report E.3.2-F. 34 pp.

Holthuijzen, A. M. A. 1998. An investigation of small mammal communities in the C.J. Strike Study Area. New license application for the C.J. Strike hydroelectric project. Technical Appendices. Volume 2. Idaho Power, Boise, ID. Technical Report E.3.2-G. 48 pp.

Huschle, G. 1975. Analysis of the vegetation along the middle and lower Snake River. M.Sc. Thesis, Univ. Idaho, Moscow, ID. 268 pp.

Johnson, C. G. Jr., and S. A. Simon. 1987. Plant associations of the Wallowa–Snake province, Wallowa–Whitman National Forest. U.S. Dept. Agric. For. Serv. PNR. R-6 ECOL-TP-225A- 86. 272 pp.

Johnson, W. C., and B. L. Keller. 1983. Examination of the area of effect of snap-trap transects in Idaho desert. Can. J. Zool. 61:403-410.

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Jones, C, W. J. McShea, M. J. Conroy, and T. H. Kunz. 1996. Capturing mammals. Pages 115-155 in D. E. Wilson, F. R. Cole, J. D. Nichols, R. Rudran, and M. S. Foster, eds. Measuring and monitoring biological diversity: standard methods for mammals. Biological diversity handbook series. Smithsonian Institution Press, Washington, D.C.

Kauffman, J. B. 1988. The status of riparian habitats in Pacific Northwest forests. Pages 45-55 in K. Raedeke, ed. Streamside management: riparian wildlife and forestry interactions. Symposium Proc. University of Washington, Seattle, WA.

Koehler, D. K., and S. H. Anderson. 1991. Habitat use and food selection of small mammals near a sagebrush/crested wheatgrass interface in southeastern Idaho. Great Basin Nat. 51:249-255.

Knopf, F. L., and T. E. Olson. 1984. Naturalization of Russian-olive: implications to Rocky Mountain wildlife. Wildl. Soc. Bull. 12:289-290.

Lewke, R. E., and I. O. Buss. 1977. Impacts of impoundment of vertebrate animals and their habitats in the Snake River Canyon, Washington. Northw. Sci. 51:219-270.

Marshall, D. B. 1986. Oregon nongame wildlife management plan. Oregon Dept. Fish and Wildl., Portland, OR.

Miller, T. B. 1976. Ecology of riparian communities dominated by white alder in western Idaho. M.Sc. Thesis, University of Idaho, Moscow, ID. 154 pp.

Miller, T. B., and F. D. Johnson. 1976. Ecology of riparian communities dominated by white alder in western Idaho. Pages 11-123 in Proc. terrestrial and aquatic vegetation. Eastern Washington State College, Cheney, WA.

Natural Resources Conservation Service (NRCS). 1995. Soil survey for Adams and Washington counties. Draft report. Idaho. Weiser, ID.

Nichols, D. W., H. D. Smith, and M. F. Baker. 1975. Rodent populations, biomass, and community relationships in Artemisia tridentata: Rush Valley, UT. Great Basin Nat. 35:191-202.

Olinger, M. F., and K. Lee. 1979. Small mammal populations in free flowing and impounded reaches of the Snake River. In E. Conners, ed. Studies of water use on the Snake River drainage, southern Idaho. University of California, Irvine, CA.

Ports, M. A., and L. K. Ports. 1989. Associations of small mammals occurring in a pluvial lake basin, Ruby Lake, NV. Great Basin Nat. 49:123-130.

Reynolds, T. D. 1980. Effects of some different land management practices on small mammal populations. J. Mamm. 61:558-561.

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Rogers, L. E., R. E. Fitzner, L. L. Caldwell, and B. E. Vaughan. 1988. Terrestrial animal habitats and population responses. Pages 181-257 in W. H. Richard, L. E. Rogers, B. E. Vaughan, and S. F. Liebetrau. Shrub-steppe: balance and change in a semi-arid terrestrial ecosystem. Developments in agriculture and managed-forest ecology 10. Elsevier Publ., Amsterdam, the Netherlands.

