Medium-Sized Mammal Resources in the Hells Canyon Study Area Natalie J. S. Turley Wildlife Technician Anthonie M. A. Holthuijzen Wildlife Ecologist Technical Report Appendix E.3.2-25 January 2001 Revised July 2003 Hells Canyon Complex FERC No. 1971 Copyright © 2003 by Idaho Power Company Idaho Power Company Medium-Sized Mammal Resources TABLE OF CONTENTS Table of Contents ............................................................................................................................. i List of Tables..................................................................................................................................iii List of Figures ................................................................................................................................iii List of Appendices .........................................................................................................................iii Abstract ........................................................................................................................................... 1 1. Introduction ................................................................................................................................ 2 2. Study Area.................................................................................................................................. 3 2.1. Location............................................................................................................................. 3 2.2. Physiography..................................................................................................................... 4 2.3. Land Features and Geology............................................................................................... 5 2.4. Soils................................................................................................................................... 5 2.5. Climate .............................................................................................................................. 6 2.6. Vegetation ......................................................................................................................... 6 2.7. Land Use ........................................................................................................................... 8 2.8. Plant Operations ................................................................................................................ 8 3. Methods...................................................................................................................................... 9 3.1. Survey Technique.............................................................................................................. 9 3.2. Sampling Design ............................................................................................................. 10 3.3. Survey Protocol............................................................................................................... 11 3.4. Data Analysis .................................................................................................................. 11 4. Results ...................................................................................................................................... 11 5. Discussion ................................................................................................................................ 12 6. Summary and Conclusions....................................................................................................... 14 Hells Canyon Complex Page i Medium-Sized Mammal Resources Idaho Power Company 7. Acknowledgments.................................................................................................................... 15 8. Literature Cited ........................................................................................................................ 15 Page ii Hells Canyon Complex Idaho Power Company Medium-Sized Mammal Resources LIST OF TABLES Table 1. Medium-sized mammals potentially occurring in the Hells Canyon Study Area and vicinity. .................................................................................................. 21 Table 2. Cover-types (acreage and percentages) present in the Hells Canyon Study Area. ...................................................................................................................... 22 Table 3. Number of surveys conducted in spring, summer, fall, and winter in upland and riparian habitats, Hells Canyon Study Area, 1995–1999. .................. 23 Table 4. Observations of medium-sized mammals during point-count surveys, Hells Canyon Study Area, 1995–1999.................................................................. 24 Table 5. Red squirrel density (number/ha) by cover-type and season, Hells Canyon Study Area, 1995–1999......................................................................................... 24 Table 6. Medium-sized mammal densities (n/ha) along various reaches of the Snake River, Idaho. ............................................................................................... 25 LIST OF FIGURES Figure 1. Location of the Hells Canyon Study Area and mammal survey points. ............... 27 Figure 2. Köppen climate diagrams for the Weiser, Richland, Brownlee, and Lewiston weather stations, Hells Canyon Study Area, Idaho–Oregon border. ................................................................................................................... 29 LIST OF APPENDICES Appendix 1. Criteria and definitions used to identify cover-types in the Hells Canyon Study Area............................................................................................................. 31 Hells Canyon Complex Page iii Idaho Power Company Medium-Sized Mammal Resources ABSTRACT Idaho Power Company (IPC) investigated the medium-sized mammal community in the Hells Canyon Study Area between 1995 and 1999. The objective was to determine the presence and relative abundance of these animals. Four-hundred forty-two points were established and monitored. Of these, 288 were riparian points and 154 were upland points. Surveys were conducted during four seasonal periods: spring (May), summer (June), fall (late September through early October), and winter (late January). Five species were observed during point-count surveys. The red squirrel (Tamiasciurus hudsonicus) was the most common species, followed by coyote (Canis latrans), mountain cottontail (Sylvilagus nuttallii), badger (Taxidea taxus), and beaver (Castor canadensis). Fifteen other medium-sized mammal species were observed incidental to other IPC studies. The density of medium-sized mammals that serve as prey for coyotes, raptors, and other predators was very low for upland and riparian habitats, with the exception of red squirrel in riparian habitats. The black-tailed jackrabbit (Lepus californicus) was only observed on one occasion. Even though the mountain cottontail was observed throughout the study area, densities were low (< 0.01/ha in upland and riparian habitat) compared with their densities in other areas along the Snake River (C.J. Strike: 0.02 to 0.34/ha, Sunderman et al. 1998; Hagerman Valley: 0.05 to 0.18/ha, Holthuijzen 1995). The red squirrel was observed in riparian and wooded upland cover-types in moderately high densities throughout the study area. The highest density was reported for fall (1.24/ha), which was significantly higher than those for summer (0.24/ha), winter (0.18/ha), or spring (0.15/ha). In general, highest densities were observed in the Forested Wetland (0.17 to 1.52/ha) and Forested Upland (0.00 to 1.37/ha) cover-types. However, significant differences were found only in fall when the Forested Wetland cover-type had higher densities than the Mountain Shrub cover-type did. Most species—including red squirrel, mountain cottontail, coyote, bobcat (Lynx rufus), and raccoon (Procyon lotor)—were observed throughout the study area. However, several species had more restricted distributions. The mink (Mustela vison) and muskrat (Ondatra zibethica) were limited by the lack of extensive riparian habitats throughout most of the study area. The red fox (Vulpes vulpes) was only observed in the southern portion of the study area along Brownlee Reservoir and above Cobb Rapids. Red fox are most abundant in areas with a mixture of croplands, grasslands, and woodlands (Verts and Carraway 1998). Thus, the absence of agriculture in the northern portion of the study area may explain the red fox distribution. Hells Canyon Complex Page 1 Medium-Sized Mammal Resources Idaho Power Company 1. INTRODUCTION Medium-sized mammals serve as prey, animals for hunting, indicators of habitat quality, and models for ecological research (Chapman and Willner 1986). A diverse group of animals— including lagomorphs, rodents, and carnivores with varied functional roles in ecosystems—are classified as medium-sized mammals. Twenty-seven medium-sized mammal species may occur in the Hells Canyon Study Area (Table 1). This report focuses on information about medium-sized mammals of the orders Lagomorpha and Rodentia collected during point-count surveys. Information on the furbearer and carnivore community is found in another report focusing on data collected with scent-station surveys and camera detection systems (Edelmann 2001). In general, lagomorphs have high reproductive rates and are short-lived. Population levels are regulated by mortality and dispersal. The quality