Ross, S. H., and C. N. Savage. 1967. Idaho earth science: Geology, fossils, climate, water, and soils. University of Idaho, Idaho Bureau of Mines and Geology, Moscow, ID. Earth Science Series No. 1. 271 pp.

Stamp, N. E., and R. D. Ohmart. 1979. Rodents of desert shrub and riparian woodland habitats in the Sonoran desert. Southw. Nat. 24:279-289.

Sutton, D. A. 1992. Tamias amoenus. Mamm. Species 390:1-8.

Tisdale, E. W. 1979. A preliminary classification of Snake River canyon grasslands in Idaho. University of Idaho, For., Wildl. and Range Exp. Sta., Moscow, ID. 8 pp.

Tisdale, E. W. 1986. Canyon grasslands and associated shrublands of west central Idaho and adjacent areas. University of Idaho, For., Wildl and Range Exp. Station, Moscow, ID. Bull. No. 40. 42 pp.

Tisdale, E. W., and M. Hironaka. 1981. The sagebrush-grass region: a review of the ecological literature. University of Idaho, For., Wildl. And Range Exp. Sta., Moscow, ID. 31 pp.

Tisdale, E. W., M. Hironaka, and M. A. Fosberg. 1969. The sagebrush region in Idaho: a problem in range resource management. University of Idaho Agric. Exp. Sta., Moscow, ID. Bull. No. 512. 12 pp.

U.S. Department of Agriculture (USDA). 1990. Final environmental impact statement and land resource management plan: Wallowa–Whitman National Forest. U.S. Dept. Agric. For. Serv., Pac. North West Region, Baker City, OR. 367 pp.

U.S. Department of Agriculture (USDA). 1994. Final environmental impact statement: Wild and scenic Snake River recreation management plan. U.S. Dept. Agric. For. Serv., Hells Canyon Nat. Rec. Area, Wallowa–Whitman Nat. For., Pac. North West Region, Baker City, OR. 243 pp.

U.S. Department of Energy (DOE). 1985. Final report: Hells Canyon environmental investigation. U.S. Dept. of Energy, Bonneville Power Administration, Office of Power and Resource Manage., DOOE/BP-11548-1.

U.S. Department of the Interior (USDI). 1979. Snake River birds of prey special research report. U.S. Dep. Inter., Bur. Land Manage., Boise Distr., Boise, ID. 142 pp.

U.S. Department of the Interior (USDI). 1987. Proposed resource management plan and final environmental impact statement: Cascade Resource Area. U.S. Dept. Inter., Bur. Land Manage., Boise Distr., Boise, ID.

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Verts, B. J., and L. N. Carraway. 1998. Land mammals of Oregon. University of California Press, Berkeley, CA. 668 pp. Yensen, E., D. A. Stephens, and M. Post. 1986. An additional Idaho mole record. Murrelet 67:96.

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Page 24 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities

Table 1. Small mammals of the Order Rodentia present or potentially present in the Hells Canyon Study Area or vicinity.

Present in Study Present in Species Common Name Scientific Name Area Vicinity1) Study Area2)

Preble’s shrew Sorex preblei X ?3) Vagrant shrew Sorex vagrans X X Montane shrew Sorex monticolus X - Water shrew Sorex palustris X ? Merriam’s shrew Sorex merriami X X Coast mole Scapanus orarius X ? American pika Ochotona princeps X - Least chipmunk Tamias minimus X - Yellow-pine chipmunk Tamias amoenus X ? White-tailed antelope squirrel Ammospermophilus leucurus X X Townsend’s ground squirrel Spermophilus townsendii X X Belding’s ground squirrel Spermophilus beldingi X X Columbian ground squirrel Spermophilus columbianus X X Golden-mantled ground squirrel Spermophilus lateralis X X Southern Idaho ground squirrel Spermophilus brunei endemicus X ? Northern pocket gopher Thomomys talpoides X X Little pocket mouse Perognathus longimembris X - Great Basin pocket mouse Perognathus parvus X X Ord’s kangaroo rat Dipodomys ordii X X Western harvest mouse Reithrodontomys megalotis X X Deer mouse Peromyscus maniculatus X X Canyon mouse Peromyscus crinitus X X Bushy-tailed woodrat Neotoma cinerea X X Southern red-backed vole Clethrionomys gapperi X - Heather vole Phenacomys intermedius X - Montane vole Microtus montanus X X Long-tailed vole Microtus longicaudus X ? Water vole Microtus richardsoni X - Sagebrush vole Lagarus curtatus X - House mouse Mus musculus X X Western jumping mouse Zapus princeps X X 1) Based on Marshall (1986), Csuti et al. (1997), and Verts and Carraway (1998). 2) Based on Asherin and Claar (1976), Groves and Marks (1985), and Hall (1981). 3) Possibly present.

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Table 2. Cover types (acreage and percentages) present in the Hells Canyon Study Area.

Habitat Vegetation Cover Type Acreage (acres) Percentage Riparian Forested Wetland 963 < 1.0 Riparian Scrub-Shrub Wetland 2033 1.7 Riparian Shore & Bottomland Wetland 2220 1.8 Upland Agriculture 6019 5.0 Upland Cliff/Talus 6729 5.6 Upland Desertic Herbland 870 < 1.0 Upland Desertic Shrubland 1362 1.1 Upland Forested Upland 179 < 1.0 Upland Grassland 42,484 35.5 Upland Grazing Land 1435 1.2 Upland Lotic 19,252 16.1 Upland Shrub Savanna 25,092 21.0 Upland Shrubland 7895 6.6 Upland Tree Savanna 570 < 1.0 119,534

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Table 3. Trapping locations, trapping year, first trapping night, and trapping effort, Hells Canyon Study Area, 1997 and 1998.

Vegetation Cover Type1) Trapping First Trapping Study Reach Sample Site Year Night SBW SSW FW DS G SS S MS FU Σ Brownlee Reservoir Dukes Creek 1997 2 April – – 1402) 134 148 137 – 147 – 706

Grouse Creek 1998 15 April 125 – 143 138 144 –- 136 – – 686 Quicksand Creek 1998 22 April – 140 – 141 296 –- 132 – – 709 Below Hells Canyon Dam Klopton Creek 1998 29 April – – – – 134 –- – – 138 272

Kurry Creek 1998 29 April – – – – 134 –- – – – 134 Pittsburg Landing 1998 29 April – – 137 – – –- – 144 – 281 Hells Canyon Reservoir Bob Creek 1997 9 April – – 134 143 150 –- 144 142 – 713

Eckles Creek 1998 8 April – – 145 – 145 –- – 134 – 424 Limepoint Creek 1998 8 April – – – 139 – –- 141 – – 280

Σ 125 140 699 695 1151 137 553 553 138 4205 1) G–Grassland; DS–Desertic Shrubland; SS–Shrub Savanna; S–Shrubland; FU–Forested Upland; MS–Mountain Shrubland; FWS–Forested Wetland; SSW−Scrub-Shrub Wetland; and SBW–Shore & Bottomland Wetland. 2) Number of trap nights

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Table 4. Location, operating dates, trap days, and species of small mammals caught in shrew trapping arrays in the Hells Canyon Study Area, spring 1997.

Species1) Trap Trap Site Date Days MOVO VASH DEMO NOPG Dukes Creek 1–11 April 12 3 1 22–25 April 3 1 4 1 6–8 May 3 2 Σ 18 4 7 1

Cottonwood Creek 1–11 April 12 1 22–25 April 3 1 1 6–8 May 3 2 2 1 1 Σ 18 3 4 1 1

Powder River 1–11 April 12 22–25 April 3 6–8 May 3 3 Σ 18 3 ΣΣ 54 7 14 2 1 1) MOVO–montane vole; VASH–vagrant shrew; DEMO–deer mouse; NOPG–northern pocket gopher.

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Table 5. Species and numbers of small mammals caught per 100 trap nights, Hells Canyon Study Area, 1997 and 1998.

Species1) Cover

Reach Tributary Type MOVO DEMO GBPM WHMO VASH WJMO LTVO BTWR Σ H''' E Dukes Creek DS 0.7 19.4 0.7 8.2 29.1 0.81 0.58 FW 7.1 10.8 1.4 5.0 1.4 25.9 1.36 0.84 G 10.8 3.4 0.7 2.7 17.6 1.03 0.74 MS 6.2 6.2 2.1 14.4 1.00 0.91 SS 3.7 23.7 4.4 31.8 0.74 0.67 Grouse Creek DS 0.7 11.6 12.3 0.22 0.32 Brownlee FW 7.8 7.8 0.00 0.00 Reservoir G 2.1 9.7 0.7 0.7 13.2 0.82 0.59 S 13.2 1.5 14.7 0.32 0.46 SBW 41.6 41.6 0.00 0.00 Quicksand DS 15.6 0.7 16.3 0.17 0.59 Creek G 0.3 6.1 0.3 0.3 7.1 0.56 0.46 S 16.7 16.7 0.00 0.00 SSW 12.8 1.4 14.2 0.32 0.46 Bob Creek DS 0.6 20.3 0.7 21.6 0.28 0.25 FW 0.7 28.4 7.4 36.5 0.60 0.54 G 0.7 0.7 0.00 0.00 MS 0.7 14.8 0.7 16.1 0.35 0.32 Hells Canyon S 3.4 7.6 2.1 13.1 0.95 0.87 Reservoir Eckles Creek FW 0.7 17.9 0.7 0.7 20.0 0.44 0.32 G 1.4 14.5 15.8 0.29 0.42 MS 11.9 11.9 2.2 1.5 0.7 28.3 1.18 0.73 Limepoint DS 23.0 23.0 0.00 0.00 S 1.4 33.3 1.4 36.1 0.33 0.30 Pittsburg FW 30.9 0.7 2.2 33.8 0.34 0.31 Landing MS 0.7 16.0 1.4 2.1 20.1 0.71 0.51 Below Hells Canyon Klopton Creek FU 2.9 35.0 2.2 40.1 0.46 0.42 G 1.5 29.3 1.5 32.2 0.37 0.34 Kurry Creek G 29.8 29.8 0.00 0.00 1) MOVO–montane vole; DEMO–deer mouse; GBPM–Great Basin pocket mouse; WHMO–western harvest mouse; VASH–vagrant shrew; WJMO–western jumping mouse; LTVO−long-tailed vole; and BTWR–bushy-tailed woodrat 2) G–Grassland; DS–Desertic Shrubland; SS–Shrub Savanna; S–Shrubland; FU–Forested Upland; MS–Mountain Shrubland; FWS–Forested Wetland; SSW−Scrub-Shrub Wetland; and SBW–Shore & Bottomland Wetland.

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Table 6. Small mammal relative abundance (average number of mammals per 100 trap nights ± 1STD) for each cover type and reach sampled in the Hells Canyon Study Area, 1997 and 1998.

Study Reach Cover Brownlee Hells Canyon Below Type1) Reservoir Reservoir Hells Canyon Dam Study Area

SBW 41.6 (1)2) – – 41.6 (1) SSW 14.2 (1) – – 14.2 (1)

FW 16.9 ± 12.8 (2) 28.8 ± 11.7 (2) 33.8 (1) 24.8 ± 11.5 (5) MS 14.3 (1) 22.7 ± 8.6 (2) 20.1 (1) 19.8 ± 6.2 (4) G 12.6 ± 5.2 (3) 8.3 ± 10.7 (2) 31.1 ± 1.8 (2) 16.5 ± 11.4 (7) DS 19.2 ± 8.8 (3) 22.3 ± 0.9 (2) – 20.5 ± 6.4 (5) SS 31.8 (1) – – 31.8 (1) S 15.6 ± 1.4 (2) 24.7 ± 16.2 (2) – 20.2 ± 10.8 (4) FU – 40.1 (1) 40.1 (1)

x– 18.8 ± 9.8 (14) 21.2 ± 10.8 (10) 31.3 ± 7.2 (5) 21.8 ± 10.5 (29)

1) G–Grassland; DS–Desertic Shrubland; SS–Shrub Savanna; S–Shrubland; FU–Forested Upland; MS–Mountain Shrubland; FW–Forested Wetland; SSW–Scrub-Shrub Wetland; and SBW–Shore & Bottomland Wetland. 2) Number in parentheses denote sample size.

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Table 7. Shannon diversity (H΄) and evenness (E) indices for small mammal communities trapped at each of the three study reaches and vegetation cover types, Hells Canyon Study Area, 1997 and 1998.

Cover Type1) Study Reach Index SBW SSW FW DS SS S MS FU G Brownlee H < 0.01 0.33 1.21 0.61 0.75 0.19 1.01 − 1.09 Reservoir ΄ E < 0.01 0.11 0.31 0.14 0.19 0.05 0.33 − 0.26

Hells Canyon H − − 0.59 0.16 − 0.58 1.02 − 0.29 Reservoir ΄ E − − 0.13 0.04 − 0.13 0.25 − 0.09

Below Hells Canyon H΄ − − 0.35 − − − 0.72 0.47 0.23 Dam E − − 0.09 − − − 0.21 0.11 0.05

Study Area H΄ < 0.01 0.33 0.83 0.45 0.75 0.50 1.03 0.47 0.69 E < 0.01 0.11 0.16 0.09 0.19 0.10 0.21 0.11 0.13

1) G–Grassland; DS–Desertic Shrubland; SS–Shrub Savanna; S–Shrubland; FU–Forested Upland; MS–Mountain Shrubland; FW–Forested Wetland; SSW–Scrub-Shrub Wetland; and SBW–Shore & Bottomland Wetland.

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Table 8. Small mammal community composition (% of total captures) in shrub-steppe vegetation communities, Intermountain West.

Species2)

Source Location Habitat Species1) DEMO LECH OKRA CHKR GBPM WHMO MOVO CAMO NGHM HOMO VASH

Fautin (1946) western Utah sagebrush 6 38 5.5 25.5 22.2 0.6 8.1 Alldred (1973) southeastern Idaho sagebrush-grass 9 (+) (+) (+) (+) (+) (+) Nichols et al. (1975) northern Utah sagebrush 4 54 24.3 20.6 1.5 Asherin and Claar (1976) west central Idaho sagebrush-grass 6 81 12.5 southeastern Lewke and Buss (1977) Washington sagebrush 1 100 Olinger and Lee (1979) southwestern Idaho riparian/upland 5 74 9.2 <1.0 <1.0 14.8 USDI (1979) southwestern Idaho sagebrush 5 78 3.9 3.2 7.2 7.2 Knopf and Olson (1984) southwestern Idaho sagebrush 6 71 1.3 11.8 10.4 <1.0 Groves and Steenhof (1988) southwestern Idaho sagebrush 4 86 1.8 Reynolds (1980) southeastern Idaho sagebrush 9 70 11.2 1 1.6 5.8 <1.0 6.4 Groves and Keller (1983) southeastern Idaho sagebrush 9 51 12 10 6 <1.0 Johnson and Keller (1983) southeastern Idaho sagebrush 7 47 30.2 <1.0 15.3 1 3.1 Germano and Lawhead (1986) northwestern Utah sagebrush 9 57 10.6 Rogers et al. (1988) western Washington sagebrush 5 11 46.6 2.9 Ports and Ports (1989) east central Nevada sagebrush 4 32 7 2 59 Koehler and Anderson (1991) southeastern Idaho shrubland-grass 7 75.7 2.4 4.2 Boone and Keller (1993) southeastern Idaho shrubland-grass 6 72.0 (+) (+) (+) (+) (+) Holthuijzen (1995) southwestern Idaho sagebrush 9 74 4.6 2.2 16.3 1.7 <1.0 <1.0 <1.0 <1.0 Holthuijzen (1997) southern Idaho sagebrush 7 86 3.7 2.7 <1.0 Holthuijzen (1998) southwestern Idaho sagebrush 10 71.9 9.1 2.1 11.0 1.8 This Study Oregon– Idaho border shrubland-grass 5 84.0 0.8 6.1 8.2 0.9

1) Only the most abundant species are reported. 2) DEMO–deer mouse; LECH–least chipmunk; OKRA–Ord’s kangaroo rat; CHKR–chisel-toothed kangaroo rat; GBPM–Great Basin pocket mouse; WHMO–western harvest mouse; MOVO–montane vole; CAMO–canyon mouse; NGHM–northern grasshopper mouse; HOMO–house mouse; and VASH–vagrant shrew.

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Table 9. Small mammal community composition (% of total captures) in riparian vegetation communities, Intermountain West.

Species1)

Total Source Location Habitat Species2) DEMO LECH OKRA VASH GBPM WHMO MOVO CAMO NGHM HOMO BTWR WJMO

Asherin and Claar (1976) west-central Idaho riparian 9 63.4 3.7 4.4 24.6

Lewke and Buss (1977) southeast Washington riparian 5 87.7

Olinger and Lee (1979) southwestern Idaho riparian/upland 5 73.6 9.2 < 1.0 < 1.0 14.8

USDI (1979) southwestern Idaho riparian 2 99.0 < 1.0

Knopf and Olson (1984) southwestern Idaho riparian site #1 5 62.7 2.3 2.3 13.9

riparian site #2 6 48.1 1.8 12.0 19.4 17.6

Holthuijzen (1995) southwestern Idaho riparian 7 77.2 3.0 5.1 7.5 < 1.0 < 1.0 1.8

Holthuijzen (1997) southern Idaho riparian 6 79.3 <1.0 < 1.0

Holthuijzen (1998) southwestern Idaho riparian 8 60.1 < 1.0 < 1.0 13.7

This Study east-central Idaho riparian 7 76.5 7.1 2.8 11.0 0.8 1.1

1) Only the most abundant species are reported. 2) DEMO–deer mouse; LECH–least chipmunk; OKRA–Ord’s kangaroo rat; VASH–vagrant shrew; GBPM–Great Basin pocket mouse; WHMO–western harvest mouse; MOVO–montane vole; CAMO–canyon mouse; NGHM–northern grasshopper mouse; HOMO–house mouse; BTWR–bushy-tailed woodrat; and WJMO–western jumping mouse.

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Page 36 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities

Weiser 2 SEa (641m)b 10.1d 286mme Richlanda (675m)b 10.6d 298mme 60 60 60 60 55 55 55 55 50 47, 47c 50 50 49, 49c 50 45 45 45 45 42.8i 42.8i 40 40 40 l 40 35 35 35 35 33.4h 33.8h 30 n l 30 30 n 30 25 25 25 25 20 20 20 20 15.7j 17.3j 15 15 15 15 10 10 10 m 10 5 5 5 k 5 k m (mm) PRECIPITATION (mm) PRECIPITATION 0 0

DEGREES CENTIGRADE 0 0 DEGREES CENTIGRADE -5 -5 -5 -6.8f -7.7f JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC -32.8g -33.9g o MONTHS o o MONTHS o

Brownleea (562m)b 12.3d 445mme Lewiston WSO APa (438m)b 11.3d 326mme 60 60 60 60 55 33, 33 55 55 55 c 51, 51 50 n 50 50 c 50 46.1i 45i 45 45 45 45 40 l 40 40 40 39.4h 35 35 35 n 35 34.7h l 30 30 30 30 27.4j 25 25 25 25 20 20 20 20 15 15 13.1j 15 15 10 m 10 m k 10 10 PRECIPITATION (mm) PRECIPITATION 5 5 (mm) PRECIPITATION 5 k 5 DEGREES CENTIGRADE 0 0 CENTIGRADE DEGREES 0 0 -5 -5 -5 -5 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC -13.3f JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC o MONTHS o -30g o MONTHS o

a: Station b: Elevation c: Number of years of observation (temperature, precipitation) d: Mean annual temperature in °C e: Mean annual precipitation in millimeters f: Mean daily minimum of the coldest month g: Lowest recorded temperature h: Mean daily maximum of the hottest month i: Highest recorded temperature j: Mean daily temperature range k: Monthly means of temperature in °C l: Monthly means of precipitation in millimeters m: Arid period (horizontal hatched) n: Humid period (vertical hatched) o: Months with an absolute minimum below 0 °C

Figure 2. Köppen climate diagrams for the Weiser, Richland, Brownlee, and Lewiston weather stations, Hells Canyon Study Area, Idaho–Oregon border.

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MS

G

FW

MS SS FU Axis 2

FW S S S G MS SBW G G FW DS G MS FW DS DS DS S G SS S FW G

Axis 1

Figure 3. Principal Component Ordination of small mammal trap sites for each of the vegetation cover types, based on small mammal composition and abundance, Hells Canyon Study Area, 1997 and 1998.1)

1) Acronyms for the vegetation cover types can be found in Appendix 1.

Page 38 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities

Appendix 1. Criteria and definitions used to identify cover types in the Hells Canyon Study Area, eastern Idaho.

1. EHW Emergent Herbaceous Wetland is dominated by emergent, erect, rooted and herbaceous hydrophytes excluding mosses and lichens. This vegetation is present for most of the growing season in most years and is usually dominated by perennial plants. It has less than 30% cover of woody vegetation and a total vegetation cover of at least 30%. The lands in this cover type are usually saturated with or covered by water at least for part of the growing season. However, because of the difficulties in distinguishing between species and interpreting hydrologic indicators during remote sensing activities, some lands in this cover type may be dominated by upland species (FAC, FAC-, and UPL hydrologic indicator status) and located in areas without the necessary hydrologic regime to be considered "jurisdictional wetlands" by the U.S. Army Corps of Engineers. Actual extent of jurisdictional boundaries are not indicated on cover type maps and must be determined on the ground through formal wetland delineation techniques.

3. SBW Shore & Bottomland Wetland may consist of bare sand, gravel, or rocky areas along the riparian zone. If vegetation is present, its cover is less than 30%. Examples of this cover type include Rock Bottom, Unconsolidated Bottom, Streambed, Rocky Shore, and Unconsolidated Shore, as defined by Cowardin (1979). Actual extent of jurisdictional boundaries are not indicated on cover type maps and must be determined on the ground through formal wetland delineation techniques.

4. SSW Scrub-Shrub Wetland is dominated by woody wetland vegetation less than 6 m (20 feet) tall. It has a total vegetation cover of at least 30% and at least 30% cover of woody vegetation. Because of the difficulties in distinguishing between species and interpreting hydrologic indicators during remote sensing activities, some lands in this cover type are dominated by upland species (FAC, FAC-, and UPL hydrologic indicator status) and located in areas without the necessary hydrologic regime to be considered "jurisdictional wetlands" by the U.S. Army Corps of Engineers. Actual extent of jurisdictional boundaries are not indicated on cover type maps and must be determined on the ground through formal wetland delineation techniques.

5. FW Forested Wetland is dominated by woody wetland vegetation that is 6 m (20 feet) tall or taller. It has a total vegetation cover of at least 30% and at least 30% cover of woody vegetation. Because of the difficulties in distinguishing between species and interpreting hydrologic indicators during remote sensing activities, some lands in this cover type are dominated by upland species (FAC, FAC-, and UPL hydrologic indicator status) and located in areas without the necessary hydrologic regime to be considered "jurisdictional wetlands" by the U.S. Army Corps of Engineers. Actual extent of jurisdictional boundaries are not indicated on cover type maps and must be determined on the ground through formal wetland delineation techniques.

6. LS Lentic (Standing Water) is nonmoving open water habitat such as ponds and lakes.

7. LM Lotic (Moving Water) is moving open water habitat such as rivers and streams.

8. FU Forested Upland is dominated by trees (taller than 5 m) and has a tree canopy cover of at least 25%.

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9. S Shrubland is an upland vegetation community dominated by shrubs (including small trees shorter than 5 m) and having a shrub canopy cover of at least 25%. Total vegetation cover is greater than 25%. Mountain Shrub is an upland vegetation community dominated by shrubs that are typically associated with riparian cover types, but occur extant to streams due to edaphic and topographic conditions.

11. SS Shrub Savanna is an upland community with a canopy cover of shrubs (including small trees shorter than 5 m) between 5% and 25%. This cover type has a total vegetation cover of at least 25%. The area between shrubs is typically dominated by grasses or other herbaceous vegetation.

13. DS Desertic Shrubland is an upland community, with 1 to 25% total vegetation cover and shrubs (and small trees shorter than 5 m) forming the dominant vegetation stratum. This cover type includes sparsely vegetated habitats in nondesert areas.

14. DH Desertic Herbland is an upland community with 1 to 25% total vegetation cover and nonwoody plants (including lichens and mosses) forming the dominant vegetation stratum. It includes sparsely vegetated types in nondesert areas.

15. G Grassland is an upland community with a total vegetation cover of at least 25% dominated by nonwoody plants (including lichens and mosses), of which grasses (native or introduced) are dominant. This cover type may include prairies, rangeland, and upland subalpine meadows.

16. F Forbland is an upland community with a total vegetation cover of at least 25% dominated by nonwoody plants (including lichens and mosses), of which forbs (native or introduced) are dominant. This cover type includes many weedy fields, old fields, and other types in early successional stages.

18. CTS Cliff/Talus Slope consists of nearly vertical rock or bare soil faces or slopes of unconsolidated rock material with a total vegetation cover of 5% or less.

19. D Disturbed is land with more than 50% of the area disturbed by human activities and a total vegetation cover of less than 15%. This cover type may include off-road vehicle areas, rural trash dumps, and soil barrow pits.

23. R Residential is land principally associated with human housing. This cover type may include homes, garages, yards, gardens, sidewalks, driveways, and small livestock pens and pastures (1 to 2 acres).

24. I Industrial is land principally used for larger businesses and corporations, such as office complexes, manufacturing plants, and warehouses.

25. PR Parks/Recreation is cultivated landscape principally used for human recreation such as city or county roadside rest areas and picnic areas.

Page 40 Hells Canyon Complex Idaho Power Company Description of Small Mammal Communities

Appendix 2. Two-Way INdicator SPecies ANalysis (TWINSPAN) of the Hells Canyon small mammal trap sites, based on relative abundance (small mammal species/100 trap nights), 1997 and 1998.

Cover Type1)

SFSSGSGDDGFFMFDGDSDGMSFSFGMGM

SW B SS WWSWS S S SSU W S S

BTWR2) ------222------1 LTVO 11------1 GBPM ----111------111111------1 DEMO 43441555445544455543355343424 1 WJMO ------111------111------11 0 VASH ------131113111311------3122131221 0 WHMO ------111131222211112111131222211112 0 MOVO ------111111---111111111---1111132223214411111322232144 0

00000000000000000000111111111 0000000000000000000011111100001111100000000111111000011111 00000000001111000011 00011

1) SS–Scrub-Shrub Wetland; FW–Forested Wetland; G–Grassland; DS−Desertic Shrubland; SS–Shrub Savanna; S–Shrubland; MS−Mountain Shrubland.

2) MOVO–montane vole; DEMO–deer mouse; GBPC–Great Basin pocket mouse; WHMO–western harvest mouse; VASH–vagrant shrew; WJMO−western jumping mouse; LTVO–long-tailed vole; and BTWR−bushy-tailed woodrat.

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